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Parasound HCA-2003A, Bad Channel Repair Help

Mastagrog

Mastagrog

New Member
First off, Hello to all! I have been creepn' on this site for years and has provided tons of useful information and decided to finally join up!


The Back Story:
Bought a Parasound HCA-2003A amplifier off craigslist about a month ago for a decent price in assumed good condition. I did not test it before I paid, of course, as it looked to be well taken care of by a reputable looking gentleman (lesson learned, again...). To my dismay, when I tested it at home channel 2 was dead. Channel 1 and channel 3 still work brilliantly, so not a totally dead amp! I must say, what a great sounding amplifier!
​

Testing Equipment:
  • DMM
  • Arduino built component tester

What has been done:
With some help and direction from Saabracer23 (Dan) via PM and a thread he had started a while back, I got neck deep in tearing this thing apart and testing everything. I actually was able to find a schematic from somewhere on this site that linked to another site in some random country and have been making comments on a local copy, which can be seen here.

I found:
  • 2 output transistors (MJL21194, MJL21193) that were shorted
  • 1 Driver(J200, MOSFET) that would not function
  • 1 Emitter resistor that was close to open (47kOhm, should have been 0.33Ohm)
  • 2 100Ohm resistors open and fried, on the input section
  • 1 A1360 transistor shorted, on the input section (pre-driver?)
  • 2 blown 10A fuses from the Power Supply for channel 2
  • Display, Standby continues to stay lit
  • Display, channel LED's continue to stay lit
I Replaced:
  • Both MJL21193-4 with OnSemi of same type, matched as close as I could to the others
  • Both the J200 and K1529 with "genuine" Toshiba replacements (from China...)
  • All emitter resistors in channel with new 0.33Ohm, 2W, 1%
  • Both 100Ohm resistors on input section
  • The A1360 with a new one
  • The fuses

The Current Issue:

The first time I fired it up after all replacements, it got super hot pretty quick and threw it's self into protection. I promptly turned it off, waited a few seconds, then turned it back on and the channel fuses blew right away again. I promptly face-palmed and started tearing things apart again. I tested pretty much everything, looked over all of the solder joints, and checked for shorts. I cant seem to find anything but know I am missing something.

I put it all back together and decided since it took a minute to get hot, I got some short bursts of time to check voltages. I checked the bias on the other channels before putting new fuses in channel 2 and set them at 15mV. When I put fuses in channel 2 I got my test leads set up to check bias voltage and turned it on. This sucker was chugging away at above the mV range for my DMM! I promptly turned the amp off and the biasing pot all the way closed to about 1.8kOhm's (the others are at about 900Ohms). I turned on the amp again and it is still cooking away at about 175mV.

Another thing I noticed was the voltage coming into the channel behaves oddly. When powered up, the voltage comes up to about 68v, which is the same as the good channels; however when I turn off the amp, the voltage stays at 60+ volts and very, very slowly drops off. The other channels when powered down, drop to about 10v and then slowly drop off. I have had the amp powered down now for a good few hours and it is still hovering around 60v. So, for whatever reason, something is not allowing the voltage to drop when powered off.

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So this is where I am at and figured I would turn to some expert advice as I am definitely a novice at this level of testing. I would greatly appreciate any constructive advice that this forum can offer!

Thank you in advance!
 
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Mastagrog said:
! I promptly turned the amp off and the biasing pot all the way closed to about 1.8kOhm's (the others are at about 900Ohms).
Click to expand...
In circuit. What value are they suppose to be according to Hoyle?
 
avionic said:
In circuit. What value are they suppose to be according to Hoyle?
Click to expand...
The playing card company? Just kidding, I am unfamiliar with what Hoyle is. I have also been pulling all components and testing them out of circuit (aside from the biasing pots of course). I don't know if my sweet little component tester can test in-circuit... If you could enlighten me on Hoyle, I may be able to better answer your question.

avionic said:
Pull these and test them...Very likely fakes.
Click to expand...
I did read that these are highly counterfeited but it is slim-pickings out there and decided to give it a shot. I do have 6 pairs and they didn't cost too much. If I knew how to read the spec sheet and translate that to what I am seeing on my tester I would probably be better off.

Thank you!
 
Mastagrog said:
. If you could enlighten me on Hoyle,
Click to expand...
LOL "According to Hoyle" = According to the schematic or service manual

Idioms

  1. according to Hoyle, according to the rules or to the authority; correctly.
 
Haha! Thank you for that. I did a quick Google search and saw Hoyle and was sure he couldn't be what I was looking for, well, guess I was wrong!

Unfortunately, the only piece of service information I have is the schematic that I found in the depths of the interwebs. I am totally guessing on the bias voltage but have a feeling I was close with 15mV as there is a chart with some Parasound amps (not the one I need of course) and their bias parameters. It was also an average between the 2 good channels before I adjusted them. The bias pots are 2K TVR. 1.8-ish is pretty close to that.
 
How did the parts all around the (maybe) fake outputs...test out.

Try to check some voltage points....

Also apart from new old stock output transistors or parts from a donor Amp... where in 2019 is the best place to buy very good quality transistors .... would like to buy a set of output transistors for the future.
 
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Reliving. said:
around the (maybe) fake outputs
Click to expand...
Outputs were not the questionable fakes. The Toshiba MOSFET drivers are questionable and,I think, no longer available. (2SJ200 and 2SK1529). New "old stock" pieces are few and far between.
 
Last edited:
Alright, update time!

So, it works now! The only issue I am still having which is not impeding functionality that I can see is the "Standby" LED and the channel LED's are still lit which at this point I don't know if I am going to spend the effort on right now.


What I did:

This morning while waking up with Joe I decided to put the original drivers (2SCJ200 and 2SK1529) back in and see what will happen. Worst case scenario it bursts into flames and I was ready with a fire extinguisher. The K1529 was thought to be good but the J200 I thought for sure was dead, I even wrote "bad" on it. When testing them, the K1529 came up as a MOSFET and the J200 came up as a diode junction of sorts (not real good at identifying yet) and not a MOSFET, so I thought it was safe to assume it was bad. However, I remember Saabracer23 having a similar experience when testing these. He opted to replace them with a comparable set but the thread ended with pondering whether they were good or not.

Once I got everything kinda back together I fired it up with the test leads on the emitter resistor ready for another ridiculous value, and..., it was 0.0. It was a moment of mixed feelings, then I remembered that the bias pot was maxed out. Got the screw driver and started to slowly turn, and sure enough the voltage slowly climbed into normal operating range. I had to take the kids to the pumpkin patch today, which meant that properly setting the bias had to wait. It was ok though, I had some time to clear my head and I left with half-satisfaction that I had a small victory to solidify when I got back. Once back, I got the amp warmed up and ready to adjust bias. I was a little hesitant at first that earlier was just a fluke and I was in for more work, but everything was running perfectly. I got the bias adjusted/readjusted on all three channels and plugged in a speaker to do the final check, and sure enough beautiful music coming through the channel once more!

​
The Moral:

  1. An obvious one, but don't trust MOSFET's from China.
  2. The 2SCJ200 does not test out like a typical FET, in fact I don't even know how to test it at this point.


Thank you Avionic and Reliving for weighing in on the matter and teaching me about Hoyle haha!

P.S. Avionic, thank you for your service! I got some time under my belt as well, not enough to have retired though, so good on you for sticking it out!
 
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