In for the long haul…

There is a certain joy in getting a repair in, diagnosing it quickly, obtaining the spare parts locally, and then getting it finished the same day. If there was a Service Guy’s dream this would probably be it.

Alas this very rarely turns out to be the case, the variety of equipment in the workshop and in storage at any one time results in a very convoluted chain of spare component acquisition, often with several streams of parts arriving in short spaces of time from all corners of the world.

Also for thorough investigation and knowledge of the equipment under repair at the time, both the service and owners manuals have to be read. This leads to an endlessly rotating intimate knowledge of hundreds of pieces of music equipment at any one time, it is endlessly rotating because if a particular machine doesn’t come in for a while, it drops below the current info radar and has to be relearned again the next time one ariives in.

Most pieces of equipment do get to leave us in a reasonable time, but some are just so broken, or difficult to obtain parts for that they are in for the long haul.

The Juno 60 mentioned back in the April blog is actually coming along nicely, its only remaining electronic faults are in two of the filters, the resonance control is non existent. This could be due to the Resonance VCA chip, but it could also be due to faulty coupling capacitors, obviously the latter will be cheaper to repair.

The Polysix also from April also got another going over in late May, more components were cut out, the circuit board area underneath thoroughly cleaned, and components replaced, but this one is still not right, voices 5 and 6 are just out of tune in a random way every time the synth is turned on.
We monitored the Korg forum for any advice, and some was given, and it was good advice, but it either didn’t work or didn’t apply to this particular problem.

These kinds of repair are the long haul *uckers, but both of these are the result of buyers hunting for silk purse synths at sows ears prices.

We suspect that during the Analog Renaissance, a lot of the dross of the synthesiser world is being dug up and offered for sale, after being dumped into sheds and attics all across the world. As for the non-smoking studio use only line, all we can say is “please knock it off “, you are only fooling the purchasers, but not the service engineers. Everything that comes through our humble workshop gets scrupulously cleaned while it is dismantled, and the amount of Ammonia cleaner and cleaning cloths that get used tells us that no synth ever lived in a smoke free environment.
And another thing, what really grinds my gears is the insertion of the phrase “RARE” on every entry on E-Bay these days, (is a Juno 106 rare, or a DX7). In our opinion, there are less than two dozen synths that are actually rare.

Rant over for now, there are three more weeks in June to go…
Teisco a go go

A Teisco S110F arrived in a couple of weeks ago, apparently working fine until recently, but now only producing weird buzzing noises from the output.

The obvious culprit here was going to be the power supply, and indeed something about it was more than a bit flakey, the 15 volt positive rail was absolutely fine under all circumstances, but the 15 volt negative supply seemed to have a mind of its own.
On switch on of the synth, the negative voltage wanders from -9v to -13v as it warms up, it does get better as time goes by but it is never useable..
As the S110F is built from 3 circuit boards behind the front panel, the logical thing to do was to disconnect them all from each other and try to trace what was upsetting the power supply.

As all the circuit boards are single sided, there are a lot of wire links on the top side, and much care was taken carefully isolating one part of the circuit board from the next to attempt to track down a faulty component.

A hint was leading towards an OpAmp that fed the uA726 on the left hand board, this is VCO 1, when it was isolated, the -15 V seemed to hold up accross the entire circuit board, and as this board is responsible for all keyboard control including Portamento and Sample and Hold, this is a good place to get right.
Replacement of this Op-Amp did seem to lead to a temporary respite, we had good plus and minus voltage accross the entire circuit board, and for a while it seemed stable.

We knew that plugging in the second pcb would upset that again, due to some extensive initial testing, which led us to believe that there could be more than one dead IC in the synth. The same isolationist technique was used on the second pcb to try and ascertain which chip it was on this board. This board has VCO2, the mixer and the filter, so it is an important one for the synth.

As expected, the negative rail collapsed when the second board was plugged in, so for confirmation it was unplugged from board 1 and the system tested again with only the VCO 1 board plugged in.
The Negative rail had collapsed again.

The power supply pcb was taken out and had all electrolytic capacitors replaced and the big ones upgraded with higher capacitance and voltage rating as the originals are old, and no harm would be done.

Still not a lot of joy, a closer exam of the voltage rails on the scope showed a lot of ripple on the negative rail directly at the power supply itself, and as all the caps had been replaced it couldn’t be that.

A break of a day or so and we got back to this little baby.
Logic dictated that if it wasn’t the power supply capacitors, then it was likely to be the power transistors that were suspect, and it turned out one of them was. The measurements of the device out of circuit seemed to indicate it was ok but some kind of instinct kicked in and said that it might not be.
We didn’t have the exact transistor as a spare but substituted a European over specced equivalent just to be sure, and lo and behold, instant power supply joy.

We replaced both PSU transistors with a complementary pair of Euro equivalents and it was all good.

Soak testing for many hours and checking out all the functionality of the synth showed good results.

One slightly unusual aspect of this synth is in its filter, it is a Moog style Ladder filter built with the same type of matched transitor pairs used in the TB303 (only more of them), but the interesting thing is the size of the filter capacitors, as in the electrical value.
The value of them is 220 nanoFarad (usually abbreviated to nF and indicates the amount of electrical charge it can hold).
If you substitute the concept of electrical charge for the bucket of water analogy, then simply think of more nanoFarads being a bigger bucket. If you imagine that the bucket can only be filled by a hosepipe of a fixed size and that it also has a hole in it, then you are getting close to a rough capacitor model.
We are not going into a long diatribe on capacitor theory, but a few numbers may illustrate our point.

Teisco S110F capacitor 220nF
Moog Taurus capacitor 100nF
Minimoog capacitor 68nF
Micromoog capacitor 33nF
Moog Prodigy capacitor 27nF
Moog Source capacitor 10nF

The pattern is obvious, the size of the capacitors in the ladder filter got smaller as time progressed, yet the 2 Moogs at the top of the list are regarded as the ultimate Bass machines, does the Teisco have a secret weapon that has been kept hidden for a few decades?

Not for us to say, but the bass end is certainly good, but not quite like a Moog, which considering the filter architecture, is a little surprising…. getting late more to come…

Room 101

As anyone who has read the book or seen the movie of George Orwell’s 1984, room 101 is where you meet your greatest fear.
Normally a Roland SH101 should hold no major fears for a synth tech, there are several quite common faults with these, the blown power supply, the dead Curtiss oscillator chip, the odd Op-Amp failure in the LFO or elsewhere, but nothing that will tax the competent soldering iron wielder.
And then… from beyond the grave… lurched in this one…

It all began when the phone was answered, “I have been offered a dead SH101 on and I am thinking of putting in an offer”. We naively answered in the Top Gear idiom, “How hard can it be?”

The synth was purchased, and a week later came our way to be returned to its former glory and then when examined, the true horror began to unfold.

The legend was that this synth was bought a long time ago as faulty, but never got repaired as the original owner just bought another one to replace the dead one, and never got around to it.

We are seeing this story or something like it more and more on auction sites these days, along with lines like
“I never got around to it” or “it should be an easy fix”. There is no more profitable way of clearing your attic than this kind of chicanery, and if you say it is faulty, and sold for spares, then you are not liable for any counterclaims by the subsequent new owner, and the current greed and lust for anything analogue at a cheap price is only adding to the misery.

The power supply in this one was faulty, the main power transistor in it had already been replaced by a previous solderer, and the transistor type used (not an original) seems to be a good choice. But another transistor and diode in the power supply was also dead.
The Curtis Oscillator chip was actually missing, none of the LED’s worked, sending noise through the filter produced no output. Further testing showed the filter chip to be also dead.
Hunting down why all the LED’s were dead led to the discovery that all the transistors involved in the LED switching were blown, as was the IC that also drives some of them, and one of the LED’s too was blown.
Having replaced 7 other transistors on the main pcb and replaced any necessary IC’s, we finally had some semblance of a functioning 101. The synth powered up, the correct LED’s came on, the function switching for the Arpeggio, Hold, and Sequence Load and Play were now all working, The CPU chip also seemed to be working, the only survivor on the board so far.
After getting this far, time to see if the unit will calibrate its DAC and keyboard interface, there is a test diagnostic routine built into the CPU firmware, you just hold a couple of buttons down at switch on.
Guess what? the keyboard CV’s were all over the place, and the demultiplexer chip also seemed dead.

The only parts of this synth that actually work are the LFO, the noise generator, and maybe the CPU, (I say maybe because one of the pins is producing a strange waveform unlike any of the others, and it does pertain to the DAC system.

We are waiting for a new CEM3340 Oscillator chip before proceeding any further, our inclination was this one was a true scrapper, only the keys of the keyboard are worth anything, although the slider pots are also good.
However the client wants it restored, and it won’t be cheap, but it can be done.

As of now the timescale is November, but for continuity purposes the following text is here.

The new Curtis chip was installed and worked fine, the new (?) filter chip was also fine, the only remaining problem seemed to be that the calibration still didn’t work, and one Octave of the keyboard wouldn’t play.
Guess what, the CPU was faulty after all, only one pin of it but it controls the missing octave of the keyboard as well as one section of the DAC.
A replacement is available from Vintage Planet ( but is €50 and means the SH101 will never run on batteries again, unless you own the Duracell company.

This synth has been an absolute dog from start to finish, over 75% of the transistors in it were faulty as well as 80% of the chips (including all the expensive ones), a couple of rare and valuable slider pots had to be replaced and the obligatory new power switch.

The reason for the long delay between May and November, there was an option of a free badly damaged 101 which the owner was giving away which we hoped had a working CPU chip. Alas the owner of said SH101 has decided that he wants it restored, the ridiculous prices on E-Bay for this little plastic POS have changed his mind to the extent that it is worth spending some money on, so we will probably see this one soon.


The trouble with Forums

The month of May is nearly over and yet only now have we had any time to put computer keyboard to html.

Some synths are still haunting us, the Polysix from earlier is back with ongoing issues with voices 5 and 6 (what is it going to take to sort this?)

The Prophet 5 refuses to take tape loads despite experimenting with every possible parameter, and checking with all the test gear that tape signals are getting as far as the processor.

The Juno 60 despite having the entire front panels rebuilt still has no LFO control, and weird problems with filter frequency control when moving the front panel back and forth. Signs of more problems with broken tracks and connectors.

Funnily enough, over a decade ago when the synthesiser side of the internet was young, someone posted to a bulletin board that Roland connectors could be iffy, and that myth was promulgated across the net for many subsequent years. When Forums came on line, we saw that old chesnut rearing its head again and again.

Over 3 decades of experience with Roland equipment of all kinds from synths, drum machines and effects units, we have never had issues with their connectors (assuming those plug-on connectors that were used until quite recently on all Roland products).

This Juno is the exception, but the amount of abuse this synth has had, and the apalling standard of attempted repairs, would to our mind still enable us to say that Roland connectors are very reliable and not something that would normally concern us.

The other trouble with forums is trying to administer one…

My good friend and Webpage designer Dave who wrote the template for this site rewrote the forum section as an extermal link as the original built in forum was spammed so much as to render it useless. I switched it off while Dave tried a different approach.

Now that the new forum is live, the spamming issue is still not gone, just become more sophisticated.
Either actual people or clever bots are creating new users and then posting a variety of spam from viagra ads to hotel adverts from far off places. We haven’t had one relevent synth related post yet.

The real “fun” is that the forum interface is about 10 times more complex than the web site management system (and learning that wasn’t fun),
In fact we did several years of Windows Server administration, and the forum admin seems far more complex than the Windows Security Policy editor.

I thought the forum might be useful for repair issues for Irish musicians, no subject would be taboo (except viagra and cialis), analog, digital, synths or not, we would create new groups as required.

As it is now, all new posts have to go through us before going live, not a desirable state of affairs right now, as there are only so many hours in the day, and we have no moderators yet.

Shot through the foot (and we’re to blame)!

During a conversation with a client, a desire to find a Jen SX1000 was expressed, and we mentioned that our attic had one. It was fully working before it went there, and it looked fine when checked on last year, so a deal was struck, with the promise to dig it out sometime soon and check it out.

Unfortunately, the heavy snow from last year led to consequences that years of heavy rain failed to achieve, a leak in the roof directly above the Jen. The front panel is now rusted almost beyond recognition, it is a hideous sight. Still we were optimistic that the actual synth was ok, but even that glimmer of optimism was swiftly snatched away.

It had become one of the Zombie synths from last month, and it was one of ours!

Obviously as moisture ingress was involved, nothing could be taken for granted. Even when a piece of equipment is not even powered up (and the Jen has no batteries) rainwater can pick up enough pollution contaminents to form mild acids that will eat through component legs, and it also particularly loves oxidising solder joints.

Opening up the synth for an under the hood examination showed that despite the horrendous state of the front panel, all the front panel pcb’s were absolutely clean, between the knobs and the multiple locking nut system of the pots, not a drop of anything had got onto the boards. A result? wait and see. . .

The keys of the keyboard were filthy, the dripping water and rust from the front panel had run down the sloping panel onto the keys, and seeing as the expensive and rare M110B keyboard interface chip lives here, this was where the life and death decision was to be made. Scrap or resurrect?

The keys were filthy, and all had to be removed for thorough cleaning, and this was done.
The surprise in this section of the synth was that the worst effects of the long storage time weren’t water related but due to the old Italian Synth disease, silver plated contacts turning totally black due to atmospheric pollution. Many of you will have seen how your grannies’ silver, your parents’ silver, or even your own tends to turn black and require polishing regularly.
According to the chemistry textbooks, the black is silver sulphide, and is the result of some complex element exchange due to sulphur dioxide in the atmosphere.

In case anyone thinks we are raining some kind of special criticism on the Italian synth generation, then that is only partially true, but any repairs of Siel’s or Crumar’s or in this case the Jen have always led to special attention to all the contacts, keyboard, tab switches on organ stops, and anything in the machine that was silver plated, especially input and output sockets.
Isopropyl alcohol, the solvent for every occasion just doesn’t cut it when it comes to this kind of tarnish and resort to silver polish is needed.
We use Silvo which is a wadding polish available in most supermarkets. It does a great job of removing tarnish but leaves behind a dry powdery deposit which is probably as non-conductive as the tarnish itself. This deposit can be removed by Isopropanol, and the part dried and polished.

Despite the long term water dripping and the filthy keyboard keys, once the keys were removed, the keyboard bed just showed the usual symptoms of 30 years of age, lots of dust and fluff. We always find it amazing how much detritus gets into any keyboard over the years. You would think that the keys are very close together and there would be no space for anything to get in there, but dust and airflow can surprise us all.


The Zombie Synths

A strange month April has been, a lot of DIgital DSP based stuff has been through the workshop lately, it’s not what we really do, not being Vintage, Analogue or a Synth. The time consuming part of all these kinds of things is that the online forums have to be read and the owners manuals likewise, to see if anything is actually wrong or if it is pilot error.
The manufacturers will tell you nothing of any issues with their products, and their technical support is not just second to none, it is just none.

Nevertheless there have been a couple of Analogue nasties this month…

We got an Ebay special Juno 60 which was bought from a region of what used to be Yugoslavia.
Ostensibily it was in perfect working order but they all say that from thousands of miles away.

The new owner was someone who had switched from a very digital Waldorf Blofeld to his first analogue synth. He brought it to us to ascertain whether this was how a Juno 60 was meant to be, and we had to break the bad news that no, this is not how a Juno 60 is meant to be.

The presets mostly worked and the keyboard seemed perfect (apart from 3 broken keys, the contacts still worked fine) , but most of the buttons didn’t work, a lot of the sliders didn’t work, it was strange.

You could play it if you did not need any programming facilities, but this is not why you buy an analogue synth.

The Voice card was quite dirty and corroded, all the trimmers have a green patina from where the metal plating has been eaten through and the copper underneath has oxidised.
This was one of the first synths we have ever had where the option “to scrap for parts” was seriously considered.
The first and most important thing for us to do first was to check the functionality of the rare and expensive envelope generator chips and the filter IC’s, as if any or many of these were faulty, then it was game over.
Despite their very fetching green legs, all of these seemed fully functional.
The left side front control panel board had lots of wire links tacked onto the back, and lots of the connectors had been touched up with solder, and as none of the switches worked properly and the sliders were either not working or just hideously scratchy, this pcb had to come out.
Taking out the 60’s front panel is a tricky job, there are a lot of screws and a number of cable ties to be cut.
To avoid straining the connectors, the right hand side pcb has to come out as well.
With the left side control panel board on the bench and in good light it was time to see what the damage was…

It was nasty, in the past someone or something had punched through the Arpeggiator on/off switch and had cracked the pcb and broken several tracks, not least the ones on the switch itself.
The half-assed soldering on the connectors had lifted many tracks and actually broken some, so continuity checks on all connectors had to be done after repairs were made.
A google and ebay search fairly well confirmed that new sliders were not available, neither were the push switches to select waveforms, so they all had to be stripped and rebuilt.
Actually the Juno’s waveform select switches have a tiny conductive rubber button at their heart, and unlike most tact switches in synths, these are capable of being dismantled and cleaned and rebuilt, so this was done.

I guess at this point in time, We should make some reference to the heading of this month’s blog.

At what point can a synth be said to be really alive?
How many faults should a synth have before it’s one of the living dead?
When should you just shoot it through the head? (or scrap it for parts)

This Juno is one of those, as was the Polysix from last months blog, the number of hours required to successfully rebuild this exceeded its value many times.

Of course it is not just synths that can be the living dead.
Boss BF1 flanger

We get a steady stream of guitar effect units through the shop, most of them are analogue and most are
vintage and most of them have relatively simple faults.

Most effects pedals have only a handful of IC’s and a few transistors in them, so most are relatively quick and inexpensive to repair. The most common issues are related to the power supply section (if an external power supply can be used), battery connectors, jack socket issues or broken wires.
But not always…

This particular pedal was another internet buy and was sold as not working, so no surprise that it wasn’t.
On opening up the pedal, there was an obvious black scorch mark near where the power supply regulator lives, and signs of some rather bodged repair attempts, and the replacement of 2 diodes, one of which was the wrong type, and the other was put in backwards. There was no power to the pedal until this was rectified.
According to the label on the bottom of the pedal itself, power is to come from a 9 Volt centre pin negative similar to the type used by all later small Boss pedals, but the schematic and the BF1’s onboard power regulators both indicate a power supply voltage of at least 12 and a half volts.
After buying new components for the power supply, and new capacitors for the whole pedal, and having installed them, it was time to power it up from a 12.5 Volt power supply.
The pedals power supply was now putting out a nice clean 11 and a bit Volts at the regulator but a lot less at the important circuitry. While poking around with a multimeter, there was a lot of heat coming from something, and that heat smell from components that never bodes well.
The 2 CMOS chips that provide the clock pulses to the BBD delay chip were too hot to touch, something that CMOS IC’s should never normally do, so they had to be replaced, and good quality IC sockets put in to take the new ones.
Once this was done, the power was correct across the entire pedal’s circuit board but it still didn’t work.

There were clock pulses for the BBD now, and the manual control changed their frequency, but the modulation oscillator didn’t change the frequency at all, and the essence of a flanger (or chorus) unit is the up and down sweep of the BBD clock frequency.
Guess what, the LFO chip was dead. Another nice socket and new IC and we had the clocks doing something similar to what the service manual said they should, but still no flanging.

Input signal went into the BBD chip and suitable clocks also did, but there was no output from the BBD at all. A lot of testing was done to make sure that everything else was OK and that the BBD itself was the next culprit. It seemed to be and in time another rare and expensive SAD1024 chip was obtained at a cost of nearly €50 .
Another nice socket went in and the replacement chip was unpacked to go into it.
Easy and job done… like heck it was.
The new chip looked liked it had been stepped on with work boots, all the pins were crushed and bent into the underside of the chip body. It took a lot of very careful manoeuvering with precision pliers and tweezers to even line the chip legs up to go into the socket, and when it did the flanger still didn’t work.
In the vain hope that the new chip might be good, another chip in the post BBD section was replaced.
Still no joy, 5 out of 7 of the chips in the pedal have been replaced, and no one is going to invest in another SAD1024 BBD to double check if the so called new BBD was actually faulty.

It is on hold until either satan skates to work or another pedal comes in using the same BBD IC so that we can confirm one way or the other.

Zombie equipment, landfill was too good for this one.


Prophet 5

March has been an interesting month, with a wide variety of equipment coming through, but amongst the most challenging have been a Rev 3 Prophet 5 and a Korg Polysix.

Prophet 5

This particular synth is a Rev 3.3 with 120 Presets, one of the later ones made in July 1982.
It used to belong to a hire company here in Dublin, and was for sale for quite a while through the local internet trade site. Unfortunately during this sales drive, it died totally, and one of our clients took the gamble of purchasing it at a much reduced price in the expectation that it could be repaired.

The electronic repair of the synth was the easy part. An important chip in the microprocessor section had failed but it wasn’t too difficult to diagnose and replace. After that it booted, tuned and played fine, there is no issue with expensive CEM chips and all 5 voices seem to be perfect.

The main issues with this synth turned out to be related a period of non use and storage in a less than ideal environment, probably cold and damp and not in a flightcase. Also the synth had heavy things dropped on some of the pots (or had fallen heavily on something else) as there were dents on the front panel at both ends of the panel and a couple of broken pots.

It was time to dismantle the front panel pcb’s.
Apart from obvious damage to a few pots, the main concern was corrosion of the pot bodies, it took WD40 rust release spray to even unbolt the pot locking washers to release the front panel boards.
The pots themselves were completely coated with a white powder from oxidation of whatever plating they originally had, and the lubricant grease had turned to something resembling candle wax.
As a result, all of the pots had to be desoldered from the circuit board, dismantled, cleaned, regreased and reinstalled onto the panel boards
The hardest and most time consuming part of the operation is removing the pots from the P5’s front panels, as they are plated through holes with very large track pads, no fear of dry joints with a Prophet front panel. Care must be taken to clear the pots’ mounting pins on both sides of the circuit board, as dragging the pots out will break tracks and you don’t want that to happen.
Replacing the pots afterwards is also tricky as they have to be carefully aligned for height and flatness as the pot bodies float in large holes in the front panel pcb’s, they don’t just lie flat on the boards.

The pots themselves are made by a company called Centralab in the US, not a name we’ve come across often, but the pots themselves are a joy to work with. They dismantle easily into 4 parts which can be individually cleaned and greased, and they reassemble neatly and without fuss.

With the rebuild of the front panels complete, it was time to take a hammer to the front panel.
The metal front panel was removed from its walnut sleeve (don’t hammer a Prophet while its wearing the walnut). The dents were around the Polymod Osc pot at one end, and around the Amplifier Release pot at the other. Pieces of 50mm square wood were used to cushion both sides of the panel and to prevent scratches as Harry the hammer (our financial controller!) did his work.

With that done,it was time to reassemble the front panel with its pcb’s which went smoothly, all the pots lined up with their holes and the WD40’d locking nuts tightened up nicely.

As this project moved from being a repair to becoming a restoration, the keyboard itself was next to get some TLC. A set of keyboard bushes were obtained from Arcsound in the US.
We were a little sceptical at first with the claims made about new bushes on a Pratt-Read keyboard, but we were pleasantly surprised by the results.
The old bushes were a shade of grey (originally they were black) as the lubricant on them dried out and turned to a powder like talc. The black and white key tops had to be removed, and a sharp craft knife used to cut out the old bushes.
When all 61 keys were re-bushed, we were impressed by the smooth action of the keyboard, and particularly the absence of key clack during fast releases, a feature of most old P-R keyboards.

Final assembly and test are imminent as soon as the benches can be cleared…


Needless to say this went well and the synth has gone back to its owner
Korg Polysix

The other intriguing synth of the month is a Polysix.
Bought as a fixer upper, the symptoms all pointed to the leaky battery and acid problem.

The Programming system didn’t work, all the presets sounded the same, and random lights came on in the programming section, and a lot of the programming switches didn’t work.

The obvious first port of call was the pcb near the battery, full cleaning with an Ammonia based cleaner followed by Isopropanol to remove any traces of the original battery acid.
Ironically some previous owner had taken the original battery from the CPU board and put a Lithium battery in a custom holder to the right of the Voice card. Unfortunately the damage was already done and the modifications to the CPU board that are necessary to cope with a Lithium battery were not done which meant that the large new battery was also dead on arrival.

Taking out the KLM367 CPU board after some preliminary diagnosis told us what the internet folklore says. IC31 was faulty and lots of tracks on the topside were open circuit due to the battery acid eating through them.

Careful and thorough point to point measuring of the track resistance, and also checking plated through hole resistances, the replacement of IC31 and the use of Kynar wire links to replace damaged tracks got us to first base (repairwise).
Now the synth booted and the programmer section did most of what would be expected. At this juncture it was obvious that a lot of the tact switches in the Programmer section were faulty, another clue was that the pcb the switches live on was severely bowed inward from endless repeated attempts to make buttons work. A new CR2032 coin cell holder (and battery of course) were installed on the KLM367 to take over the backup duties.
The Programmer section looked good and the arpeggiator was working well, so time to maybe load the factory presets into it from a Laptop file. The file appeared to load faultlessly but there were still no presets, just the random gibberish from before. More Scope and Logic Analyser analysis said the Memory chip was dead, none of the tracks were, that had been checked thoroughly in Phase 1 of testing.
The old RAM chip was removed , a socket put in and a 6514 RAM chip from a Moog Source put in as a temporary measure. The presets were reloaded and lo and behold they were there, even after a switch off and back on again, and they have been since.
The next major niggle was that only 3 voices made any noise, and they were very different from each other now that the factory presets were present and correct.

Now for an additional surprise, there was acid damage on voices 5 and 6 on the KLM366 voice card.
Much thinking was done and some consultation with other Polysix owners was had to figure out how battery acid could leap from the left hand side of the CPU board to the bottom right hand side of the voice card over 50cm away without damaging anything inbetween. There was no storage scenario which could lead to those effects.
Voice 6 was dead and Voice 5 was flaky, so a thorough investigation of the tracks in that area was undertaken, as it turned out there were more damaged tracks on the voice card than on the CPU card,
After considerable thought it struck us that whoever took the original battery from the CPU board had replaced it with equally dangerous battery technology in a custom holder to the right of the Voice card which did the same damage there. We are thinking Zinc batteries for the replacement as we had to cut out and replace not only the resistors in the Voice 5 & 6 section but also the IC’s and most of the transistors.

Having got this far, it was time for some calibration, the acid test to see if a synth is working properly.
It wasn’t, we now had 6 oscillators working perfectly but still only 4 voices, two of them just produced thumps when activated. (but please see addendum at the foot of this section).

As it surprisingly turned out, 5 out of the 6 filter IC’s were failed, and the 6th wouldn’t calibrate properly, it would make sound and some resonance but not enough. In more detail, 2 of the filter chips (SSM2044’s) had no output at all and 3 others had no resonance control. The 6th IC had output and resonance but ran out of bandwidth far too soon.

Lots of double, treble and quadruple checking was done to see if we had missed something, but no we had not, we also could not believe that all the filter chips were faulty, but they were.

Our client procured a full set of filters on Ebay for a reasonable price and when they arrived we installed them. Immediately there were 6 voices and they all calibrated beautifully.

While waiting for the filter IC’s and a complete set of 19 tact switches for the programmer section to arrive, attention had to be paid to the other issues that the synth had.

The keyboard had multiple faulty keys across its entire span,which obviously required a complete strip and clean of the whole contact strip pcb (several times). Quite commonly with many of these older rubber contact keyboards, if you fix one key problem, another will appear elsewhere and it often takes many attempts before the whole keyboard works properly..
The volume pot was unusably intermittent and scratchy, needing to be removed from its front panel pcb, and then dismantled, cleaned and rebuilt. Surprisingly enough, both output sockets were so corroded and dirty that they too didn’t work. They had to be removed from the rear panel and the contacts cleaned and polished with metal polish.

The addendum is the latest bad news from this Cerberus like synth.
Each time the synth was turned on, Voices 5 and 6 would be out of tune with the others, they could be recalibrated fine and would work for the time the synth was switched on but after a switch off and back on again they were way out of tune again. As the Polysix has no Autotune feature, this is something that has to be rectified.
After removing the voice card yet again, and cutting out the remaining IC’s around Voice 5 and 6 along with the remaining resistors and more transistors (the reason being not so much because the components themselves are faulty but because it is almost impossible to thoroughly clean the pcb with the components in place). Also, the Oscillator section of the Polysix is very densely packed and even getting meter probes in there is almost impossible, added to the fact that the acid corrosion makes the outside of the solder joints an insulator, thus making continuity and resistance measurements at least unreliable, and at worst impossible.
As of early May, voice 6 is fine but voice 5 is still flat and non-linear, not by much but still not right.
Tomorrow is another day…

Another day dawned, and the keyboard was taken out once again to allow test equipment access to the oscillator section. Apart from the K30A O FET, everything in voice 5 was brand new but also of the original type. In a moment of desperation we replaced the TLO72 with a TLO82 just to see what difference it made.
It did make a difference, voice 5 was now sharp, we thought great, trim it down and job done.
Not so, when voice 5 was flat, the tune low trimmer ran out of track before tuning was achieved, when it was sharp the same thing happened at the other end of the trimmer.
We next tried a TLO62, and in a Goldilocks moment, it was just right.
Finally as of May 6th, this one was put to bed.


ARP Axxe

Out of the blue we got one of these recently. It was built into a very thick plywood flightcase which meant that cosmetically it was very good, and weighed nearly as much as a Jupiter 8. As it arrived it was not a synthesiser as nothing worked, and the reason was the usual ARP one of faulty sliders. The action of these was unsurprisingly awful, very stiff and jerky and not making anything resembling a good contact.

The obvious thing to do is to strip out all the sliders from the main PCB, dismantle, clean and carefully rebuild them, but this is a job that is fraught with difficulties. Getting the sliders off the circuit board cleanly is hard enough, due to the mechanical clamping mechanism that CTS designed into the system. Dismantling them is also tricky, as the means used to hold the two halves of the slider pot together is a crimping system that doesn’t repond well to being pried apart, and often breaks. We did out of necessity develop a technique of repairing this failing.
Then original grease used as the slider lubricant has turned to some kind of dark sticky sludge, and is partly responsible for the poor slider action, but dust and dirt under the skirt of the slider cap is to our mind the main culprit, as an experiment we tried to resurrect a dead slider by removing all contamination from the slider skirt to see if this was a viable possibility. It certainly improved the action of the slider but didn’t actually repair the fault.

To cut a long story short, we did strip and rebuild all of the sliders, they took half an hour each, and the synth worked perfectly after.
Do we want to do it again… We don’t think so… Please buy replacement sliders from anywhere else.
Or buy a Pro 1…