Hi,
Yes, it's 27.7V between the pins 3 & 4. These are also the pins I short to establish bias.
I can remeasure the pins to ground when I get home.
Yes, it's 27.7V between the pins 3 & 4. These are also the pins I short to establish bias.
I can remeasure the pins to ground when I get home.
These voltages suggest the enable circuitry is likely OK. Of course, these pins need to be shorted together to enable troubleshooting.
How do I test for this:
Also, I checked the diodes in the circuit and found D9 & D20 to show 0.6v in forward, and 0.78v in reverse. I haven't removed them from circuit to really check them, but do you see a reason they would measure that way? If not, I'll take them out and measure again.
Also, I checked the diodes in the circuit and found D9 & D20 to show 0.6v in forward, and 0.78v in reverse. I haven't removed them from circuit to really check them, but do you see a reason they would measure that way? If not, I'll take them out and measure again.
Hello again.
Remeasuring the inductors again... it seems I transposed Q36 and Q29 collectors. Which was obvious if I had looked at Q24 and Q37 bases. Sorry for that.
Q29 -15, -78, -14.5
Q36 15,2, 71.6, 14.7
So it seems this is where the imbalance begins. Could it be the earlier observed diodes, from my previous mail?
Going over the others, I get:
Q24 -78, -80.5, -74.2
Q37 71.6, 78.6, 71.1
Q25 -73.7, -72.9, -73.9
Q38 70.7, 54.4, 71
Q9 -75, 49.1, -72.8 this base goes directly to 75, whereas Q11's base goes slowly up to 54.2V. I don't want to leave it on too long as the resistors get hot, but maybe that's not a problem?
Q11 54.2, 51.2, 67.8
C26 each side to ground 52.2, 50.1
R13 each side to ground -74.5, 71
Okay, this is strange... 80V rails = 88.8/-88.8
Then through R2/R23, which both measure 146.2ohm
R2 -81.8
R23 80.1. How can this be?
Remeasuring the inductors again... it seems I transposed Q36 and Q29 collectors. Which was obvious if I had looked at Q24 and Q37 bases. Sorry for that.
Q29 -15, -78, -14.5
Q36 15,2, 71.6, 14.7
So it seems this is where the imbalance begins. Could it be the earlier observed diodes, from my previous mail?
Going over the others, I get:
Q24 -78, -80.5, -74.2
Q37 71.6, 78.6, 71.1
Q25 -73.7, -72.9, -73.9
Q38 70.7, 54.4, 71
Q9 -75, 49.1, -72.8 this base goes directly to 75, whereas Q11's base goes slowly up to 54.2V. I don't want to leave it on too long as the resistors get hot, but maybe that's not a problem?
Q11 54.2, 51.2, 67.8
C26 each side to ground 52.2, 50.1
R13 each side to ground -74.5, 71
Okay, this is strange... 80V rails = 88.8/-88.8
Then through R2/R23, which both measure 146.2ohm
R2 -81.8
R23 80.1. How can this be?
Sorry for slow reply. My wife had eye surgery today. So far, so good.
I've been starring at the numbers for a while. There are probably lots of clues, but this is the most obvious mystery to explore:
As I read the description, base of Q9 rises quickly to +75V, but Q11 base rises slowly to 54.2V. !!!!
The base of Q9 should be only a few volts more positive than the -80V rail, i.e. the voltage across R43 plus two diode drops, D13, D11. Q9 base should be roughly -75V rather than +75V. In analogous fashion, the base of Q11 should be only a few volts below the +80V rail. Almost all the voltage between the +80V and -80V rails should appear across R13. The fact that you find +75V on the base of Q9 suggests an open along the bias path, somewhere along the path of R47, D13, D11, R43, and -80V rail.
Good luck!
BTW, which resistors are getting hot?
I would apply power, and do a divide and conquer voltage search between R47 and the -80V rail.
I've been starring at the numbers for a while. There are probably lots of clues, but this is the most obvious mystery to explore:
As I read the description, base of Q9 rises quickly to +75V, but Q11 base rises slowly to 54.2V. !!!!
The base of Q9 should be only a few volts more positive than the -80V rail, i.e. the voltage across R43 plus two diode drops, D13, D11. Q9 base should be roughly -75V rather than +75V. In analogous fashion, the base of Q11 should be only a few volts below the +80V rail. Almost all the voltage between the +80V and -80V rails should appear across R13. The fact that you find +75V on the base of Q9 suggests an open along the bias path, somewhere along the path of R47, D13, D11, R43, and -80V rail.
Good luck!
BTW, which resistors are getting hot?
I would apply power, and do a divide and conquer voltage search between R47 and the -80V rail.
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I misconstrued your comment about Q9 base going directly to 75V. Base of Q9 is -75V. 😕
Channeling Gilda Radner, "Never mind."
Channeling Gilda Radner, "Never mind."
I do believe your comment about base of Q11 rising slowly is relevant.
What voltages appear along the bias divider string: +75V, R76, D22, D18, R13, D13, D11, R43, -75V? Do they all bias quickly to nominal? Is path from Q11 base through R72 to D18, R13 intact?
What voltages appear along the bias divider string: +75V, R76, D22, D18, R13, D13, D11, R43, -75V? Do they all bias quickly to nominal? Is path from Q11 base through R72 to D18, R13 intact?
Okay, so I have an apology to make... I had both Q9 and Q11 pin-outs backwards. They're on the other side of the board, and through hole, unlike the other inductors measured here. I'm sorry about that.
I checked the string from R43 - R76 and besides the fact that those two resistors show different voltages as mentioned earlier, the rest look okay.
Then I checked the next obvious string:
D21 70.7/70.1
D10 -73.6/-72.9
D17 69.9/ 69.2
D12 -72.6/-71.9
Looks good so far...
Now, maybe the oscillation you were worried about ...
D9 -73.8/-74.5
D20 70.7/varies from 69.2 to 71.6!
I checked Q37 base and it was doing the same. It's hard to tell exactly, the numbers just blink rapidly and those are the extremes I saw.
However, Q36 collector doesn't seem to be affected... or wasn't when I checked (see below).
This didn't show up immediately when I turned it in and checked... but after a bit it started varying.
This sounds interesting. What do you think?
Peter
I checked the string from R43 - R76 and besides the fact that those two resistors show different voltages as mentioned earlier, the rest look okay.
Then I checked the next obvious string:
D21 70.7/70.1
D10 -73.6/-72.9
D17 69.9/ 69.2
D12 -72.6/-71.9
Looks good so far...
Now, maybe the oscillation you were worried about ...
D9 -73.8/-74.5
D20 70.7/varies from 69.2 to 71.6!
I checked Q37 base and it was doing the same. It's hard to tell exactly, the numbers just blink rapidly and those are the extremes I saw.
However, Q36 collector doesn't seem to be affected... or wasn't when I checked (see below).
This didn't show up immediately when I turned it in and checked... but after a bit it started varying.
This sounds interesting. What do you think?
Peter
Hello again.
It seems to calm down sometimes when I remove the dmm probe. When I go back, it takes 10-15 seconds to start changing. Does that make sense?
It seems to calm down sometimes when I remove the dmm probe. When I go back, it takes 10-15 seconds to start changing. Does that make sense?
That’s interesting, but I can’t fathom a cause.
As quick experiments, I suggest moving the 22k resistor from the -16V supply to the +16V supply. The nodes we’ve been observing should move from +45V ish to negative 45V ish. If nothing obvious presents itself, then connect the 22k either side of C26 and see where voltage goes.
As quick experiments, I suggest moving the 22k resistor from the -16V supply to the +16V supply. The nodes we’ve been observing should move from +45V ish to negative 45V ish. If nothing obvious presents itself, then connect the 22k either side of C26 and see where voltage goes.
With +16 supply
Q22 7.5, 6.7, 8.1
Q34 -7.5, -6.7, -8.1
Q39 6.8, 1.2, 7.4
Q35 -6.8, -1.0, -7.4
Q36 15.1, 70.5, 14.6
Q29 -15.9, -71.6, -14.5
Q31 0, 14.6, -0.4
Q28 0, -14.5, 0.9
Q33 15, 69.3, 14.5
Q27 -15, -71.7, -14.5
Q30 0.1, 14.6, -0.3
Q26 0.1, -14.5, 0.7
Q37 70.8, 77.4, 71.2
Q24 -72.2, -78.5, -70.7
Q38 71, 51.7, 68.8
Q25 -71.1, -70.6, -71.5
Q11 65.3, 48.2, 51.8
Q9 -70.3, 46.8, -70.6
Do you want the same measurements with the resistor attached to C26?
Q22 7.5, 6.7, 8.1
Q34 -7.5, -6.7, -8.1
Q39 6.8, 1.2, 7.4
Q35 -6.8, -1.0, -7.4
Q36 15.1, 70.5, 14.6
Q29 -15.9, -71.6, -14.5
Q31 0, 14.6, -0.4
Q28 0, -14.5, 0.9
Q33 15, 69.3, 14.5
Q27 -15, -71.7, -14.5
Q30 0.1, 14.6, -0.3
Q26 0.1, -14.5, 0.7
Q37 70.8, 77.4, 71.2
Q24 -72.2, -78.5, -70.7
Q38 71, 51.7, 68.8
Q25 -71.1, -70.6, -71.5
Q11 65.3, 48.2, 51.8
Q9 -70.3, 46.8, -70.6
Do you want the same measurements with the resistor attached to C26?
Not yet. You’ve landed in a useful place. Q9 and Q11 collectors should have been roughly minus 45V, but they remain stuck at around plus 45.
I’ll have study and get back to you. Chores intervene, I’m afraid.
I’ll have study and get back to you. Chores intervene, I’m afraid.
In the latest configuration (+16), I see Q37's (NPN) emitter is higher voltage than it's base. Also, Q38 and Q11's (PNP) emitters are lower voltage than their bases. Q38 was the same with -16v. These are all in the same immediate circuit, so it seems the problem is with them, or whatever is connected to them.
I'll remove the +/-16 volt and test them all again. I'll also look them over with a magnifying glass to see any bad traces or bridges.
I'll remove the +/-16 volt and test them all again. I'll also look them over with a magnifying glass to see any bad traces or bridges.
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These readings suggest that the voltages are being sourced through clamp diodes, D21 and D17. That seems reasonable, as there should be little current flowing through Q38. The amp should be attempting to drive spreader voltage toward the negative rails. Question is, why isn't this happening?
Try measuring emitter currents appearing across R78 vs. R43 for insight. Current through Q9 and Q25 should be pulling voltages negative.
16v jumper removed.
Q22 7.3, 6.7, 7.9
Q34 -7.3, -6.7, -7.9
Q39 6.8, 1.2, 7.4
Q35 -6.8, -1.1, -7.4
Q36 15.1, 74.5, 14.6
Q29 -15, -73, -14.5
Q31 0, 14.6, -0.4
Q28 0, -14.5, 0.5
Q33 15.2, 71, 14.7
Q27 -15.1, -73, -14.5
Q30 0.1, 14.6, -0.4
Q26 0.1, -14.5, 0.5
Q37 71.4, 78, 71.1
Q24 -73.2, -79.5, -72.7
The above look more or less identical to their compliment.
Q38 71.2, 53, 70.3
Q25 -72.8, -72, -73.4
Q11 67.2, 50.2, 53
Q9 -72.2, 48.5, -72
again, the Q38 collector and Q11 emitters read low.
D22 69.8, 69
D18 68.9, 68.2
D11 -72.9, -72.3
D13 -72.2, -71.5
R47 39ohms
R72 39ohms
Can it be that Q11 is bad, so it's emitter output is low and therefore Q38 gets a low collector value? Or do I have that backwards?
With this in mind, I checked Q9 vs Q11 with the diode function...
B to C 0.6v on both
B to E 0.6v on both
C to E on Q9 shows 1.2 in one direction, 0 in the other.
C to E on Q11 shows 0.1 in both directions! If I was a guessing man, I'd say Q11 is junk.
Q22 7.3, 6.7, 7.9
Q34 -7.3, -6.7, -7.9
Q39 6.8, 1.2, 7.4
Q35 -6.8, -1.1, -7.4
Q36 15.1, 74.5, 14.6
Q29 -15, -73, -14.5
Q31 0, 14.6, -0.4
Q28 0, -14.5, 0.5
Q33 15.2, 71, 14.7
Q27 -15.1, -73, -14.5
Q30 0.1, 14.6, -0.4
Q26 0.1, -14.5, 0.5
Q37 71.4, 78, 71.1
Q24 -73.2, -79.5, -72.7
The above look more or less identical to their compliment.
Q38 71.2, 53, 70.3
Q25 -72.8, -72, -73.4
Q11 67.2, 50.2, 53
Q9 -72.2, 48.5, -72
again, the Q38 collector and Q11 emitters read low.
D22 69.8, 69
D18 68.9, 68.2
D11 -72.9, -72.3
D13 -72.2, -71.5
R47 39ohms
R72 39ohms
Can it be that Q11 is bad, so it's emitter output is low and therefore Q38 gets a low collector value? Or do I have that backwards?
With this in mind, I checked Q9 vs Q11 with the diode function...
B to C 0.6v on both
B to E 0.6v on both
C to E on Q9 shows 1.2 in one direction, 0 in the other.
C to E on Q11 shows 0.1 in both directions! If I was a guessing man, I'd say Q11 is junk.
Way back in posts 256-258, I surmise measurements were taken with U1 in unshorted state, correct? Voltages look similar with bias ostensibly disabled. I’m kicking myself for not noticing.
Would you remove U1 short and take quick samples of Q9, Q11 collectors? If still elevated, load Output with 10k to ground (to absorb stay currents) and look for any changes.
Would you remove U1 short and take quick samples of Q9, Q11 collectors? If still elevated, load Output with 10k to ground (to absorb stay currents) and look for any changes.