Marantz 2275 rebuild, saved from the dump

Been there with as mine as well. I resoldered the whole board and checked every trace point to point. The smallest things can cause the biggest problems.
 
Been there with as mine as well. I resoldered the whole board and checked every trace point to point. The smallest things can cause the biggest problems.
Yes, I just resoldered everything with no changes, I think its time to call in the big guns....
 
Update,
I have spent several days banging my head against the work bench with nothing to show but a headache. Still fighting the bias adjustment R742 going from 0v to 600mv and higher, no way to get 10mv set. I have verified that R742 is working properly. I have sound out of the amp but things heat up quickly if its turned up any higher then background music. With the volume turned down I am getting 155mv on H711 collector when the sm shows 600mv, other than that the voltages look close to the SM. H711 base and emitter voltages are good so I guess maybe the diode H710 could be bad or C721 is leaking DC volts. Last time I checked H711 passed ohm meter test, but H711 & H712 have not been changed. I have changed out H706 - H709, H713 - H714


Think I will give it a couple more days and then its time to send the board out to a pro
 
Did you change the bias transistor, or put it in upside down? (H709)

Check H710 or H719 for open or incorrect resistance. I believe you said you did.

Did you install a matched differential pair ?

Solder bridges on 711/712 will feed incorrect base to 713/714, and overheat them and the outputs.
I hope your not running this without a dbt.
Do not let the transistors get over 130 degrees. Shut it down and cool it before running it.

The drivers are only rated for 150 deg use.

Buy a can of Dr Scholls Freeze Off and start cooling each transistor (before the drivers), as you monitor your 711/712 base voltages.
Your base voltages should tell you were things start going downhill.
 
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Did you change the bias transistor, or put it in upside down? (H709)

Check H710 or H719 for open or incorrect resistance. I believe you said you did.

Did you install a matched differential pair ?

Solder bridges on 711/712 will feed incorrect base to 713/714, and overheat them and the outputs.
I hope your not running this without a dbt.
Do not let the transistors get over 130 degrees. Shut it down and cool it before running it.

The drivers are only rated for 150 deg use.

Buy a can of Dr Scholls Freeze Off and start cooling each transistor (before the drivers), as you monitor your 711/712 base voltages.
Your base voltages should tell you were things start going downhill.
,
I did not order matched pairs of transistors, didn't even think about it. Showing my lack of experience here. Do all the pairs need to be matched? Is there an option on Mouser for that ?
Thanks, I will check your other suggestions tonight
 
Yes, mouser will be fine. Ask them to match your pairs if they can. Otherwise buy 20 of each and do it yourself.
It is real important that you do this. A flaky transistor could give you a lotof grief.

Make darn sure that you check your EBC on each transistor to make sure you didnt get solder twix any of them.
Look the whole board over and make sure you can account for cut off transistor/ cap legs before powering itup with the dbt.
John
 
Update,
In the interest of getting this unit back in the rack and making music I reluctantly decided to send the amp board out to one of our own to be repaired. I really was hoping to fix it myself but this was really stumping me.
I got the report back last night that I had put the bias transistor H709 in backwards with the emitter and base swapped, maybe that's why the Idle current would not adjust, ha ha...
Yes kutzlerTrans you even to me to check that, but at that point I think that I had already thrown in the towel.

I feel really dumb but I am also very happy that its fixed now and on its way back to me.
I want to thank everyone that has pitched in to help me on this project, I also what to thank everyone that has "liked" or even read this thread. If nothing else I hope that it serves as inspiration to anyone else that wants to partake in this rewarding hobby.

I should have the amp board back next week. I will post photos of the 2275 once its back in the rack...
 
Update
The amp board is back in the receiver and it sounds great!!!
The tech did a great job fixing the amp. He even removed the burned areas of the board and filled it in with epoxy. I thought this was only a visual thing, but it turns out the charred bits of the board can act like a resistor. I was using an older schematic during my work, so a couple of the resistors that I had installed were off, he replaced them and also fixed some lifting pads from the back of the amp.
I am Very happy with the results, this receiver should last another 40 years.

It's been a long 5 months!!!
Here is the before pic

IMG_5901.JPG

And now a pic of the restored receiver in its new home

IMG_6556.JPG
 
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Congrats Rossm. Great to see you finally have yours back in action. I know I'm loving my 2275 as well due in no small part to Leestereo's help. Thanks again, Ben!
 
Hey, dont feel dumb. If you think about it... how do you think i learned about having that thing installed upside down.
I think i bought the peak atlas soon after.
 
It is a nice little transistor tester.
It has 3 wires w/ mini clips that you clip to your transistor. You hit the test button and it displays info on transistor, including ebc identification.
Until i bought that, i had a few unscheduled firework displays.
 
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