Crumar Performer trouble

[Midphase]

I recently got my hands on a Crumar Performer from 1979. It does power on, but there is no sound coming out of any of the three outputs. The LFO mod rate LED is pulsating correctly, and the buttons activate their respective LED's. Other than that, there is no activity on the outputs whatsoever.

The power supply rails voltages seem to be spot on where they need to be, and visually nothing seems damaged or otherwise, as a matter of fact I would say it's actually quite clean inside. No bloated or leaky caps, no burned resistors or diodes, and so far all of the wires seem to have good continuity.

Does anyone have any experience with these synths and willing to share some insights into what I should be looking for? It feels a tad overwhelming having nothing to start from since, unlike some of my other repairs, there is no specific fault that I can narrow down to, and instead it could literally be anything.

Any tips or advice is much appreciated. Thank you in advance!

 

[rock soderstrom]

Any tips or advice is much appreciated. Thank you in advance!

It's been a while since I repaired two of these cool instruments.

I would work my way from the sound generation to the output with an oscilloscope (or sniffer) and see where the signal is lost. Definitely check the subdivider chip MK50240 by Motek! Good luck.

Here is the service manual with schematics.

 

[k brown]

Given it's age, I wouldn't be surprised to find some/many bad electros; they don't need to be bloated or leaky to have gone bad.

No matter what else you find, I would highly suggest replacing all the PSU filter caps, regardless of the voltage readings.

 

[NoisyIndividual]

Start at the volume sliders. Good chance these need replacing.

 

[rock soderstrom]

The power supply rails voltages seem to be spot on where they need to be

Given it's age, I wouldn't be surprised to find some/many bad electros; they don't need to be bloated or leaky to have gone bad.

No matter what else you find, I would highly suggest replacing all the PSU filter caps, regardless of the voltage readings.

A functioning PSU is of course the basis. All voltages must be correct under load and with all modules connected. Nevertheless, it's not a bad idea to retire the electrolytic capacitors in the PSU...you also have a lot of tantalum caps in the Performer, which also likes to cause trouble.

The structure of the performer is actually quite simple and clear. I would check if the main oscillator is working and then look at the MK50240 to see if all the tones are there. If so, follow the signal until you find the error.

Start at the volume sliders. Good chance these need replacing.

Yep, the volume sliders and also the other slide pots are of modest quality, it is quite possible that you have problems with them. Clean and check them all.

 

[NoisyIndividual]

The volume sliders are very good places to scope for signals.
This can check whole sections, and the sliders themselves, in a couple of minutes, so you will have a much better idea what is actually going on and what isn't.

 

[Midphase]

The volume sliders are very good places to scope for signals.
This can check whole sections, and the sliders themselves, in a couple of minutes, so you will have a much better idea what is actually going on and what isn't.

Could malfunctioning sliders cause the entire output to be silent? I would expect more of a scratchy and intermittent output.

Also...the Crumar uses these "sideways" polarized electrolytic caps...I assume I can just replace those with standard upright ones (that I can adjust to lie flat)?

 

[Midphase]

I would work my way from the sound generation to the output with an oscilloscope (or sniffer) and see where the signal is lost. Definitely check the subdivider chip MK50240 by Motek! Good luck.

Thanks, that's what I was thinking. I'll start by reseating all the IC's and see if that changes anything. I have a scope and I downloaded all the data sheets for the various IC's.