No sound from Sony STR-K850P, HELP!

bizwiz41

Member
2010-09-18 1:33 pm
Hello All,

I've tried to no avail with other forums, and I found this forum looks to be the bes for real information regarding problems, so here's mine.

I purchased a Sony STR-K850P AV receiver on E-Bay, appears it "may" have been damaged in shipping. Seller stated it was working before shipping, but I cannot get any sound out of it, from any speaker connection or input. Below is a list of items looked at, and reviewed so far:

No Sound from any input, through any speaker connection (tested w/ 8 ohm speakers). Tuner will not “Auto Tune”, even with antenna attached. Will direct tune to a station number, but no audio.
· Unit powers on, display lights up, react to button inputs
· Unit does NOT “heat up” when left on
· Unit responds to remote control commands
· Checked main fuse (125V, 6A), fuse functional
· Relay on standby power circuit board “clicks” once when powered on
· Both power circuit board connections seem to be functional (receiver did not power up when disconnected connectors)
· Unit does detect input signal (i.e. optical vs analog, 5.1 vs stereo)
· Unit does NOT show “PROTECT” message
· Have NOT tried headphone jack for sound output (no headphones w/ ¼” plug)
· “Sleep” function works: unit will power off
· Have tried “reset & Memory clear” per Sony manual-No effect
· Very slight hum from power transformer when powered on.
· Nothing internal visibly broken, not connected.
· Was told that unit was fully operational before shipping. Received with dent above volume control. Internally looks like nothing is damaged w/volume control.
I've read that a likely cause is the thermal fuse may be blown, but wouldn't that prevent the unit from powering on at all?

Any help is appreciated, and please excuse me that I am really a novice. I am merely trying to check everything, and decide if a trip to the repair shop is worth it.

Thanks so much for any help or direction.
 
Try this: connect an amp (+ speakers) to the tape rec out, connect any source device to let's say CD input. Now you should be able to select the source with the Sony.

If you have no sound there could be something wrong with the input selector or it's power supply. If you have sound I would definately check the volume pot, it might have been internnally broken, you can check it with a multimeter.
 

bizwiz41

Member
2010-09-18 1:33 pm
Try this: connect an amp (+ speakers) to the tape rec out, connect any source device to let's say CD input. Now you should be able to select the source with the Sony.

If you have no sound there could be something wrong with the input selector or it's power supply. If you have sound I would definately check the volume pot, it might have been internnally broken, you can check it with a multimeter.

Thanks boyof wax,

I did not try any pass through for either audio or video, and I was wondering about that.

I have equipment that I can set up to try your suggestion, so I'll give it a try. I'll post my results.

Thanks!
 

bizwiz41

Member
2010-09-18 1:33 pm
Try this: connect an amp (+ speakers) to the tape rec out, connect any source device to let's say CD input. Now you should be able to select the source with the Sony.

If you have no sound there could be something wrong with the input selector or it's power supply. If you have sound I would definately check the volume pot, it might have been internnally broken, you can check it with a multimeter.

Well, it looks like we're narrowing it down to the input selector or the power supply.

I tried your suggestion of connecting an amp/speakers, no sound at all. I tried it across various inputs og both MD/Tape amd video in/out. I did verify all of the components were functional.

I'm thinking there is something in the power supply; the unit does not even "warm" when left on. My other Sony receivers tend to get very warm even after 5-10 minutes. The heat sink is ice cold, and the power transformer isbasically at room temperature.

One last question; do you think a power supply repair would be a costly one? I pretty much have nothing into this receiver now, so I hope to avoid "good money after bad".

Thanks again!
 
Hey bizwiz, if you suspect the power supply('s) here are some ideas to check em out!

For the amplifier's power stage you can put a voltmeter across the big power supply caps. For input circuitry specifically I would recommend you'd google the partnumbers of the IC's and measure the voltage across the supply pins. Voltage and pinout are listed in the datasheet's.

Is this amp discrete or does it have power opamps?? Power opamps usually have a mute or standby pin, there might be a fault controlling it. If it uses power opamps you can also check the pin-status from the datasheet.

Any repair you can DIY is very cheap, except for the transformer if it was broken. If you'd bring it to a repair shop you'd be charged for the hours of labour. Not to mention that most repair's involve PCB swap.
 

bizwiz41

Member
2010-09-18 1:33 pm
Hey bizwiz, if you suspect the power supply('s) here are some ideas to check em out!

For the amplifier's power stage you can put a voltmeter across the big power supply caps. For input circuitry specifically I would recommend you'd google the partnumbers of the IC's and measure the voltage across the supply pins. Voltage and pinout are listed in the datasheet's.

Is this amp discrete or does it have power opamps?? Power opamps usually have a mute or standby pin, there might be a fault controlling it. If it uses power opamps you can also check the pin-status from the datasheet.

Any repair you can DIY is very cheap, except for the transformer if it was broken. If you'd bring it to a repair shop you'd be charged for the hours of labour. Not to mention that most repair's involve PCB swap.

Okay,

This is where I admit my complete ignorance!

Exactly what are the "big power supply caps"? Where would they be located?

Are the "I/C"s the black rectangular items which have part numbers on them?

I am not sure if this amp uses discrete or power opamps. I think I know what you mean by these.

Thanks again for your help, you're the best I've found so far. At this point it is more of the challenge of finding the failure cause, and perhaps the adventure of a DIY repair. I must add this is a long way from the crystal radio I built as a kid!
 

Tekko

Banned
2005-01-01 3:33 pm
The caps look like two big cans on the board and say something like 4700µF or 10000µF on them.

A transistor look like a small black blob with 3 legs or like the large ones on the heatsink. If the heatsinked items have more than 3 legs, they can be power opamps.

An ic look like a black rectangular box with 8 or more legs.
 

bizwiz41

Member
2010-09-18 1:33 pm
The caps look like two big cans on the board and say something like 4700µF or 10000µF on them.

A transistor look like a small black blob with 3 legs or like the large ones on the heatsink. If the heatsinked items have more than 3 legs, they can be power opamps.

An ic look like a black rectangular box with 8 or more legs.

Thanks,

Though now I really feel dumb, I looked at "caps" again and realized what that meant! Wow, what a 'duh' moment.

I do have another question re: power supply root cause; during some more review, I disconnected the connector to the speaker selector switch, and of course the display went out. But since the power comes from the amplifier board, does this mean the amp is getting power?

Thanks again for your patience and help.
 

bizwiz41

Member
2010-09-18 1:33 pm
Sony STR-K850P; okay, sound but no volume?

As an update, I had this receiver looked at by a service tech.

He replaced some of the relays, and was able to get the audio, but he said it played fine, then just went to distorted sound and no volume. He sumary was that the problem had moved "downcurrent" to the main board. Estimate was about $275.00 for repair.

Obviously I did not go the repair route. I was wondering if there are any suggestions for a potential fix here. The unit does produce sound now, but very minimal and distorted. Increasing volume has no effect. If the volume is turned to 0, it will mute sound.

All other functions now work (i.e. tuner tunes, all inputs do produce this same minimal sound, etc.) Does this sound like the amplifiers may be gone? Any suggestions for a last ditch check?

Thanks again for all the help!
 

bizwiz41

Member
2010-09-18 1:33 pm
As an update, I had this receiver looked at by a service tech.

He replaced some of the relays, and was able to get the audio, but he said it played fine, then just went to distorted sound and no volume. He sumary was that the problem had moved "downcurrent" to the main board. Estimate was about $275.00 for repair.

Obviously I did not go the repair route. I was wondering if there are any suggestions for a potential fix here. The unit does produce sound now, but very minimal and distorted. Increasing volume has no effect. If the volume is turned to 0, it will mute sound.

All other functions now work (i.e. tuner tunes, all inputs do produce this same minimal sound, etc.) Does this sound like the amplifiers may be gone? Any suggestions for a last ditch check?

Thanks again for all the help!

As a further update; I opened up the receiver and dug a bit deeper. The issue I found the most readily was that a relay (RY851) was not closing. Though, manually closing the relay did not change the audio at all. I checked all the other relays and they all closed upon powering. Though, the main board's realy takes 5-6 seconds to close after turning on power, is this strange?

At this point, I'm trying to satisfy my curiousity as to why this receiver failed. Is there a predominant reason a relay would fail (not close)? Is there something else I should try to investigate?

Thanks,
 
sorry to say that ...but with your level of knwoledge arround those things and the procedure you follow you have one chance in a million to find out what is wrong with the amp .....

since vintage audio repairs is what we do for living in my company i can asure you that in 150 amplifiers we repar per year the chances that a relay was broken was 3-4 a year ...and that is vintage equipment we are talking here so relays can be from 10-40 years old ...

Then again this all behaviour reminds me of just a simple crack on any of the pcb ...often traces down under are cracked open but still on the upper leyer you see nothing .... areas where this can happen is next to screws and down under in the belly of the amp ...

still ....with the way you think it will be impossible to trace and fix the fault ..sorry for that no hard feelings ....its just from what i read

kind regards sakis
 

bizwiz41

Member
2010-09-18 1:33 pm
sorry to say that ...but with your level of knwoledge arround those things and the procedure you follow you have one chance in a million to find out what is wrong with the amp .....

since vintage audio repairs is what we do for living in my company i can asure you that in 150 amplifiers we repar per year the chances that a relay was broken was 3-4 a year ...and that is vintage equipment we are talking here so relays can be from 10-40 years old ...

Then again this all behaviour reminds me of just a simple crack on any of the pcb ...often traces down under are cracked open but still on the upper leyer you see nothing .... areas where this can happen is next to screws and down under in the belly of the amp ...

still ....with the way you think it will be impossible to trace and fix the fault ..sorry for that no hard feelings ....its just from what i read

kind regards sakis

Thank You sakis,

No hard feelings here, thanks for the feedback. I admit that my knowledge is very limited, and my experience even less. But, I am a persistent type of guy, and I love a challenge.

I am keen to your suggestion of a cracked board, as I've been thinking this might be the case. If I look at all the symptoms and data, I'm assuming there is a crack or broken solder point somewhere that I cannot see.

You're entirely correct that there is no visible crack on the upper side of the board. I cannot easily get to the underside to view. Perhaps removing the board isworth diving into.

Any sugestions for better troubleshooting would be appreciated.

Thanks,
 
oooops i thought the a minute ago you located the fault in the power supply .... but may be i'm wrong....

troubleshooting is about procedure .....trying to provide you with that will be a post 3pages long and you need to follow it step by step and very precise ....obviously it cannot be done

after verifying that all voltages are present you need to make sure that allis working stage by stage .... starting from the input till the output .... the sequence that all is wired is very importand in stage by stage procedure ...requires expirience and or schematic .... even if i find you a schematic i will have to presume that you are unable to read it ... so how to work from here ???
 

bizwiz41

Member
2010-09-18 1:33 pm
oooops i thought the a minute ago you located the fault in the power supply .... but may be i'm wrong....

troubleshooting is about procedure .....trying to provide you with that will be a post 3pages long and you need to follow it step by step and very precise ....obviously it cannot be done

after verifying that all voltages are present you need to make sure that allis working stage by stage .... starting from the input till the output .... the sequence that all is wired is very importand in stage by stage procedure ...requires expirience and or schematic .... even if i find you a schematic i will have to presume that you are unable to read it ... so how to work from here ???

Hi Sakis,

Thanks, I'm not trying to get you to put me through a complete electronics course here, only looking for the most probable items first.

I have gone through all the checks of input/output etc. (as to functions). I did take this to a shop, where initial power relays were replaced, which then to the receiver from no audio at all, to distorted audio and no volume. It also caused the tuner to function as well.

All the inputs function (limited), all the speaker connections work. The reason I questioned the relays was that on this round of testing, there originally was no sound at all. "Tapping" on a relay (RY851) caused the limited audio to come back on. Opening up the relay and cleaning/aligning contacts caused the receiver to have the limited audio consistently.

The other reason I questioned relays was I noticed a long lag (6 seconds) between powering on, and the relay on the main board "clicking on". As I said, I found the RY851 relay broken inside (plastic guide off of metal post). However, put back together it would still not close. But...in my stupidity, this may be the relay for the A/B speakers. I need to check that out.

I do keep coming back to your idea of the cracked PCB. The receiver "supposedly" fully functioned per the EBay seller. The service tech also stated he had full sound initially after replacing the initial relays. Then, it just stopped and created distored audio with no volume.

So, my next step is to take the board out and examine the underside. I've really nothing to lose on attempting this. I suppose I should also be looking for bad solder joints as well.

So, tapping your experience, am I correct that if the PCB is cracked, the only remedy is to replace the full board?

Thanks again for your patience.

P.S. I can read schematics a bit; I can read mechanical drawings, and I have had some exposure to electronics drawings from career experience.
 
Hi Sakis,

Thanks, I'm not trying to get you to put me through a complete electronics course here, only looking for the most probable items first.

I have gone through all the checks of input/output etc. (as to functions). I did take this to a shop, where initial power relays were replaced,never had to replace many of those ...its like you have a broken engine and you rplace tyres to make it work which then to the receiver from no audio at all, to distorted audio and no volume. It also caused the tuner to function as well.

All the inputs function (limited), all the speaker connections work. The reason I questioned the relays was that on this round of testing, there originally was no sound at all. "Tapping" on a relay (RY851) caused the limited audio to come back on.that can happen in the relay ....seriously tapping on it might caause momentary contacts to close rear but possible for small relays Opening up the relay and cleaning/aligning contacts caused the receiver to have the limited audio consistently.

The other reason I questioned relays was I noticed a long lag (6 seconds) between powering on,THAT IS ABSOLUTELY NORMAL FOR SUCH AN AMPLIFIER and the relay on the main board "clicking on". As I said, I found the RY851 relay broken inside (plastic guide off of metal post). However, put back together it would still not close. But...in my stupidity, this may be the relay for the A/B speakers. I need to check that out.

I do keep coming back to your idea of the cracked PCB. The receiver "supposedly" fully functioned per the EBay seller. The service tech also stated he had full sound initially after replacing the initial relays. that is very hard to belive my friend Then, it just stopped and created distored audio with no volume.fair enough ...and then what ??? your so called "technician" expected the holly spirit to tell him what is wrong ??? what was the next step ..??? to his opinion |??

So, my next step is to take the board out and examine the underside. I've really nothing to lose on attempting this. I suppose I should also be looking for bad solder joints as well.

So, tapping your experience, am I correct that if the PCB is cracked, the only remedy is to replace the full board? no you may as well do some patchwork ....depenting on the loacation of the crack if any ....there are some that are possible to fix and some others not .... obviously depents on the proximity and thickness of traces

Thanks again for your patience.

P.S. I can read schematics a bit; sorry a bit is not enough ....and then to troubleshoot you need to fully understand the sequence of conections so you are going to be able to trace tha fault/conectivity from point a to b and so on I can read mechanical drawings, and I have had some exposure to electronics drawings from career experience.
 

bizwiz41

Member
2010-09-18 1:33 pm
Thanks Sakis,

This does help, and give me some hope.

I'll examine the board, at the least it will be fun to learn. Again, this makes sense as there is a good chance the problem was damage during shipping.

As for the tech's recommendation, it was to replace the entire main board ($300.00 +/-)
 
I'd suggest you might have a bad ground connection somewhere. The amp worked momentarily for the tech because all the movement etc. made the bad connection work for a while, until something warmed up or moved a little... then gone.

A bad ground can also can problems where the audio works for a few seconds to minutes then distorts and fades away. This can happen because a coupling (DC blocking) capacitor loses its ground reference (a resistor to ground) and is charged slowly over time by the input offset current of the following opamp (etc) that it is connected to. Eventually, it charges right up to the rail, so the audio distorts and eventually the opamp can't respond to the signal at all any longer.

The chassis on most Sony amps is not connected to safety earth ground, as they use a 2-prong plug. But the chassis is connected to the floating ground (audio ground) of the transformer secondary. And, often, the input stages get their ground from the chassis only... no other direct connection to ground. So a loose or corroded screw can cause the ground reference to be lost and the above can happen. Try loosening and re-tightening every screw that holds anything to the chassis... PCBs, input jacks, etc. Unplug and re-plug every connector a couple times to remove contact corrosion. I once fixed a Sony receiver by doing only those two things.
 

bizwiz41

Member
2010-09-18 1:33 pm
I'd suggest you might have a bad ground connection somewhere. The amp worked momentarily for the tech because all the movement etc. made the bad connection work for a while, until something warmed up or moved a little... then gone.

A bad ground can also can problems where the audio works for a few seconds to minutes then distorts and fades away. This can happen because a coupling (DC blocking) capacitor loses its ground reference (a resistor to ground) and is charged slowly over time by the input offset current of the following opamp (etc) that it is connected to. Eventually, it charges right up to the rail, so the audio distorts and eventually the opamp can't respond to the signal at all any longer.

The chassis on most Sony amps is not connected to safety earth ground, as they use a 2-prong plug. But the chassis is connected to the floating ground (audio ground) of the transformer secondary. And, often, the input stages get their ground from the chassis only... no other direct connection to ground. So a loose or corroded screw can cause the ground reference to be lost and the above can happen. Try loosening and re-tightening every screw that holds anything to the chassis... PCBs, input jacks, etc. Unplug and re-plug every connector a couple times to remove contact corrosion. I once fixed a Sony receiver by doing only those two things.

Thanks Macboy!

This is something I will definitely look into! I really appreciate the help!