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SR9000G Repair Questions (Or my first rebuild...)

secondslc

secondslc

mmmmmarantz
As I wait for three final transistors to ship, I wanted to make sure I wasn't missing anything.

I bought this unit for cheap on e-bay because one of the channels burnt out. The main amp board had a nice scorch mark and crispy components. I measured continuity between both sides, and found no full carbon paths.

The main Sanken power transistors burnt out, as well as most of the smaller signal path ones. I have replaced them all with the exact same parts. The Sanken transistors are part of a matched set of four. I am reluctant to touch the other side as I was told it worked.


Now the questions...

I assume the previous owner shorted two speaker wires to cause this failure. He did admit to using the working channel on A+B after the other channel failed. Can a speaker short cause all this damage?

Was I right in assuming I could just solder replacement parts in since the single layer board didn't completely carbonize?

Other than the diodes, transistors, and resistors that measured as a short or way off from the matching component on the other side, is there anything else I should look for? I ordered a full set of capacitors for this receiver, but I want to wait for the thing to work. I don't see any reason for the caps to have failed, none of them look bad.

Picture of the board pre-surgery. More pictures tonight after work.

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If it were me, I'd grind out the burned part of the board with a Dremel tool or something similar and fill the hole with a mix of epoxy and ground up circuit board material. If you destroy any traces, just use the component leads to replicate them. It may not be pretty, but it works.

Tom
 

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Cutting a hole in the board sounds like a good idea, I already replaced the components before your reply however.It doesn't look too bad on both sides, and I will test for weird continuity before powering up.

Any other advice?



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crispy!
 
I think you will be OK, the first picture you posted made it look worse than it is.
Nice work.

Tom
 
Sigh

Well, plugged it all in, everything checked out fine. Then I turned it on...

smoke and flames ensued....

Note to self, the two green capacitors that you didnt check....BAD. I think i found out why the channel died.

Most of my new components survived. And im glad i have spares of everything. The board is no more scorched than it was, as the resistors that blew were not close to it.
 
The diode tested OK. As far as transistor checking, I set the fluke to diode and try to get a short beep across two junctions....thats all I need right?
 
My Fluke reads the forward junction voltage drop, so look for around .6 one way and OL the other. I never noticed the short beep before as I usually have music going while I work.
The bias diode may have two or three junctions in it, so look for a forward drop of 1.2-1.8 and OL the other way.

Tom
 
ITS ALIVE! But I have idling issues

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:banana:
I know what went wrong the first time. Apparently, SOMEONE had replaced the power transistors on the WORKING side of the board, leaving the bad ones to short and smoke all the hard work from the night before, yeah that was me. :stupid:

I adjusted the voltage offset to a perfect zero, but I have a problem with the idling current adjustment on the repaired side. The service manual says to adjust to 6mV+-.1mV. I can get that on the untouched side just fine. But I cant get lower than 150mV on the repaired side. I maxed out the pot. I wonder if I should replace that "just in case" or if there is something I should look for??

When listening, the right side sounds fantastic, but the repaired left side is staticy and sounds as if a radio station was cutting out. Bringing the volume up makes it sound better, but it still does not sound proper. The parts I used were EXACT replacements, except for the idling pot, which is a different form, but same resistance.

I have a video of how it sounds, its digital camera recording, so its rather poor, but you can tell the difference in sides.
http://www.youtube.com/watch?v=WQkV6x_NSlk
Any ideas?

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Sr9000g

Take measurements of R785 & R787, these get damaged when those high voltage output trannys go south! .27 OHM 5Watt white rectangle radial resistors. I have one on my bench now.
Jim
 
Where do I find

Where can i get .27 ohm 5 watt resistors? It seems newark,digikey, and mouser either do not stock them in low order numbers or carry the axial versions. Digikey sent me axial...so now i need to look for a radial version.

Anybody have an idea?
 
I found some on mouser, it will take some time to get in as theyre not in stock, but I am tackling my SD9000 in the mean time.
 
I didn't give up

As i wait for resistors that are still "on order", I decided to try cleaning the contacts as I don't think I had done it before.

I think it worked....reason i said think is because I couldn't test on some speakers (angry neighbors?), and only did it through headphones. The channels were choppy before, and she sounds clean now. Am I right in assuming that the headphone jack has the same amplification source as the main amp?

I also wanted to put it back together and look at it. I think its got a cool look.

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Volume up on the "headphone" and no distortion
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Ideas?
 
Done Done Done Done

boulderbros said:
These might work, but the leads are SHORT (3.5MM) with a 5mm spacing. The board spacing is 10mm. Maybe add leads?
http://canada.newark.com/64K7711/passives/product.us0?sku=ohmite-tww5jr27e
Click to expand...

I finally gave up looking for resistors with longer leads and added some to the ones I got. Once I got those in, she sings in both channels again!

I can finally move on and repair the next item in line. I will re-cap this beast eventually, but both channels sound nice even if I did re-cap the left channel during the rebuild.

Thanks for all your help! im :banana:

ONE LAST THING

My fader pot broke one of its ears when I was pulling the knob. Is there somewhere I can find a new fader?
 
Another SR9000G

Great job. Mine as well works great for my shop setup. The 2325's are in the house! I like the detail of the 2325 over the SR9000G though. have to keep them all going, running out of rooms and speakers:music::banana:
 
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