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Onkyo Tx-8500 Trouble

str8tlk

str8tlk

Active Member
Ive got a question about my Onkyo receiver :sigh:, had two sets of speakers hooked up to it had it cranked pretty loud , it cut out then turned back on but the right channel did not sound so good so i shut it down. really bad smell came from the vents.

opened it up. the amplier board for the right channel has several 5w resitors 1 of them was getting extremely hot when pluged in, smells coming from this board. I noticed a little blue I think resistor is discolored can not make out the lettering on it. has Original output transistors on this side to heatsink.

the amplifier board for the left channel dosent smell and all the 5w ceramic resistors do not get hot. nothing looks discolored. i noticed the output transistors on the left channel board had been replaced in the past.

How can I fix it? replace every thing on the right channel amp board? maybe replace the output transistors as well for the right? I ordered a service Manuel for it but waiting for the download link from them.

If any body would like the service manual Ill have it in pdf format.
 
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A. Check for open fuses.
B. Check for shorted output devices. (Check center conductor to the right leg for shorts, and that's a truncated test)
C. Check for shorted driver transistors (same method as outputs)
D. Check for open resistors.

That's sort of the meat of what to do. There's always some tangents to that, so it's good you're downloading the manual.

If all seems successful in the end, use the manual to set the bias. Variations in replacement devices might require a bias adjustment.
 
Thank you for your help. I did check for open fuses (none found). I do have a multimeter but the only thing Ive used it for is adjusting the DC-Offset on several receivers. I have learned quite a bit so far here but still am an extreme novice with electronics. When fixing receivers in the past Ive just replaced mass parts in the problem area as trial and error. (which worked for me) although I know the proper way is to diagnose and take measurements of everything. So I would have to pull the board out power the unit on then take measurements. what do I set the meter to, I know these seem like stupid questions pls forgive.

ok so.. I found the source of the smell :D Its a small blue resistor the glows orange in the middle when i turn the unit on.

PICT0046.jpg



PICT0047.jpg
 
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.....can you post the section of the schematic where the blue (but sometimes red) resistor is schematically?

It's indicating that a larger than normal voltage drop is developed across the resistor. It sounds like a short that the circuit is "fighting".
 
Thank you Jon Logan. Ill take a snap shot and post that area of the schematic as soon as they email the pdf to me. Your ability and technical skill to diagnose this problem is a wonderful help :tresbon:
 
The link for the manual appears stale. The hosting page loads, but there's no link.

It looks like the resistor that is glowing is R-30 47/1W. You can perform an ohm-meter/diode check on the transistors on that amp channel.

If you have a diode test function, select that and with the metal can transistors on the heatsink (T-03's) find the transistors that start with "2SBxxx" put the black lead on the case of the big transistor and the red lead to either of the two other leads connected to the transistor socket. You want to see something like 0.650 ...........something like that. You do not want to see numbers like 0.00~100. If you've have these low numbers, you probably have a shorted transistor or a leaky transistor. If you find those, remove them from the circuit and re-measure them. If they are low numbers out of circuit, replace them.

Find the big output transistors that start with "2SDxxx" and do the same test, only this time swapping the polarity of the leads. ....Red to case, black lead to the other transistor "legs".

If you have an ohm-meter that doesn't have the diode function, not a big deal, just look for the low readings and don't worry about getting the 0.65 type of readings. reading open circuit is okay, at this point.

That covers outputs. report back what you find, it may require going further, but sometimes you get lucky and the damage stops at the output transistors.

Try to re-link the manual, so that we can be more specific and helpful.
 
ok pulled the output transistors out, set the metter to 200 ohm, metter set to DC. Followed your intructions on testing them.

The 2SBxxx's, 1 Measured .3 the other Measured .2

The 2SDXXX 1 measured 532 the other 538 only when negative probe is on the base

There is a diode test function that beeps at you if the resistance is less than 30ohm. the 2SBxxx's beep 0.00 the 2SDxxx's do not beep
 
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str8tlk said:
ok pulled the output transistors out, set the metter to 200 ohm, metter set to DC. Followed your intructions on testing them.
Click to expand...

Okay, make sure you set the meter to ohms, not DC(V)

str8tlk said:
The 2SBxxx's, 1 Measured .3 the other Measured .2

The 2SDXXX dont measure anything the metter reports nothing back.
Click to expand...
This doesn't mean much if the meter was in DC(V) function.

str8tlk said:
There is a diode test function that beeps at you if the resistance is less than 30ohm. the 2SBxxx's beep the 2SDxxx's do nothing again, no beep.
Click to expand...
This is telling. It sounds like the 2SBxxx (554?) is shorted, and the the 2SDxxx (424?) is okay, or open. Open is no good. If you look at the transistor on the bottom where the leads come out, rotate the transistor so the two leads out of the bottom are on the top half of the case. If it's oriented correctly, the Base is on the left side and the Emmiter is on the right. Measure (diode function) from the emmiter to the collector (case) on the 2SB554. Then reverse the leads (for good measure). If it beeps both directions, it's toast. For the 2SD424, put the red lead on the Base and the Black lead to either Collector/Emmiter, then measure Base to Collector and Base to Emmiter. You should get reading. Some meters report differently so say what it reads


str8tlk said:
Am I measuring these right?
Click to expand...
Mostly
 
ok gave it another go, could still be doing it wrong. Used both of these settings on the meter. Thanks for the info on orientation of the leads for the transistor.

2SBxxx- negative probe on (base) positive probe on (emitter)

#1 520

#2 550

2SDxxx- positive probe on (base) negitive probe on (emitter)

#1 563

#2 566

these tests where done with the lower diode test setting (in the picture) selected.

PICT0050.jpg
 
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You are measuring correctly.

Those readings look good. Those appear to all be Base to Emmiter measurements.

Perform the same type of measurements, but this time, measure from the case (Collector) to the Emmiter lead. Don't worry about meter lead polarity. I think your going to find 1 or 2 beeping (shorted). It sounds like it will be the 2SB554's. If you find that this is the case, I'll have you do a few more measurements on the 2SD424's.
 
KingBubba said:
Here is a good tutorial.

http://www.audiokarma.org/forums/showthread.php?t=201303&highlight=transistor+testing

See if you can also find the transistor tutorial done by echowars, good stuff.

I found it:

http://www.audiokarma.org/forums/showthread.php?t=43186&highlight=transistor+testing
Click to expand...

:thmbsp: Very good info here ty.


You are measuring correctly.

Those readings look good. Those appear to all be Base to Emmiter measurements.

Perform the same type of measurements, but this time, measure from the case (Collector) to the Emmiter lead. Don't worry about meter lead polarity. I think your going to find 1 or 2 beeping (shorted). It sounds like it will be the 2SB554's. If you find that this is the case, I'll have you do a few more measurements on the 2SD424's.
Click to expand...

Cool :thmbsp:, moving right along then.


*2SB554 (collector, case) to (emitter) tests

Both showing: 0.00 - beeeeeep (continuous), like you predicted.
 
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okay, good work, the 2SB554's are toast. They are conversation pieces now. I didn't follow the transistor testing link, but use those instructions to test the 2SD424's. If those look good, you may have gotten off cheap.

Okay, there is some pleasant news on how you can verify if there is further damage than the output devices.

On this amp, you can power it up without the output devices loaded. So keep the output devices removed from the damaged channel, power it up and take a voltage (DC) reading from "B1" and "B2". You should measure around 1.2V(DC). Next measure DC volts from ground to "B1". You should measure around +600mV (0.6 volts). This test will let you know if it's a safe bet to put replacement transistors back in at this point.. Also, go back and see if that 1W green resistor is still getting hot. My guess is, it's probably running cool now.

If any measurement isn't close to these expectations, turn it off and write back.
 
Ok well went and got replacement output transistors (4), the same ones that had already been replaced on the other side. The only replacement resistor I was able to get is a 47ohm 5 watt ceramic.

now, just followed your instructions, turned it on and waited heard relay kick on and then seconds later saw a sprk and little smoke come from the amp board :no: turned it off right away.

I inspected the board and didnt see any visual damage. looks like that 1w 47ohm resistor is toast though. So I just got finished replacing it with the 47oh 5w. Fits just fine.

Turned it back on and now it does nothing. I don't hear the relay click at all.

Awaiting further instructions...
 
Okay, no biggie. If there was colateral damage, it's low cost loss. ...the outputs were not put in.

It looks like we go back towards the drivers. The resistor that sparked.... ....was that R-30? That is the driver that "feeds" the 2SB554's. You should first perform the transistor tests on Q-11 (2SA839) and Q-09 (2SA818). Replace as necessary.. Before turning it back on, check the complements to those drivers Q-08 and Q-10.

After that, check the resistors R-31, R-32 (10 ohm/1W) R-29, R-30 (47 ohm/1W), R-33,R-34, R-35, R-36 (2.7 ohm/1W), R-39, R-40, R-41, R-42 (0.47 ohm/5W)

That is a pretty thorough check. I don't think an damage would get further back than that.

Don't worry, this is a pretty typical amp repair. Many times, it gets much uglier than this.
 
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