Question on Marantz 250 rebuild

[bisonguy]

Just about to recap my Marantz 250 amplifier. Other than somewhat weak right channel no other issues found. However, I have read all the service bulletins and they seem to apply for the most part to serial numbers after 6549. Mine is 4552. I would have thought that most changes would be applied to earlier, not later models. Should I assume that serial # 4552 does not require any mods for increased reliability??

 

[rBuckner]

I'd double check to make sure they are done. I don't know that I'd change out transistors if the ones in there are working though. I'd definitely do the flyback diodes on the amp outputs that's in one of the updates.

 

[wlhd1610]

As I read the 250 service bulletins it states that M-250-3 applies to S/N above 6549 as you indicate.
However service bulletin M-250-2 indicates that it applies to "all"S/N.
It indicates that "correct beta must follow the parameters given in the tables below"
I have found the predriver and driver pairs to be far outside those parameters on several units I've had in for restoration.
The history of this particular model has indicated a propensity to fail again even after a repair because this amp is/was running at its design limitations when produced.
I believe that is why Marantz issued the M-250-2 service bulletin.

When a 250 or 250M leaves my bench I don't ever want it to come back .

Just sayin....


Bob

 

[Dingman]

As I read the 250 service bulletins it states that M-250-3 applies to S/N above 6549 as you indicate.
However service bulletin M-250-2 indicates that it applies to "all"S/N.
It indicates that "correct beta must follow the parameters given in the tables below"
I have found the predriver and driver pairs to be far outside those parameters on several units I've had in for restoration.
The history of this particular model has indicated a propensity to fail again even after a repair because this amp is/was running at its design limitations when produced.
I believe that is why Marantz issued the M-250-2 service bulletin.

When a 250 or 250M leaves my bench I don't ever want it to come back .

Just sayin....


Bob

I work on alot of units but when my 250 failed, I took it to the pros. First pro failed miserably and could not repair.
Second tech got it working. For about 20 minutes.
3rd tech - applied all the SB updates and amp has been find since.

I can get the serial # if you wish, but really you just need to make sure to get the needed updates and you should be fine.

 

[Beamer302]

So I too have all the service bulletins now and my serial # is 3184 . Only service bulletin M-250-2 says to be performed on "all" units . The flyback diode update in service bulletin M250-3 says to be applied to serial # 6549 and above . My question is should all the service bulletins be applied to any Marantz 250 regardless of the serial # . My 250 works fine at the moment after recapping the amp , meter, and relay boards . I also replaced the output transistors with MJ21193G and Mj21194G 's . It does not have the flyback diodes as mentioned in service bulletin 3 . Should I perform this update on this unit ?

 

[Beamer302]

I have found out my boards do not look the same on the foil side as the service bulletin shows . Not even close ! I was getting ready to put in the flyback diodes . Here are a bunch of pictures . I will use the schematic to connect to the diodes to the proper places . Looks like from the end of R546 that joins connection 19 ....to the end of R544 going to connection 18 and from the same point on R546 to the end of R545 going to connection 21 There is a number on the board and it reads A/W115-1022 Rev D . Was this a newer replacement board (back in the day) ? I repaired the meters and the dates on them showed September 23 1971 .

 

[Beamer302]

Here are some pictures of this 250 . Looks and sounds great and the meters work great as well . I did all the service bulletins so I answered my own question about serial numbers and such .

 

[Steven Tate]

Great looking work. Beautiful result. Congrats!