Korg Forums

[sanmandon]

I am trying to repair an 01/WFD and can't seem to get -12VDC to work. I see some cut traces and a wire mod on the board. I am concerned these may not be factory mods. I am looking for a good hi res photo of the component side of the KLM-1528C board.

[smoonbeast]

Do you need service manual, maybe?
There's pretty clear schematics in it.
Let me know, if you need it.
I have Pro and WFD sm versions in pdf format.

[sanmandon]

I do have the schematics in PDF and will try to compare them to the physical board. Basically I see three cut traces and a jumper wire. I measure -11.85V at the pin header connecting to the power supply, but everywhere after that I get .75V so I'm missing both the -11.5V and -5.0V that is produced by a voltage regulator on the board. There was a point when the voltages were present but -11.85 wasn't getting to some op amps in the last stage before the output jacks (so no sound was coming out). I traced the problem down to a broken trace, but as soon as I connected it I lost the -11.85V all together. Now I can't get it back and even if I do, I still need to figure out how the get -11.85V to the op amps without causing problems.

Thanks for your offer though.

[smoonbeast]

I am no that familar with 01/w PSU, but I suggest you to try a substitute for a working one PSU. All voltages can be found at ATX PSU, for example.

It sounds like faulty transistor in PSU, or modded PSU, so cuted traces were make sense. I hope you didn't burned opamps.

Thought I am big fan of AI2 synths, I found that I've no photo of 01/w mainboard in my collection, sorry.

[AJ]

Hi Sanmandon, I've only just joined this Forum and have come across your post. Do you still need some pics of the main board? I have a couple of good working 01/Wfds, so I could take some pics if you still need them...
Best regards.
_________________
AJ, London, UK.
Keyboards owned: 01/W fd, Hohner Clavinet/Pianet Duo, DX7S.

[samriccijr]

Sanmandon:

If the caps leaked, then the fluid could have damaged the circuit components or circuit traces. If caps were replaced then the traces and eyelets could have been damaged. Then you have to jumper with wire..on both sides of the mainboard.....I learned this after rebuilding four 01/ws....l

You can find the service manual online.

Unplug the mainboard and check the two diodes on the power supply for stable plus/minus 12vdc. If it starts at twelve then drops or flutters then consider replacing the 79m12 voltage regulator. It might just be broken solder joints here. This is a good time to recap the power supply too.

Plug in the mainboard and check c18 and c20. If 12v is missing here it could be the power harness, c20 or a damaged eyelet trace between them. Replace caps on these power rails. Be careful not to damage the trace when you replace the caps.

Check IC 39/40 in the audio circuit for -12v. If none here then suspect a damaged circuit trace between here and c20. Likely the eyelet at c20.

Switch to resistance and Check R143 and R144. (they are next to the famous c95 and c96). They should measure 20 ohms. If higher than 30 ohms replace with a 20 ohm resistor. This is a common failure especially if the caps leaked.

There should be continuity between one side of each resistor back to c19/c20. There should be continuity between ic52 pin1 and ic53 pin 2 back to c19/ c20.
There should be continuity between each resistor and the inputs of ic52 and 53. there should be continuity between one side of each resistor and C95/96. There should 12v here too. If not suspect a damaged trace and maybe a damaged surface mounted 0.1uf capacitor.

Check voltages on c95 and c96. Should be around 12v dc on each. These are the famous leaky capacitors. Replace c101 and c102 too.

Check voltages on ICs 47-51 in the audio circuit. They Should be around 12v here. If not then suspect the traces or eyelets near ic96.

Check the output of ic52/53. It should be around 12v. If not suspect one of these chips. Also check the input voltage at IC34 and ic35. If no voltage here then suspect ic52/53.

Got it? Check these then we move to the audio mute battery circuit.

Good luck!

Sam in NJ