Marantz 2270 repair issues

[nickdinatale]

Hey everyone!

So I've had a Marantz 2270 on my bench over the course of the past few weeks. I've recapped all of the boards aside from the AM and FM boards (everything was working okay following the recap), and I replaced a bad transistor as well. After adjusting voltage, DC offset, and idle current, I went to test it out with audio. My result was not good as I turned up the volume (a spark and smoke somewhere around the halfway point). Now my speaker relay won't click in any longer. Not sure where to go from here. Transistors seem to still be good, so I'm not sure where the problem would be. Any direction would be greatly appreciated!

 

[NAD80]

Hello nickdinatale, Welcome to AK. Need pics to see where the spark and magic smoke escaped from. In order to repair need some where to start from. What got damaged?.

 

[Robisme]

Isn't there a misprint in the 2270 service manual about setting bias? Were you aware of this error?

Sounds like maybe bias was high. Was it running hot, or didn't you notice?

Can you see which part smoked?

Rob

 

[nickdinatale]

Yeah, I was aware of the service bulletin. It looks like there may have been a short somewhere and R786 is what burnt (100ohm).

 

[Robisme]

I would start by looking at H758 and the output H003.

Rob

 

[Steven Tate]

When you reattached the bias transistor - H760 - to the heat sink, did you insulate it with a mica washer? It must be electrically insulated from the heat sink, preferably with a touch of thermal compound on both sides of the washer.

 

[nickdinatale]

When you reattached the bias transistor - H760 - to the heat sink, did you insulate it with a mica washer? It must be electrically insulated from the heat sink, preferably with a touch of thermal compound on both sides of the washer.

Going to go back through it and double check this/make sure there's enough compound. In a lot of cases I believe I just used the same old washer, but I think I'll try replacing them with new ones (a few were missing pieces). Will report back.