MA AUDIO HC4002

[mike49504]

I got this amp in for repair . The problem im having is on the left channel It has 52 volts DC on the output.

Heres what i measure on the pads for the outputs on the left channel with outputs removed

Tip35
1:-54.8
2:56
3:0

Tip36
1:-56 v
2:-56 v
3:0

The right channel measures the following and right channel works perfectly

TIP35
1:.02
2:56.4
3:0

TIP36
1:-.02
2:-56.4
3:0

Any thoughts on what to check?

[Perry Babin]

If 1 is the base, it's not coming from the outputs.

[mike49504]

I put a different tip41 and 42 in the amp and it lowerd leg 1 to -26.1 volts.

So heres what i have on the tip 41's and 42's


Left channel

TIP 41C
1:-35v
2:54.4
3:-32.5

Tip42C
1:-38.8
2:-54.2
3:-39.8

Right channel

Tip 41C
1:.09
2:54.8
3:.02

Tip42C

1:-.08
2:-54.3
3:-.03

Do i need to go further back in the circuit in the left channel?

[Perry Babin]

I don't think these numbers are reliable. The emitter of both left channel transistors should be very nearly identical unless the emitter resistors are well out of tolerance. The emitters should also be very near the output voltage. It appears that the voltages aren't constant and that they change between readings.

Leave the amp on to see if the voltages will stabilize.