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Post by tibimakai on Dec 25, 2020 23:15:38 GMT -5
I have picked up this receiver, that turns on and in a few seconds shuts down. Typical shorted amp channel. I have identified the two channels, that are having issues. I have removed the connectors, that connect from the vertical pre-amp board to the bottom main board. This way the receiver turns on. As soon as I resolder any of the two channel connector, the receiver shuts down after a few seconds. I have tested both channels multiple times, and replaced anything that was suspect, but it still shuts down. I have even removed all the electrolytic caps and measured them, but they all look good. Initially, I have found three bad resistors(somebody worked on it already, each resistor's leg was unsoldered already), which I have replaced already. Usually, I manage to take care of amp issues, but this one is a puzzle, that it seems like I can't solve myself. I would appreciate any help. Elektrotanya has the service manual for multiple revisions: elektrotanya.com/onkyo_tx-nr737_sm_parts_rev6.pdf/download.html |
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Post by tjmotter on Dec 26, 2020 21:52:37 GMT -5
Replace C5010 (or the equivalent on the channels that are blowing). Also replace Q5000 and Q5030 equivalents for both channels.
I had this exact same problem and eventually narrowed it down to C5010. The problem is that it looked ok with my meter but it was passing AC causing damage to the two transistors downstream from it. You will find that the transistors will test ok but they will measure a little different than a good working channel. Fact is that they receive damage when that capacitor is bad. Replacing these 3 parts is likely to fix it.
HTH
Todd
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Post by tibimakai on Dec 26, 2020 22:42:24 GMT -5
Thank you Todd.
I have even measured all of them(out of the circuitry), with an ESR meter and they all looked OK. That is interesting.
That was my next step, to replace all the capacitors, but I don't have all of them at the moment.
Happy holidays!!
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Post by tibimakai on Dec 27, 2020 0:37:07 GMT -5
You are sure that is C5030? I see C5020 and maybe C5040 around the first transistors.
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Post by tjmotter on Dec 28, 2020 20:03:00 GMT -5
Yes sir. C5030 is the first device in the pre-amp. If you trace it back you will see that the output from the Op-amps (output from the DAC) go directly to one of these capacitors (depending on which channel) and they seem to be responsible for filtering out all DC voltage so that only the signal passes into the pre-amp. What I found was that I had one of these that went bad and it would immediately damage those two downstream transistors. The difficult part was that they all seemed to test ok. No shorts, no opens but the resistance measurements were different than a good channel. I spent hours working on that board and came to realize that it was the only thing left. Once I replaced it, the amp would pass diags but I was getting static on that channel. Once I changed those two transistors, the amp was fine.
HTH
Todd
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Post by tibimakai on Dec 29, 2020 16:19:39 GMT -5
The first caps are C5000 & C5010.
Can I replace the 221 capacitor, with light blue round ones? I'm not sure, if they are the same type of capacitors.
I have replaced them, and something else is still causing to shut down. It stays on for a few more seconds though. So, you must be right about this.
The transistors are damaged as well?
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Post by tjmotter on Dec 30, 2020 20:12:48 GMT -5
If I am thinking of the same ones, the blue round caps are tantalum. I don't think that will work properly. The originals should be a standard electrolytic capacitor.
Yes, the transistors get damaged when that capacitor fails. On my first attempt at changing the capacitor, I blew it again because the transistors were bad. I then changed the two transistors and they blew again. On my third attempt I changed the capacitor and both transistors and that fixed my problem.
Yours may be different but this is what worked for me.
HTH
Todd
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Post by tibimakai on Jan 4, 2021 18:35:18 GMT -5
I was thinking about those red 221 (ceramic/tantalum?)capacitors(C5006). 
I have replaced C5016 and C5006(but I guess with the wrong type of cap). There is a third cap that needs replacing? I will replace those two transistors as well. |
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Post by tibimakai on Jan 4, 2021 21:41:04 GMT -5
221, it seems like it is a polyester mylar film capacitor.
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Post by tibimakai on Jan 5, 2021 0:25:02 GMT -5
This pre-amp is killing me.
I have replaced those two transistors with brand new ones, I have replaced C 5016 with a brand new one and I have swapped the C5006 from another channel(I don't have a replacement) and it still shuts down. The board looks like crap, after so many solder jobs, ripped pads, traces. And I still have problem with the next channel SR. Most likely the same thing. Right now, I have the main plug unsoldered from that channel that makes the connection to the mainboard.
Could I just remove transistors, and just keep trying until it won't turn on?
All the pre-amp board is really black as well, specially in the middle area.
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Post by tibimakai on Jan 6, 2021 18:57:33 GMT -5
I have realized, that I did not tell the whole story.
When I have got the receiver, I have found three resistors with one leg unsoldered. So, somebody had an attempt at it, before me.
I have replaced those resistors and the two INA6006 and INC6006 transistors and since then, anything that measured suspect.
I'm just saying that my issues may not be the same as we were discussing above.
Those three resistors were: R5226, R5176 and R5166.
I'm wondering, it could be C5096 and maybe C5086?
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