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Marantz 2275 - Right Channel P700 rebuild question

P

photoenergy

New Member
Howdy folks and happy new year!!

I’m working my way through my first 2275 rebuild (thanks for all the prior documentation!) and have come across a stumper. My amp has been working fine for a while and I’m stumped to fine the H704 transistor mis-wired. The traces seem to match the printed board markings so I believe the transistor is incorrectly wired (I plan on fixing that). But before I do that - why does that channel still function as expected with this mid-wired transistor?

I’ll work though the rest of them first but just curious if folks have thoughts or should I just put my curiosity aside and wire in the replacement as I’ve found the working board?

Many thanks!

Chris
 

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I finished the right channel board last night and decided to keep in the H704 transistor for now. I tested the amp with my DBT and proceeded to bring full power to the amp without any issue. Right channel worked so I thought I was in the clear - that was until I started to see smoke coming from the left channel board. Quickly powered down the amp and inspected the left channel board had a burnt R734 (see photo). I’m replacing all electrolytic caps, PCB transistors, diodes and output transistors.

I had completed the left channel rebuild yesterday and upon testing it seemed to work fine with no issues. I was able to set the bias and DC offset without issue so I’m scratching my head on why there’s an issue now.

For those who have experience with these boards I’d appreciate any thoughts on where I should start when I get to the amp later today.

I have also completed the power supply rebuild but no issue on powering up after that board was completed.

many thanks in advance!
Chris
 

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Welcome to AK!
First, if you post this thread to "Marantz Audio" forum you will receive more responses.
Next, it would be helpful for readers if you give complete details on what work you have performed. If you replaced transistors what is the replacement you used etc. In your first post you said H704 is wrongly placed but from the picture, it is impossible to see. It will be better if you mark the position of interest in the picture. Also, it is better to read all posts on 2275 rebuilt here in AK beforehand.

Cheers
 
Much appreciated - I’ll repost in the Marantz forum. I thought I had seen a few discussions on Marantz rebuilds here but appreciate the recommendation. Was able to make a bit of progress tonight but still stuck. I’ll provide a more detailed set of questions (and photos) once I find I’m at a real dead end. (I think it’s the pesky relay on the power supply board that’s causing me issues).

see you over on that board - hopefully not too soon

thanks again.
 
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