Perhaps a bad 4051 pot multiplexer on the KLM-369 board?

Sounds like a stuck data bit or bits going to the DAC (which in this case is just fixed resistors). I'd check the buffers (inverters) on the data bus ahead of it with a logic probe or scope. IC18 & IC21.

Google "how does a voltage divider work" and you'll see why it doesn't matter if the pots aren't exactly the same values, or if they are replaced with different ones.

Yeah, you'll need a 2732 EPROM. Each manufacturer had their own prefixes and most of the time, the only differences were the programming voltages. So you just need to find a chip that your EPROM programmer is compatible with... Then maybe download the datasheet for it and compare the pinout to the O...

Sounds like you just need to burn an EPROM and you're good to go!

It's been a while since I worked on one with JL Cooper MIDI, but to revert to stock most likely all you need to do is: 1. Unplug the daughterboard from the main board (I think 2 ribbon cables? 1 into processor socket as pictured and probably another into a DIP-14 socket which was for a CD4011) 2. Tr...

There are a bunch of chips (the ones you listed included) that were on earlier revisions of the main board, but were removed by your revision.

I think I may have showed this in one of my Prophet 5 repair videos, but a good reason is if the oscillator isn't stable, and it comes in and out of tune. Find the oscillator in question and attach a scope to the CEM3340 chip and you'll get to the bottom of it very quickly.

You have an oscillator that's out of tune. You hear it every 6th keypress because it's a 6 voice synth and it round robin assigns key presses to a voice.

Ashe37 wrote: ↑

Fri Jun 12, 2020 3:31 pm

'new digital versions'?

I would assume he means new surface mount clones.

To the OP, I would recommend using an oscilloscope to find what your actual problem is before guessing and changing stuff. You may wind up doing more damage than good.

They didn't want to make it easy on anyone, they're not labeled on the board. The test points are listed on the schematic, and you need to figure out where those parts correspond to on the PCB using the PCB layout diagrams.

Most transformers that are available off the shelf have 1 or 2 secondary windings. This one has 4 secondary windings. (basically it's 2 separate center tapped transformers in one unit).

Mouser has 4,651 power transformers listed on their website. Only 11 of them have 4 secondary windings.

If drilling holes bothers you, you can always make an adapter, like this adapter I have to mount a modern fan in a Memorymoog: https://synthchaser.com/product/memorymoog-fan-adapter-plate/ Mouser sells the 18VCT and 36VCT transformers. Based on what you said about your skillset, I'd recommend you ha...

I don't think you'll find a drop in replacement for this configuration. You should be able to put in 2 separate toroidal transformers, one with 18VCT secondaries and the other with 36VCT secondaries. In fact, I may consider doing this in mine...

The service manual has 6 pages of test points listed, with illustrations of what waveforms you should be seeing on them with your scope. I'd check it out before trying to fix anything. And spraying these sliders is a bad idea, there are some good videos on how to clean them.