Korg Mono/Poly

Hello Chase

first my usual disclaimer:
THIS MAIL DESCRIBS AN ACTION THAT REQUIRES TO OPEN THE CASE OF THE 
MONOPOLY. THIS SHOULD ONLY BE DONE BY PEOPLE, WHO KNOW HOW TO HANDLE THE 
DANGEROUS VOLTAGES INSIDE OF THE SYNTH PROPERLY WITHOUT ENDANGERING THE 
LIFE OF OTHERS OR THEMSELVES!!! IF YOU DON'T HAVE THE REQUIRED 
EXPERIENCE - KEEP YOUR HANDS OFF!!! DOING THE WRONG THINGS INSIDE AN 
ELECTRICAL INSTRUMENT MAY KILL YOU OR PEOPLE, THAT RELY ON YOUR WORK. I 
WARNED YOU. I REJECT ALL LIABILITY FOR ALL CONSEQUENCES OF THE FOLLOWING 
INSTRUCTIONS!

> So even if I replace this fuse and it seems perfectly fine, wouldn't a 
> fuse blowing be indicative of a problem?  There wasn't really a power 
> surge as far as I could tell and I think this fuse is only a few years old.
It might(!) be indicative for a problem - especially because the 
transformer was that hot.

I recommend the following procedure:
* Switch of the synth, and remove the powercable from the power outlet 
in the wall.
* open up the synth
* take a thick and stabile sheet of paper and cover all parts at the 
bottom and rear side of the synth right side of the transformer with it 
(powerswitch, main fuse pcb, transformer-connections)
* Do NOT switch on the synth until you replaced the fuse.
* Remove both fuses on the powersupply pcb - still do not switch on the 
synth.
* Disconnect all cables from the powersupply pcb with exception of the 
cable coming from the transformer.
* Prepare a digital voltmeter, which can read DC and AC up to 50 volts.
* Connect the minus measuring cable to the wire coming out of the right 
side of C14 (the largest capacitor on the right side of the power supply 
pcb)
* Set the voltmeter to AC
* Plug in the power cable to the power outlet in the wall
* Switch the synth on
* Measure the voltage at the frontside contact of the fuse sockets => it 
should read about 15 to 20 Volts, but both contacts should read the same 
voltage
* Switch of the synth
* Insert good fuses to the sockets
* Set the voltmeter to DC and be prepared to measure immediately after 
switching on the synth
* Switch on the synth
* Measure the voltage at the most rear contacts of diodes D2/D3 and 
D4/D5. It should read somthing around 20 to 25 Volts DC; again I can not 
tell now exactly what voltage, but it should be the same on both 
measuring points.

If any of these measurements fails or if the fuse blows again, then get 
the synth to a technician, who knows to handle this.

If the mesaurements before read ok, then:
* Measure the voltages at CN33. They should read from left to right: 
+15V, -15V, +5V, 0V. The pins for -15 and +15 may read a little bit 
different values like 14.98 or 15.02, but it should NOT be like -15.01 
and 17.5; if this is the case, then switch off the synth and bring it to 
a tech.
If both read a similar but wrong value like +13 and -13, then try to 
adjust the voltage with the trim potentiometer VR3. VR3 affects both 
voltages.
If +5V reads a slightly other value (like +5.02) it is ok. If it reads a 
very different value (like 9.02), then switch off the synth and bring it 
to a tech.


Florian