Kole Audio Amp

[mike49504]

I got this amp in for repair . It had no output so i removed the board from the sink and redid some solder connections.

With the board out of the sink it will power up and produce audio.

If i put the board back in the sink and put all clamps back in the amp will power up fine but not produce audio and the rca jacks will spark like the heatsink has voltage.

Something conducting?? Or what might cause this

 

[Perry Babin]

With it clamped down and no power applied, what is the resistance from the B+ terminal of the amp to the RCA shield?

 

[mike49504]

2.032 k ohms and it continues to climb

 

[Perry Babin]

Try twisting the transformer to see if it changes.

 

[mike49504]

Twisted the transformer and got 3.92 k ohms now. Left channel produces clean audio right channel still dead

 

[Perry Babin]

Does the heatsink have any voltage on it?

Do the RCA shields have any AC or DC voltage on them? Check with your scope as well as your multimeter.

 

[mike49504]

Heatsink has 45.2 volts on it. Rca jacks have -0.72 volts on them

 

[Perry Babin]

Check the resistance from the tabs of the rectifiers and outputs to see if any are shorted to the sink.

 

[968driver]

Check isolation between power transistors and heathsink.
Some amplifiers used metal anodized isolators, and these can break down.

 

[mike49504]

Ok i found one shorted to the sink.

I took the entire board out of the sink again since the right channel still doesnt work.

I see alot of crappy solder joints on this board so i will re solder them and see it i can get this amp up and running.

 

[Perry Babin]

Can you post a photo of the board?

 

[mike49504]

Perry,

Ill get a pic up on here in a few.

Next thing is i got the amp to produce audio out of both channels.

But if i flip the crossover switch from full to low pass or high pass the amp wont produce audio on the right channel.

The switch has to be in full range mode in order to get audio out of both channels.

So i sparyed contact cleaner in it and went back and fourth with the switch 200+ times i still have the same issue Bad switch or maybe something else??

I checked all op-amps all test fine.

Any thoughts?

 

[Perry Babin]

The switch should be similar to the one in the photo. Use your meter to confirm that you have approximately 0 ohms between the contacts that are connected by the blue line in each position.

 

[mike49504]

Ok I have 0 ohms between the pins.

 

[Perry Babin]

Do all op-amps have +/- supply voltage?

Do any op-amps have any significant DC offset on the output pins?

 

[mike49504]

All op-amps

1:-0.72
2:-0.72
3:-0.72
4:-16.05
5:-0.72
6:-0.72
7:-0.72
8:14.75

 

[Perry Babin]

Are there any other switches?

If so, set the crossover switch so that there is no output and move the other switches to see if the audio plays through intermittently.

 

[mike49504]

If o push or twist the transformer i can get output but very low

 

[Perry Babin]

I don't think is has anything to do with the transformers if it plays on one of the crossover settings.

If all else fails, you'll have to trace the signal through the op-amps to see where the signal is lost.