M1.0t died with a pop

Readings for Q112 & Q111

Q112:
Neg to C Pos to E= 4.14
Neg to C Pos to B= 3.75
Neg to E Pos to B= get no reading
Reversed= 4.20
Pos to C neg to E= get no reading
Pos to C neg to B= 6.54 drops slowly

Q111
Neg to C Pos to E= 3.71
Neg to C Pos to B= 3.71
Neg to E Pos to B= 1.71
Reversed= 1.73
Pos to C Neg to E= 6.47
Pos to C Neg to B= 6.47

Readings for Q112 & Q111

Q112:
Neg to C Pos to E= 4.14
Neg to C Pos to B= 3.75
Neg to E Pos to B= get no reading
Reversed= 4.20
Pos to C neg to E= get no reading
Pos to C neg to B= 6.54 drops slowly

Q111
Neg to C Pos to E= 3.71
Neg to C Pos to B= 3.71
Neg to E Pos to B= 1.71
Reversed= 1.73
Pos to C Neg to E= 6.47
Pos to C Neg to B= 6.47

It's tough to read this in circuit, since the transistor is in parallel with another diode and a few resistors. There's no short, which is good, but a couple of things look weird.

Q112
Neg to E Pos to B= get no reading,,,,,on the one hand, you should at least get a read from the parallel Resistors R150 and SVR102. On the other hand, this probe configuration should 'forward bias' the NP junction emitter to base (neg to poas) and give a very small reading from the transistor (like it does with Q111)

Q112 looks suspect because of this. Q111 and Q112 are both the same Xistor. the three wire ribbon cable is connected to the board by pressure fit, you may be able to work them loose one at a time by pressing down on the spring pins with an awl of some such (don't press too hard as to bend them permanently, just release their grip on the wire).

Since Q112 doesn't appear to be shorted (it's emitter base junction seems to be open or getting there), you can swap Q112 and Q111 and see if the problem moves to the other channel; this shouldn't destroy anything.

Ok Rich, I wanted to take a second reading before I swapped them out, so I scraped the legs to get a better contact. Looks better now.
Q112

Neg to C pos to E= 3.76
neg to C pos to B= 3.75
neg to E pos to B= 1.76
Reversed= 1.77
pos to C neg to E=6.39
pos to C neg to B= 6.38

Looks almost identical to Q111
Should I swap them or do think it's ok?

John

Ok Rich, I wanted to take a second reading before I swapped them out, so I scraped the legs to get a better contact. Looks better now.
Q112

Neg to C pos to E= 3.76
neg to C pos to B= 3.75
neg to E pos to B= 1.76
Reversed= 1.77
pos to C neg to E=6.39
pos to C neg to B= 6.38

Looks almost identical to Q111
Should I swap them or do think it's ok?

John

No, those new readings look pretty good; that transistor and in fact the bias network in general is looking pretty good now.

Earlier, you were getting about 2 1/2 times the span on the good channel as compared to the bad.....is that still true?
(pins 2 and 1 of the ribbon cables)

I went to check pin 1 and 2 and noticed it move around when I touched it with the probe. I unhooked it and took it off, the solder joints on the transistor broke loose. Need to resolder them. I noticed many of the solder joints in this amp have very little solder on them.

Ok, touched up the solder joints and remounted it to the heat sink. My readings for pins 1 & 2

Bad side
Pin 1= .0266v
Pin 2= .0276v

Good side
Pin 1= .0138
Pin 2= .0198

Here's what your readings were before:

Bad side
Pin 2= neg .12
Pin 1= .013v

Good side
Pin 2= .140.
Pin 1= neg .0149

now they're

Bad side
Pin 1= .0266v
Pin 2= .0276v

Good side
Pin 1= .0138
Pin 2= .0198

According to those readings, both channels shouldn't be working at all.....there's no symmetry around zero (a positive and a negative) and the span is only about 5mv on the good side and 1 mv on the bad.

I don't know what to make of this.

Here's the readings I took from my M-1.0t when troubleshooting a DC offset problem awhile back:

MP102 pins 2 and 3: +99.4 and -99.2 (about a 200V span centered near zero)
Q108 and Q110 outputs (pin 2 and 1 of Q112): + and - 3 volts (a 6 volt span)
Q118 and Q120 outputs: + and - 2.5V (a six volt span)
Q122 and Q124 outputs: + and - 2V (a 4 volt span)

so, all through the stage here, you should be getting a positive and a negative swing, with a span in the volts (not millivolts).

After sleeping on it, I still have no idea why your readings aren't both in the Volts range AND of opposing polarity centered around zero.

I've tried to ignore this, and go with the reading you ARE getting, but It's quite difficult to discern the nature of the problem. Sometimes it does look as if there's a problem in that bias network, and sometimes it seems the trail is cold.

You mentioned buzzing when the input board is plugged in. Very rare that the input board would have failed; not much current being thrown around, but it can happen.

Does it buzz with just the power ribbon connected? Does this mess with the power supply rails?

Ok Rich, dummy me, was taking readings at Q112, brain dead!!
Yes, pin 1 and 2 read 100v and -100v.

I did try just plugging in the power cable to the input board and cannot leave it plugged in. The top LEDs light up yellow and stay on.

John

Ok Rich, dummy me, was taking readings at Q112, brain dead!!
Yes, pin 1 and 2 read 100v and -100v.

I did try just plugging in the power cable to the input board and cannot leave it plugged in. The top LEDs light up yellow and stay on.

John

The yellow lights'll happen because the feedback loop is broken (the other two ribbon cables aren't connected. But the transformer doesn't buzz and the power rails are still good?

So + and - 100 at pins 1 and 2 of the small ribbon cable, AND + and - 100 at MP102 pins 2 and 3? That's extremely odd....the top and bottom of the bias network should be reading something like + and - 3V (a 6 V span)

Nope, that's + and - 100v at pin 2 and 3 at MP102 with the input power cable hooked up and off.

Q112 Pin 1 reads .0356v, and pin 2 reads .0521v with the input power cable hooked up.
Q111 Pin 1 reads .115v and pin 2 reads .032v with the cable hooked up

No buzzing and power is good.

Nope, that's + and - 100v at pin 2 and 3 at MP102 with the input power cable hooked up and off.

Q112 Pin 1 reads .0356v, and pin 2 reads .0521v with the input power cable hooked up.
Q111 Pin 1 reads .115v and pin 2 reads .032v with the cable hooked up

No buzzing and power is good.

earlier you said:

Yes, pin 1 and 2 read 100v and -100v.

which is bad, now they're reading in the millivolts again, which is also bad; what happened to that?

I honestly don't know how to proceed from here

Yeah I know makes no sense. I wanted to try something so I hooked the input board back up and wanted to check the bias on each channel, get no reading, and turning the pots on each channel has no effect what so ever.
Still get a good + and - 100v on TP5 and 6 and turning that pot does effect the voltage.

I'm lost at this point as well.

John

Sounds like it needs take a journey to RichP

Yeah I know makes no sense. I wanted to try something so I hooked the input board back up and wanted to check the bias on each channel, get no reading, and turning the pots on each channel has no effect what so ever.
Still get a good + and - 100v on TP5 and 6 and turning that pot does effect the voltage.

I'm lost at this point as well.

John

So the channel that was good is now bad?