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R611 reads 1.43 V & 0.94 V
R615 reads 46.4 V & 46.4 V
Q601 reads
47.2 V ==>C
46.5 V ==>B
43.2 V ==>E
Q603 reads
00.2 V ==>C
00.8 V ==>B
43.4 V ==>E
Q605 reads
43.2 V ==>E
44.0 V ==>C
43.9 V ==>B
Rick,
Q601,Q603 readings look "swapped" C and E,can you please confirm that.
Q605 readings are very strange and don't confirm the readings of Q601 and Q603.
You see, the B of Q605,C of Q601, and C of Q603 are connected together and should have the same voltage.
Here are the pinouts please re-measure.
Please add the measurements on : R621 and R633 and Q607 (re-measure).
Q601,Q603 readings look "swapped" C and E,can you please confirm that.
Q605 readings are very strange and don't confirm the readings of Q601 and Q603.
You see, the B of Q605,C of Q601, and C of Q603 are connected together and should have the same voltage.
Here are the pinouts please re-measure.
Please add the measurements on : R621 and R633 and Q607 (re-measure).
Attachments
Sorry about that, some are facing the opposite way on the board and I was getting mixed up writing them down on paper. I'm gonna be more careful and double check.
Q601 reads
43.4 V ==>C
46.5 V ==>B
47.2 V ==>E
Q603 reads
43.4 V ==>C
00.8 V ==>B
00.2 V ==>E
Q605 reads
44.1 V ==>E
44.1 V ==>C
43.4 V ==>B
Q607 reads
43.4 V ==>E
44.1 V ==>C
44.1 V ==>B
R633 reads 44.1 V & 47.7 V
R621 reads 47.2 V & 47.7 V
Yes, the readings are correct
O.K disconnect the receiver from mains.
Verify there is no voltage on Q605 C,E.
In diode mode test check the resistance between C and E of Q605 and reverse the probes as well.
Do the same measurements in Resistance non-diode test mode.
What do we get(a total of 4 measurements)?
Verify there is no voltage on Q605 C,E.
In diode mode test check the resistance between C and E of Q605 and reverse the probes as well.
Do the same measurements in Resistance non-diode test mode.
What do we get(a total of 4 measurements)?
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OK, Q605 In diode mode it reads .578 & nothing in reverse
In what setting do I put the meter for measuring just resistance?
Attachments
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In any resistance that will show anything .
You may start high ,like 2M and if it shows lower resistance set it to a lower range.
After you have checked the above.
Please disconnect the GND wire we have connected to the leg of R627 (820ohm/2w) and leave the leg open.
Measure the voltages on Q605 and Q607.
What do we get?
You may start high ,like 2M and if it shows lower resistance set it to a lower range.
After you have checked the above.
Please disconnect the GND wire we have connected to the leg of R627 (820ohm/2w) and leave the leg open.
Measure the voltages on Q605 and Q607.
What do we get?
With meter On 200k setting, Q605 reads 93.0 & 93.0
With the ground wire off R267 leg,
Q605 Reads...
43.9 V ==>E
43.8 V ==>C
43.1 V ==>B
Q607 Reads...
43.0 V ==>E
43.9 V ==>C
43.8 V ==>B
OK, for Q603, Amp disconnected and R627 leg lifted and not connected to anything...
In the 200 ohm settings I get 42.3 ohms for E
I tried all the ohm settings and got nothing for C
Please measure the voltages on both sides of D605.
What do we get?
As per #51,
there shouldn't be that 93(K?) reading between C and E of Q605.
With receiver disconnected from mains.
Please remove Q605 from the board (mark it's orientation on the board for later),
and measure it in diode test mode
(B-E,B-C and E-C in both directions ,a total of 6 measurements).
What do we get?
When Q605 is out:
Measure the resistance in it's C-E location on the board.
Measure Q607 in board in diode test mode?
What do we get?
What do we get?
As per #51,
there shouldn't be that 93(K?) reading between C and E of Q605.
With receiver disconnected from mains.
Please remove Q605 from the board (mark it's orientation on the board for later),
and measure it in diode test mode
(B-E,B-C and E-C in both directions ,a total of 6 measurements).
What do we get?
When Q605 is out:
Measure the resistance in it's C-E location on the board.
Measure Q607 in board in diode test mode?
What do we get?
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Leakage on Vce is very much voltage dependant.
thus DMM readings may not indicate.
Q603 NPN normally has high Vce , while Q605 PNP is low Vce.
Therefore voltage at Q603 , Q601 junction is far more sensitive to Q603 on output bias error.
The offset adjust pot is thus designed to null this offset voltage at output from Q603 leakage, with much less sensitivity to variations in hFE or leakage in any other part.
Q603 is in fact the highest impedance part in the whole design. acting as a current sink, while offset pot and Q605 are lower impedance current sinks with lower voltage drop on Vce. Nominal collector currents ought to be < 1mA shared by Q601 and base current of next stage.Q605.
Presently collector currents are (0.2V/330R, which also suggests Q603 leakage resistance at Vce>43V is ~100k
My money is still on Q603 as a leaky transistor.
thus DMM readings may not indicate.
Q603 NPN normally has high Vce , while Q605 PNP is low Vce.
Therefore voltage at Q603 , Q601 junction is far more sensitive to Q603 on output bias error.
The offset adjust pot is thus designed to null this offset voltage at output from Q603 leakage, with much less sensitivity to variations in hFE or leakage in any other part.
Q603 is in fact the highest impedance part in the whole design. acting as a current sink, while offset pot and Q605 are lower impedance current sinks with lower voltage drop on Vce. Nominal collector currents ought to be < 1mA shared by Q601 and base current of next stage.Q605.
Presently collector currents are (0.2V/330R, which also suggests Q603 leakage resistance at Vce>43V is ~100k
My money is still on Q603 as a leaky transistor.
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When the loop feedback R was changed to 0V feedback instead of high offset out,
Q603 reads
00.2 V ==>C
00.8 V ==>B
43.4 V ==>E
Vbe of Q603 ib is low (0.6 vs 0.65) and thus Ic is low and thus Q605 Ib is low and thus Q605 Vce =0
Normally Q603 Vb=1.5V with loop closed.
make sense? thus Q603 is at fault with leakage resistance which offsets the constant DC current sink and thus output offset voltage is +7 ~ 11V here when loop is closed.
Q603 reads
00.2 V ==>C
00.8 V ==>B
43.4 V ==>E
Vbe of Q603 ib is low (0.6 vs 0.65) and thus Ic is low and thus Q605 Ib is low and thus Q605 Vce =0
Normally Q603 Vb=1.5V with loop closed.
make sense? thus Q603 is at fault with leakage resistance which offsets the constant DC current sink and thus output offset voltage is +7 ~ 11V here when loop is closed.
when Q607 Vce =Vbe=0.7 then Q605 becomes Vce=0
Q605 reads
44.1 V ==>E
44.1 V ==>C
43.4 V ==>B
EDIT **** Q607 Vce=0.7 = Vbe therefore Q605 Vce=0 ***
Q607 reads
43.4 V ==>E
44.1 V ==>C
44.1 V ==>B
Since the feedback point on input is inverted a positive output offset has to be caused and a leakage to ground in Q603.
65V = Vceo max.BC546B if this parameter has reduced with aging or rise in junction temp then leakage will occur.
Q605 reads
44.1 V ==>E
44.1 V ==>C
43.4 V ==>B
EDIT **** Q607 Vce=0.7 = Vbe therefore Q605 Vce=0 ***
Q607 reads
43.4 V ==>E
44.1 V ==>C
44.1 V ==>B
Since the feedback point on input is inverted a positive output offset has to be caused and a leakage to ground in Q603.
65V = Vceo max.BC546B if this parameter has reduced with aging or rise in junction temp then leakage will occur.
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