Korg Mono/Poly

Hi all,

I'm a owner of a japanese old revision MP4 that died on me yesterday.

What happened:
- I just finished modding the MP4 with several great mods I found here (the MG1 speed and EG speed). It was working fine than I decided while I was on it to check on the FX on switch that was not working correctly.
So I had to remove the KLM354 board first (I never did it so far) to reach the switch. I resolder the switch and then I powered the synth on, while still having the 354 board not in place (but fully plugged). I check that there was no shorting whith the 354 board floating. It seems ok.

But when it powers on I did not see the leds go on and a few seconds later I saw smoke coming from the 354 board. I immediately turned it off. I checked where it could come, it seemed coming from the SSM2033 but I could not confirm, I could not find a part that was really hot.
I put the 354 back in place, checking every connector to see if there was some loose or some shorts.
When I second turn the synth on the MG2 led showed, followed by MG1, though they seemed dimmed. I could play the synth for a second and then it completely died and I could not turn it on since that.

Now I don't know the exact damages and would like some help to revive it.

What is sure is that the 376 board is damaged because I don't have the +15v -15V or 5V.
So far the reading I got are (schematic is here: http://fa.utfs.org/diy/korg_monopoly/mp_10_klm-376_powersupply_klm-357_vcoheater_schemo.gif):
- 26.5v out of the transformer (on KLM376/ cn37 connector)
- +37v and -37v from the 1S1885 diodes to the inputs of the M5230L (pin 7 and 4)

I have no output reading from the M5230L. So does it means this one is fried or can it be some other componant that makes that I have no output from the M5230L ?
I'm not a real technician, I don't know much but if someone can explain I can track the problem.

Hope someone can help.
Thanx in advance

Hello iscrites

first of all before you switch on the synth: unplug the five connectors
CN 31 - CN 35 from the powersupply before you start working again. Do
not reconnect them until den power supply works correctly. After the
powersupply has been repaired. Connect them one by one and measure the
voltages after adding each connector.


To the problem:

> - 26.5v out of the transformer (on KLM376/ cn37 connector)

26.5V AC between the two hot transformer outputs looks reasonable.

> - +37v and -37v from the 1S1885 diodes to the inputs of the M5230L

(pin 7 and 4)
Did you measure this against ground (pin1 of M3250L) or did you measure
7 against 4? If 7 against 4, then it sounds reasonable. What does read 7
against 1 and 4 against 1?

What is broken then I cannot judge? And often it does not make sense to
repair such an old powersupply.

You may use simply a completely different powersupply, which provides
+15,-15 and +5 Volts. You may use also a switching powersupply block
like a Mean Well or a Traco. I prefer Tracos as they are nearly
undestroyable.

Florian





Am 23.10.2012 14:45, schrieb iscrites:

> What is sure is that the 376 board is damaged because I don't have the +15v -15V or 5V.
> So far the reading I got are (schematic is here: http://fa.utfs.org/diy/korg_monopoly/mp_10_klm-376_powersupply_klm-357_vcoheater_schemo.gif):
> - 26.5v out of the transformer (on KLM376/ cn37 connector)
> - +37v and -37v from the 1S1885 diodes to the inputs of the M5230L (pin 7 and 4)
>
> I have no output reading from the M5230L. So does it means this one is fried or can it be some other componant that makes that I have no output from the M5230L ?
> I'm not a real technician, I don't know much but if someone can explain I can track the problem.
>
> Hope someone can help.
> Thanx in advance
>

--
http://fa.utfs.org/

Thanx for the reply.

I took the precaution of unpluging the 5 left connectors.
Though when I did it I have the 4 VCO leds that lit. I guess the power comes from the KLM357 board but how does this one get it ?
There is a red wire connecting + side of KLM376 C14 to input of KLM327, so I guess it come from that.

To answer your question:
- I got -37v between pin 1 and 4 of the M3250L
Actually I have a fried resistor on R15 so I can't read pin 7 but I read 37v on + side of C14, so it should be the same on pin 7 wasn't it for the fried resistor.
I fried that resistor (I guess) by reading C13 yesterday and I guess I short circuit the C13, there was a explosion and the R15 was fried. Well maybe it was fried before the explosion but I didn't notice it.
I did not mention this because I guess it should still get the -15v and +5V even without it, no ? (I just don't have a 130 resistor on hand)
Another thing is I don't always get the same readings. Sometime it's more 35v and sometimes more 37v.

I thought of changing the power suplly completely (and using a 230v one) but I lack some knowledge:

- what current rating does it need to be ?
- how should I feed the 36v to the KLM327 ?
- how do I make the 5 connectors (by cannibalizing the KLM376) ?

Can you point me with an appropriate power supply ? (on ebay, mouser, conrad etc)

Thanx a lot

Hello

> I thought of changing the power suplly completely (and using a 230v one) but I lack some knowledge:
>
> - what current rating does it need to be ?

I think you will need 150mA for each section, but I am not sure. The
specification in the servicemanual does not name it.

> - how should I feed the 36v to the KLM327 ?

argh! I forgot about these. It will make it complicated.

> - how do I make the 5 connectors (by cannibalizing the KLM376) ?

Yes

> Can you point me with an appropriate power supply ? (on ebay, mouser, conrad etc)

If my specifications are right
http://de.farnell.com/tracopower/tmp-15515/wandler-ac-dc-5v-15v-15w-module/dp/1672148


Maybe you should look out for a used Polysix PSU. They might be identical.


Florian

--
http://fa.utfs.org/

So I guess without the 36v for the KLM327 it is not possible to use another power supply.

Also forgot to ask earlier but if you use another power supply, how can you fine tune the voltage to make it meet the specifications in the service manual ?

Some news:
After several attempts of reviving the power supply I bought a 15v, -15v and 5v power supply and installed it today.

Good news is that it works and almost every aspect of the monopoly is working.
The only problem I have now is that if the KLM398 board is connected, the sound of the osc is a weak distorded high pitched sound and I can not pitch the sound (either with the keyboard or arp or transpose).

If I disconnect the board, I have 4 perfectly sounding osc which I can change waveform, but still no pitch control.

I thought the 398 was the culprit but I changed the 2x TL072 and it did not change anything.

I guess the problem is with voltage control of the OSC. Where should I investigate ?
i checked the voltage on the connectors of every board and I read the 15v, 15v and 5v.