Circuitbenders Forum > Banter

EMU DRUMULATORS

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Ciderfeks:
Hi Gordon, thanks for your reply, I'll certainly take a look into that. I've only just seen your reply actually - for some reason it wasn't picked up in the "show replies to your previous posts" section that I usually go to first when I log on here, so I just chanced upon it now.

When I opened up the Drumulator, there was some dodgy looking repairs and mods that had been carried out buy a previous owner which I have been slowly going through and returning to normal but still no go, but I have some suspicions....

I am wondering if the problem may be with IC 9B (LM 3086N a transistor array?) which had a diode added, bridging pin 7 and 8. There are signs of heat damage to the surface of the IC where the diode had been.

There was also a repair to pin 1 of IC 12A (CP8251) but as yet I cant find any info on that one. Hopefully the service manual will help. The pin had been pulled from the board and hard-wired to one leg of 3 nearby components, but with no obvious trace damage between those components and the IC, I don't know why this would have been done.

I'm waiting for the service manual to download now...

Gordonjcp:
When I opened up the Drumulator, there was some dodgy looking repairs and mods that had been carried out buy a previous owner which I have been slowly going through and returning to normal but still no go, but I have some suspicions....

Are you certain these were "dodgy-looking repairs"?  There were *masses* of ECOs for the Drumulator, which consist of cut tracks and bridging wires, and extra components tacked on here and there.  Without these, you haven't a hope in hell of getting it running!

Ciderfeks:
Yes, indeed - a quick glance at the service manual when it arrived showed that two of the "repairs" were in fact ECO's (namely the diode added to IC 9b and a bridged cap at C75). These will be going back in, but looking at what they do in the notes, they shouldn't be critical even with them reversed? The machine didn't work with them in place either  :-[ Interestingly the service manual showed up an ECO for my revision that hadn't been carried out, but first things first...

This project is currently beyond my capabilities really but I've been meaning to learn about fault finding and how to read service manuals  so this could be the place to start, but it will probably be slow going. One thing that does look somewhat worrying is that the traces look like they've crinkled and raised in places - a bit like wrinkled tin foil. Its difficult to tell whether its the trace or just the blue masking layer. The continuity doesn't seem to be affected but the machine has been stored in a shed for years apparently, which has got to hurt...

Gordonjcp:
You do get that wrinkly effect, as an artifact of wave soldering.  Don't worry about it, but be careful soldering near it.  It should really only be an issue on large areas of copper.

Ciderfeks:
Ok good, thats one less thing to worry about then!

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