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Marantz 250 service addendum confusion questions

tonefoto

tonefoto

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I have a Marantz 250 amp with 85xx serial number. I bought it from someone who thought it had been restored. I got it with blown outputs on the left side along with a cooked emitter .15 5W and its adjacent driver transistor SJ2586 NPN shorted. I'm reading over the SM downloaded on the web called marantz_250_service_en_alt_scan which has the 2nd Addendum attached. My question is; do I follow the parts list on the 2nd addendum for checking resistor and cap values? They differ from the original 250 service manual. I don't find any service bulletins for the 250 amp, only 250M. Confused about where to start, with so many revisions on the amp boards, I'm not sure I should change anything except the shorted and smoked components. Any advice from those who've been here is greatly appreciated. My amp revision is AW-115-1071 REV NC, with what appears to be flyback diodes attached to the foil side of the amp boards.
 
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I would replace all the outputs drivers and or drivers or at-least test to make sure they are matched or in same range as the 250 manual specifies. Matching the transistors is very important on this amp. While you are there replace the caps with same spec and replace the larger high power resistors and bias transistor if it’s not the original block kind. there’s some good resto threads on here you can follow to help too.

Post a few photos as there’s so many revisions it’s good to see what you’re dealing with

good-luck we’ll worth the effort when it’s all done!
 
I would check resistors too. And use a DBT until you the channel working.

I might even disconnect power to the working amp board.

There are a lot of threads on the 250. They should help.

What does the addendum #2 recommend?
 
rickl said:
I would check resistors too. And use a DBT until you the channel working.

I might even disconnect power to the working amp board.

There are a lot of threads on the 250. They should help.

What does the addendum #2 recommend?
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I'll post photos soon of the amp, I'm looking at Addendum 2 which has a parts list. I'm crosschecking resistors now and replacing if necessary. I don't see any written recommendation on the Add2 just parts list, but maybe I'm missing something. Planning on replacing all output transistors and at least the drivers on the blown amp. Will check pre-drivers for gain as well.
 
tonefoto said:
I'll post photos soon of the amp, I'm looking at Addendum 2 which has a parts list. I'm crosschecking resistors now and replacing if necessary. I don't see any written recommendation on the Add2 just parts list, but maybe I'm missing something. Planning on replacing all output transistors and at least the drivers on the blown amp. Will check pre-drivers for gain as well.
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When the bulletins are referring to serial numbers, Marantz reset the 250M serial numbers back to the beginning. They should not have. It’s confusing.
 
Also forgot to mention the differential transistors check them they need to be high gain and matched of course I forget the substitute codes now but it’s listed here on the forum
 
quadmatrix82 said:
Also forgot to mention the differential transistors check them they need to be high gain and matched of course I forget the substitute codes now but it’s listed here on the forum
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I was about to ask what others use for the differential pairs.
 
Coolhandjjl said:
Marantz reset the 250M serial numbers back to the beginning.
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Sorry to extend this conversation again, but AFIK @tonefoto has a Marantz 250, not 250M, so I would think that he would need to refer to the original 250 serial numbers as stated in the two addendums and not the 250M service bulletins that you refer to, right?
 
dankik said:
Sorry to extend this conversation again, but AFIK @tonefoto has a Marantz 250, not 250M, so I would think that he would need to refer to the original 250 serial numbers as stated in the two addendums and not the 250M service bulletins that you refer to, right?
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The plot thickens regarding 250 vs 250M documentation. dankik is correct, I have the 250 version with a serial number in the 8500s. I'm so confused, not sure what direction to take at this point, conflicting info.he At this point I'm going from Addendum 2. There are no fly back mods as far as I can tell reading the addendum 2. From my photo of the amp's foil side would somebody be able to tell if I'm ok with the flyback diodes there now? It looks the same as Bob Speece rebuild photos here
 
EDIT: I did take a look at the M-250-3 Service Bulletin (and the others) and it looks like they apply to the Model 250, based on serial number. So, it looks like both should apply, the ones that I found are addendums to the SM while the Service Bulletins that @Coolhandjjl found are bulletins for modifications to the design because of flaws in the original design. I stand corrected.
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Here's the way I look at it (mind you that I DO NOT own and have not worked on a 250 or 250M).
The 1st Addendum says this:
1696729122167.png
The 2nd Addendum says this:
1696729206988.png
So, my reasoning is that since you have a 250 (not 250M) with a serial number above 6549, (your is S/N 85xx) then the Original 250 SM and 2nd Addendum apply to your case. @Coolhandjjl says that the serial numbers were reset the 250M SN back to the beginning, but AFAIK you do not have an M. But, whatever... I don't want to start an argument. ;)

2nd Addendum has the following board PN's (you could check against what you have to see if they match):
1696729935743.png

1696729970258.png

1696730041086.png
 
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dankik said:
Here's the way I look at it (mind you that I DO NOT own and have not worked on a 250 or 250M).
The 1st Addendum says this:
View attachment 3004585
The 2nd Addendum says this:
View attachment 3004586
So, my reasoning is that since you have a 250 (not 250M) with a serial number above 6549, (your is S/N 85xx) then the Original 250 SM and 2nd Addendum apply to your case. @Coolhandjjl says that the serial numbers were reset the 250M SN back to the beginning, but AFAIK you do not have an M. But, whatever... I don't want to start an argument. ;)
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I am thinking along the same logic, using the Addendum 2. IN any case its confusing to say the least. I don't know what the differences are between the 250 and M-250. I have a later serial number so I'm following both the addendum 2 and the recommendations on the M-250 service bulletins. Mine has the fly back diode mod in place. I'll probably replace the pre-drivers with the 2n5415 and 2N3440. I'm looking for Driver replacements in TO-66 case style to keep the looks original. I found diff pair replacement at Mouser: MPS6519
 
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