QRX-8001 no sound

[KeithD]

That might be entirely normal, I have seen a few amplifiers that do that.
I don't think it is going into protection? - the action of plugging in the headphones is almost certainly 'by design'(?) opening the speaker relay. I just checked the schematic - the action of plugging in the headphones (front or rear) opens a contact that removes power from the speaker relay.

Ahhh... thanks John! I've not seen that before, but now makes sense. That's one worry off my mind.

There are a lot of fuses in that thing, have you checked these? have you checked all the PSU voltages are getting to the right places? If for example, you have lost the +/-46V supplies (2 fuses), or the +/-38V (6 fuses) it will be silent.

I did a visual inspection, but will need to go back and specifically test each one with a DMM. I did check voltages on F-2639 (pre-power supply) and was getting readings, but now can't remember what voltage on what pin, so will go back and document that as well. Will report back what I find.

 

[AE Bob]

I have seen many of the QRX-x001 receivers with no sound at all, due to open feed through connections on the F-2634 four channel selector switch PC board (like on the x0x0DB Dolby boards). It is quite a job to repair. The board needs to be partially removed (after removing the pugged in decoder boards), then the push button switch assembly needs to be removed from the board (to gain access to some of the feedthrough rivets on the top of the board). After gaining access to all the feed through rivets, they all need to be re-soldered on BOTH SIDES of the PC board, with a good thick solder fillet between the board and rivets. It is quite a job, but I have had several that needed this to get the audio back.

 

[KeithD]

I have seen many of the QRX-x001 receivers with no sound at all, due to open feed through connections on the F-2634 four channel selector switch PC board (like on the x0x0DB Dolby boards). It is quite a job to repair. The board needs to be partially removed (after removing the pugged in decoder boards), then the push button switch assembly needs to be removed from the board (to gain access to some of the feedthrough rivets on the top of the board). After gaining access to all the feed through rivets, they all need to be re-soldered on BOTH SIDES of the PC board, with a good thick solder fillet between the board and rivets. It is quite a job, but I have had several that needed this to get the audio back.

Thanks for that insight. I have been testing with the speaker selector switch set to either 2 channel mode, and/or pushing in the 4 channel/CD-4 button. I have not taken a close look at the schematic, but I assume the signal does not go through the quad synthesizer board when in 2 channel mode. Is that correct? I've pulled the quad boards during all of these tests just to make sure something doesn't get damaged. Would like to correct the "no sound" problem before moving on to other parts. Thanks!

 

[Skywatcher]

Anyone have any thoughts?

Yes. Headphones shuts down the speakers. That's normal.
The "adapter" jacks are just like another "tape loop" and used for the Dolby Adapter.
You said you "cleaned all controls", then said "may be a dirty selector"... Well, you need to clean "all" controls. Switches are also controls.
And as @Hyperion mentions, check all the fuses. And check all voltages.
The speaker relay points could be bad, but you should at least still get some "noise" from the speakers.

 

[Skywatcher]

Thanks for that insight. I have been testing with the speaker selector switch set to either 2 channel mode, and/or pushing in the 4 channel/CD-4 button. I have not taken a close look at the schematic, but I assume the signal does not go through the quad synthesizer board when in 2 channel mode. Is that correct? I've pulled the quad boards during all of these tests just to make sure something doesn't get damaged. Would like to correct the "no sound" problem before moving on to other parts. Thanks!

The CD/4 is for the phono "quad" setting. Put it in any other "quad" mode.
Make sure the "meter" button is out or the power meters won't work.

 

[KeithD]

The CD/4 is for the phono "quad" setting. Put it in any other "quad" mode.
Make sure the "meter" button is out or the power meters won't work.

The CD-4/4-CH setting is for what you mention but ALSO for 4 channel discrete input. So anything connected to the AUX or Tape inputs will pass directly through to the respective channels (not go through the quad processing boards).

I don't know what you mean by the "meter" button. What are you referring to?

 

[Skywatcher]

The CD-4/4-CH setting is for what you mention but ALSO for 4 channel discrete input. So anything connected to the AUX or Tape inputs will pass directly through to the respective channels (not go through the quad processing boards).

I don't know what you mean by the "meter" button. What are you referring to?

My bad, I was thinking of the 9001 that has the built-in Dolby. I believe in the 8001, that is the FM Mute button in that position. Are the other relays functioning? There is a reed relay, and another Omron relay that switches signals. The larger Omron usually holds up well, but the reed relay sometimes quits.

 

[KeithD]

Checked all the fuses with the DMM, all good, none open.

After power up I hear two relay clicks. First one is after a couple of seconds, which I assume is the speaker relay, a second one sounds like it is coming from f-2634.

Measured voltage readings on f-2639 pre-power supply board. I've listed them as wire color, pin number, measured VDC:

orange, 04, 39.4
red, 01, 39.4
brown, 02, 23.85
black, 07, 0
on opposite end of board:
red, 05, 49.8

I found a previous thread regarding no sound in a QRX-9001. In that thread @sKiZo posted correct voltage readings for those pins, and it looks like the value for pin 01 should be 24.3 VDC? His board in the 9001 has a wire connected at pin 02 (yellow) that my 8001 doesn't have. Also, don't know if pin 05 voltage is correct. I'm not seeing voltages on the schematic for any of those pins.

 

[Skywatcher]

Checked all the fuses with the DMM, all good, none open.

After power up I hear two relay clicks. First one is after a couple of seconds, which I assume is the speaker relay, a second one sounds like it is coming from f-2634.

Measured voltage readings on f-2639 pre-power supply board. I've listed them as wire color, pin number, measured VDC:

orange, 04, 39.4
red, 01, 39.4
brown, 02, 23.85
black, 07, 0
on opposite end of board:
red, 05, 49.8

I found a previous thread regarding no sound in a QRX-9001. In that thread @sKiZo posted correct voltage readings for those pins, and it looks like the value for pin 01 should be 24.3 VDC? His board in the 9001 has a wire connected at pin 02 (yellow) that my 8001 doesn't have. Also, don't know if pin 05 voltage is correct. I'm not seeing voltages on the schematic for any of those pins.

Pins 01 and 02 are the same. BUT without the 2 quad boards in, the voltage on pin 01 will read high because the circuit is unloaded. Pin 02 feeds the CD4 board and is loaded with that board attached. So ignore the pin 01 reading. they both feed from the same source, but go through the two 180 Ohm sandblock resistors, then to each pin. The pot on this board is what you will adjust to 25v exactly for Pins 01/02 once the quad boards are back in, and on straight AC wall power. But you can adjust it using pin 02 with the quad boards out to around 24v to be "safe", insert the boards, and tweak it to a final 25v after a minute or so for the voltages to stabilize. Pin 04 feeds the EQ board and the F-2626 and looks close enough. Pin 05 looks good coming from the main power board. Pin 07 is ground. The voltages are in the schematic, but it's a pain in the ass to follow them to a different section where they are noted. I printed it out in sections, then taped together a mosaic that made it much easier to follow.
You are hearing the speaker relay, then the Omron MH4 signal relay (RL02). The reed relay is right beside it (RL01) and you'd be hard pressed to hear it, though not impossible.
Go on HiFi Engine and download the sansui_qrx-9001_schematics.pdf. It has the matrix quad board schematics in it which are identical to the 8001, 7001, and 6001. The CD4 is just 8001/9001 though.

 

[Hyperion]

The pot on this board is what you will adjust to 25v exactly for Pins 01/02 once the quad boards are back in, and on straight AC wall power. But you can adjust it using pin 02 with the quad boards out to around 24v to be "safe", insert the boards, and tweak it to a final 25v after a minute or so for the voltages to stabilize.

This is very important, as I understand the IC's on the quad boards are unobtanium, and if they ever 'see' more than 25V it will destroy them.

 

[kevzep]

Hey, just a complete outside thought and one I have had several times on these amps.
Its not the shaft has slid out of the rotary function selector and is not turning and therefore no selecting the input you want?
I had to modify a customers QRX8001 so the shaft wouldn't slide out....It did have me scratching my head for a while the first time it came in for "no sound"....

 

[Skywatcher]

This is very important, as I understand the IC's on the quad boards are unobtanium, and if they ever 'see' more than 25V it will destroy them.

Yes, they are very sensitive to operating voltage. A little above 25v won't outright kill them, but will take it's toll. It needs to be dropped to 25v to prevent damage. 18v is the rock bottom minimum, and 25v is the "optimum" to get the best sound. When I got my "basket case" 9001, the voltage would drift up to a little over 26v. I have no idea if it was run at that, or was because it sat for a number of years and the power supply simply deteriorated from sitting. But it didn't seem hurt the ICs. Of course I completely rebuilt the whole thing before running it any length of time. I do have a couple of spare and rebuilt boards in case Murphy happens to drop by.

 

[KeithD]

Pins 01 and 02 are the same. BUT without the 2 quad boards in, the voltage on pin 01 will read high because the circuit is unloaded. Pin 02 feeds the CD4 board and is loaded with that board attached. So ignore the pin 01 reading. they both feed from the same source, but go through the two 180 Ohm sandblock resistors, then to each pin. The pot on this board is what you will adjust to 25v exactly for Pins 01/02 once the quad boards are back in, and on straight AC wall power. But you can adjust it using pin 02 with the quad boards out to around 24v to be "safe", insert the boards, and tweak it to a final 25v after a minute or so for the voltages to stabilize. Pin 04 feeds the EQ board and the F-2626 and looks close enough. Pin 05 looks good coming from the main power board. Pin 07 is ground. The voltages are in the schematic, but it's a pain in the ass to follow them to a different section where they are noted. I printed it out in sections, then taped together a mosaic that made it much easier to follow.
You are hearing the speaker relay, then the Omron MH4 signal relay (RL02). The reed relay is right beside it (RL01) and you'd be hard pressed to hear it, though not impossible.
Go on HiFi Engine and download the sansui_qrx-9001_schematics.pdf. It has the matrix quad board schematics in it which are identical to the 8001, 7001, and 6001. The CD4 is just 8001/9001 though.

Put the quad boards in, and I was getting 25.3 V on pin 01, so that seems ok, right?

So for next steps, are you saying to use the schematic to check every voltage I can find to see if the readings are correct?

@kevzep Thanks for the suggestion, but I don't think the selector switch is the issue. If I understand it right the AUX, Adapter, and tape switches override the selector switch, and I'm getting no sound regardless of input. I did check the signal to the driver boards from the pre-amp and I was getting sound at that point. I did find the 180 Ω and 150 Ω fuse resistors measured open, so replacing them should have helped. Is it unlikely the driver board has a fault now that I've done the basic replacements? After the drivers, looks like it's the PS and protection boards for the signal path. Is there a way to check if the signal is making it through the driver board? I'm getting no sound at all, not even static or clicks/pops when turning any knobs, so the signal seems to be going dead at some point in the path.

 

[Skywatcher]

Put the quad boards in, and I was getting 25.3 V on pin 01, so that seems ok, right?

So for next steps, are you saying to use the schematic to check every voltage I can find to see if the readings are correct?

@kevzep Thanks for the suggestion, but I don't think the selector switch is the issue. If I understand it right the AUX, Adapter, and tape switches override the selector switch, and I'm getting no sound regardless of input. I did check the signal to the driver boards from the pre-amp and I was getting sound at that point. I did find the 180 Ω and 150 Ω fuse resistors measured open, so replacing them should have helped. Is it unlikely the driver board has a fault now that I've done the basic replacements? After the drivers, looks like it's the PS and protection boards for the signal path. Is there a way to check if the signal is making it through the driver board? I'm getting no sound at all, not even static or clicks/pops when turning any knobs, so the signal seems to be going dead at some point in the path.

That's the only really critical voltage to worry about as far as being spot-on. Myself I would hit the 25v right on the nose. It's not regulated voltage so any AC voltage fluctuations would change it some.
You really need to change all fusible resistors no matter what they measure "cold" if you haven't already. They heat up and change under load. However since the speaker relay kicks in, that isn't the source of "no sound". At least not from a DC Offset perspective.
You also need to have the driver board input connectors connected. They provide the ground to the input circuit of the board. It's the same for all F-2624 boards.
You're missing signal from somewhere. You gotta find where the "missing link" is. You gotta check for the main voltage to the F-2624 boards and that comes from the fuses, plus solder joints through the plug sockets. If you have sound to the driver inputs, but not outputs, then the missing link is between there.

 

[KeithD]

That's the only really critical voltage to worry about as far as being spot-on. Myself I would hit the 25v right on the nose. It's not regulated voltage so any AC voltage fluctuations would change it some.
You really need to change all fusible resistors no matter what they measure "cold" if you haven't already. They heat up and change under load. However since the speaker relay kicks in, that isn't the source of "no sound". At least not from a DC Offset perspective.
You also need to have the driver board input connectors connected. They provide the ground to the input circuit of the board. It's the same for all F-2624 boards.
You're missing signal from somewhere. You gotta find where the "missing link" is. You gotta check for the main voltage to the F-2624 boards and that comes from the fuses, plus solder joints through the plug sockets. If you have sound to the driver inputs, but not outputs, then the missing link is between there.

Yes, I've completely re-done one driver board: all fusible resistors replaced with 1/2 W metal film, all e-caps replaced with Nichicon UPW (KMET film in for the two 0.47 µF caps C01,02), two 1N4148 in series for VD1212.

I'm putting the reconditioned driver board in the Front position. I assume I don't need to have the Rear driver board for testing. If I do, I'll have to restore that board as well. Just testing for sound out of the two front channels, anything, really.

Always have the 4 pin input connector in place on the driver board (can't expect any sound without that!)

I agree, logic says there is a loss of signal somewhere between the pre-amp and the output. Also agree I am not getting bad DC output at the protection relay, but I might be getting zero signal, so that would be no surprise.

Will check voltages to the driver board. Will also try the restored driver board in the Rear position, haven't done that yet. Loss of power to the drivers makes more sense than all four channels individually having a fault, unless there is something else common to them.

Thanks! The odyssey continues!

 

[Skywatcher]

Yes, I've completely re-done one driver board: all fusible resistors replaced with 1/2 W metal film, all e-caps replaced with Nichicon UPW (KMET film in for the two 0.47 µF caps C01,02), two 1N4148 in series for VD1212.

I'm putting the reconditioned driver board in the Front position. I assume I don't need to have the Rear driver board for testing. If I do, I'll have to restore that board as well. Just testing for sound out of the two front channels, anything, really.

Always have the 4 pin input connector in place on the driver board (can't expect any sound without that!)

I agree, logic says there is a loss of signal somewhere between the pre-amp and the output. Also agree I am not getting bad DC output at the protection relay, but I might be getting zero signal, so that would be no surprise.

Will check voltages to the driver board. Will also try the restored driver board in the Rear position, haven't done that yet. Loss of power to the drivers makes more sense than all four channels individually having a fault, unless there is something else common to them.

Thanks! The odyssey continues!

Yes, put both driver boards in. Set BIAS (about half on DBT) and DC Offset on both when both are in, it's necessary, and go from there.

 

[KeithD]

Yes, put both driver boards in. Set BIAS (about half on DBT) and DC Offset on both when both are in, it's necessary, and go from there.

OK, to do that I will need to restore the other driver board first. I assumed I could put the selector to 2-channel mode and just test for sound on the Front speaker outputs. Does that not work?

Not sure how I will set DC offset when I have no signal at the outputs?

 

[Skywatcher]

OK, to do that I will need to restore the other driver board first. I assumed I could put the selector to 2-channel mode and just test for sound on the Front speaker outputs. Does that not work?

Not sure how I will set DC offset when I have no signal at the outputs?

You might find that you will. Just try to set the 2nd board's pots about the same as the 1st board. That way you should be in the ballpark, and the relay should click. Yes, 2 channel mode, but not X2.

 

[kevzep]

Put the quad boards in, and I was getting 25.3 V on pin 01, so that seems ok, right?

So for next steps, are you saying to use the schematic to check every voltage I can find to see if the readings are correct?

@kevzep Thanks for the suggestion, but I don't think the selector switch is the issue. If I understand it right the AUX, Adapter, and tape switches override the selector switch, and I'm getting no sound regardless of input. I did check the signal to the driver boards from the pre-amp and I was getting sound at that point. I did find the 180 Ω and 150 Ω fuse resistors measured open, so replacing them should have helped. Is it unlikely the driver board has a fault now that I've done the basic replacements? After the drivers, looks like it's the PS and protection boards for the signal path. Is there a way to check if the signal is making it through the driver board? I'm getting no sound at all, not even static or clicks/pops when turning any knobs, so the signal seems to be going dead at some point in the path.

I know you are more onto it than that, but I tell you, I was confused for a bit when this happened to the 8001 I was working on.

Can you scope the input of the driver board? Have you done that yet? Then you can follow the signal through each stage until it stops.

I have been following along, and its a real head scratcher this fault, but i am sure you'll get to the bottom of it.

 

[Hyperion]

Not sure how I will set DC offset when I have no signal at the outputs?

I am sure this is just a typo or something, but you don't need or want a signal to set DC offset.