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Pioneer SX-780 Diagnose No/Little Sound

Using MM correctly now ... voltages on power transistors all check out. I have not re-soldered them, but they look good. I get just over 41v on the relay coil, not 48. That OK?

Realizing I need to come up with a better road map and starting point instead of randomly checking things ...
 
Last edited:
Go to the basics:
Like others have said. Check the PS voltages.
Check the amp settings.
 
deskfull said:
I get just over 41v on the relay coil, not 48. That OK?
Click to expand...

Doesn't sound good.

Measure the AC voltage on it; if the cap is poor, it won't hold the voltage, and there will be a large ripple. Your DC reading will be an average, and may be an optimistic average...
 
I think you should see 36v with the relay energized. It may not be pulling in tightly.
First check all the PS voltages and give the receiver a good visual check.
 
cpt_paranoia said:
Doesn't sound good.

Measure the AC voltage on it; if the cap is poor, it won't hold the voltage, and there will be a large ripple. Your DC reading will be an average, and may be an optimistic average...
Click to expand...

Tested for AC volts: it jumped around a bit and then settles on 0.6 volts AC.

At the time of testing, DC was exactly 41 volts.

Power Supply voltages (AC & DC) checked out based on recommendations in another thread I found.

Thoughts? Thanks!
 
Should I be getting voltage across the relay terminals other than the coil? I do have continuity across all of them, but no significant voltage (occasionally see small millivolts like .08mv).

During the period of clear, audible sound from the left channel just after power-up, I seem to be able to cut it out before it fades out by tapping on the relay. My uneducated guess still wonders about a problem in the relay or between it and the power source. As mentioned, PS #s seem good.

Any suggestions on what to test to see if it is the relay itself or before it? A capacitor was mentioned. I'm a little overwhelmed looking at the schematic and service manual, but definitely interested in getting a better grasp of it.

Thanks for all of the suggestions!
 
OK. q27 is easy to find:

1. 13.5v
3. .684v
4. -.02v
5. 0v
6. -7.1v
7. -.02v
8. 7.1v

I think I am finding q26 correctly (foil on board leads to it from #3 on q27:

b. .6v
c. 0v
e. 0v

Thanks!
 
relay should be clicked in looking at those voltages ..
however i would expect some mv at q26 collector .
how it works is like this . q26 switches on with the 600mv or so at its base and creates ground connection through its collector emitter junctions .
if it wasn't getting 600mv it would be off and you would see about 42v or more at its collector .
it is looking like relay coil is possibly bad or a bad solder connection on relay .
or possibly bad solder on q26 .
 
petehall347 said:
relay should be clicked in looking at those voltages ..
however i would expect some mv at q26 collector .
how it works is like this . q26 switches on with the 600mv or so at its base and creates ground connection through its collector emitter junctions .
if it wasn't getting 600mv it would be off and you would see about 42v or more at its collector .
it is looking like relay coil is possibly bad or a bad solder connection on relay .
or possibly bad solder on q26 .
Click to expand...

Let me make sure I am listing these and reading my multimeter correct for you:

The receiver is powered on and I have heard the single relay click ...

on "b" of q26, my display reads: 0.652v

If I put my multimeter to measure millivolts (mv) in DC, I get "OL."

Is .652v not the same as 652mv?

Thanks.
 
yes they are the same .
its the collector mv i was interested to see . its a bit academic though as relay does click in . so the contacts must be worn/burned .
 
Dang! New relay didn't do it :(

Same symptoms. Relay clicks on correctly. Brief sound to of left channel until it fades to silence or distortion.

I still see the voltage on the relay coil go from 51v on both sides of the coil before click to 32mv on one side and 42v on the other.

The nearby d5 does the same thing (51 on both sides to 32mv on one and 42v on the other). And R321 goes from 51v on both sides to 51v on one side and 42v on the other.

All this sound correct? Or should I begin looking elsewhere?
 
Here we go. Gathering all voltages I can, mostly based on what had been requested/provided in other threads. Let me know if I should check something specific ...

Pin
1: -40v
2: 40v
10: -40v
11: 40v

15: -40.1v
16: 40.1v

17: 30.32VAC
18: 30.32VAC
19: 39.66VAC
20: 39.66VAC

Q17: E. 24.33 / C. 36.77 / B. 24.92
Q18: E. 19.02 / C. 19 / B. 18.29 (This one appears off. Service Manual diagram says these should be -24.6, -34, -24)
Q19: E. 39.6 / C.49.9 / B. 40.2
Q20: E. -39.9 / C. -51.9 / B. -40.5
Q25: E. 13.60 / C.24.37 / B. 14.19

Power Packs

Left
1. -1.31v
2. -40.1v
3. -96.7mv
8. -77.2mv
9. 40.0v
0. 1.173v

Right
1. -1.241v
2. -40.1v
3. -27.6mv
8. -77.2mv
9. 40.0v
0. 1.173v
 
Q18: E. 19.02 / C. 19 / B. 18.29 (This one appears off. Service Manual diagram says these should be -24.6, -34, -24)
check r307 12k . c306 47uf . and q18 . and r306 430 ohms . and also check the soldering in that area .

looking at those voltages q18 appears bad or installed incorrectly .
 
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