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Old 13th February 2013, 03:34 PM   #1
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Default Parasound HCA 3500 Left Channel Runs hotter than right

Hello to all fellow DIYers I am hoping someone here can help me with an issue I'm having. I bought a Parasound HCA 3500 about 4 months ago from an estate sale, I was really fortunate to get everything for it, including the packaging, and its in mint condition which is always a plus.

Anyway I just got it set up 2 nights ago since I finally purchased a set of speakers that can handle this beast. My issue is not with sound quality, but with temperature. The left channel runs considerably warmer than the right amplifier does.

I thought at first it could have been the speakers or wire so I reversed them, and the left amplifier is still just as warm as it was before. I havent installed it into my rack yet because I don't want it to overheat. I am hoping someone here can assist me with repairing the unit? I am quite skilled in electronics repair (its what I do everyday )so that base is covered.

Any help at all will be welcome. I would love to keep this amplifier going for as many years as possible.

Jeremy
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Old 13th February 2013, 09:15 PM   #2
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Did you check bias? also check DC offset just in case. I have seen many amps that have bias problems because dry-out caps, electrolytic caps tends to dry-out with time and they change values and affect bias voltages.


PS: I found theses posts, so this is C/P:

Get two medium size clip leads. Attach one end of each to a multimeter that can measure milliVolts. When you open the case, find ONE convenient EMITTER RESISTOR to put the opposite clip lead ends, across the resistor. Now you are in a position to measure .015-.025 Volts.
Attach clip leads BEFORE turning on the amp. Wait at least 1/2 hour before determining the final quiescent current as determined by the voltage drop across the EMITTER RESISTOR.
IF the voltage drop, over time is NOT in the range of .015-.025 Volts, then find the trim pot that adjusts the measurement. You have to look for it. BE VERY CAREFUL NOT TO TURN THE POT TOO MUCH, until you get a feel for its range.
That should do it, but BE CAREFUL!


I would let the amp idle for at least 30 minutes before doing this. The HCA-3500 amplifier also has a dynamic bias adjust and you set TVR3 to 18mV(+/-2mV) DC while applying an audio signal (music will do). After removal of the audio signal, it will take a couple of minutes for the bias to drop back down to idle. I have seen a number of HCA-3500s with the dynamic bias around 40-50mV and the heatsinks are quite hot

Last edited by lanchile; 13th February 2013 at 09:37 PM.
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