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Old 8th February 2006, 12:35 PM   #1
mourip is offline mourip  United States
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Default 2020 T-Amp Kit: One Dead Channel

Hi All,

I just finished up a new Autocostruire.com/Audiodigit T-Amp kit. It uses the 2020 chip. While I did not get smoke and I get very nice sound from one channel the other channel is dead.

Here is what I have tried and found...

1. No sound at all on R channel. L sounds good.
2. No DC voltage on input jacks, 2.5 volts DC between input caps and board. I assume that this means that the inputs both have continuity and are OK.
3. Since the amp does fire up and does not shut down I am guessing that there is not a short on the R output.
4. The binding posts are wired properly with L and R isolated one from the other and the grounds lifted from chassis.

I tried resoldering the connections on the board but got no joy. My next plan is to start checking the output signal path for continuity. I am assuming that if the chip was bad I probably would not get any sound from either channel.

Any ideas?

Thanks a lot,

Paul
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Old 10th February 2006, 03:12 AM   #2
Pano is offline Pano  United States
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Can you do a "Buzz" test? I.E. use your finger or a bit of wire to induce buzz into the inputs. You should be able to induce hum and buzz all the way from the RCA connectors to the chip.

Just keep tracing upstream until you find a point where the silent channel buzzes. If you find a point where you can induce hum, the problem is near by. If not, then it is something a bit more tricky, you may have to start pulling parts.

Let us know.
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Old 10th February 2006, 12:10 PM   #3
mourip is offline mourip  United States
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Thanks for the tip. Right now there is just stoney silence. I will try to track backwards from the speaker terminal. I am also going to make another run at resoldering.

So close yet so far :-)
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Old 10th February 2006, 07:55 PM   #4
Pano is offline Pano  United States
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Sorry you get no buzz. You are not likely to induce hum on the output side but you can do some measuring there.

Check with a volt meter around the outputs. See if you have any voltage across the outputs. Then check to see if you have voltage at the diodes. You should see voltage on one side of each diode. COnnect the negaitve lead of the volt meter to earth. The reading should be the same on each channel. What do you get?
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Old 12th February 2006, 02:24 AM   #5
mourip is offline mourip  United States
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Well, I had another pass at getting the amp working but had no luck. One channel is still dead after a lot of careful resoldering.

I have continuity in all parts of the input and output. The inputs are both biased to about 2.5v. The outputs have about 3.6v on each of the legs of both channels. When I put the RCA jack into the channel that works I get a brief buzz until contact is secure. Doing the same on the bad channel gives no sound at all. I have resoldered all of the circuit board joints even though continuity was OK.

I did get an email from Audiodigit with a couple of ideas to try. Unfortunately they require me to have an oscilloscope. I just have a good Fluke DVM. I am going to email them back to see about repair or replacement. I guess this is where I find out how well buying overseas kits works out...

Thanks to those who responded.

Best,

Paul
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Old 14th February 2006, 01:09 AM   #6
mourip is offline mourip  United States
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It Lives!

It turned out that one of the output chokes did not have enough of the enamel scraped from the lead. I just kept tracing out continuity until I found it.

Boy this thing stomps my modded SI and it isn't even broken in. It has all of the detail, a richer midrange, and the bass is back.

Listening to Eva Cassidy...

Good night...
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