Orion HCCA 2100 no rail voltage.

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Perry, I'm not sure if you seen my question in post #250 about your recommendations on what 10uf 50v capacitors to use in these amps...actually my question also applies to all of the old school Orion amps?
I've been using Nichicon UHE1H100MDD1T. Yes, those are the capacitors that I had two of fail in this amp. Mouser, who I bought them from, replaced my entire order of 100 after I told them about those two failing as they did.

While UHE1H100MDD1T has seemly been working well in most of circuity where a 10uf 50v capacitor is needed, it is not working well in the muting circuit. I just finished repairing and recapping an XTR 2250 and used a UHE1H100MDD1T in the muting circuit. The muting circuit would function as it is supposed to for few minutes then the negative DC voltage on the third leg of the muting transistor would start rising and pulsing. After checking a number of other components in that circuit I pulled the UHE1H100MDD1T and replaced it with a different brand of 10uf 50v capacitor and the circuit works as it should. I then pulled that capacitor and I tried another of the UHE1H100MDD1T's it did the exact same thing the first one did. After that I put the other brand back in and again the circuit functions as it should. I'm thinking the resistance of the UHE1H100MDD1T is too low to function properly in the muting circuit. That is what lead me to asking you again about your recommendation of which brand an model 10uf 50v caps to use. Also would it be better to use a different model capacitor in all the 10uf 50v locations through out the amp?
 
The muting circuit uses incredibly high values of resistors and relies on those resistors for the voltage at the muting transistors. If the capacitors have ANY (electrical) leakage, they're likely to cause problems.

I don't have a recommendation, really. The Nichicon caps would likely have worked perfectly well as designed (for filtering/bypassing noise). CDE caps have had a good reputation. If you want something that is almost impossible to fail, use a film capacitor. It won't look the same but it shouldn't have any leakage.

Tantalum capacitors have low leakage and used to be considered unreliable but are OK today.
 
Pulled this amp back off the back burner to work on it again. DC voltage on pin 4 of the 494 is +0.138. Installed a 6k resistor between pin 4 and pin 7 and it brought the voltage down to +0.036v. Found that if I install a 5k resistor or lower between pin 4 and pin 7 the amp won't power up and shuts my power supply down...
Also noted that the amp starts clipping (lighting the clipping indicator lights) at a lower volume than is should be (can be heard through the speakers)...

Any thoughts?
 
Connecting a resistor of any value between 4 and 7 should cause no problems. In many amps, pins 4 and 7 are directly connected.

What could be happening is that whatever is driving the voltage back to pin 4 is connected to a circuit that's sensitive to the voltage being pulled down.

With the 5k in place, does the voltage on pin 3 of the 494 go below 0v? Place the black probe on pin 7 to test. It's critical that you use pin 7 for this test.
 
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