Amp In Protection Mode

[Rick79]

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?

D605 reads 42.7 V & 43.4 V

In a few minutes I'm gonna remove Q605 from the board and do the measurements you asked.

 

[Rick79]

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?

Q605 diode mode readings (off the board)
B - E .692 & nothing
B - C .662 & nothing
E - C .653 & nothing

Q607 diode readings
B - E .525 & .515
B - C .576 & nothing
E - C .662 & nothing

In 200k mode, Resistance on E & C location on the board is 96.8
This reading starts around 20 climbing up fast and then slows down and takes about a minute to stop at 96.8
It did the same thing when it was on the board. I don't know if that means anything.

 

[dorke]

Please verify the 0.653 E-C reading of Q605,
If it is indeed 0.653 we have a bad Tr !

 

[Rick79]

Please verify the 0.653 E-C reading of Q605,
If it is indeed 0.653 we have a bad Tr !

I just double checked the readings, the probe must have touched B when I took the E-C reading because I don't get nothing between E-C anymore.

 

[dorke]

O.k
so we have for Q605 diode mode readings (off the board)
B - E .692 & nothing
B - C .662 & nothing
E - C nothing & nothing
If so Q605 is fine.

What about the C-E of Q607 of 0.662,can you verify that?
If you still get that 0.662 take Q607 out of the board(mark/note it's orientation for later) and re-measure it.

 

[Rick79]

Please verify the 0.653 E-C reading of Q605,
If it is indeed 0.653 we have a bad Tr !

O.k
so we have for Q605 diode mode readings (off the board)
B - E .692 & nothing
B - C .662 & nothing
E - C nothing & nothing
If so Q605 is fine.

What about the C-E of Q607 of 0.662,can you verify that?
If you still get that 0.662 take Q607 out of the board(mark/note it's orientation for later) and re-measure it.

Yes the 0.662 reading for E-C is correct.

These are the Q607 readings now after I took it off the board...
B - E nothing & .634
B - C nothing & .631
E - C nothing & nothing

 

[dorke]

O.K.
Looks like Q607 is fine as well.

The situation we have now is Q605,Q607 out of board and R627 Leg lifted and not connected to anything,correct?

If so,
please check at the location on the board of Q607 C,E in diode test (please note the color of the probes when measuring) and then in ohm test.
What do we get ?

Please check D605 in board(diode test).
What do we get?

 

[Rick79]

O.K.
Looks like Q607 is fine as well.

The situation we have now is Q605,Q607 out of board and R627 Leg lifted and not connected to anything,correct?

If so,
please check at the location on the board of Q607 C,E in diode test (please note the color of the probes when measuring) and then in ohm test.
What do we get ?

Please check D605 in board(diode test).
What do we get?

Correct, Q605 & Q607 is off the board and R627 leg is lifted & not connected to anything.

Q607 E-C location in diode mode reads nothing and nothing when probes are flipped.

Q607 in 200k ohms setting red probe on E & black probe on C it reads 96.6 and when flipped it reads 92.3


D605 in Diode mode with black probe on cathode, Red probe on Anode it reads .589 & flipped it reads nothing.

 

[Sunnysky]

you might consider using Q603 from Good channel in bad channel,,restore all connections and try to null.

 

[dorke]

I wonder where did that 0.662 C-E of Q607 disappeared?
could be a short during testing.

At this point it is time to take Q603 out of the board and check it in diode test mode(6 measurements).

Edit: Test Q603 in ohm test as well.
Please post a clear photo of the bottom (legs side of Q603,Q605 ,Q607)looking for dirt/corrosion ).

What do we get?

 

[Sunnysky]

Q603 will pass diode test

 

[dorke]

Q603 will pass diode test

Do you think it would pass diode test and still be faulty?

 

[Rick79]

I wonder where did that 0.662 C-E of Q607 disappeared?
could be a short during testing.

At this point it is time to take Q603 out of the board and check it in diode test mode(6 measurements).

Edit: Test Q603 in ohm test as well.
Please post a clear photo of the bottom (legs side of Q603,Q605 ,Q607)looking for dirt/corrosion ).

What do we get?

OK, I pulled out Q603 and in diode mode it reads...
C-B with black probe on C it reads .708 & flipped, nothing
B-E with black probe on B it reads nothing & flipped, .714
C-E nothing & flipped, nothing

In the ohms settings I get nothing.

 

[Sunnysky]

Do you think it would pass diode test and still be faulty?

yes as I calculated only 50-100k leakage resistance with Vce~45V, this would appear as a slope on a beta curve tracer.

 

[dorke]

Rick ,
I see dirt and corrosion on Q603 /Q065(or could it be a flash return?).
This should be scraped well and cleaned with rubbing alcohol till it is shiny(black plastic and silver legs).
What is the state of Q601?

 

[Sunnysky]

Yes I believe Q603 is at fault, but not from appearance

 

[73's de Edd]

Sir Rick 79 . . . . .

After having now seen all of the "front end" transistors from this units LEFT CHANNEL having progressively been tested from Q601-3-5-7 and 9 . . . . . all inclusive.
(And little D605 . . .saying me too . . . .ME TOO ! )

The most likely suspect now for a transistor fault would be the Q601 Q603 pair since they are a complementary pair that have the lowest V CBO*** specs of the set of 5. With a breakdown spec of`~ 65VDC.
The Q605-7 and 9 are being up in excess of 100VDC on their VCBO high-voltage ratings specs.
( Our power supply's total summed differential voltages only add up to ~90VDC.)

*** VCBOis the maximum specified voltage threshold, above which, a bipolar transistor could avalanche / break down and conducts between its collector and emitter.

A simple matter of testing now might be the use of the units properly operating RIGHT channel.
Power up and spot check the common shared emitter resistor junctions of R646-648 with reference to chassis ground It should STILL be right at 0 vdc.
(Whereas . . . .I believe that you found this voltage being in the order of 11VDC on your currently BAD LEFT CHANNEL section, on its equivalent emitter resistors.)

On the safe side, in case parts get flying around back and forth, put a dot of red fingernail polish on those just mentioned 5 transistors associated with the BAD left channel.

Test time:

Take your presently pulled Q603 and pull its Q604, like counterpart, on the RIGHT channel and install your now loose Q603 in Q604's place.
Power up and see if the emitter resistor junctions of R646-648 of the RIGHT CHANNEL are still holding, OR if they have NOW developed a noticeable offset voltage presence . . . .such as your BAD left channel had with its improper 11VDC presence...

If no effect at all, that now tested Q603, being used in the Q604 position must NOT be at fault, so pull the Q601 of the left channel and install it in place of the Q602, of the RIGHT CHANNEL which gets pulled.
Power up and see if the emitter resistor junctions of R646-648 of the RIGHT channel are still holding with no change at ~0 VDC.

In this prescribed testing manner, you can clear Q601 and Q603 of the left channel of not having failure due to a lower VCBO breakdown than their specs.
Since . . . . . . they had no adverse effect on the RIGHT CHANNELS operation.


If the RIGHT CHANNEL emitter resistor junctions of R646-648 shifted to BAD, a VCBO spec decline of either of the subbed in left channel transistors that were then used in the Q603 or Q604 positions was / were being at fault.


Thassssit . . . . .

ADD ON:
Just NOW read as far back as # 69 and caught the short statement by Sir Sunnysky.
My off the cuff statement above, entails the specific logic of those parts suspicions.

73's de Edd

 

[Sunnysky]

I agree @de Edd, except I've been saying all along , a positive DC output to speakers will only be caused by leakage R in Q603 in spite of working diode junctions.

 

[dorke]

Rick,
I would go with Edd's and Sunnysky's suggestion at this stage:
replacing the Trs from the bad channel and inserting them in the good one, after they are cleaned well(photo?).
but first inspect Q601 visually for corrosion etc.
and please measure the voltages relative to Gnd on the output (junction of R646 and R648 ,if it is easier measure the voltages on both sides of R628 instead),and the voltages on Q608.Q606

 

[Sunnysky]

I agree @de Edd, except I've been saying all along , a positive DC output to speakers will only be caused by leakage R in Q603 in spite of working diode junctions.

The reasons are clear to me but I can demonstrate with a simulation if anyone indicates with a "like".