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Moog Source Repair Question

Posted: Thu Dec 25, 2008 12:15 am
by djthomaswhite
Hi all,

I have a Moog Source in "fair" physical condition, but the sound engine is not working. The panel membrane is intact and all buttons register as the function they should. When I opened it up I found someone had removed all of the CA3080's and many of the other IC's. So I put new IC's in all of the sockets per the service manual "hoping" it would magically work. Alas, it doesn't work right. On the output I hear a squarewave that is effected by the LFO rate and it is VERY quiet.

Bottom line, I want to get this synth fixed. I was curious to get any recommendations of a repair person in the So Cal area that could take a look at this for me. Any suggestions? Thanks in advance for your help!


Posted: Thu Dec 25, 2008 2:49 am
by Kevin Lightner
I gotta ask... :)

What happened to the chips that were in it?
You bought it as-is?
I assume you put in CA3080s (or LM3080s) correctly in place?

Posted: Thu Dec 25, 2008 3:20 am
by djthomaswhite
Chip summary:

Missing all CA3080's (now correctly replaced)
Missing the z80 processor (now replaced)
Missing all sorts of other op-amps (dual tl072 compatible types, ca3046 I think, and many miscellaneous other IC's)

I replaced all that were empty with the identical type shown on the service manual commonly available on the web for free. Anything in particular I should look out for?

BTW, I just bought the a Rev3.3 Rom from you on eBay to add to it. I had it given to me from a friend a couple of years ago and I was much less repair inclined at the time. I have since fixed three voices in my TR-909, upgraded and swapped caps in many of my synths, and most recently fixed a broken Oberheim DX with my slowly growing repair skills (although no official training, it is getting easier to use my scope and read service manuals/schematics). Happy Holidays Kevin,


Posted: Thu Dec 25, 2008 6:49 am
by Kevin Lightner
Off the top of my head I can offer these ideas..

1. CPU type the correct speed?
2. Is there a reset pulse occurring when the unit is turned on?
3. CPU clock present?
4. Power supply ok? (all voltages)
5. Anything getting warm?

Posted: Thu Dec 25, 2008 1:37 pm
by djthomaswhite
CPU "correct speed" = Big Uh Oh... I thought they were all the same speed essentially and that might be my big problem. Any tips on a part number or spec so I can make sure the one I got is the right one?

Thanks Kevin!


PS. I'll have to check the other functions when I get back from vacation.

Posted: Thu Dec 25, 2008 3:27 pm
by Kevin Lightner
It should be a 2mhz.
You can probably put a 4mhz or higher, but a 1mhz version is a no-no.

Also check pin 26 with a scope to see if the reset signal is working.
The reset is like the start button to a cpu.
No reset, no cpu'ing. :)


Posted: Sat Jan 03, 2009 12:01 am
by djthomaswhite
Kevin and co.,

Got my scope and meters out today. Couple of notes about my unit.

1. Has 2.2 ROM
2. Can hear Mod Osc at audio range at output
3. No other sounds at output
4. All voltage correct at supply and at board (10v DC)
5. Z80 is 4mHz type
6. Has miscellaneous visible mods (official looking) on circuity boards. On Digital board = White wire from one end of C3 to End of C12. Analog board is more complicated= White wire from end of C1 to end of C25. Also, 10K trimmer from pin 1 of U10 with unknown resistor off wiper to end of R65. From same end of R65 a resistor to pin 4 of R25.

When testing for reset pulse on Z80 I found power ripple (wobbly tri-sinish) wave between any point of the circuit board and ground. No visible pulse, but I might be measuring it incorrectly. My scope skills are very rudimentary so far.

When trying to change to Eprom 3.3 I found a broken socket tab which may have been shorting one pin of the Eprom. Lots of junky corrosion stuff (not rust though) on U14.

So, I am looking to do some maintenance to get this board up to snuff and then hopefully working after that. I have never seen "tubular" capacitors like the ones on these PCBs. Are they film, or ceramic? I figure replacing them with disc type would be fine? The tantalum ones need to be changed I am sure as they are old. I'll definitely be changing the electrolytics in this process.

What else should I be looking for? Trimmer replacement? IC's that tend to go bad? Any further help is of course appreciated. Many thanks,


Re: Moog Source Repair Question

Posted: Tue May 11, 2010 10:09 am
by loedown
The corrosion you mention on U14 is probably the battery leaking or left over flux from an earlier attempted repair. You should be checking for things like adjustment on the op amps that control the LM3080A chips, that will tell you that the rotary encoder is working, check your voltage rails + - 15, + - 5, +10, replace every axial electrolytic in the PSU, the logic board and the oscillator board. Check the functionality of the membrane switches, if the edit LED is constantly lit, but only half bright, check U11, U12 and U13 functionality. Failing all that you can send me the unit and I'll repair it, but postage too / from Australia will be expensive.