Korg M1 - No Power. Help/Advice needed

[Zarg]

I hope someone can enlighten me.

I have a Korg M1 that has been a faithful servant since 1989. I haven't used it for the last few years. Recently I have gone to switch it on, and it is totally dead. No power....nothing.

I have tried eliminating the obvious possible causes (lead / fuse) without success. I have also opened it up to see if there was anything oviousely wrong inside (ie broken fuse), but did not spot anything.

I phoned up a synth repair centre who quoted £60 + vat per hour to have a look at it (seems a bit steep to me). Before forking out on expensive repairs, is there anybody here who has either experienced this kind of thing, or has a gut instinct on how to go about solving this as inexpensively as possible. I don't mind attempting basic electronic repairs.

BTW i'm in NW London if anyone can recommend someone in this neck of the woods.

Hope to hear from someone....

[synthjoe]

I don't mind attempting basic electronic repairs.

Do you have some experience with it and potentially with switching PSU's plus mains level voltages, or you just don't mind attempting? Because in the latter case I'd say that a SW PSU (or SMPS for Switching Mode Power Supply) might not be the best project to start with. Voltages over 300V and some intricate circuitry and electronics priniples are involved, so it is an involving and dangerous path you're putting your foot on...

WARNING!!! If touching or approaching the inappropriate soldering point, lead or component on the board, you can really get yourself seriously injured or even killed! If you feel comfy with all of the above, check first the presence of the approx. 315V on the first buffer capacitors in the PSU (probably the two largest capacitors on the board, pos. No. C11 and C12), after the rectifier bridge. If you have it, then fuse, bridge and capacitor are OK, so a simple fix is unlikely, you'll have to get into measuring and analysing other parts of the power supply, which will require some other equipment I'm not sure you have.

You can have some reading material here. Let me know if you want to proceed and need further help.

[Zarg]

Thanks for the reply.

I haven't any previous experience of this kind of repair, so I appreciate your safety warning.

I do have plenty of experience of opening up synths etc, to replace keys / pads / springs / plugging in boards, etc. When I opened up the M1 this afternoon I saw (assumed) that the power supply was the whole of the board in the picture on the thread you linked to in your reply. Following my logic, I was thinking that if I could replace that whole board with a working one it would be a simple matter of replacing like for like, with nothing too complicated. Am I barking up the wrong tree here? If it is a case of just swapping the boards over is the danger factor reduced?

[synthjoe]

Yes, of course the risk is reduced, but you'll need to find a replacement. Which is currently likely to be inside another M1 that is working. So effectively you'll be buying a working M1 to make it non-working - what would be the point of taking that apart? On the other hand you can try to order the board from Korg, but it'll be probably not cheaper than either of your other options (fixing or getting another M1).

If I were you I tried to find a friendly old guy still fixing old radio or TV sets (maybe as a hobby) and try to bargain. With the schematic they'll go a long way. The component to replace is probably not a big expense, but zeroing in on it is time consuming and takes skills and tools, that's what you'll have to pay for, unless you have it up your sleeve.