All these readings look ok. So there's no indication of that mysterious 4V base-emitter observed earlier?
Would you report the voltages on Q9? I expect Q9 collector to be near the negative rail. Now would be a good time to check the bias spreader. What voltage variation do you find across C26 as you adjust R23 through its range?
Would you report the voltages on Q9? I expect Q9 collector to be near the negative rail. Now would be a good time to check the bias spreader. What voltage variation do you find across C26 as you adjust R23 through its range?
Q9: -69.8, 46.3, -70
C26 1.7V-3.2V across when turning R53.
Sorry about the lost hope... there is still ~4V difference between Q24 base and emitter to ground. My battery died in my second DMM just now, so I guess it gave me a strange result that doesn't correlate. I'll get a new battery and repeat.
C26 1.7V-3.2V across when turning R53.
Sorry about the lost hope... there is still ~4V difference between Q24 base and emitter to ground. My battery died in my second DMM just now, so I guess it gave me a strange result that doesn't correlate. I'll get a new battery and repeat.
The diode voltages suggest that D9 is near 0V and not conducting any significant current. D20 appears to be reverse biased.
Your Q9 voltages in post 248 seem to indicate base emitter voltage is only 0.2V, not enough for Q9 to be conducting any significant current. Something odd, still.
Did replacing meter battery change anything?
Your Q9 voltages in post 248 seem to indicate base emitter voltage is only 0.2V, not enough for Q9 to be conducting any significant current. Something odd, still.
Did replacing meter battery change anything?
Hi!
If I pull the rest of the unit apart and get the other channel powered with current limiting resistors, as the other side, what would you like to see checked?
I was thinking of the numerous test points that are all over the board... the problem is I don't have them in the SM pages so I'd have to try to figure out what they are connected to.
If I pull the rest of the unit apart and get the other channel powered with current limiting resistors, as the other side, what would you like to see checked?
I was thinking of the numerous test points that are all over the board... the problem is I don't have them in the SM pages so I'd have to try to figure out what they are connected to.
Hi,
I suppose having more current limit resistors on hand would give you that option, but I'd be reluctant to subject a working channel to that much added jeopardy. My instinct is to retain the working channel as a reference to nominal voltages. And in the interest of caution, keep all but the tip of your meter probe shrouded with heat-shrink to minimize mishaps, and be very cautious about possible .slips of a probe that could wreak havoc.
I would keep searching for the apparent defect in the front end. The approach is to conduct experiments and look for behavior that doesn't make sense. Explore there until you understand what's happening and why. That eventually leads you to the problem. Easier said than done.
Many of the experiments we've contrived should force the front end into a rail. The most recent in posts 248/249. I would return to that point and try to learn why Q9 didn't conduct. Whenever when thinks don't make sense, it make sense to worry about oscillation making a scope the instrument of choice. I doubt oscillation is the explanation on this occasion, but can't be sure.
Take readings to get again acclimated.
Thanks.
I suppose having more current limit resistors on hand would give you that option, but I'd be reluctant to subject a working channel to that much added jeopardy. My instinct is to retain the working channel as a reference to nominal voltages. And in the interest of caution, keep all but the tip of your meter probe shrouded with heat-shrink to minimize mishaps, and be very cautious about possible .slips of a probe that could wreak havoc.
I would keep searching for the apparent defect in the front end. The approach is to conduct experiments and look for behavior that doesn't make sense. Explore there until you understand what's happening and why. That eventually leads you to the problem. Easier said than done.
Many of the experiments we've contrived should force the front end into a rail. The most recent in posts 248/249. I would return to that point and try to learn why Q9 didn't conduct. Whenever when thinks don't make sense, it make sense to worry about oscillation making a scope the instrument of choice. I doubt oscillation is the explanation on this occasion, but can't be sure.
Take readings to get again acclimated.
Thanks.