Marantz Model 2238B amp section burning resistors

[Potato Cakes]

Hello, everyone,

I have this Marantz Model 2238B that I have been asked to see if I could get it working. It did not pass audio but when switching speakers sets there was small pop. I opened up and found that one of the fuses for the power transformer secondaries was missing. I replaced the fuse and powered it on and one of the resistors slowly started cooking and then stopped and still measures 30R. The receiver passed audio for about 30 seconds then there was a pop and no audio. Shortly after that, one of the small caps blew. I powered it off and that is when I noticed another resistor was burned up before I installed the fuse. It measured about 34M and I believe that is not the correct value and is likely completely destroyed.

I'm still looking for a schematic but in the meantime I was wondering if anyone here has worked on these before and have experienced anything similar. This is the second vintage Marantz receiver I have worked on in the past year. It seems that old stereo equipment is becoming more popular.

Thanks!

Paul

 

[CJ]

Turn the volume down when using the speaker switches otherwise the relay contacts can get pitted, if it has a relay.

I usually replace the diff pair with KSA and KSC part numbers , maybe match few if you have time, and all the caps and zener diodes on the power board, and check the HFE of the rest of the transistors.

Have you been over to AudioKarma - Marantz section? Lots of Marantz brainiacs and searchable information.

 

[Potato Cakes]

Thanks for the manual, CJ!


The resistor that measured 34M is supposed to be 150R. I hope that I don't have a shorted transistor that burned this guy up.


I have been on the Audiokarma site a couple of times when searching for other subjects. I'm trying to not get in the habit of doing too many of these as are a bit more work that I am looking to spend time on with a number of other projects I'm doing.

I'll start with the caps and Zener diodes.

Thanks!

Paul

 

[CJ]

The caps and zeners are just part of the service routine, many are still good, especially the Elna's

I suspect an output transistor also. I use those MJ21193/4 or the 2196 if the 4 is out of stock.

I have about 60 of those Marantz receivers on the bench so don't feel bad, the boss went on a spree after he figured out that he could pay me 100 each and clear 2 grand. This 4400 is a pain, quad output with the built in scope.