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Recapping of Marantz 2275

sanjib

sanjib

AK Subscriber
Subscriber
Hi
I have started the recapping of my Marantz 2275. I got it in working condition with all lights out and scratchy tone control switches. My immediate plan is it clean all the switches and replacing capacitors and transistors in P400 (Phono), P700 (Main amp), P800 (Power supply) and PE100 (Pre and tone control) boards. I hope this will bring this Marantz in to nice condition. I have finished the power supply board it works fine. Next I started right main amp (P700) board I replaced all the capacitors, replaced H701- H704, H717-H718 and H720-H721 (I don't have any H719 on the board!). After putting the board in and I adjusted the bias to 10mV and it was steady and DC offset was varying between -0. mV to +0.1 mV.
After running for few minutes The transitor at H714 blew (I did not replace it, it was the old 2SB537). I think this the driver transistor mounted on heat sink.
My question: It blew because it is old or it is due some wrong doing in my recapping work. I have ordered replacement (MJE15030G/MJE15031G for 2SD382/2SB537) but before putting those replacements I would like to understand the why it blown.

Any help will be great! I will post my progress here I will need some help from Marantz experts here in order to succeed!
Thank you!
 

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It didn't blow because it was old.
It worked before you started in on it correct?
You did something to make it fail.
I would look over everything you changed/worked on.
You replaced and regreased all the mica insulators?

Bob
 
Thank you all!
I am waiting for replacement of H713 and 714. After getting those I will be able to report the progress. I will double check all the connections of replaced components. One more interesting thing is that there are no mica insulators underneath heatsink of H713 and H714 and also there is no thermal compound either. I guess on those transistors the normal collector pin is snipped and the metal tab is used as the collector. Should I regrease those transistors when I put the replacement?
 
Either will work, I prefer the KSC/KSA as they match the originals a little better.
I don't generally replace semiconductors unless they (or their complement) is defective.

Tom
 
If there was no mica there to begin with then it is probably not required. I would use thermal compound, though, less is better, you just want it to fill the tiny gaps between the transistor surface and the heat sink.
I only buy parts from reputable suppliers.

Tom
 
catrafter said:
If there was no mica there to begin with then it is probably not required. I would use thermal compound, though, less is better, you just want it to fill the tiny gaps between the transistor surface and the heat sink.
I only buy parts from reputable suppliers.

Tom
Click to expand...
Tom thank you. Here is little update. I replaced the H713 (KSC2073) and H714 (KSA940) on the right channel main amp and now it is working and heat sink with those transistors are not heating badly as it was last time. I put a bit of thermal compound as Tom suggested. Now on the right channel I replaced all caps and transistors at H701-H704 and it is running fine. I did not replace any diodes in this channel (on right channel I replaced all the diodes) and also the old transistors remains at H713 (2SD382) and H714 (2SB537) .
My question: Should I do the same exact replacements in the left channel as right channel to keep balance? One quick observation, right channel is sounding much better than left channel.
Please advise.
Thank you!
 
catrafter said:
If there was no mica there to begin with then it is probably not required. I would use thermal compound, though, less is better, you just want it to fill the tiny gaps between the transistor surface and the heat sink.
I only buy parts from reputable suppliers.

Tom
Click to expand...
PLEASE HELP.....

Here is the full update. I have recapped and replaced H701- H704, H713, H14, H717-H718 and H720-H721 in both amps. I replaced all film and electrolytic cap in pre amp PE01. After puting all boards in. Bias is set nicely for both right and left channel. DC offset in right channel is varying between -1 to +1 mV which is fine but for left channel DC offset is all over the map! trimmer is not helping at all. Next I connected the right pre in to left main in then DC offset is steady and can be controlled by trimmer. If I connect left pre in to right main in then the DC offset in right channel is all over the place. Does it mean the problem is in PREAMP left channel? If so where I should look. In this preamp board I can not differentiate two sides (L/R)!

Any help will be great. If I run the amp it is running but I can see the woofer jumping around way more in left speaker than in right speaker!
 
I would say you are correct the problem lies with the preamp board if the issue switched channels when crossing the preamp cables.
Look for solder bridges,etc. on the preamp board.
You may also have a faulty transistor in the preamp board left channel which a shot of freeze spray might isolate.
I have only had a bad BA312 once but anything is possible.

Those are a couple of ideas off the top of my head.

Bob
 
wlhd1610 said:
I would say you are correct the problem lies with the preamp board if the issue switched channels when crossing the preamp cables.
Look for solder bridges,etc. on the preamp board.
You may also have a faulty transistor in the preamp board left channel which a shot of freeze spray might isolate.
I have only had a bad BA312 once but anything is possible.

Those are a couple of ideas off the top of my head.

Bob
Click to expand...
Thank you Bob! I checked all the solder it seems to be ok. I will check the transistors tomorrow and report back.
 
wlhd1610 said:
I would say you are correct the problem lies with the preamp board if the issue switched channels when crossing the preamp cables.
Look for solder bridges,etc. on the preamp board.
You may also have a faulty transistor in the preamp board left channel which a shot of freeze spray might isolate.
I have only had a bad BA312 once but anything is possible.

Those are a couple of ideas off the top of my head.

Bob
Click to expand...
Blown the power transistor in one amp by simple stupidity!!
I found the capacitor in preamp connected in the wrong way and after correcting it I was checking the bias in the right amp. After setting the bias I switched off the amp and immediately taking out the probes from pin J704 and during that my probe toches both pin J704 and J705 I saw a spark and the fuse in back blown. After replacing the fuse it failed DBT. When I disconnect the right amp everything works fine.
I am going to replace the output transistors H001 and H002 with MJ21193 and MJ21194. Now my question is what other components may also be blown due to this incident? I can see the immediate transistors connected to Pin J704 and J705 is H713. I will obviously check that. Should check all other transistors too? Di I also need to check capacitors?
Any help or advice will be great!
Thanks
 
For starters just renew both output transistors and power it up using a 60w bulb in your DBT.
If it passes check bias and DC offset.


Bob
ps- get yourself some Pomona mini grabber test leads.
 
Yep.. mini grabbers are your new best friends for troubleshooting and not having a accidental light show .. been there.. done that ;)
 
wlhd1610 said:
For starters just renew both output transistors and power it up using a 60w bulb in your DBT.
If it passes check bias and DC offset.


Bob
ps- get yourself some Pomona mini grabber test leads.
Click to expand...
Bob: Thank you. I have ordered transistors and have to wait until Wednesday next week! I will report back the result. Also ordered mini grabbers!
 
That should be ok.

Never saw an 85w incandescent bulb though (Usually 60/75/100 were most common).

If you have time over the weekend ,since you're ordering and waiting for new outputs,it wouldn't hurt to check your driver transistors and the emitter resistors.
What are you using to test transistors?

Bob
 
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