NAD 2200 repair

[MPS532]

What a marathon. Did you ever get it running? I have a 2200 with blown left outputs, but no other signs of damage. I am hoping I can get it figured out. I do plan on a complete recap very soon once I figure out whether it will run or not. Do you know if I remove the PS cable from the left channel board, will the remainder power up if it is OK?

Thanks,
Mark

 

[pwdiya12]

remove the cable from the left channel and see if the amp fires up and protection disengages.

Make sure you drain the main power caps before reinserting the power cable

 

[MPS532]

Thanks for the reply! That is my course of action. Physically everything in this amp looks ok, but the outputs are shorted. I am in the process of checking backwards in the print to make sure everything else measures OK. Would you happen to know how to check the two adjustments on the board, once I do get it running? I will be using a DIM bulb setup to bring it back up.

Thanks,
Mark

 

[pwdiya12]

the manual is on HiFi engine, the two adjustments are for bias (7.5mv) measure on the two vertical pins and DC measured on the speaker terminals (0mv)

shorted outputs can often take out drivers and diodes and zeners

 

[MPS532]

So far, all outputs are shorted, and two of the transistors directly upstream are as well. All other devices are looking OK, but I will reserve judgement until I replace the popped parts and compare measurements to the opposite side.

Thanks again,
Mark

 

[pwdiya12]

check the resistors and caps around the shorted transistors and the emitter resistors as well- good luck!

 

[MPS532]

Thanks for the reply and I will come back once I have the results.