More screw ups, CR620 this time.

srinath

Super Member
So atleast I am failing at a bigger and bigger scale.

This one was DOA, atleast I didn;t pop fuses and ruin my good set of fuses.

The transistors was my first suspect, I pulled them all out. Yeaaaaaa ... great. Even better one of the 4 had 2 ohm in both directions between E and C. yeaaaaa, dead great. OK so I was going to fit it back with 3 and see if it works ... only ... there is 2 2sb531's and 2 2sd371's and like a dummy, I didn't notice which came form where.

Can someone point me in the right location.

Thanks y'all.

Cool.
Srinath.
 
And its not showing any signs of life at all with all the transistors removed. Does that mean something else is dead ? Transformer ? Input power supply ?
Thanks.
Srinath.
 
If you have all the outputs removed..Apply power and measure the collector voltage at the transistor sockets. Negative voltages will be the PNP's (2SA,2SB) . Positive voltages will be the NPN's (2SC,2SD)..
 
Wow ... please elaborate.
Negative voltage @ the collector - which I thought in this type was the body ... OK OK I get it, collector to emitter ... with the collector which is the chassis being negative prong of the DMM, then the emitter is Positive or negative ... got it, time o start measuring.
BTW This amp is not lighting any of its lights and not doing any thing else either. Those are right off the first step off the transformer. Could it just have a dead transformer ?

Cool.
Srinath.
 
Its simple.Don't try to make it harder.With your multimeter Black test lead connected to chassis ground,Use the Red test lead to probe the collect pin on the transistor sockets.Remember that the collector on a TO-3 is the transistors case.
Just be careful not to short the collector connection to the heatsink with your test lead. The heatsink is connected to chassis ground.
 
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I got 112v ac or so going into the transformer. Nothing comming out.
Its fried inside - can a shorted output transistor do that ?
Thanks.
Srinath.
 
The input side reads open on the transformer. I got 1 ohm and 3 ohm etc various points on the low voltage side. I'm calling DOA on the transformer. Maybe I could open the transformer and check if its burnt a wire @ a solder joint.
Cool.
Srinath.
 
Sounds like bigger problems than output transistor placement. Can you say doorstop..Unless you find a parts unit. Most likely a power surge took out the primary ie..Lightning

can a shorted output transistor do that ?
Thanks.
nope..And oversized mains fuse and a voltage surge.Some of these transformers have fusible links built in to the transformer.
 
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I have a nice collection of yamaha transformers ...
r500 needing a chip, r700 needing 2 chips, cr440 needing chips and god knows what else, probably some other stuff lying about ...
So any of them can donate ? I know I need 12 and 30v and what not, I'd look and see what is around ...
Also I am pinning my hopes on a dead solder joint inside the transformer. God knows I have screwed up my share of motorcycle alternators ... a low reading indicates shorts and burns. A open reading indicated detached wire ... especially since there is no external sign of the thing melting into a blob.
I mean, alternators in bikes start turning dark as they internally short and die. Alternators fail mechanically, if all else was fine and you saw to that in the course of its death, a alternator from where it starts to die, till it is DOA can run for over 15K miles. Atleast on a motorcycle. In a car sadly, the regulator is mounted right on it, and the excess heat from a shorting alternator fries that pronto. I ran a bike that way for 6months, just keep it revved first past 3K, then 4, then 5 then I fixed it, and dont do short rides, and keep a good battery in it.
Anyway today its getting diced open. lets see what pours out.
Cool.
Srinath.
 
Looking at the heat sink from the left side of the receiver, the position of the power transistors is 2SD, 2SB, 2SD and 2SB

Good luck with the transformer.
 
Thanks so much ecluser.
Yea transformer is DOA, for sure.

I checked and that CR440 has one that is alive, though I have to check it for voltage etc. Also overall power ability, that 440 is a much smaller amp and has a better design.

Now the R500 and R700 also are candidates. I need to check em. They both have good transformers I know that.

Thanks y'all for your help.

Cool.
Srinath.
 
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