On Tue, Mar 1, 2022 at 07:34 AM, Colin Herbert wrote:
...
I removed the two transistors A2Q9 and A2Q8 and they
both check as OK with my MK-328 transistor-checker.
....
Puzzlingly, there
doesn't seem to be any current at all passing through A2R44 (100R) or
A2Q8.The voltage seems to be at 24.5 VDC from TP2 (should be +8 VDC) all the
way to the collector of A2Q8 (should be +0.77 VDC). The voltages at pins 10
and 11 of the A2 board are both about -24.7 VDC with respect to ground, not
the -4 VDC that they should be.
A2Q9 can't be good if its emitter (=collector of A2Q8) is sitting at 20+ volts. You should see one Vbe above ground since base is grounded. Unlikely but ground connection of the base could be bad too (i.e. base is not really connected to ground anymore).
If you check A2Q9 base-emitter junction do you see a diode? If you check connectivity between base of A2Q9 and ground when the unit is off do you see essentially zero ohms?
Ozan
