My E-mu Proteus FX died!

[Byron Dickens]

After getting my Proteus FX hooked up and starting to explore it, it died on me one night.

Will not power up. Got 9VAC to the switch. Voltage drops when I close the switch. Even jumpered the contacts on the board & still no dice.

Damn! I was so looking forward to using it!

Do any of you electronics gurus here have any insight? Maybe there's something else I can look at.

I am sad.

[Xoo]

Onboard battery?

[Byron Dickens]

No. It was replaced and it won't prevent the unit from powering on anyway.

Edited May 13, 2021 by bdickens

[twelvetone]

Cannot find any circuit diagrams on the interwebs, but if it has an external AC 9V supply, then rectification and regulation happens inside the device.

If there is 9V AC at the switch, does it drop right down when it is switched on?

Are there any large electrolytic capacitors that look like anything is leaking out?

Is there a fuse perhaps?

There must be 4 (or 2?) black diodes for rectifying, or a rectifier block with AC sine wave symbols on two terminals and plus and minus on two others. There may be printed markings on the board, too. Can you measure between 9-11V on the + and - symbols?

 

Edited May 13, 2021 by twelvetone

[Byron Dickens]

Thanks!

 

Capacitors don't appear to be leaking, but that doesn't mean they are good.

No fuse that I can see.

Voltage drops across the switch. Not to 0.

 

I couldn't find any circuit diagrams either.

I used to be really good with automotive electrical before arthritis forced me to put my wrenches up., But electronics is a different ballgame

[twelvetone]

Just to check, (please don't take offence if I ask basic questions).

- Is the switch double-throw? (so you had both meter probes on the switch) or is it single-throw? (so you had the plus meter probe on the switch and the negative on common)

But if the voltage is dropping, either

1.  the regulator has failed short-circuit, possibly because an electrolytic capacitor is bad (esp. on old equipment) or

2. a rectifier diode has failed (unlikely) or

3. the AC adaptor is bad.

...or there is a failure on the main circuit, causing it to draw excessive current.
If so, that's going to require hands-on from an expert.

So I suggest you leave it on for about a minute, pull out the AC adapter and then, with slightly moistened fingers (NOT wet), check for semiconductor components that are hot.

I assume you can locate the rectifier/regulator section? There is probably a regulator in there, typically LM317, but possibly LM7809 or 7805.

Check first there for overheating regulator integrated circuits (they look like power transistors).

It is also possible that the regulator is made up of individual transistors, not single regulator ICs.

This look-for-the-hot-electrical-part trick is a good way to quickly find a faulty component.

 

Edited May 14, 2021 by twelvetone

[Byron Dickens]

Well, I left it plugged in for a few hours and nothing seems to have gotten warm at all.

I happen to have another 9VAC adapter and I get the same results with it.

 

[Promidi]

Is there DC voltage coming out of the rectification stage? (should be present across the electrolytic capacitor, if present)

Edited May 20, 2021 by Promidi

[Byron Dickens]

Now we're getting to the point where I need pictures? I would be ever so thrilled if I could get this thing working

 

Edited May 20, 2021 by bdickens