Another worthwhile repair/upgrade

billbillw

I've had my Parasound HCA-2200mk2 for about 6 months now. It wasn't perfect when I got it. It had a faint hum in the right channel. Supposedly, these amps are known for having humming problems. Some of that can be attributed to transformer hum, but that shouldn't be heard through the speakers if everything is working properly. My observation was that the transformer only made noticeable hum when you first power up and there was a current in-rush. The hum I was hearing was through the speaker.

I looked into the persistent hum it a week or two after getting it and looked like a cap or two was loose (cold solder joint), in the secondary power supply, so I tore it down. As suspected, I found a couple loose and re-soldered the joints and put it back together. The hum seemed to be gone. Well, when I was in there, I noticed the electrolytic caps didn't looks so good. I suspected there might be a leak or two because of some brown stuff that I could see. I planned to eventually replace all the caps in the secondary power supply (powers the input/pre section).

Well several months later, I started to notice the hum in the right channel again, so I started to figure out what parts I needed to change out the Electros. I talked to Parasound and Tony recommended that I change out a couple pair of small transistors too. Took awhile to spec replacement transistors because many of the parts are obsolete on this 15 year old amp. I did find some suitable replacements made by Fairchild and ordered them and 8 Nichicon HE and 4 PW caps to replace the old ones. Probably talking less than $20 worth of parts.

Did the job last night, took about 3 hours all told. Found out that my suspicions of leaky caps were correct. There was at least one leaky cap in each channel. The right channel was worse of course.
The caps in question are the light blue ones that are clustered together. Here is what they looked like before.




The caps used by Parasound were Richey, rated at 85 and as far as I can tell, the are probably rated at 2000 hour life. Over 15 years, that's only 133 hours per year or 11 hours per month. I'm sure this amp has seen more use than that, and 85c inside of an amp is not unheard of (that's 185F)
In my opinion, amps need 105 rated caps to be safe.


After the job...the Nichicons look much better, don't they?



The Nichicons I used are low ESR, high reliability. They are all rated at 105C and have a life of 8000-10000 hours at that temp, 4-5 times the Richey's. Hopefully, these should last the life of the amp.

Anyway, after changing all these parts out, the noise floor on the amp dropped to completely undetectable by ear. I mean, with my ear right next to the tweeter or mid, I can't hear ANYTHING until I turn on the preamp and a source. Before, I could hear faint noise from both channels, plus the hum in the right channel. The overall effect of this is a noticeable improvement in low level detail. Well worth the effort and minimal money spent.

Lesson here is that the electrolytic caps used in most amps will need to be looked at after 10 years. I'm not talking the large cans, but the smaller caps used throughout. They are cheap to replace and could give you great gains in your sound.

I next plan to go through the input board and replace all the E caps in there and remove some extra tacked on cheapy caps that were installed by Parasound in Taiwan (but not initially spec'd by John Curl). Mr. Curl talks about these mods over at DIY and Audioasylum.

engtaz

Nice write up.

thanks

bikezappa

Your a brave man.

billbillw

bikezappa wrote: »

Your a brave man.

?

Not really. Small electrolytic caps are one of the easiest things to replace. You only need the most basic soldering skills. The hardest part is getting the old parts off the board. You need to use de-soldering wick and/or a pump. I use both

Replacing the two pair of epitaxial NPN/PNP silicon transistors took a little more skill, but they are still pretty easy. Just can't let them get too hot. A quick touch is all you need.

bikezappa

billbillw wrote: »

?

Not really. Small electrolytic caps are one of the easiest things to replace. You only need the most basic soldering skills. The hardest part is getting the old parts off the board. You need to use de-soldering wick and/or a pump. I use both

Replacing the two pair of epitaxial NPN/PNP silicon transistors took a little more skill, but they are still pretty easy. Just can't let them get too hot. A quick touch is all you need.

The hardest part for me getting at the boards. All the small screws need to be removed. And finding them "ALL" is the trick. You must have a lot of practice.

I always fear that I won't get it all back together correctly.

billbillw

bikezappa wrote: »

The hardest part for me getting at the boards. All the small screws need to be removed. And finding them "ALL" is the trick. You must have a lot of practice.

I always fear that I won't get it all back together correctly.

I always snap a few closeup pictures in case I have a memory lapse. Getting these boards out was actually easier than it looks. These boards actually are suspended and connected to the main filter caps beneath. After the top panel was off, I only had to remove 4 screws on each side that hold the board and main power wires to the main filter caps and one screw in the middle that allows a bracket to lift up. Also had to unplug a couple of wire connectors on each side, plus the a few cables coming into the main power rectifiers on each side. Most of these wires are so stiff, that they fall back into place once you put stuff back, that is, if you don't bend things too much while removing the boards.

I fear that removing the input board will be a little more work (and small screws)

hearingimpared

Damn Bill you are quite the tinkerer!

hypertone

Nice write up, and nice job. Those caps smooth out the pulsing DC waveform coming out of the rectifier diodes, so if they are bad, you will definitely get some hum. I'll bet most hum problems can be attributed to the power supply caps. One safety tip: Be sure that caps are disharged before servicing. There's a possibility of getting a nasty shock from a big cap that has a stored charge.

billbillw

hearingimpared wrote: »

Damn Bill you are quite the tinkerer!

Joe, I hardly hold a candle to you. How much time have you spend tinkering on your turntable(s) and/or your SDAs? VTA, VTF, alignment, isolation, cartridge loading, record cleaning, speaker crossovers, basket dampening, etc.

Its all part of the hobby!

hearingimpared

billbillw wrote: »

Joe, I hardly hold a candle to you. How much time have you spend tinkering on your turntable(s) and/or your SDAs? VTA, VTF, alignment, isolation, cartridge loading, record cleaning, speaker crossovers, basket dampening, etc.

Its all part of the hobby!

Yea but you're going down to component level in the guts.:cool: I haven't done that in over 20 years. :eek:

Even with all the patients I've acquire in my old age it is getting harder to do these things due to the eyes going and the body hurting!:rolleyes: I spent all day on the rig and . . .

. . . I'm so friggin frustrated by the days events that I feel like taking the whole rig and throwing out into the street in front of traffic!!!:mad:

Sorry for the derail.

Paul in Canada

I think that is great that you know enough about electronics to be able to work on your own stuff. Where could a guy that knows nothing about electronics start to learn some basic stuff like what all those little **** things are and do in that picture. Again that is great, wow.

billbillw

Google is where you start. The internet is loaded with basic circuit design/theory descriptions of the various components, and their uses. From there, its just experience. Doing it part time as a hobby, the learning curve tends to be pretty long. I've been opening up electronics and trying to figure out how they work since I was a pre-teen more than 20 years ago. In the last 2 or 3 years, I've actually taken the time to learn how the basic amp, preamp, CD player, DVD player, etc is layed out and what does what. I still don't really know **** though. I can replace simple, through board components, but beyond that, I'm lost.

bikezappa

Another possible approach is to find a not very valuable or broken electronic component. Take it apart and try to put it back together. You will know very quickly if you like doing that.

billbillw

I should have also added that my brother is an electronics technician and I pick his brain frequently too.

Paul in Canada

Thanks guys. I have always been interested in how electronic things work but just never got around to trying to learn something about them. I see if I can find sometime to do some searching. Thanks again.

hearingimpared

Paul in Canada wrote: »

Thanks guys. I have always been interested in how electronic things work but just never got around to trying to learn something about them. I see if I can find sometime to do some searching. Thanks again.

There are tons of tech schools, at least in the US, that have basic electronics courses. The biggest thing here is to get the confidence to dig in and start tinkering. . .the only way to gain that confidence to do it over and over again and to just realize that if you break something, 99% of the time it can be repaired.

The idea of taking an old piece of gear apart and rebuilding it is excellent advice.