The Strange Case of the Poly 800

There is nothing particularly unusual about us receiving a Korg Poly 800, there are lots of them and they are often destroyed by acid from batteries left in them for years while it was stored in an attic or garden shed, or else the complicated internal power supply damaged by incorrect wall warts. This one was a little bit different though as it turned out. It was totally dead, no lights, no sound, nothing, so it was obviously the power supply.

Except that it wasn’t, the chassis and keyboard were in pretty bad shape, and there was a little battery acid damage on the main pcb, but the power supply was perfect, it had never been damaged and no work had ever been done on it, which for us was a first. So why was it dead ? All power rails were correct and stable, and the Master clock for the CPU was also correct, but nothing Digital seemed to be working.

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The above picture is of the Poly 800’s main board, and the majority of the Digital circuitry is in the bottom right hand quadrant of the pcb. The red and yellow dots on some IC’s were added by us as they were all the IC’s that were replaced, and some kind of explanation as to why and the order they were done in.

There was obvious battery damage to one of the keyboard encoding chips which also does the front panel switches, the 800 treats them both the same on a bigger matrix, as it’s legs were green and the solder joints had that matt grey look about them that acid damage does, so IC33 a TC40H240 was replaced with a 74HC240. We got better signals out of the 240 but nothing still worked. With the obvious possible damage dealt with, it was time to dig out the big gun, the newly rebuilt Tektronix scope mentioned over the last couple of entries. The next logical culprit was the 81C55, which is a 40 pin IC that handles the displays and all the DAC stuff, as none of that worked either. The clincher on this was that the Timer Out on pin 6 was dead, master clock went in but no timing clock came out, this signal is the source of the clock for the tone generator chip, so replacing this was next.

The 81C55 we used came from a dead Poly 800 board, whose power supply had been blown to bits, and battery acid put paid to the connector blocks for much of the rest but ironically the rest of the pcb was damage free, a result of the position it was stored in. Another interesting thing is that the chip came out cleanly and easily from this board, while the same chip on the synth board being repaired just wouldn’t shift at all and had to be cut out, and trying to buy one of these chips anywhere these days will be difficult and expensive. We have seen this often before, two identical pcb’s from similar times where one is a joy to work with, and the other a total pain, the reasons are as yet unknown, but it is a real phenomenon, we’ve seen it many times before.

With a new high quality 40 pin socket in the board and the transplanted 81C55 in it, very little had changed except that the Timer clock on pin 6 was now present and correct.

In a complex Digital system, where there are multiple problems in every aspect, diagnosis is very difficult as the closed loop that is a Microcontroller system will produce absolute rubbish everywhere if there is a fault, and instinct and luck are your friends here. The next IC to be replaced was IC16, a TC40H032 as it is used as a glue logic device to handle Enable logic in several parts of the system, and there seemed to be no wish for it to write Data to the Waveform Generator chip, the M5M5232. Replacing this with a 74HC32 didn’t change a thing, this was getting really annoying. Purely because so little of the system was still actually working, we replaced the Address Latch, a 40H373 with a 74HC373 in a nice new socket, and lo and behold the displays started working, and some of the buttons too, but still no keyboard and no sound. The next logical candidate was IC34, a 40H138, which is also part of the keyboard and switch scanning system. The synth still didn’t work but more and more parts of it gradually were creeping into life. The last chip to be replaced was IC29, another 40H138 which is responsible for a lot of the main sections of the synth. We now had most of the synth, keyboard working, displays working, MIDI working and Joystick working but still no sound output.
Although this particular synth had a coin cell battery fitted as standard, and it was still perfectly good, the presets just didn’t exist, and a dead battery scenario in a P800 will switch off all oscillators meaning no sound. What electrical scenario could kill so many components in the CPU section while not being power supply related?

It is still a bit of a mystery, but loading the factory presets from a wav file worked once the synth was finally functional, and all was good, and it has gone back to it’s owner.

Why did we actually take the considerable time it took to complete this repair ? The cost in terms of hours far exceeds the value of the synth, and Poly 800’s are not rare or particularly valuable.

The same client brought us a Korg Poly 61 a few months ago with severe battery acid damage, so severe that corrosion had got as far as the plastic ribbon connector that links the CPU board to the voice card, and destroyed the ribbon and its socket. Attempts were made to breathe some kind of life into it but it stayed resolutely lifeless.

We had a battery damaged Poly 61 of our own, which we had ignored as probably unsalvageable, and couldn’t be made saleable without some new parts. But while we were working on a Poly 61, we dug out our dead one for comparison purposes, and while it was very faulty there were a least signs of life, segments of the displays, random noises when keys were pressed. Some previous owner had replaced the large CV and Gate connector with a Tyco style connector (battery acid had eaten the Korg original one) and while this measured fine, it rendered the CPU board incompatible with the clients one.

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Our Poly 61 board still took a fair bit of work, all the passive components in the area were cut out and replaced after scrupulous cleaning of the area, all diodes and transistors were also replaced. All PCB traces in the area were checked for continuity and repaired if necessary, and plated through holes cleared and resoldered. A new coin cell battery was fitted along with a modification to stop the Poly 61 from trying to charge it. A few details relating to the new connector for the gates and CV’s were tidied up and we were ready for switch on. All looked remarkably good, the displays were reading correctly, and the button functions did what they were supposed to do mostly, as dead Tact switches are a common thing in Poly 61’s, as there are not many and they take quite a beating, but with some strong switch bashing, it seemed that all functions were working, so we created and stored a few presets, switched off and waited a while, and then switched back on again.

All the new presets were present and correct and have been since. The only remaining issues were that somebody in the past had replaced the Arpeggiator speed Pot with a totally inappropriate type and value, and the Joystick handle was broken off, so with the consent of the client with the dead 61, we used the Arpeggiator PCB board and the Joystick assembly from the dead Poly 61 to make our one as good as it can be. It still needs and will get a full set of new Tact switches (17 of them) at some point soon, because picking a full set of working switches even from two PCB’s just isn’t worth it when the switches are 30 years old, and they are still being produced by Omron.

This links back to the Poly 800, we have a dead one that will never see the light of day again, in medical terms we have pulled the plug on this one, but it does (or did) have a lot of good parts, and the client’s 800 needed a lot of good parts, so his 800 got a lot from ours (some IC’s and the display and button board and cassette interface sockets which were destroyed by battery acid, and two keys). So in the end honours were even, parts were exchanged from a bunch of synths that were dead to create two that were back to specifications, and the Poly 800 has MIDI, which of course the Poly 61 does not.

From the two pictures above, on the Poly 800 board, the IC’s marked with red squares are the ones that had to be replaced, the ones with yellow markings were replaced but we can’t be sure if it was necessary.

The second picture is of our Tektronix Scope after being rebuilt showing something from the Poly 800, we can’t remember which measurement it was, but it has been all good after the rebuild.

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The Andromeda Strain

We got our first Alesis Andromeda A6 last week, with a voice which passes it’s own internal calibrations but which is obviously out of tune afterwards, the client had pre-ordered 3 of the VCO ASIC’s in advance so we thought that all the bases were covered, a replacement chip and a couple of spares.
These chips were not cheap, even direct from Alesis so expectations were high of a satisfactory result from this. The IC’s themselves are surface mounted quad flat-packs which inherently carries it’s own difficulties. Lifting a dual sided SMD chip requires heating of one side of the chip until all the pins break free of their pads, then proceed to the other side to lift the chip out cleanly, but with quad packages this cannot be done without access to some very expensive tooling.

We actually carefully cut out all the pins of the VCO ASIC on the faulty voice (which is one option) and then carefully removed all the IC pins, the idea being that this would stress the PCB the least, and their delicate tracks, and this turned out to be the case, a nice clean removal and no pad damage. Lining up a QFPP with 64 pins is not a trivial matter either, the pins are only a millimetre apart and over four quadrants this isn’t easy, but the new chip went in, and after a long time under a magnifying light (which really wrecks your eyesight) we were happy to go for a test. This seemed to go well, the errant voice was now tuning every aspect and was staying there, all looked good apart from an adjacent voice which was always a semitone flat on Osc 1 and even more wayward on Osc 2 despite passing the Autotune routine. Repeated Autotuning showed this to be more than a transient abberation, this voice was faulty too in a similar way. This time we tried a different technique for chip removal, using very thin wire under the pins to lift out one side of the chip at a time while it was being heated with a temperature controlled Hot-Air rework tool. We did some rehearsals in advance on some old DVD drive and Hard drive circuit boards to get the temperatures, timing and techniques as perfect as possible for this form of IC, and then we went for it, and thankfully it went well, a clean chip lift and no damage to the board. Putting another one of the new chips in went well except that it didn’t work at all. no output whatsoever, the tuning sequence struggled with it and then gave up disabling the voice.

We checked and rechecked all of the connections and then gave up on it and next day installed the last of the three Osc chips into it. This seemed to work fine, and we regarded the synth as good to go, and indeed it was collected and went back to it’s owner, who after resetting the tuning tables started to run into a litany of problems with both of the new IC’s installed, and indeed a different voice has started to be problematic ( each oscillator ASIC handles two voices as does each Filter ASIC). Alesis UK have offered to send another two Osc ASIC’s free of charge to the client, but our main worry is about the number of times we can replace these chips before the pcb gets terminally damaged. This synth would seem to be a work in progress, and this is a shame, as what was done should have been enough to sort it completely, but the vagaries of the Osc chips make this a difficult problem.

The Tektronix Conundrum

As mentioned in a previous blog, we bought a Tektronix TDS420 scope for dealing with the Digital side of synth problem analysis, it has four channels, 100 MHz bandwidth, and lots of groovy DSP functions for Fourier analysis if necessary but also does funky things like reading out fairly accurately the frequency of the incoming signal, previously if we wanted to know if a CPU clock was correct, we would have to connect the Frequency counter but the Tek would onscreen give you a sufficient answer immediately.

Like the old Queen song Save Me says, “It started out so well” when we bought it, it passed all it’s boot diagnostics, which is why we bought it, but within a week it was starting to fail it’s front panel CPU diag’s and not much later on the Aquisition module started to randomly fail. Ironically perhaps we bought it to tide over a major rebuild of our Analog scope, a Fluke 3082 whose front panel controls had become totally shot, and indeed the Tek did tide us over this transition period while we rebuilt the Fluke.

Ironically the Fluke turned out to be a lot easier to repair than we expected, the switch contacts which looked like they should have been Gold plated turned out to have just been so dirty that they looked that way, scrubbing with Isopropanol brought them back to a nice silver colour. The weird surprise was that a lot of the Encoders on the front panel didn’t work either, and the reason was failed SMD diodes attached to them, about 9 if memory serves, and these were replaced with 4148 SMD equivalents which worked fine, the Fluke was now better than it had ever been, but it is a Digitally controlled Analog scope, not so dissimilar from most of the synths that pass through here, it is programmable, it has presets, and you can save your favourite settings. That being dealt with, and a great number of synths in the interim, we got back to the Tek for another try at the problem.

The Service Manual is available online but is largely hopeless as it doesn’t contain circuit diagrams and just recommends changing this board or that assuming that spares are going to be available for a 20 year old Scope, which they are not. We found the killer bug and it does have relevance to the modern synth world. as it seems to be all the Electrolytic SMD power supply capacitors on both of the failing boards, they leak something akin to battery acid across these tightly packed boards, and it does similar damage to the components and pcb tracks in their vicinity. This is Tektronix and they never knowingly used cheap components in their products, but here we are cleaning up noxious fluids fron the pcb’s and replacing about 50 capacitors and using Kynar wire to rebuild burnt out tracks on both of the failing pcb’s, and a few IC’s also, thankfully nothing that cannot be obtained locally.

About 50% of the capacitors measured were absolutely faulty and as for the rest we are dubious, the new replacements give far better readings. This Scope is from 1993 which is 20 years ago, how many synth time bombs are there waiting to expire for the same reason.

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The Curious Case of the C Zero Polysix

We got a Korg Polysix in on a Saturday afternoon, the client said that the keyboard didn’t work anymore, and thus we were resigned to a keyboard strip and rebuild with a couple of shims for the most recalcitrant keys that failed to respond to our TLC. Ourselves and the client had communicated during the previous weeks and he had opened it up to see if the Gate LED’s were firing, and indeed they were, but we thought he was describing the voices being triggered by the one working key on the keyboard.

When it arrived here and we got it up on the bench and opened up and switched on, and discovered that while every key on the keyboard worked (which is rare) all the voices produced a note that was a very low C, it was as though no CV’s were getting to the Oscillators, and yet -9.45 Volts was, though we suspected that this wasn’t right. Octave switching and pitch bend as well as Master tune also didn’t work, this was a bit weird.

The programmer section was fine, and still had an enormous NiCad battery in it which looked original but was also absolutely fine, good voltages and no sign of any corrosion or breakdown at all, this synth was a new production model imported at some point directly from Japan, and was in general in astounding condition apart from the current major flaw that it was currently unusable.

Everything looked to be pointing to a problem with the Key Assigner system, so that chip was replaced with a spare, but no difference, so we explored the Digital to Analogue converter section that produces the VCO CV’s but that seemed to be working fine also. After that many hours were spent ‘scoping all the relevent parts of the famous Antilog CV generator to see if some sense could be made of it all. It didn’t really help, there are two multiplexers driven by the CPU surrounded by a maze of Transistors, Resistors and Op-Amps, any one of which could have been the culprit, (and the circuit diagram is practically unreadable even in the best version the web can supply). It was time to make a decision, the two 4051 multiplexers were obviously primary suspects, so they were replaced one by one, IC31 first (no joy) and IC39 (result ! ).

Once the synth was working again, the final touches were dealt with, recalibration and the replacement of all 8 program select switches, which some previous user had danced on with great gusto.

This synth was ready in 24 hours, primarily because the client had driven 200 miles to bring it here, tying it in with a personal commitment, and if it hadn’t been repaired in this timeframe, would have required another long trip at some future date at great expense.

Internet folklore hints that Antilog Generator problems do occur but this is the first time we have seen this for ourselves, but the 4051 Multiplexer IC is notorious for several different ways of failing, and these days is one of our most frequently purchased items.

The Korg M3X ressurected

About a month ago a client dropped in a Korg M3 which wouldn’t power up, as it had a 3 pin IEC connector we assumed that maybe a fuse had been blown, or a rectifier failed. Opening up the unit revealed an enclosed Laptop style power brick that fed the whole synth, rated at 12 Volts at 5 Amps, and quite small to boot.
A quick measurement of the output showed the PSU to be quite dead, and in true Korg tradition, it had a weird sleeved central pin connector used in Laptops, (although no Laptop actually runs on 12 Volts, it’s usually 15 to 20 Volts). A quick e-mail to Korg UK got a surprising result, that PSU is discontinued and no replacement is available. It seemed crazy that a 2 grand synth from 2006 should be left so high and dry, so a long and convoluted hunt for something suitable was begun. Apart from the weird DC connector, the overall dimensions were quite constraining, which ruled out a lot of readily available supplies from a variety of manufacturers and distributors. Don’t even consider using an old Laptop supply in there, even though it might fit !, the power supply board which converts 12 Volts to everything else that the synth needs contains the same types of components as the MS2000, Microkorg and others, and will self destruct if it sees more than 14 Volts, possibly destroying the entire synth.

Because finding something suitable was proving difficult, we cracked open the original supply to see if it was repairable, if a simple resistor or even a diode had failed, it was worth an attempted repair. Checking through everything in the old supply didn’t show up any obvious failures, but it was still dead. The logical failure was the small chip that runs the entire supply, but this was a Surface Mount IC with a Hieroglyph on it’s top which defied all searching as for what it was. It is possibly a standard PWM control IC, but without the information we couldn’t take any chances.

By chance we mentioned the dilemma to a fellow Tech who buys lots of these things to replace dead PSU’s in LED lighting controllers, and he suggested CPC which is a division of Farnell. Hunting through the long list of suitable supplies led to a magic number, so we set up an account and ordered it. It arrived very quickly and we cannot conceive of a better supply for the job than this, it has an IEC connector (which the Korg has internally) and it fits very well, and weighs a lot more than the original which we hope bodes well for longevity. The only extra work required was replacing the DC connector on the power supply board with a more standard 2.1mm DC connector, as this was what the new supply came with. You have options on this, cut the new PSU output cable off and graft the original power supply connector onto it or leave that alone and make the synth suit the supply. We chose the latter as years down the road power supplies with 2.1mm DC connectors will be far more available than weird custom configurations which in fairness is what the M3 has.

The new supply is about 3mm deeper than the original, but a metal saddle secures it in place, and the replacement of the saddle screws with some longer self tappers sorts this one out perfectly.
The important details, the part number we used was PW02712 manufactured by a Chinese company ProPower, and the internet address depends on where you are in the world, for us in Ireland it was cpcireland.farnell.com.
If anyone out there has a dead M3, we hope this was of some help!.

The Oberheim OBXa

This synth arrived in for a battery change, at least that was the original premise, someone in the past had fiited a NiCad to it to replace the original Lithium but hadn’t modified the circuitry to allow battery charging, so it didn’t really work. On the plus side, no harm was done to the circuitry. Putting in a new Lithium battery and restoring the factory presets sent us further down the rabbit hole, the tuning was bad and a lot of the normal functions of the synth behaved somewhat strangely, we hadn’t had a OBXa before but we do know when something is not right.

One of the main issues of dealing with old (and especially classic and valuable synths) is trying to track it’s service history purely based on what you see in front of you, there may be new chips with dates long after the synth’s manufacture date which may provide a clue as to what may have been troublesome in years gone by, but unlike buying a classic car, you don’t have a service history with a synth. A lot of the more expensive synths have been toured worlwide by fairly well known musicians and when they gave trouble desperation kicked in and who knows where in the world immediate problems were sorted out, just surviving from one gig to the next was good enough in those days!

Basic testing made it apparent that the power supply voltages were well out of tolerance, and testing the modulation panel showed similar issues. Correcting both of these issues ended up with the result that the synth would not Autotune at all, all notes were a Fifth out of tune and all 8 lights would flash after any attempt at an Autotune. Endless ‘scoping and analysis of the Autotune state machine didn’t help, as didn’t replacing all of the IC’s in the Autotune system. After a lot of hours with the scope, we tried disabling all but one voice, and trying to make it tune. Logically for a 1981 synth, turning off all the voices but one made a nonsense of the Autotune indication system, no lights blinked but at least the selected voice was vaguely in tune.

Previously the tuning was a fifth out for each voice but also random tuning anomalies in random voices were a regular and repeated occurence, and the source of these were looking more and more likely to be the connector pins on the voice card motherboards. We took out the top tray (Voices 5 to 8) and took the motherboard out and used metal polish to clean every individual pin on all the connectors. These looked very tarnished, and polishing was done until no more black oxide could be seen on a cotton bud. This took some considerable time, and a lot of cotton buds. Putting the motherboard and the voice cards back in afterward didn’t really improve things much, but after trimming voices 5 to 8 so they were in tune with each other, they were more likely to stay together and be more consistent than the bottom tray (Voices 1 to 4), so we cleaned and polished all the connectors in the bottom tray. It really does need to be done, those connectors have been tarnishing for a long time, and poor contact between voice card and motherboard can only lead to randomness, and it’s only when you polish them, that you discover how blackened they are.

A lot of research and checking out of relevent forums yet again failed to deliver anything that was actually useful, so it was back to basics, working out how the synth was meant to work and how it achieved it. The power supply was now fine, the modulation section was thoroughly checked and rechecked and was also fine, and all of the motherboard voice card connectors were polished and pristine, all of the oscillator chips had been taken out of their sockets and cleaned and replaced, so what next ?

Back to basics in essence, we knew what was good, so we had to figure out what was not, one clue was that of all the trimmers on all the voice cards, only the initial frequency trims of the oscillators looked like they had seen some action in the past, almost every other trimmer in the machine still had the latex type compound in the middle of the trimmers, indicating that they had never had to be adjusted before (or at least never were), so we were led back to the original question at the head of this section. What was the service history of this machine? What servicing had this machine seen in the past, and what forms did the problems take?

This particular synth was in remarkable electronic condition as well as great physical and cosmetic condition, the only obvious replacement IC was a CEM3310 envelope chip on one voice, but as this synth was an early model there were a few ECO’s (Engineering Change Orders) which we implemented to improve reliability and update the synth to it’s later brethren.

The OBX-a has an 8 way internal bank of switches which enable each voice to be physically switched off, or more usefully one voice at a time can be calibrated by switching off all the others, so we calibrated all 8 voices one by one until when you played an A, you got an A, and following this and reinstating all 8 voices and running the Autotune sequence, it actually passed. Further testing showed a weird resonance behaviour on voice 3 in 12dB mode which turned out to be a faulty capacitor in the filter coupling stage, which was replaced. The last problem was voice 5 being out of tune and failing Autotune at random, which turned out to be a faulty Initial Frequency trimmer on Osc 1 of that voice which we also replaced. The interesting thing we discovered about this problem was that the Autotune system will not even correct for a Semitone which was surprising for a 16 Bit Autotune system which infers that on an OBX-a the oscillators have to be inherently quite accurately trimmed and in a stable condition, because the Autotune will do nothing to help beyond the very slightest drift.

Roll on next month…

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When Nice Beverages Go Bad!

When people think about equipment getting drinks in them, the first thoughts are of wild parties and raucous gigs and if a synth is going to be destroyed, at least it went out in style, like the end of a 60’s Who gig.
Alas the truth is far more banal, about 90% of all liquid damaged (or ruined) equipment that comes through here has met its end courtesy of the humble tea or coffee. Perhaps this is not so surprising, as musicians working in their studios think nothing of parking a cuppa next to their pride and joy while they fine tune their greatest work. Despite the greatest of care and attention, accidents will happen, a curl in an instrument cable being repatched, a careless elbow, the possibilities are endless. How do we fight this scourge on Synthkind, and still enjoy a brew?

Obviously having no liquids near your gear is one option, but a little draconian given the many hours spent with our music gear, but how do we have a brew and yet keep the gear safe?

In the workshop we enjoy a cup of tea as much as anybody, and after several hours spent searching for a dead gate on a chip in the CPU of a synth, we will have drunk many cuppa’s during the search, and have a celebratory other one when the culprit is found! The answer, be sensible and organised, find a space in your work environment where if the worst happens, no damage to electronic gear will result, and always put your beverages there, you won’t have to think about it, just reach out and touch your coffee. In over 20 years of repairing synths, and countless thousands of cuppa’s there has not been a single accident of that type, (electric shocks and solder burns, deep flesh wounds and splinters yes, but no liquids in a synth or piece of test gear).

The effects of liquids in music technology equipment has increased in the last two decades due to the small size of modern devices (especially those 200 pin IC’s that are in everything now), and one drop of any liquid is enough to short out at least 3 pins, and surface mount devices tend to suck any liquids under them by capillary action, which may short out a lot more than that and take a considerable time to dry out even if the gear is not used. If it is, then electrical damage is possibly being done, slowly eating away at the tiny pins of these IC’s until the pins break and the circuit board won’t take solder any more, and these IC’s impossible to obtain.

Not just tea and coffee by the way, Atlanta’s finest. and any of the sugary soft drinks will be equally if not more destructive, as will any spirit and a mixer.

If you have to have a liquid of any sort near your Tech Gear, organise a routine where you know exactly where it is without thinking about it, put it always in the exact same place, and maybe we won’t ever have to tell you “sorry it’s gone”.

There were a great many liquid infested synths here in the last couple of months, most were fixable, a couple were not, and this is why we made this a blog subject.

The Oberheim Deluge

After many years of not seeing many of Tom Oberheim’s products at all barring the odd Matrix 6 or 6R (the rack mounted version) we have been inundated in the last few months with some of Tom’s finest, a couple of dead Xpanders, a couple of unwell Matrix 6R’s and an OBXa, and the Matrix 12 is also still with us. Joining every relevent forum has not been very productive, but perhaps no surprise there. They are all well built and engineered but also all have weird problems that defy most of the more common and logical diagnosis techniques, and on forums there are no shortage of those solutions that one person or other swears is the Holy Grail of advice and this is how they made their Obie perfect once more. We have read them all and none of them are in any way relevent to any of the issues here right now. The great “Recap everything” thread will always be there and some people may have got lucky with that one, but it is not going to help with anything we have here.

Last week we bought a Tektronix TDS420 Digital Oscilloscope to aid in some of the more arcane problems that even Analogue hybrid polysynths can be prone to, hopefully between it and its analogue scope counterpart we will be able to see what the problems actually are, although even with the best of equipment you have to measure the right question, and obviously figure out which measurement question to ask, and this is part of the legendary diagnosis time that Tech’s worldwide charge for. All the Obie’s here have weird and obscure problems that will take a lot of time to figure out, already a lot of expensive spare parts have been purchased, just to have them in house if a suspicion is raised about any particular IC, and possibly we have the best collection of those parts in Europe. One of the Xpanders had been to some well known Tech’s in England, and it had been both pillaged for valuable IC’s and also butchered by what I hope was an apprentice, (if not, God help you all in the UK), we bought every spare to restore this if the damage hasn’t been too great, and while we are not massively confident about this particular synth, we are as good to go as is possible.

Keeping Old Korgs Going

Some of Korg’s offerings from the early 80’s are becoming more desirable as time rolls by, such synth’s as the Trident, the Polysix, the MonoPoly and the Poly 61. All of these are interesting and good sounding machines but they share a common failing after 30 years, the Panasonic keyboards used in them. The rubber contact strips for these have become pretty well unobtainable (and have been for several years now, although the Poly 800 shares the same type of keyboard and there are lots of dead Poly 800’s due to battery damage).

Last week we got two Polysixes which we had already seen in the last year, one got a CHD MIDI interface fitted only 8 months ago and at the time the keyboard was surprisingly perfect for an EBay purchase, but it wasn’t last week, 14 keys across the keyboard didn’t work at all. The other Polysix had lot of dead keys about a year ago, but a complete strip and rebuild of the keyboard fixed that at the time, but that didn’t last. It seems that these old Panasonic keyboards require constant playing to keep them working, we had a Poly 61 over the weekend whose keyboard was completely stripped and rebuilt 6 months ago, but after getting the synth working the keyboard still had about 20 keys that didn’t work, but that number reduced to 2 after the keyboard was exercised for a while. Yet if you dismantle the keyboard completely and “play” the rubber pads alone on their PCB, a freshly cleaned keyboard will be perfect until you put the keys back in, so what is going on here?

Over the last year we have been fitting thin plastic shims on the bottoms of the rectangular key actuators on any Panasonic keyboard that has been completely stripped and cleaned, but still had the odd key intermittent, repeated dismantling and rebuilding of the keyboard doesn’t seem to improve things very much, in fact every time you dismantle and reassemble the keyboard pcb, a different random bunch of keys won’t work any more, and they require a lot of repeated playing to bed them in again.

The shims are simply pieces of 1mm thick modelling Polystyrene used by modellers and architects and available from most good model shops worldwide, and Superglue (Isocyanoacrylate or Crazy Glue as I believe it is called in the States) is the ideal bonding agent, just cut a rough sized piece of Styrene, glue it on and then trim the resulting assembly with side cutters. It seems to cure those rogue keys which defy all cleaning.

The reason for all the preamble is that we put shims on every key on both Polysixes from last week, it was very time consuming but all the keys worked fine after this, only time will tell if this is a permanent solution to this problem, and we hope it is, as the Matrix 12 here has the same make of keyboard, as does an OBXa which got a shim on a black key which didn’t respond to anything else.

There is a kind of logic in this solution to the problem, the part of the key that presses the rubber button is rectangular while the button itself is circular, something about square pegs in round holes comes to mind.

One of our two Polysix owners reported back that the feel of the keyboard had also been improved, apart from actually working, he felt the response to be better also, time will tell.

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The Perils of Batteries

Batteries are great things, they start your car in the morning, they are in the emergency torch that you need if the lights go out, your mobile phone wouldn’t be mobile without them, and the list goes on…
But their story in Synths is very much a mixed experience, for the most part they back up your editing and work, so when you call up your killer preset on stage it will be exactly what you meant it to be, and for the most part this is true. But perhaps for inhabitants of the 21’st century some of the unforeseen issues of the past battery technologies are starting to rear their ugly heads.

There seem to be two types of batteries that cause damage in Synths and other Electromusic products, rechargeable Ni-Cad’s and dry cell batteries (the kind you would put in a torch).

Large cylindrical dry cell batteries were used in a few Pro synths such as the SH101 and the Poly 800, so they could be played portably on stage, and as memory backup for some Drum Machines such as the TR808 and 909. A lot of home keyboards by Casio, Yamaha and others had them as well but any bad consequences of leaky batteries in these have probably led to Land-Fill many years ago, thankfully we all recycle now.

Currently the SH101 has achieved quite a high value, and the Poly 800 is only a couple of hundred of your currency behind but an incredible amount of damage can and has been done by leaving a full set of Alkaline or Zinc Chloride batteries in one of these for a few years. Whether the damage is terminal or not depends on the physical attitude of the synth in storage, is the synth stored on it’s back or on one of it’s ends, or flat (as in a playable position) or upside down in a box?

From our experience, the position that assures it’s possible resurrection is flat on it’s back, in the playable position, any of the others is probably terminal, but not leaving any dry cell batteries in these machines long term is definitely the safest option. You might lose the onboard presets in an early Mk1 Poly 800 or your sequence data in your SH101, but it is a small price to pay in the end.

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The above image is of the metal base plate of an SH101, the other end of this part was just as bad, and the output jack board had to be completely stripped and rebuilt and many components replaced, in order to make this synth any way reliable. The battery terminals themselves had to be replaced and a tremendous amount of cleaning had to be done to remove the legacy of battery acid from the inside of the synth. This one was stored in the playable position, can you imagine how bad it would be if it had been otherwise?

We have the carcass of a Poly 800 here, it was stored upright with the joystick side on the ground, the battery acid had eaten through parts of all the connectors that link the front panel and the main board, but had also managed to eat through a lot of the PSU circuitry and the relevent unobtainable connectors. Even the filter chip in it’s socket had a lovely green patina on every pin and cannot be assumed to be a survivor. The front panel board and the Chorus board seemed to survive intact as they were away from the direction of the batteries leaking and they look fine. They will do for spares.

The other major source of damage to older synths is the Nickel Cadmium rechargeable batteries (NI-Cads) that are commonly thought to be only in a few synths but that list seems to be growing. The original idea was that a battery that was trickle charged when the synth was switched on would never need replacing. and this theory was good for about 15 years before they started to decompose into their constituent chemicals and start to leak a corrosive cocktail all over the PCB. As this is always the main CPU for the synth, this is going to lead to major problems. Originally the Korg Polysix was the most infamous for this, but the Korg Trident 1 and 2 both have them, the Korg Poly 61 is another, and the list also includes the OSCar, the PPG Waves, the Siel Opera 6 and recently the GEM S2/S3 Turbo, and there are probably many more. We have a Lexicon M200 Reverb unit which was also almost destroyed by a Ni-Cad battery in it. The Lexicon truly didn’t need to have a Ni-Cad in it, it only has 2k of lower power RAM in it, and a Lithium Ion battery would easily have supplied it’s needs for 20 years or more.

The picture below is of a Korg Polysix which had the luckiest escape from Ni-Cad disaster that we have ever seen, it was stored in the Polysixes sweetspot, upright and on it’s back, the rear panel towards the floor.

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The corrosive compounds leaked directly from the battery to the rear chassis just avoiding the power supply and only spattering the cables and connectors on that end of the CPU board.

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This is rear panel after cleaning, all of the connectors were stripped down, checked, repaired and rebuilt and the back panel is about as good as we can make it. All in all, a remarkable escape.

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The above picture is part of the interior of a Lexicon M200 Reverberation unit and shows all of the circuitry related to the power on reset, muting and control panel interrupt timing. The RAM chip is at the top right of the picture and this is also tied into this block of circuitry as only after a successful reset will the RAM be enabled.

When acid starts leaking onto a pcb, it eats into the Lead and the Tin of the solder joints, Oxidising them and making them very reluctant to accept heat from a soldering iron and to thus melt. It turns even cutting out all the damaged components and trying to clear their pin holes extraordinarily difficult. Just cutting out the components and clearing the component holes took more than 3 hours, and this took a lot of heat, liquid solder flux and patience to do.

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The above picture is after everything was replaced, the Lithium Ion battery now backs up the RAM and the diode resistor combo at the right centre of the picture is to stop the Lexicon trying to recharge the Li-on battery.

The 2 IC’s to the left of the picture both had to be replaced and the the Z80 main CPU had also gone faulty probably as a result of the battery damage.

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