SAE 2200 - One channel distorted

70smidfiguy

Active Member
Hello all,

I have a stubborn SAE 2200.

I received a pretty beat up unit.

I recapped all, replaced output transistors and unit powers on both channels working however:

I have distortion on channel A. Volume is fine just distortion.

I replaced a few older looking components on the driver board (including 2SA798) but no luck.

DC offset looks ok on both channels 0 to -10/+10mv.

I did not replace the filter caps.

Thoughts?

Cheers
 
Access to O-scope?
Sometimes current limiter transistor or diodes get cooked when amp fails. Also check for bad, or arced, connectors to driver board.
 
I dont think you can adjust the BIAS on the 2200?

That's what the pots on the output board are for. At least, that's the case with the 2200 I have in the shop at the moment.

What the manufacturer specified for the adjustment procedure, I don't know - probably someone on AK does. (If I have to take a guess on my own, I'll probably set mine to 20mA after temperatures stabilize.)

To the suggestions in the previous posts, I would add a suggestion to check the emitter resistors, and the B-C junctions of the driver transistors.

Cheers,

chazix
 
The emitter resistors appear to be .2ohm (one was defective) can I use .27ohm or .33 ohm as I cant find .2ohm anywhere locally.

Thanks.
 
Note that if an emitter resistor failed, it's very likely that there was collateral damage to the over-current protection circuitry. Look for signs of overheating in resistors on the driver board. The area between the connectors and the driver heat sink is where the protection circuitry is located.
 
Ok, so I found .20 5W resistors and all is working again.

For any future reference:

- Output trs were replaced with MJ21194/95
- All diodes were replaced on power output board.
- Main filter caps were replaced.
- all caps on driver board were replaced.
- bias control pots replaced.

Unit sounds great!

Thanks for your help.
 
Ok, so I found .20 5W resistors and all is working again.

For any future reference:

- Output trs were replaced with MJ21194/95
- All diodes were replaced on power output board.
- Main filter caps were replaced.
- all caps on driver board were replaced.
- bias control pots replaced.

Unit sounds great!

Thanks for your help.
Did your 2200 have Sangamo filter caps?
 
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