Korg Mono/Poly

This could be a long post so I'll split it into several parts as it probably won't be interesting to most. I though that I would share my complete rebuild experience with you as there could be some useful info for other MP owners out there. I've only posted once before on this group - that's because my Mono/Poly has been in the corner of the workshop doing nothing for a couple of years. Tell me if these postings are inappropriate or need to be put elsewhere as I appreciate the requirement of brevity on these forums.

I bought it a few years ago as a non working synth as the previous owner had connected it to the mains supply here in the UK not realising that it was a US model. That didn't do it a lot of good I can tell you! The power supply in a MP is a potential weak link at the best of times and doesn't do the rest of the electronics any favours when faced with double the incoming mains voltage, but more on that later. The regulator transistors shorted and put sky-high levels of what should be +15, -15 and +5 into the boards.

I like to work backwards on a synth rebuild project so that the audio stages are available when it comes to getting the VCOs working and I can use the synth's own wiring harness too as I go along. First, I removed the KLM-353 board (out/headphone amp, MG1&2) and powered it up from my external supply - there was a dead short on the power rails. Every IC had blown; all five of them. I replaced them and powered up the board again. This time I was rewarded with a sound in my phones when I injected a signal into pin 3 of connector 2. The LEDs for the two LFOs seemed to blink correctly as the frequency pots were advanced so I left it at that. With the board back in the synth and wired in, I turned my attention to the KLM-355 board (VCF, EGs, Noise Gen & VCA) and powered it up - again there was a dead short on the 15 volt rails and again, every IC had blown, including the SSM2044 VCF chip. That's 9 ICs in total for that board. With those ICs replaced, everything on that board seemed in order. With the VCF sweeping nicely and the EGs/VCA doing their bit when triggered from an external push button I'd wired up, I put that board back in the synth.

This was going well but what I didn't realise at this stage was that I'd just tackled the easy bits and the real problems were yet to come.

Steve

Hello Steve

As every good author of a thriller, you know when to end the chapter
still keeping the suspense... ;-)

If I am allowed to forbeode:

Chapter 2: the VCO-chips were blown too, and it was impossible to finde
some, so you added interfaces to four CEM3340

Chapter 3: The CPU was blown too of course; no spares here too. So you
decided to rewrite the Firmware for arduino and implemented also full
midi controll for all CV-controllable parameters

;-)


Florian

fanwander@mnet-online.de wrote:

> Hello Steve
> As every good author of a thriller, you know when to end the chapter
> still keeping the suspense... ;-)
> If I am allowed to forbeode:
> Chapter 2: the VCO-chips were blown too, and it was impossible to finde
> some, so you added interfaces to four CEM3340
> Chapter 3: The CPU was blown too of course; no spares here too. So you
> decided to rewrite the Firmware for arduino and implemented also full
> midi controll for all CV-controllable parameters
> ;-)
>
> Florian
>

Chapter three isn't entirely beyond the realms of possibility! A guy over on
the Roland Jupiter forums built a replacement CPU for the Jupiter 4 that added
editing of patches and support for MIDI control of a number of parameters. He
also upped the patch memories from a measly eight to sixty four.

Chris

I'll keep the suspense going a bit longer Florian :-)  Some damn fine ideas you've got there though..........