KR-8600 Help

[Professor`]

ok more tinkering, the relay that clicks over when the power is turned on has 4 pins 2 pins have voltage to them that fluctuates with the volume, same should be for the other 2 pins, 0 voltage, when i supply my own voltage, the left channel works. the prob appears to be in the power supply.

 

[Professor`]

i cannot find a single bad item in the psu, what gives.......

 

[Professor`]

Here is a photo of the backside on the PSU, where the arrows are is where i seem to be having a problem, They both go to the speaker selector switch, At max volume i should have near or at 10 volts from these points. In the pic, the left one has the correct voltage, the right is dead and so is my right channel, i checked everything on the board, i cannot find a issue, If i jump the 2 together i get the sound in both channels but it cannot handle it long and starts to get hot. Anyone Have a Clue on this, Iam baffled!..!

 

[Watthour]

To summarize:

The pre-amps are working in both channels as verified by connecting them to a different final amp (post 20);

If you jumper the speaker leads at the isolation relay both sets of speakers work (post 23). This effectively eliminates any problems with the speaker selector switch downstream;

Does the relay itself ever operate (close)?

What is the condition of the 10Ω/2W resistors on that board?

When you jumper the two traces together both of the speakers are being driven by ONE of the final amplifiers. The other (dead) channel is also being loaded onto the good channel, so with the lower speaker impedance and extra load it will almost certainly get hot. Avoid doing this or you will have a completely dead unit.

If you check upstream of the relay toward the power amplifier (X07-1450-10) you may find that the left channel final amp has some problems. Check for good audio signal on pins 9 and 10 on that board. Those are the left channel audio out, just as pins 19 and 20 are the right channel out.

 

[Professor`]

To summarize:

The pre-amps are working in both channels as verified by connecting them to a different final amp (post 20);

If you jumper the speaker leads at the isolation relay both sets of speakers work (post 23). This effectively eliminates any problems with the speaker selector switch downstream;

Does the relay itself ever operate (close)?

What is the condition of the 10Ω/2W resistors on that board?

When you jumper the two traces together both of the speakers are being driven by ONE of the final amplifiers. The other (dead) channel is also being loaded onto the good channel, so with the lower speaker impedance and extra load it will almost certainly get hot. Avoid doing this or you will have a completely dead unit.

If you check upstream of the relay toward the power amplifier (X07-1450-10) you may find that the left channel final amp has some problems. Check for good audio signal on pins 9 and 10 on that board. Those are the left channel audio out, just as pins 19 and 20 are the right channel out.

The resistor test fine, it seems that i am not getting anything out on pin 19 and 20 but i cannot find anything bad on it unless i start pulling part by part and testing. And the power transistors are fine, i pulled them and tested them and there is no issue, even swapped to other channel to test, there fine. The relay works fine also.

 

[Watthour]

Is the signal into the final amp board the same in both channels? Pins 1 & 4 are the two channel inputs to that board.

Can you compare voltages on the final amp board from left to right channels? You might want to start by comparing the collector of Q7 to Q8 in the other channel. That's the first stage upstream of the final drivers.

 

[Professor`]

Is the signal into the final amp board the same in both channels? Pins 1 & 4 are the two channel inputs to that board.

Can you compare voltages on the final amp board from left to right channels? You might want to start by comparing the collector of Q7 to Q8 in the other channel. That's the first stage upstream of the final drivers.

Q7 & Q8 tested good.

 

[Professor`]

Voltage on the collectors is showing -1.12 volts on both q7 and q8 and thats with the negative meter probe on the chassis
Pin 1 shows 13.86 volts Pin 4 shows 15.73 volts

 

[Professor`]

Think i found the problem, Pin 4 goes right to R4 at R4 there is no voltage present and there is a trace from pin 4 to R4... seems the trace is bad, when i jump it, it works.

 

[Watthour]

Is there a roughly equal signal at Pins 1 and 4 on the amp board?

If so, move your voltmeter downstream toward the finals. Look at Q17,19 in the left and Q18, 20 in the right side.

 

[Professor`]

Thanks for all your advice, It turns out that it was a bad trace from Pin 4 to Re4 on the Power Amp Board.

 

[Professor`]

all fixed ! ! ! !

 

[Watthour]

Great! Now if you want, you can send it to me for evaluation and durability testing for a period of time. I'll be happy to make regular reports on the results of the testing every six months or so.

 

[Professor`]

haha Ill pass, i just gota adjust to bias and it should be good.

 

[Professor`]

F**K I was adjusting the bias and i accidently shorted the one leg of the power transistor to ground, now its toast and R60 resistor turned bright red lol, need a new resistor now and a 2SD427.....

 

[Professor`]

Well i replaced the power transistor with a new 2SD427 and the toasted resistor, it is still not working, i am getting over 10 volts on pin 19 on the power amp board and i know its not supposed to be that, the relay will not click over unless i unplug that pin thus making it a one channel amp again, i cannot find anything outa spec on the power amp board , i have to be missing something, can you chime in Watthour or any other member ? Thanks in advanced.

 

[Professor`]

http://www.youtube.com/watch?v=Hp6yGTg6ibI

ALL FIXED

 

[sregor]

http://www.youtube.com/watch?v=Hp6yGTg6ibI

ALL FIXED

That's what you said last time. Hope no more oops! :thmbsp:

 

[70WR]

wow - good thread to follow. Also looks like on the 2nd page, the pic with yellow arrows, the trace above the right arrow has seen better times.

 

[Professor`]

That's what you said last time. Hope no more oops! :thmbsp:

wow - good thread to follow. Also looks like on the 2nd page, the pic with yellow arrows, the trace above the right arrow has seen better times.

Don't worry the owner picked it up today, Its all taken care of now.