Discussion in 'Pioneer Audio' started by KeithD, May 6, 2018.
corrected my post now
Ok, replaced all transistors. Replaced Q1-3, no change. Voltage on pin 8 (+B3) improved a bit after replacing Q4. Did the rest of the transistors, no change. Replaced D2, 3, 6, 7. Still no change. Here are the readings:
6: 9-12VDC (should be 13.5V)
8: 13.8±3VDC (+B3, should be 30V)
14: -44.4VDC (-B3, should be -42V)
17: -13.3VDC (-B4, should be -13V)
So something is still not right on the circuit fed by pins 4, 5 and out put at pins 6, 8. All that's left are a couple of ceramic caps and resistors.
or as i thought but never mentioned it something might be pulling the voltages down further on .. need to look for the current limiter resistor on the high side and measure voltage drop across it ... its 2.16am here .. will check back in the morning .
I will test transistors on the power supply board tonight. Looks like R6, 7 ,8, and 9 should be tested. Will lift one leg and see if reading is ok. Anything else to look for?
Checked R6, 7, 8, 9: all good.
So, that leaves me with what Pete mentioned about something down circuit pulling the +B3 voltage down. Looking at the schematic, YIKES! +B3 powers every board in this unit! The thing to do may be to disconnect each board one by one from +B3 and see if the voltage restores to +30V. Sound like a plan? Can't really see any way around it at this point...
yeah it sure does. two colors of wires too red and a pinkish grey. the source is pin 8. you could un do the wire wrap and use your meter and check the draw in milliamps its only supposed to be 150 total. its all yes/no and following the daisy chain
OK, disconnected all three wires from pin 8 of the power supply board. Readings are still around 12VDC and variable. So, it appears the problem is on the power supply board, but where? All electrolytic caps replaced, all transistors replaced. Replaced D2, 3, 6, 7. What's next?
Strange. Could you measure voltages on all legs of Q3 again and post a picture of how the board looks now?
Q3: E, C, B
8.6±2, 8.1±4, 10.5±1.5VDC
As you can see voltages are quite variable.
It's a bit difficult to see, but is Q3 installed correctly?
voltages say its not right .. have been working out what might happen if q3 was removed for now .. i first see emitter of q1 voltage should be higher than normal if the rest of the circuit is good .
q2 base needs to be about 1.2 volts higher than q1 emitter to count out q1 q2 problems .
so long as nothing connected to pin 8 pulling q3 should be fine for testing purposes .
Yes, Q3 is in correctly. Matches schematic and printing on the board. Repacement KSC1845FTA is ECB configuration.
Actually have another QX-949 to compare to with a good power supply (it has a bad channel on the rear power amp board). Q3 voltages on that board are (E, C, B): 13, 33.1, 13.7, with pin 8 at 30.8VDC.
Will measure some other voltages for comparison and see if I can narrow down where the discrepancy is.
q3 e to c voltages are like they should really be b to e .. b to e in most cases should be 600mv ish . if you remove q3 and check pin 8 again it should rise substantially if i am correct .
Did as you said, pulled Q3. Voltage at pin 8 still 13 volts.
Measured voltages at all four transistors before pulling Q3:
E, C, B (expected values from good power supply in parenthesis):
Q1: 15 (31), 50.5 (47.7), ~14 (32.8)
Q2: ~14 (32.8), 50.5 (47.7), ~14 (33.3)
Q3: ~7 (13), ~8 (33.1), ~10 (13.7)
Q4: 13 (13.1), 35.5 (33.7), 13.7 (13.7)
q2 appears shorted ..sort of doesn't make sense though .
check r5 r4 .. and maybe check all other resistors .
With Q3 removed, what happens if you also pull C10? If no change, then also pull C9 and see if that changes anything.
R3, 4, and 5 good.
Found the trouble, disconnected the wire from pin 6, and pin 8 came up to 30V and unit came out of protection.
Now I just need to trace back what pin 6 is powering. Something back there is shorting pulling too much power, I suspect.
tuner is powered from pin 6 . maybe q7 ha1142 took a dump or q6 ha1137 or even q8 ha1138
Oh, no! Are there replacements for those??
best figure out if it is any of those first . or a simple trapped wire or something .
try lifting r40 tuner board . or first try switching fm to am or visa versa .
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