2245 in protection

[bluescat]

Hi guys: Cold bored and shut in, so I decided to try to troubleshoot a 2245 that died while playing at high volume. I was in another room when it died, so I don't know if anything dramatic happened, just quit hearing music!
I'm old and have no electronic experience, so be patient if you decide to help me: Thanks!!
After reading all the threads I could find on 2245/70's this is what I've done so far:

On P800 board:
Checked J801to ground=13.10v
Checked J802 to ground=34.7v
Checked between J802 & J803 and got -34.8 volts
On flipside of P800 (solder side) at relay
Checked yellow wire to ground = -35.8v
Checked blue wire to ground=0v
With power off; between yellow and blue wires=4.5 ohm

Power amps:
I pulled outputs 1 side at a time and checked to see if it came out of protection after pulling each side. Stayed in protection!
Reinstalled outputs and am back to square one.

Does what I have done so far tell you anything?

 

[blhagstrom]

It tells me you should have asked some questions first.

Did you pull the outputs "one and a time" test and put them back one at a time?

You should pull them in pairs. One at a time may fry the hell out of things.

If you only checked one at a time out, try to pull one whole side, then test.
OR, pull them all and test.

AND, you should build and use a Dim Bulb Tester to do this.

 

[bluescat]

Sorry, that should have read one "side" at a time, didn't fry anything. Thanks for the warning, anyway.

 

[bluescat]

FWIW: I also pulled the relay, inspected it for any "obvious" mechanical problems, and reinstalled it after not seeing anything unusual. I didn't try to open it up.

 

[bktheking]

Relay 99% of the time is never faulty. Measure DC at J709 of each amplifier board powered on and post your findings.

 

[bluescat]

Hi BK, thanks for your help:
I can't locate J709 on the amp boards, or the schematic either. Maybe I'm blind. I'll keep looking!

 

[bktheking]

SHIT- 1 sec, wrong schematic.

 

[bktheking]

J757

 

[bluescat]

Ahh, that explains it:

j757 right ch=36.5

j757 left ch= 0

The left ch. pin was hard to access but after. 3 tries I kept getting "0" so I'll assume thats corect

 

[bktheking]

Do you have any parts such as transistors to your disposal? You already know the outputs are good based on your tests. When I see HIGH voltage like this the first thing I do is replace the differential input pair and their current source transistor and see if it behaves. Usually the first three transistors on the schematic are them. The differential input pair needs to be gain matched for HFE , not sure if your meter can do that.

 

[bluescat]

No, I don't have any transistors, will have to order. I've never orderd transistors before, if you can tell me what I need to know, I will get them ordered. Yes my meter can do that.
I assume that the right channel is the culprit ??

 

[bktheking]

Whatever side you measured is, look at the unit from the front.

Where do you live? Since it's a guess based on just replacing I can pop some subs in the mail.

 

[bluescat]

Right channel =35.6
Left channel = 0

I live in West Virginia

 

[bktheking]

OK, pm me your cooridnates and i'll dig through my stash.

 

[bluescat]

PM sent: Thanks

 

[bluescat]

Was just wondering if I can disconnect right amp board, to see if it comes out of protection. If yes, will disconnecting the black ground wire, connected to screw terminal accomplish this? (easiest to get to)

 

[bktheking]

What pin is it connected to?

 

[bluescat]

It is attached to J758!

 

[bktheking]

751 and 752 are also grounds. Just pull the outputs and J757 then it should.

 

[bluescat]

Pulled the yellow wire off pin J757 and pulled the outputs. I will wait till you tell me it's ok to turn the unit on.
I did make one mistake, hope I didn't damage the output. Forgot to dicharge my needle nose before touching the output: got a small spark: