Hey everybody. So, I’ve been saving up for a while for a genuine classic Moog. I got an Mg-1 a while ago, but that didn’t really cut it. I decided on the source as it sounds great and you can save presets. I have plenty of other synths with tons of sliders, so the wheel is not a deal breaker for me. I really just wanted something I could quickly jump around sounds on for gigs. So I watched ebay for 4 months, got a reasonably killer deal and…
First gig=raving crazy source. It was on for a while, and I noticed it getting pretty hot at the heat sink, but I figured maybe that was normal, as I’ve heard that they run hot. About halfway through the second set the source decided to take a solo. It was pretty good, actually, kind of in time, and kind of in tune, but somebody else was soloing at that time. Bad manners on source’s part. Anyway, now all I get is random numbers on the display and wheel increment display. Audio is limited to strange low machine noise that can be manipulated with the wheels sometimes. Membrane is completely unresponsive.
I’m aware of the U3 power supply fix. Somebody was in the synth before, and did all the necessary work on the power supply. The power supply is working perfectly, unwavering correct voltage to both boards. I’ve tried popping out every chip on the digital board except the eprom, and I always get the messed up display and stupid machine noise. I’m kinda flipping out. Well, if you fire it up without one of the chips in there things go delightfully berserk, but the display is still no good. So, I’m at a loss. Anybody come across this set of problems before? Any help would be hugely appreciated. Thanks!!!
My Source has the power supply fix and it does not run hot.
Someone may have been inside your Source, but you don’t know if they were a qualified tech. It could had been another novice like yourself who may had “fixed” the power supply in your unit but broken something else in the process. Popping ICs isn’t going to get you anywhere. Something is very wrong with your system and you need to get it to a qualified tech. Way too many potential causes to fix over the net.
There’s a reason this thing was a “killer deal”. You bought a handyman’s special.
I agree with everything MC wrote. Wholeheartedly.
The Moog The Source gets reasonably warm on the back after a while, but you should still be able to put your hand on the back, and keep it there without any serious pain (or burn 
). Otherwise, there is a serious PSU or power overconsumption problem inside (possibly shorted out parts or wires, defective caps, failing digital or analog chips, defective regulators, etc etc etc…).
Hey Guys,
Thanks so much for the replies!!! I’m not the most experienced synth tech, but I’m actually a very qualified tech for wurlitzer electronic pianos, rhodes suitcase, and the like. I do an awful lot of soldering for money, and would actually call myself a good judge of other techs work. The guy who did this work did it properly. Impressively, even. He removed the regulator sockets and replaced them with wires extended to the regulators and power transistors. He also did the power supply caps. The solder joints are textbook perfect, no issues there. He also properly reattached the heatsink with a new coat of goop. He did a couple other little things in there as well, all superbly executed. Dude was a pro or a vastly overqualified hobbyist, no doubt about it. I wish I knew who he was, actually.
So, caps are good, not leaking. Solid power goes everywhere it should. There are no shorts. The regulators are doing their job. Synth board is golden. That leaves me with the digital ICs.
I was not expecting any sort of miraculous cure via popping the ICs, more just seeking a change in state. I did create some, but can’t take much from it at the moment. I’m essentially at a shotgun strategy at this point, but trying to refine it to laser approach. I could use some guidance in diagnosing computer issues, as I lack experience there. If the synth board had crashed I could crush this thing.
MC, I agree about the killer deal thing. Anything too good to be true probably is. It was advertised as working perfectly though…
Alien, the PSU wasn’t hot enough to cook an egg or burn a hand, but it did seem excessively warm. I read through ( I think I’ve read every source repair thread at this point ) the thread where you helped dude with the bad logic gate in there. Could you give me some insight as to how you got towards that area? No ICs are running hot, the CPU is a little warm, but I have to assume that is normal. There was a good amount of corrosion on some of the ICs, so I cleaned the legs prior to replacing them. I’m good with a scope, but don’t know how to apply it to testing ICs, I’m usually just using it for audio purposes ( wave chasing, crossover distortion, etc )
Comrades, have a little faith in me. I’m generally good at repairs, and I’m going to fix this, one way or another. I’m one of the more experienced techs I know in the area, so I have decided to take it to myself 
. I’m just seeking guidance from the wise souls who have crossed these waters before me. Thanks again so much for any help!!!
Your embedded system is locked up. This can be caused by the address buss and/or data buss being corrupted by one or more rogue components.
When I had this problem with my OBX I had to identify all the buffers that are connected to the address and data busses. This was not easy from the service manual so I had to draw my own schematic showing only the embedded system.
From that you can divide the system up into sections. DAC, RAM, ROM, digital inputs, digital outputs, etc. More often than not, they have a buffer IC separating the cpu from the section.
First thing to check is the presence of the clock signal on the cpu.
From there you basically want to isolate each section one at a time. Isolate all sections except for RAM/ROM/digital input. These are the minimal components for the embedded system to run. Power up and check that the system is running by monitoring the address busses, they should be looping. A logic analyzer is the best tool for this. If you don’t have a logic analyzer you can probe the WR/RD pins on the cpu, but it’s not a reliable signal of a living and breathing system. Be careful not to let the probe short neighboring pins or you will blow the cpu.
If the minimal system does not run, something is wrong in that section. RAM ICs are known to fail which can render a system inoperative. There are two RAM ICs, if you swap them and the system does start looping then one of them is bad. Unfortunately those ICs are no longer available without scavenging another machine. If you want to isolate the digital input section then you may have to simulate quiescent inputs.
Once you verify that the minimal system is running, re-connect the sections one at a time and re-verify operation. When the system stops running, you have identified one section (there may be more) that is locking down the embedded system. Fan out from there to find the rogue component(s). You really need a scope at this point, popping ICs is unlikely to solve anything.
There may be more than one section locking down the system. This is why empirical popping of ICs doesn’t really solve anything. You need a logical view of the embedded system to isolate the potential cause, which is what the re-drawn schematic will tell you.
This is not an easy troubleshooting task and it separates the men from the boys. Good luck.
MC, thank you so much for your thoughtful and information packed reply. You are a champion and a warrior for good. Looks like I’m in for a bit of a thrill ride. Does anybody have a line on the eprom code for the source, out of curiosity? I’ve got OS 2.2 in here. Yes, I do have access to an eprom burner for this eprom. Just trying to cover all my bases.
Thanks again!!!
Hey all. My source is back in the land of the living. The Z80 failed. I went over to an old friends house today to work on the keyboard. He has all the test equipment one could ever want. The cpu was proved dead in short order. Thankfully this was a way more quick process than I thought it would be. I feel there may be another ghost in the machine waiting to raise its head, but for the here and now I’m back in business. Experiencing a little trouble with the membrane at the moment, but I’m pretty sure I can work that out. The ribbon connectors are badly oxidized. I think pulling them out to remove the top moved the ribbons from their happy place. Oh well, right now I just can’t access the glide rate and the '32 footing for osc 2. Could be a lot worse.
Here’s something interesting. When the system came back online it made its own series of patches, for the most part the values are in the 50s for all parameters, but there are occasional surprises. In all cases the noise gen is cranked. I guess robots love white noise. Who knew?
I made a copy of the source 2.2 OS whilst I was in there. If anybody ever needs it just PM me. I found a copy of the OS 3.something online, but I was a bit worried it would lock up my source, as there was more hardware on the later versions of the synth.
MC and Alien, thanks a million for your help in this process.
You’re welcome. Glad to read that your Moog is humming again !
Good work !
The random patches are probably due to the battery back-up being depleted ? Was the battery replaced ?
Alien, In most cases I would agree, but here I think the patches got scrambled because I popped out the ram. Whoever serviced the synth a while back put a new battery in there. Source saves patches fine. I’m preparing to do battle with the membrane ribbons, I know the entire membrane is funtional, which is a relief, but the ribbons themselves are of the least hardy variety. This makes me think that the much hyped membrane failure thing is really more of a dirty connector issue on at least some units.
I have owned my Source since 1985 and had zero problems with the ribbon cable or connectors.
I do not doubt there are issues. I think it has more to do with storage in extreme environmental conditions. IE long term storage in an attic exposes it to heat which isn’t friendly to those plastic ribbon cables.
Ah, yes of course. If the RAM chips were removed that would indeed scramble their content too! 
As for the membrane, I have a Sinclair ZX81 computer with the same kind of membrane keyboards, and with time and damp storage condition, the traces might become oxidized as it has happened to it. Fortunately, another ZX81 is still fairly easy to find and very cheaply. Not so for a Moog The Source, I’m afraid… 
Hey everybody. Much as MC predicted, my Source has proved to be quite the handyman special indeed. After reviving it with a new processor, I found that osc 1 was jittering in pitch pretty badly after about five minutes warmup time. This was traced to a bad 358 opamp, U35 on the synth board. After that I had to address a single key that had a misaligned bushing, which resulted in a bad contact with the bus bar.
Sadly, the membrane is failing at a rapid pace. It has gone from working 100% to about 60%, but I’m not hopeful for it’s prognosis . I found a post from the late great Kevin Lightner stating that tarnish was the most common membrane issue, bolstering my earlier theory. Cleaning the ribbon is easier said than done, though, as they are desperately thin. So… I’m divided by my desire to fix everything, and my desire to just buy a membrane from france and be done with repairing my new synth ( for the time being).
Brand new membranes (not cheap though) are available here (and recommended by other Moog The Source owners and members on another forum):
http://www.vintagesynthshop.com/Moog-Source-Membrane-Replacement-bbeaaaeGa.asp
As a last ditch effort for my membrane connectors, I bought one of those conductive ink pens that I have scoffed at for years. Much to my surprise, it has brought back much of the membrane function. I don’t want to jinx it, but I may be able to turn it around. At this point I feel like a doctor who brought back a patient who had been eaten by a shark and a tiger simultaneously.
I just came back from being on the road all weekend. I’d given all the leads of the membrane panel a good coat of conductive ink prior to getting in the van. Total success. All membrane buttons are doing what they are supposed to. I’m not sure how long this fix will last, but for the here and now I’m completely back in action. It has been a long road. Definitely just earned a few new tech merit badges. Thanks again to thealien666 and MC for their invaluable help in this process. 
That’s great news, spiders !
You’re welcome, and thanks for the update!
Well, I’m back. This Source clearly intends to test me heavily. New issue, not entirely crippling, but highly vexing. After a month of lightly gigging the synth, I sat down last night to do a bass line on a recording project. Much to my dismay, the synth is now greatly varying in pitch from patch to patch. I retuned the synth per service manual instructions, so now I can at least use my startup patch and treat the source like a synth with no presets. I bought the thing so I could save patches, though… We are talking intervals of difference between patches, not slight differences.
So- I’ve retuned the synth.
I checked my power rails again (±15, 10, 5.1, 4.95)…all good
I recalibrated the DA converter—it was actually a little off
I fear that the computer is once again poking me with a stick. A pointy stick. The synth board is doing what it is supposed to do, it is just receiving bad instruction from the computer. I think.
Once again, I approach the wise masters for their insight and suggestions. I’ve come so far with this synth I can’t quit now.
Hey All, the problem is definitely related to the memory, I think perhaps one of my RAM chips has kicked the bucket. Swapping the RAM yields a new set of tunings across the patches every time. But, they do correctly store all the patch info, and the level 2 functions all work, so maybe not. So many maybes. MC feel free to tell me I’m not going to get anywhere by swapping chips, just break me off a piece of your knowledge while you are at it 
Don’t neglect to check that memory back-up battery…
Hey Alain. It is at 3.3v. Sigh…
I’m going to figure this one out, probably replace every chip in there, and never take this thing to a gig again. This realization makes me sad and sort of deflated. I guess the source is a great studio piece, but this one really seemed to enjoy being played live, if that makes any sense. Synth wise I’m much more of an atmospheric/terrify the squares guy than a lead dude, but the source loves leads. It makes me play like no other keyboard has before. I love the interface and the lack of knobs. Having to really craft your sound and then commit to it liberates the player. A ton of knobs are great, interactive, etc, but I think they can get in the way of really doing something sometimes. One keeps wanting to fiddle with stuff instead of actually making music. With the source you can still edit quite quickly, but you have to be more deliberate in your thinking as to what you want. The process of creating sounds with the source allows you to more clearly express your voice, if you take it seriously. So, I’m bummed.
I will fix this, as I’ve fixed all the other problems (it actually has had a few more hiccups that I didn’t post about, quite the “handyman special” as MC put it). But yeah, once it is solid on pitch again, I feel unlikely to gig with it. This particular unit has just proven wildly unreliable. I can’t sell it to anybody in good conscience either, as I have an understanding about what is wrong with it…everything. As Homer Simpson once cried as his novelty hand bell fell apart, “DAMN YOU EBAY!!!” Oh well. Live and learn.
I’m buying a sub 37 from some dude off craigslist tomorrow, selling some other gear to make the money back. I should be excited to get such a cool new synth, but it feels off. Maybe I will totally fall in love with it, but right now I feel like I’m abandoning the best synth I’ve ever had. Like you dated this girl who was cool and hot and awesome in bed, but she had a real bad drinking problem and kept passing out at fancy dinners. It didn’t work out, for obvious reasons. Still, you can’t get her off your mind…