Moog Source Problem - Any help appreciated!

[funkballz]

My Source is poorly!

When I power on the patch display shows :1 and the edit led is permanently lit.

The rotary knob display is blank until I spin the knob, it goes through a few random numbers before sticking on some random characters.

All the membrane buttons are dead and there is no audio coming out.

Now the good bit. I'm no electronics genius but I thought I'd get inside, I've checked the rail voltages, all OK. Removed, cleaned all connectors etc, checked for any obvious signs of component failure etc.

If I pull out the IC U18 on the digital board and power on it's all working again with the exception of the rotary wheel, I can go through the presets, all the membrane switches are active and there's audio out again, so I replaced U18 with a brand new 74LS125N to no avail, back to the original problem.

Also, if I remove only U17 on the digital board it all comes back to life as above but there's no audio.

I'm hoping someone may read this and have an "aha!" moment and may be able to offer some further advice, if so it'll be greatly appreciated.

[thealien666]

Sounds like it might be a case of surface oxidation of the +5 volts digital regulator leads (common problem for The Source after many years). U3 on the supply board.

Solution: remove U3 (7805), clean leads with a pencil eraser, and re-install. U3 is located under the row of connectors on the Power Supply.

NOTE: do NOT use any type of contact cleaner. Simply rubbing a pencil eraser on the leads (or legs) of the regulator will be sufficient to remove the very thin layer of possible surface oxidation, causing noise on +5 volts digital power rail.

Hope this helps.

[funkballz]

Thanks very much for the info.

The problem first occurred a couple of months ago and the first thing I did was to replace the U3 regulator to no avail. I've just now found the time to have a further look at it.

I've just removed U3 and gave the legs the eraser treatment as suggested anyway, even thought it was a new 7805 the legs were visibly brighter afterwards but sadly it's made no difference.

[thealien666]

I would suggest trying to locate possibly defective digital chips that are hotter than usual (hot to the touch). One such failing IC could possibly affect the digital power rail. Usually, digital gates run mildly warm, and sometimes even cold. But when they start to fail, sometimes they will short out, becoming hot to the touch. But not always.

Also, if that new +5 volts regulator runs too hot, because of higher than normal power consumption from failing digital chips, it could intermittently shut itself down for micro-seconds at a time via its internal thermal protection circuit, causing glitches on the power rail.

[MC]

Check the capacitors on the power supply. I had one of them break the solder joint years ago. Same symptoms.

[funkballz]

Thanks for everyone's help so far.

I'll be replacing all the caps in the PS in the next couple of days so I'll be reporting back shortly, hopefully with some good news!

[Freeks]

I'm having similar problems. Before my Source worked fine for hour or so and the control panel went unresponsive. The "Orange" part with presets etc still worked normally. I would need to shut it down for hour or so to get it working again so it's probably heating problem.

Now it got worse. It boots to preset 7 and nothing else works. I can play another preset by pressing the preset number while playing, but when unpressed it resets back to preset 7.

It's almost like "Crazy Source" but with preset 7.

Another problem it has is that cutoff don't work. I can choose it and change parameter, but sound don't change.

I'm no electrician at all. How easy it is to clean U3 for total newbie?
Also what could be done for the faulty cutoff?

Thanx.

[thealien666]

...I'm no electrician at all.

In that case, the very best advice I could give you would be to have a certified electronics technician have a look at it. You wouldn't want to risk damaging anything, or even hurt yourself by fiddling in the power supply.

The Source is basically a micro computer, coupled with an analog sound board. Similar to a Little Phatty or a Voyager (but with 30 years old technology). Diagnosing it over the internet without proper tools and equipment, and without having access to the faulty unit itself, is very limited. Simple things can be tried, and sometimes it could work with very simple problems. But when it comes to the kind of erratic behavior you describe, It could be more serious like in the case of funkballz who started this thread. He has replaced some parts already (he seems to have some background experience in fixing electronic appliances), but still his Source isn't working correctly yet.

Best of luck to you.
Al.

[thealien666]

Good news! The OP of this thread has finally found the culprit, and his Moog The Source is working again!
It was a defective logic gate chip that had to be replaced. I've just received confirmation of this my email from him.

Just thought people would be interested to know what happened.

[Freeks]

Where to get new parts for Source?
I live in Finland and here is not too many shops that sell rare electric parts so i need some online shop for replacement parts.

[filtered]

thanks for giving the story an end alien! I hate equipment issue posts that never let on what the outcome was! what's the point?!

[funkballz]

Yes, a great result!

U21 on the digital board was the offender.

Big thanks to the Alien for steering me in the right direction.

[thealien666]

thanks for giving the story an end alien! I hate equipment issue posts that never let on what the outcome was! what's the point?!

Yeah, I'm always curious to know too. Even when the outcome isn't as good as this one.

He had to replace a few logic gates chips before stumbling upon the defective one in the incremental controller section, a SN74LS386 quadruple ex-or gates. It's not surprising for a 31 years old electronic circuit.

EDIT: I want to extend my thanks to Kevin Lightner for providing the schematics of The Source via his Synthfool site. They were of invaluable help to me during this overseas, successful long distance diagnosing!

[Portamental]

Errrr.... got this old synth. It only makes noises when I step on it. What's wrong with it ?

[thealien666]

I see your problem; there are old computer serial DB9 cables that don't belong to the synth...

You should have put a warning for sensitive analog synth lovers out there, that might be shocked by a picture of such a deeply wounded subject...

I'm afraid my remote diagnosing talent is not up to this monumental task !

EDIT:On the positive side, the foam has been removed...