Hey all, I have a Parasound HCA1000A here (schematic attached) and the right channel overload LED is permanently illuminated (amp powered on of course), even with no signal present. The left channel does not have this problem. I did some troubleshooting and found that both Q003 (right channel) and Q004(left channel) both have roughly 15 volts on the base and emitter, while Q0004 has 0V on the collector but Q003 has 5 volts on the collector which is dropped to 1.8V by R008 and is enough to turn on the LED. The surrounding components seemed to be fine so I figured Q003 had to be the culprit. However, after replacing it with another general purpose PNP transistor there is no change in the scenario. Anybody have an idea what might be going on?
J.
J.
It might have to do with the chassis grounding connection becoming less than perfect. Many (11 to be exact) years ago my HCA-1000 had overloading warning LED glowing/flashing on both channels. I opened up the amp but right before taking out the many screws, I sent an email to Parasound to see if that happened to be a known issue. Tom DeFiglio at Parasound Technical Services replied and had me to tighten the screw in the middle of the 4 big power filtering caps that secures the PCB to the chassis and see if that helps first. Worked like charm.
Thanks for the reply. I actually came across one of your posts where you mentioned that and I tried it but in my case it didn't change anything.
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Then I'd temporarily pull D204 and C232 to isolate the base drive of Q003, and go from there. This is trying to rule-out/confirm a defective/degraded Q223 and C232.
I'd also inspect R233, C245, R243, C226 for overheating or evidence of prior overheating. If you have an oscilloscope, probe for parasitic oscillation.
I'd also inspect R233, C245, R243, C226 for overheating or evidence of prior overheating. If you have an oscilloscope, probe for parasitic oscillation.
Right, I did that based on advice from someone on another forum (wasn't getting any traction here). It confirmed the issue was in the indicator LED circuit. Since then I've replaced a couple of components in that circuit and re-flowed solder joints in surrounding components and now the LED stays off. Thanks for the feedback!