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Louie, Technician
Category: Home Theater-Stereo
Satisfied Customers: 11733
Experience:  Have been in the business 25+ yrs., down to component level.
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Rusty, My Onkyo TX-SR800 receiver has no sound, today i was

Customer Question

Hi Rusty, My Onkyo TX-SR800 receiver has no sound, today i was playing a record on my turntable but there was a big hum trough the speakers as i play the record, so i disconnect the turntable rca plugs to see if those were the reason of the hum, all this was when the record was playing and the onkyo was turn on, well when i disconnected the rca plugs from the onkyo the hum gets louder, the i hear a fan inside the onkyo very fast and very noisy, almost like if the receiver wanna gets fly, and the i feel a big flow of hot air from the onkyo, then the hum was gone, but the receiver never shut off, then i reconnect the rca and gets no sound from the onkyo, nor from any source connected to it, no phono, no dvd, no tv, no nothing, so i shut off and disconnected everything, and the onkyo itself from the current, i wait a few minutes and reconnected and power on and still no sound, the power off and did a reset of the system, but still no sound, this receiver has a pure audio mode and when i press that button there is a little noise sound from the receiver but almost until i get max volume up, but when i get back to stereo or surround mode there is no sound, also i have to say that when blu ray or dvd is selected and playing, the dos, dolby digital select automatic the right format from the source, so it recognize the surround signal by the digital inputs, what can i do? help me please to fix my receiver :(
Submitted: 1 year ago.
Category: Home Theater-Stereo
Expert:  Louie replied 1 year ago.

Hi and welcome to JustAnswer,

Thank you for the question and your patience. With the indulgence of Rusty and should you still need assistance for information purposes only...

Initially, the described symptom almost always point to an internal hardware issue. If comfortably able and feel safe to do so, are you then considering a DIY (do-it-yourself) repair approach? If yes, do you have access to and familiar with a multi-meter and even a soldering iron?

Still, determine if the potential fault is at the amp side or before the amp, the pre-amp/processing half.

Proposed preliminary tries (if have not been done):

  • • feed the Onkyo TX-SR800 audio signals to its MULTI CH INPUT R & L jacks to test its output amplifiers;
  • • connect the Onkyo TX-SR800's PRE OUT R & L jacks to another receiver/amplifier to test its inputs/pre-amp/sound processing circuit..

All other checks would be with the internal circuit and with the use of a multi-meter.

Customer: replied 1 year ago.
Hi Louie, thanks for the answer, now answer to you:
yes i have a multimeter and a soldering iron
ok, i will do the test you propose, i'm not now on the site of the amp, i will let you know tomorrow what happens with the test, just another tip, for you to know, maybe it's something maybe you can use to figure what is wrong: when i turn on the amp, it hears two clicks, and then a bit later a third one, i'll writte you tomorrow, thanks :)
Expert:  Louie replied 1 year ago.

Appreciate the post back and would look forward to an update when able.

Customer: replied 1 year ago.
Hi Louie, here are the news of today:
1) i tested the multi ch input R & L jacks, i connected a cd player, then select dvd from the Onkyo's input and then in audio select multi ch, the result was it get sound very low and distorted like a bad fm signal when volume gets set from 60 and up (60/100)
2) i wasn't been able to test the pre outs cause i had no other receiver amplifier at the site, i will carry on one tomorrow and will make this test.I guess i have a clue, or maybe the reason --- you tell me if i'm not wrong --- on why the receiver was damage, between the turntable and the amplifier phono inputs i connect an Onkyo equalizer, i guess it was my mistake connected that way, searching over the internet i have found that to connect an equaliser to the amp, it must be through the tape or pre amp connections, did i hurt my amplifier for doing that? an equaliser connected the way that i did can damage the amp by overfeed the input? or it is just an add reason to damage a maybe faulty amp? or it is a matter that doesn't have to do in the fault of the amp? :(
Expert:  Louie replied 1 year ago.

Hi again Jerry and appreciate the post back + additional information.

The posted results of feeding a CD player directly to the Onkyo TX-SR800's MULTI CH INPUT R & L jacks would be indicative of a failed amp/output circuitry; i.e. more particularly the output transistor pairs.

Unfortunately, yes; feeding the PHONO inputs with a LINE level output of an equalizer has overdriven the TX-SR800. Specifically, the PHONO inputs only needs a maximum of 2.5mV signal whereas the output of most equalizers would be around 150mV. That is more than 50 times what the TX-SR800 can safely handle. Add to this the 60 cycle hum introduced and piggy rode the signals to the PHONO input jacks.

Propose preliminary internal checks would be on the big transistors attached to the large aluminum heatsink. Of particular interest would be forward & reverse of base-to-collector and base-to-emitter readings. A collector-to-emitter reading would also be needed. A reliable reading would require out-of-circuit testing.

Customer: replied 1 year ago.
wow, i really screw up this time, do u think it can be fixed? ok will do the test you said, i have the multimeter and the soldering iron, but i really had very very low to none electronic experience, so u will have to drive to point the parts and how to measure them safely and how many time i must get disconnected the amp for not having hazard with the CAPACITORS, i can be available for this tomorrow night at 7pm central time through 10pm, plus i'm attaching you pictures from the onkyo's internals, so you can point me the parts that i must disassemble and test, i really appreciate your help and you let me more confident about the firm of your answers and expertise. :)Another question, but this is about the rating, do i have to rating your services now or when the fix it's been done? and if i rating you now the asking service is over?, or until when i can use your help?thanks :)
Expert:  Louie replied 1 year ago.

Jerry, the challenge would be more on the dis-assembly as so many parts/boards have to be removed to gain access to the output transistors. These output transistors are the 3-terminal devices screwed to the 2 aluminum heatsink to help dissipate the heat.

These transistors and heat radiated by/from the heatsinks are responsible for the earlier description of "...feel a big flow of hot air from the onkyo...".

I would suggest for more pictures for your reference even before any dis-assembly. The idea is to have a fallback reference when putting things back together.

Again the objective is to reach / gain access to the big transistors screwed to the 2 aluminum heatsink. De-solder them and then when out-of-circuit, perform forward & reverse tests.

Would you be comfortable proceeding please?

Customer: replied 1 year ago.
ok i will start disassembling tomorrow, and i will give you updates from the process, when i reach and get the transistors i will contact you again to tell me how to measure them, thanks again, good night
Expert:  Louie replied 1 year ago.

I understand and would look forward to an update when able.

Customer: replied 1 year ago.
Hi, Louie, here are the updates from today:
1. I was been able to disassemble the amp, and get to the transistors, it was very laborious to get to that section and dismounted, i'm adding three pictures from the final result, in two of the them i'll show you the seven pair of transistors that you indicate me that i must get to test, but before i can reach those transistors, i have to remove a board that had five transistors smaller than the ones that you told me to check, do i have to check those too?
2. Ok now that i have access to the pair of transistors, what now? do i have to unsolder the 14 transistors? is there any other way to avoid that and check them which is the bad?
3. i'm sending you too a pic from my multimeter, to tell me which kind of measure select, and how i must test those transistors and which are the measures that i must get from the readings to know which is good or bad?4. I'm sorry if i wasn't been able to do all the checks that you have asked me, but i have to work and there is a little time free for doing this, so i ask a free day for tomorrow, and i will be available for run things faster with your further instructions for get this amp checked and get a final solution to fix it.thanks
Expert:  Louie replied 1 year ago.

Hi again Jerry and appreciate the post back + pictures.

Each output transistor pair is complimentary; i.e. 1 is PNP and the other is NPN. Please see the tutorial HERE to learn their purpose and difference.

A transistor is tested just like a diode except that it is made up of a couple of diodes internally. Click HERE to learn more about diodes.

And HERE on how to test these transistors with a multi-meter close to what you have. Note that the diode setting is used.

The simplest rule to keep in mind is that no matter how/what transistor legs are tested against the other leg(s), no reading at any instance should read 0.0Ω nor similar readings with the polarity reversed. Having posted this, then yes, the transistors may be tested while still in circuit but may not be that conclusive.

If none of the output transistors show a fault, then yes, the other (driver) transistors would have to be tested likewise.

It would also be to your advantage to test the emitter resistors. There are the white flat block with 3 legs tied to the emitter of each and every output transistor. Each out leg should read to the center leg 0.22Ω. It would rarely ever go lower than 0.22Ω but if it reads higher or even OL, then it has faulted (open).

Customer: replied 1 year ago.
Hi master Louie, here are the updates from today:While i guess i had think that today measures would be easy and fast, it took me a while, read, learn about PNP and NPN, how it works and how it measures and what the result must be, one thing that i learn is that no matter what kind of transistor you are measure, when you test collector vs emitter the test result must be OL or no measure cause it doesn't have current between those two points, am i correct?So i get a little confuse for the result of the measures, whose i'm attaching you in pdf, so you can read them and tell me what you think about.About the emitter resisters, i get reads about 0.2Ω, but while measure them, the readings gets up and down from 0.4 to 0.1, in all of the emitter resisters, that was constant in the readings, i'm attaching a video to show you this variations, i don't know if that variation is normal or show something is wrong.After you read the results, do you think i must desolder the transistors to get the readings form the multimeter? or with these results is enough for you to tell if they are good or bad?regards
Expert:  Louie replied 1 year ago.

The fluctuating resistance readings may be attributed to the resistors still being in-circuit as the other parts are influencing/affecting the values.

Might the readings/labels of the COLLECTOR EMITTER and BASE TO EMITTER have been inadvertently swapped?

Still, I am concerned that the readings are rather low both ways as it may be indicative of a near short.

Customer: replied 1 year ago.
hi louie, no, the labels are ok and correspond to the readings, do u need that i take a video of the readings from collector to emitter and base to emitter so u actually see them?what do u think that happened? it was for the equaliser connection or it was something bigger like a discharge?i'll wait your further instructions
Expert:  Louie replied 1 year ago.


If all the transistors' BASE-to-EMITTER resistance readings show ~0.5??Ω both ways (forward and reversed), then these transistors have failed and thus would require replacement.

The equalizer could have contributed and may even have triggered but I am inclined to suspect something else directly caused the total failure of all transistors with low "...BASE TO EMITTER..." readings such as a thermal issue, thermal runaway or even dried up thermal paste.

Customer: replied 1 year ago.
ups, maybe a bad thermal sensor? do i have to test the separate 5 transistors that are near those that i just measure too? i will unsolder one pair of the big transistors tomorrow and take measure again to confirm the readings? do u agree? in your experience and knowledge do u have to check the service manual to know what or where the control of the heat is managed by the system (like the sensor that activated the fan to cool the system) or what else do u think i need to check in the system,i'll wait for your instructions
Expert:  Louie replied 1 year ago.

Yes please (though understandably challenging); de-solder to enable out-of-circuit resistance checks.

Based on experience:

  • • if the COLLECTOR-to-EMITTER has shorted or low Ω value, then the emitter resistor would most likely also have failed;
  • • if the BASE-to-EMITTER has shorted or low Ω value, then the base resistor would most likely also have failed;
  • • it would be rare for all transistors to suffer the same BASE-to-EMITTER low resistance both forward and reverse;
  • • it would be expected that even if just a single transistor suffered BASE-to-EMITTER low resistance, then auto-protect would have immediately kicked in.

And yes please Jerry, a video of how the transistors were checked would be helpful.

Customer: replied 1 year ago.
Hi Louie, ok i got desoldered the first pair of transistors, the results are almost identical, i´m ataching you a pdf with measures compare. i keep thinking in what you said that the low readings results show the failure in the transistor, excuse me my ignorance, but what it would be the results that one must get to know that the transistors are good, because if you see in the new measures the transistors función properly, sign of damage, if not the readings.Also i took a video from the measures, you can download it here i have the wrong setting selected in the multimeter, i select for the readings the diode symbol, as you said in last message : A transistor is tested just like a diode except that it is made up of a couple of diodes internally.So i have made a test too in the ohm setting, you can see here let me know what you think
Expert:  Louie replied 1 year ago.

Thanks. I saw that the 527 is 0.527. Still, agree that the transistor readings check good.

While still dis-assembled and as posted above, next test the driver transistors please (even if just likewise to eliminate them as suspects).

Customer: replied 1 year ago.
ok here are the readings from the driver transistors, check them please, also i'm attaching a pic from the base of the amp board, if you can see there are a little transistors attached to the heat dissipators, do i have too check them too?
Expert:  Louie replied 1 year ago.

The part numbers 79M18A denotes that this component is not a transistor but a 3-terminal voltage regulator IC where "79" would make it a -V regulator and "18" for the output voltage hence, a 79M18A is a regulator for -18V. Conversely, 78M18A would then be +18V regulator.

Thus for the 7805, "78" would make it a +V regulator and for the "05", a regulator for +5V.

These regulators do not test like the transistors. Other than a (near) short, resistance check serves a very limited test. The prescribe test is active; i.e. supply these regulators with a higher source voltage and measure the output voltage.

Based on field experience, the 78xx regulators do not fail that often compared to the 79XX regulators. In some other instances, the input and output legs of these regulators (78xx & 79xx) may develop cold-solder over time.

Another culprit associated with regulators failure would be the electrolytic capacitors at their input and output legs.

Was the A1726 checked out-of-circuit? Again, am concerned about the 0.02 reading both ways of the Base-to-Emitter

The driver transistors would be those closer to the white resistor modules. 6 of them would have their own small aluminum heatsink per pair and the other 8 with none.

The smaller transistors encircled in red serves as thermal sensors and alters the BIAS accordingly (inversely). The higher the temperature of the big aluminum heatsink, the lower the BIAS voltage / idling current. This is meant to prevent thermal runaway of the big output transistors. These thermal sensor transistors rarely go bad.

Customer: replied 1 year ago.
Ok Louie i will test them the ones you just told me, i have a question, so in resume, until now, after the test on on main transistors:1) based on readings, all have failed? thus need to be replaced?
Expert:  Louie replied 1 year ago.

No Jerry; if I understand your readings correctly, none of the output transistors are bad.

Please see the movie HERE. I tested a pair of unused 2SC5200 and 2SA1943. The only difference is that my multi-meter does not show OL and neither does it change from "1._". Note a habit from the old analog (needle type) of checking the multi-meter itself by touching the red & black probes together before performing the tests. The readings are about the same as those of your transistors.

(Could not make the file size smaller; sorry)

Customer: replied 1 year ago.
ok Louie, thanks for the video, and your teachings, really, thanks, ***** ***** teach online, you are a good teacher, i would be one of the first to inscribe on your courses, i will post you again the next results
Expert:  Louie replied 1 year ago.


Customer: replied 1 year ago.
Hi Louie, here are the readings from the driver transistors, i guess they are ok
Customer: replied 1 year ago.
by the way, now i'm using another onkyo amp, and hear the same buzz hum but now i identified the reason, it was the conection between the pre out and the amp, by a cheap rca cable, so i replace it with a better one and the hum is gone.
Expert:  Louie replied 1 year ago.

Agree, driver transistors appears to check good.

And good to hear the loss of hum with better RCA cables.

Any update (out-of-circuit) of the A1726 tests?

Customer: replied 1 year ago.
hi louie, after desolder it , a1726 reads : base conector 0.570 base emitter 0.572 other combinations OL , i guess it is good, i wait further instructions
Expert:  Louie replied 1 year ago.

Agree Jerry.

And would you be able to do an active tests of the regulator using an external power source?

Customer: replied 1 year ago.
just tell me what do i need and how to do it, what do u mean with external power source?
Customer: replied 1 year ago.
i keep thinking so far, with the test made until today, if transistors and emitter resistors and driver transistors are ok, it means something are not allowing to get power so that's why there is no sound?
Expert:  Louie replied 1 year ago.

Agree Jerry (to an extent).

In most instances, there would be no sound if the speaker relays are not engaging. There are 2 reasons that these relays would not engage:

  • • headphones plug inserted;
  • • auto-protect mode has kicked in.

There are 3 reasons that auto-protect mode would kick in:

  • • speaker/wires has a (near) short;
  • • transistors/circuit are faulting;
  • • low or missing DC voltages.

If the speakers and their wiring checks good and the driver & output transistors passed their tests, then remaining suspects would be:

  • • all the other (smaller) transistors;
  • • low or missing DC voltages:
  • - regulator outputs;
  • - ±55V supplied to the collectors of the output transistors.

To test the 3-terminal voltage regulators, supply these regulators out-of-cicruit with an external power source (such as a regulated 24VDC power supply) similar to what is shown HERE. Then test the output with a voltmeter. Hopefully, the document HERE may shed additional insight on these regulators. Please note that the positive and negative regulators have different pin configurations. Click HERE.

Customer: replied 1 year ago.
i'm worried, did i made a test wrong? researching on internet, all similar problems like this fix with checks you told me, almost always is a bad output transistor pair and its corresponding emitter resistors :(, i will try to find a power supply as you told me, i will came back with an update.
Expert:  Louie replied 1 year ago.

If all the solder joints, resistors, transistors and regulators check good, then the amp/output may be ruled out.

Since there is now "...another onkyo amp...", then the foremost proposed check of "...connect the Onkyo TX-SR800's PRE OUT R & L jacks to another receiver/amplifier to test its inputs/pre-amp/sound processing circuit..." may now be re-considered and carried out with all parts/boards put back together.

Customer: replied 1 year ago.
Hi Louie, i just search a 24v power supply, only i can find 12v, 18v and 32 v, should i try the 32v?
Expert:  Louie replied 1 year ago.

Hello Jerry,

Yes please as that would equally work. The idea is to feed the regulator IC more than 18V and expect a consistent 18V as output.

Customer: replied 1 year ago.
hi Louie, sorry for the delay but i have been a lot busy at work, but here are the results:
in 24.17 v
out 5.01 v78m18a
in 24.17 v
out 16.33 v79m18a
in 24.17v
out 5.747905a
in 24.17v
out 18.27
Expert:  Louie replied 1 year ago.

Appreciate the post back / update Jerry.

If these readings / then:

  • • "...7805a in 24.17 v out 5.01 v..." - very good;
  • • "...78m18a in 24.17 v out 16.33 v..." - acceptable;
  • • "...79m18a in 24.17v out 5.74..." - most likely defective as expected output should be -18V;
  • • "...7905a in 24.17v out 18.27..." - similarly defective as the expected output should be 5.0V.

Or could the last 2 readings for the output voltage have been inadvertently swapped?

Customer: replied 1 year ago.
Hi Louie, I took again the las readings for 79m18a and 7905a and the are correct, could that be the reason for the failure on the amp? do I have to do more test on other components based on these bad voltage regulators?
Expert:  Louie replied 1 year ago.

Hi again Jerry and Season's Greetings!

Yes very likely as it would alter the performance of the driver & output transistors and apparently provides a false condition where the output transistors kicks in the auto-protect mode.

The confirmed "...79m18a in 24.17v out 5.74..." - most likely defective as expected output should be -18V would require a simple regulator replacement.

On the other hand, the confirmed "...7905a in 24.17v out 18.27..." - similarly defective as the expected output should be -5.0V is worrying as the circuit that the supposed -5V would be supplying has now been subjected to a -18.27 more than 3 X the expected -5V.

Customer: replied 1 year ago.
what's next Louie?
Expert:  Louie replied 1 year ago.

Since the output voltage readings of the 2 regulators have been confirmed to be different from the expected -18 and -5, then first step is to replace both the 79M18 and 7905. However, it would be to your advantage to purchase two (2) 7905 if there are still faults with the circuit using the -5V and may invariably affect the new 7905 when performing active test when both 7918 and 7905 are replaced.