Traynor Beta 800 testing

[JP-Stereo]

I still cannot adjust the bias with the TP1 and TP2.

The first part of the circuit is revised.
The High voltage rails are at +89.5 / -97.5 vdc
Low voltage rails are at +77.6 / -78.6 vdc
ZD6 cathode +15.4 / ZD7 anode -15.9 vdc
ZD9 anode +1.09 / ZD10 cathode -1.39 vdc
D14 anode 0 / D15 cathode 0 vdc

There is something odd between the first and the second version schematics.
They are originally talking about measuring the amperage to adjust the bias, without specifying the test points, look like it's Q11 emitter ?
Then on the second version they call for a voltages measurment at TP1 & TP2.



Just dynamicly test Q14, Q16, Q15 and Q17 out of circuit and they were all OK.
I also recheck Q11 and it's fine.
I will reinstall this amp board and try to adjust VR42 again.

[g1]

Quiescent current refers to the current through the output devices. To measure it directly would mean cutting traces to insert the ammeter. So instead, we measure the voltage across their emitter resistors and calculate to determine the current.
Without looking at the schematic, I would guess that there is 1 ohm between TP1 and TP2. 4mV across 1 ohm means there is 4mA of quiescent current.

You still seem to have a problem with imbalance of the higher voltage supplies.

[x-pro]

D14 anode 0 / D15 cathode 0 vdc

There should be 3-4V between the collector and emitter of Q11.
The amplifier output (at TP10) should be 0 V relative to Ground 2

[JP-Stereo]

About the power supply, i've double check everything twice, short of replacing the 6 big filtering caps.
The power supply feed only one amp board for now and i put a small 2k 2w load resistor on the second amp ps connector.
What should be the tolerances according to you and who is the possible suspect ?

Q11 Collector to GND2 +1.69 vdc
Emitter to GND2 - 1.24 vdc
differential 2.93 vdc

TP10 to GND2 0.016 to 0.018 vdc

And VR42 is affecting the Q11 Collector voltage from 1.64 to 2.2 vdc.
But the Q11 Emitter voltage do not change.

I have fixed 0.0002vdc (0.2 mv) at TP1 & TP2

[x-pro]

"Q11 emitter voltage does not change."
This is not good. Check the voltage b-e at Q13, Q19(Q19A), Q21(23/25/27). precisely b-e on their conclusions. (+) probe to the emitter, (-) probe to the base.

[JP-Stereo]

Emiter to Base voltage
Q13 - 2.34 vdc
Q19(Q19A) 0.551 vdc
Q21(23/25/27) 0.100 vdc

Bias measured at Q11
Collector to GND2 1.67 to 2.37 vdc variable with VR42
Emitter to GND -1.09 vdc fixed

Only 0.0002 v at TP1-TP2

[The Dude]

Q13 looks to have an open B-E junction. Voltage drop B-E should not be more than about .7V on a working transistor.

[JP-Stereo]

I've just measure Q12 and all the transistors on the positive rail and they mirror the negative side exept for Q13 wich have an E to B voltage way higher.
So i will change Q13 right away.

While measuring Q18 and Q18a i found that R95 and R95a are burned (5.7mOhm and 6.6kOhm) will change these too.
R96 and R96a are testing good.