No complaints so far so I'll carry on! The next job was to check out the VCOs so it was out with the mighty KLM-354 board and, being prepared for the worst, powered it up and sure enough both power rails were shorted as on the previous boards. However, unlike the previous boards this could be bad news as the MP uses 4 SSM2033 VCO chips which are not easy to come by and if you do, four of them will make a big dent in your wallet. Even with 22 ICs on this board, I decided to replace them all except for the SSM2033s thinking that a guy needs a bit of luck at least once in his life. Anyway, 18 IC changes later and the moment of truth arrived.

Although at this stage there was no power to the VCO heaters, I connected my bench supply to the board and pressed my (so far) trusty trigger button and managed to get sounds from each of the VCOs. Applying various voltages to each of the CV - Ins (pins 1-4 on connector 12) produced different pitches albeit different for each oscillator. Also the pitch jumped up and down (but not by an octave) with the octave switches. I was pleased at this but not entirely convinced that the chips hadn't suffered some kind of damage otherwise why would all the oscillators behave differently But a noise is a noise and to hope for anything more was perhaps wishful thinking. There is plenty of room in an MP to build some discrete VCOs and do away with the originals, so all wouldn't lost if the 2033s were bad - just a lot more work.

OK, it was time to take stock of the situation. I had replaced 32 ICs and got more square footage of printed circuit board operational than not. I was avoiding the big one - problem that is, not board. Earlier, when looking closely at the main 8049 mask coded CPU IC, I saw a fine crack running half way across its back. I knew this was bad news and perhaps though that it might go away or heal itself if I ignored it and moved on to the power supply - the main murderer in this synth slaughterhouse epic.

Before I started on the KLM 356 processor board I did a bit of research, as I had already decided that an option was maybe to use Paul Maddox's excellent PolyDAC and go the MIDI route but that would preclude the use of some of the MPs key assign modes. It was then that I contacted Greg Montalbano of analogsynthservice.com in the US who sent me over a programmed 8749 replacement for around £25 (it was $30 plus overseas shipping). This is the same chip as the original 8049 except it has an integral EPROM which can be user programmed. I've since seen the binary code on the Zen Mono/Poly website so it's easy to do it yourself if your EPROM programmer supports that chip. So, with new CPU in hand it was time to check out the rest of the logic board.

Next time....... why doesn't the keyboard work or any of the key assign buttons on the front panel What to do with the power supply. Stay tuned.