kx1200.1 help


2011-09-03 11:43 am
the amp powers up but no audio. I checked all the output fets already. the last place I see a signal is on the tl072 at U11. Also whats the ic at U12?


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U12 is a MC14060B. Link Below. U14 is a LM361. Link Below.

U12 is an squarewave oscillator.U12-Pin 5 feeds Pin 2 of U13-TL072C. Pin 1 of U13 feeds the base of Q103-3875GR. C266-47p at the base of Q103 integrates the squarewave and generates a triangle wave.

You should see a triangle wave at Pin 4 of U14 comparator. Pin 3-U14 is the signal or audio input. Pin 13-U14 should be the composite squarewave and audio.

If you have an oscilloscope look to see if you have the triangle and squarewave at the Pins I mentioned. Post screenshots. Also, measure the DC voltages around U14 using the negative speaker terminal for black probe and scope ground. Post the results in the following manner:

Pin 1-
Pin 2-
Pin 3-

I posted your pic of main board, that's been cropped. Please take a close up of this area and post. I tried to magnify your pic, but not able to without pixalation. I will be able to edit pic and point out test points etc

The U14-LM361 may have failed. Replace if you haven't already. Also, check the DC voltages across D107,D108,D120,D121.


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Not sure what you mean by pnp and npn banks. the terms are not relevant to Mosfet's. The cy and dy are BJT's and are npn and pnp transistors.

Each side has 3 banks-1 bank of 3 IRF640's and 2 banks of IRF9640's. You may be able to check the drive w/o any output's install or you must have at least one mosfet in each bank.


2011-09-03 11:43 am
sorry. I meant n fets and p fets. When I put 1 fet in each bank the amp cycles in and out of protect. I was able to put 1 in each bank of one side and it powered up fine. Then I took them out and put them on the other side and it started going in and out of protect again.