HK770 HOT Left Channel

J

Jacope

New Member
Hi team,

I have a Harman Kardon HK770 that I'm trying to fix up and put some real usage into. I've recapped the power and driver boards, and re-flowed any suspicious solder already.

My issue is that the Left channel runs hot pretty fast, and when I check the output with a multimeter I'm finding that it is outputting ~6v DC with no load or speakers. That is the lowest the POT will go on that channel. Right channel seems to work perfectly fine and can be adjusted to ~0v DC with the POT.
I've tried swapping transistors on the driver boards from Lch to Rch and haven't been able to narrow down the issue.

Hoping to use this project to learn more about this, so feel free to be as specific as needed.
Any ideas?
 
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Jacope said:
Hi team,

I have a Harman Kardon HK770 that I'm trying to fix up and put some real usage into. I've recapped the power and driver boards, and re-flowed any suspicious solder already.

My issue is that the Left channel runs hot pretty fast, and when I check the output with a multimeter I'm finding that it is outputting ~6v DC with no load or speakers. That is the lowest the POT will go on that channel. Right channel seems to work perfectly fine and can be adjusted to ~0v DC with the POT.
I've tried swapping transistors on the driver boards from Lch to Rch and haven't been able to narrow down the issue.

Hoping to use this project to learn more about this, so feel free to be as specific as needed.
Any ideas?
Click to expand...

While we wait for some AK'ers who have experience in this particular area, one thing you could do is compare the voltages of each leg of each transistor, one channel to the other. Start at first transistor in the power amp, compare all three legs to the same transistor in the other channel... and make a list. You'll find one or some are very different, I'd bet, and that helps you narrow down the general area of the board or components that you need to investigate deeper.

Good luck!
 
Despues de volverme loco con un canal que no bajaba de 6V a la salida altavoces y el otro canal no hacer nada.

Desolde los dos conectores de 10 pines (R) y (L) donde va conectada la placa de drivers. Habia problemas con cuatro conexiones.

Cambie los conectores y todo funcionando!!!!

salu2
 
Last edited:
En las fotografías creo que se puede observar el fallo en los conectores.
Pienso que se deben revisar antes que empezar a revisar transistores, diodos etc etc.
En la última fotografía muestro el conector usado hembra de paso 2,54mm 1 fila contactos.


Salu2
 
Can someone please tell me where I can find the connectors P403 and P404 for HK770? It is at the bottom of the image. It is a seven-pin connector.

1736580708192.png
 
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