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Toshiba SA-775 Problem - Relay clicks then.........

ecluser said:
A problem common to both channels usually takes its source to a common power supply. Compare the voltages on Q907 and Q908 with the ones on the schematic.
Click to expand...

Q907 has no voltage,
E / .1 vdc
B / .005 vdc
C / .006 vdc

Q908 looks close to normal
B / -52.9 vdc
C / -53.1 vdc

Thanks
 
looks like bridge rectifier d903 is shot or is poorly connected .test for +54v at d903 ..it is maybe marked which is + .or will be the cut corner side .
 
petehall347 said:
looks like bridge rectifier d903 is shot or is poorly connected .test for +54v at d903 ..it is maybe marked which is + .or will be the cut corner side .
Click to expand...
Hey pete,

D903 (Bridge Rectifier) / +52.7 vdc on the positive pin. Seems close to normal. Any other suggestions? Thanks AGain.
 
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i am a little confused here . the schematic isnt showing q907 . all i can go off is fig 18 . it doesn't show how vcc+ and vcc+ connect together .
ok i see it now ..try collector q601 should be +54 ..its same power en rout to q907 .. its just a matter of tracing where its missing .
 
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petehall347 said:
i am a little confused here . the schematic isnt showing q907 . all i can go off is fig 18 . it doesn't show how vcc+ and vcc+ connect together .
Click to expand...

Pete, I have the Service manual pdf, if you want it, I can email it to you. PM your email address, and I'll send it ASAP.
 
Yes, if you have +53V at the output of the bridge and you don't have that same voltage at the collector of Q907, a trace is broken somewhere.
 
petehall347 said:
i am a little confused here . the schematic isnt showing q907 . all i can go off is fig 18 . it doesn't show how vcc+ and vcc+ connect together .
ok i see it now ..try collector q601 should be +54 ..its same power en rout to q907 .. its just a matter of tracing where its missing .
Click to expand...

I'm having a hard time finding Q601 on the board ( Ifound R601) . Is it one of the 4 round transistors thats mounted to the big heatsink in the back? If so, those have very low voltage. Such as +1.5 vdc. or less. I think I'm on the wrong area. ??? Forgive me if I'm being stupid!!!!
 
ecluser said:
Yes, if you have +53V at the output of the bridge and you don't have that same voltage at the collector of Q907, a trace is broken somewhere.
Click to expand...

Hey ecluser, What do you suggest? Should I take that entire board and closely inspect it? I'd appreciate your thoughts. I'm open to about anything at this point. Thanks guys.....
 
can you find q602 collector ? and r921 ? and q515 collector . ..
q601 is 2sd425 unless someone swapped it . and yes its on the heatsink .
 
I see from the trace layout that there is a terminal +VCC1 at the output of the bridge and another terminal +VCC1 close to the first. There is a short trace between the second terminal and Q907. Look if you have voltage at the second terminal +VCC1, the one near the edge of the board.

I imagine that you have a wire at each terminal going to the main filter cap. Maybe one wire is broken?
 
petehall347 said:
can you find q602 collector ? and r921 ? and q515 collector . ..
q601 is 2sd425 unless someone swapped it . and yes its on the heatsink .
Click to expand...

Yep. Found Q515. The four transistors on the Heatsink are NOT 2sd425. They are, (2) Toshiba 2SD551 & (2) Toshiba 2SB681. I take it these are the output transistors? Has someone change them? They're not matching the schematic. the solder looked fresh.
 
ecluser said:
I see from the trace layout that there is a terminal +VCC1 at the output of the bridge and another terminal +VCC1 close to the first. There is a short trace between the second terminal and Q907. Look if you have voltage at the second terminal +VCC1, the one near the edge of the board.

I imagine that you have a wire at each terminal going to the main filter cap. Maybe one wire is broken?
Click to expand...

ecluser, Yes, I have +52.6 vdc on that trace. I've found no broken wires. ???
 
ecluser said:
Could you measure again the voltages at Q907?
Click to expand...

Q907
B / 52.1
C / 52.7
E / 51.5

Strange, I didn't have those voltages before. ??? I moved around a bunch of wires, trying to find a broken one. Maybe one has a short. ??? Should the relay click, when powered on? No click.
 
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you may have had a poor ground connection while checking it ..or if your meter leads are like some of mine one might be flakey . i am suspecting one or more resistors in each channel are high or open on the main amp board .not sure if there are any fuse resistors at all .it could be a reason for the high dc offset then again why its cycling up and down blows this theory ... ecluser will steer you better than i can .
 
TubeJunkie said:
DC voltage at the coils L601 and L602: 5.2 vdc and steadily drops over 20 seconds to less than 1 vdc, then cycles all over again.
Click to expand...

Now that we know you have good voltages at the output of the regulators, I would replace C505 and C506, and possibly C501 and C502
 
ecluser said:
Now that we know you have good voltages at the output of the regulators, I would replace C505 and C506, and possibly C501 and C502
Click to expand...

Oh well, I replaced C505, C506, and C501, C502. Still have no sound. I checked the old caps, they tested OK with my Fluke115 , out of circuit. Looked like they've seen a little heat though. Should I go back and look at some voltages again? Where should I look? Thanks Again !!!
TubeJunkie
 
Check again if you have low DC voltages at the coils L601 and L602

If your offset voltage is low try to adjust the bias. Can you adjust the bias close to the values on the schematic (16mV between the emitters of the oower transistors)?

If you have a low offset and the correct bias, it's about time to consider a possible fault in the protection circuit itself, because the protection circuit responds to three possible faults in the amp:

1- high offset voltage, detected by Q803 and Q805
2- high current in the emitter resistors, detected by Q801 and Q802
3- loss of AC voltage, detected by D802

You can confirm that the amp is running well if you have a good signal at the coils L601 and L602. I don't remember if you have a scope but if you don't have one, you can can touch the coil with the positive wire going to a (test) speaker, and the negative wire from the speaker connected to the negative speaker terminal at the back of the receiver (which are grounded all the time anyway)
 
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