Just a few days ago, we were given a Virtuoso 2000 to fix with an almost unreadable display.
You can read it at the 6 o’clock position but at no other angle.
The Virtuoso contrast control system makes a difference but nothing useful, going from +7 to -8 just makes things worse.
As techies, we know a bit about LCD’s and as the display’s contents were correct for every menu choice, and the backlight was fine, we went hunting for a fault in the V2k’s contrast control system.
A latch chip on the V2k acts as a 4 bit DAC that supplies the contrast voltage for the display. Thorough testing of this system showed it to be working fine, the only oddity was a -16 volt on one side of a 10k resistor used as a bias for the contrast system.
We didn’t pass any remarks on this at the time, and proceeded to fit a contrast trimmer to the display itself to make sure the display was OK.
It was, the trimmer was able to make the display perfectly visible from in front, the V2k’s visual angle control still worked.
We were just going to install the trimmer permanently and call it job done when we had a Eureka moment about the -16V we found earlier, could the power supply be at fault?
It was, we were getting the 5V the DSP’s need but +18V and -16V on the rails for the analog parts, this didn’t affect the audio but was messing up the contrast system.The normal analog rails are +- 12V.
We are not used to the idea of switchmode PSU’s going out of tolerance, usually they work perfectly or not at all.
We rebuilt the switcher by replacing all the capacitors on the low voltage side of it, using capacitance values from the Motorola Datasheet for the 3844 chip used in the V2k, our theory being that that the 5V rail was struggling to achieve 5V, and thus lifting the other 2 rails.
After the rebuild and test, the voltages on the PSU were 5V and +-12.5 Volts, and the standard contrast was perfect.
The bottom line, if you are techy, try what we did, and if not, try swapping power supplies if you have more than one 2000 type EMU, to confirm the contrast issue is PSU related, and then buy a replacement from EPR.
All the above was done without the aid of any EMU service manual.
The Dark side of the Korg
This is definitely not any kind of rant against Korg products, but more about the dangers of the wrong wall wart being plugged into them.
We have a Microkorg, not much more than a couple of weeks old that was brought back from the US as a present and which now sits in our workshop as dead as a dodo… the reason, someone managed to plug the US style wallwart into an Irish/UK style socket and feed 230 Volts AC into a wallwart that was expecting 120 Volts.
Apart from probably killing the wallwart, it has also killed the Microkorg. There are a few burnt components on the Microkorg’s main board, and a couple of others which get very hot but are not identifiable as they are surface mount parts and the part type is not identifiable from the 3 letter codes on them.
We also have a Kaoss Pad 3 to which the same thing happened, it also happens to use the same power supply components in it as the Microkorg.
In storage, we have a second Microkorg which also died due to US wallwart power injection, this was destined to be a donor for parts such as knobs, switches, keys and jack sockets.
We have emailed Korg UK for some assistance in identifying the failed parts, and hope for a satisfactory response.
A few days later…
Actually, Korg UK responded very quickly to our requests, the head of spares not only gave us a good price on a replacement main board for the Microkorg, but also sent the service manuals for both the Microkorg and the Kaosspad 3.
The knowledge gleaned from the Microkorg service manual and subsequent measurements across the machine said that a new main board was necessary and this was ordered.
The jury is still out on the Kaoss Pad3 due to time constraints, but kudos to Korg UK’s service department for a very prompt response, and for giving us the right information to make a competent diagnosis in a short space of time.
A level of service that maybe some other manufacturers could aspire to?
Wallwarts and how to successfully live with them
Plug in power supplies (or wallwarts as they are commonly known) are here to stay.
A great many modern Digital devices use so little power that it is not cost effective to fit a direct mains power supply into the instrument itself, and the costs for the manufacturer of meeting type approval across the many countries around the world would be prohibitive. The constraints are much relaxed when feeding a low voltage into a device, as 9 to 12 Volts AC or DC are not going to kill anybody.
A modern home studio, and even some professional studios, may have at least half a dozen or more devices running from wall mounted power supplies. Some will ouput AC, and the rest will be either positive or negative centre pin polarity, getting either voltage or polarity wrong could damage a valuable piece of equipment, (anyone out there blown up a TB303).
The key (in our view) is a combination of taping and labelling.
If your device needs an adaptor transformer (for a product bought in America with a US wallwart), then tape them together with black PVC tape, and then label the top of the US wallwart with white PVC tape and permanent marker stating the name of the product it is to be used with.
If it is a European wallwart, the concept of labelling still holds good, DC power connectors all look the same regardless of the polarity of AC/DC on the connector itself, and a good clear indication on the power block itself might save you from a world of expensive hurt. It doesn’t take long, it’s not expensive, and will make your life easier and your equipment safer from pilot error.