Harman Kardon 930 Bias Adjust

[Champ]

Reasons for not enough volts.

1. The current in the VAS transistor chain isn't enough... unlikely.

2. There is a faulty or incorrectly fitted driver transistor. Its worth checking the base-emitter volt drop across each. It should be around 0.65 volts.

3. One of the resistors marked is open circuit. If any are then the cause is likely to be a failed driver.

If I am reading correctly I am reading .081 across.

I got to stop right now I just popped a fuse. Shorted an output somewhere in there. I think this unit is cursed

 

[Mooly]

This is why you have to be so careful.

What was the "0.081" reading ? Volts or ohms ? And across what

Each transistor should have approx 0.65 volts across the base and emitter. That B-E voltage is a good clue as to what is going on and what has failed. The fact both channels are the same points to a common problem, maybe an error has occured in the rebuild. Its possible to have a faulty driver or an incorrectly fitted driver and for the amp still to work.

I would recheck everything and check the transistor types fitted and their pin outs.

 

[tiefbassuebertr]

At my device of this model BIAS isn't stable at both channels after warm up despite new variable resistor (trimmer) and small signal TO96 Transistor for Vbe multiplier (small effect and drift between 10mA and 50mA), but not really audible. After replace the resistors from the attached images from pre-driver PCB (2x100R, 2x150R and 2x3K9) this unwanted effect wasn't longer to observe - i. e. idle current through the output transistors is constant after warm up.
What kind of resistors are this and from what manufacturer ?
Should I such resistor versions (mainly to find in vintage stuff) replace in general
even without occurs of unwanted effects ?
Thanks for an advice.