Eden wt 800 no sound 'R amp/out low'

[pontiacpete]

This amp works on the 'L amp/out high' side, but there is no sound on the other side 'R amp/out low'.
There's no DC on the R out and there appears to be no shorted transistors. All resistors are measuring the same as the good side. The only sign of heat is one resistor R78 on the the front or pre amp board. This resistor is the only one that has taken too much heat. It looked to me to be a 1k 1/4 watt carbon film resistor that was still measuring 1K. I changed it out with a new one. Although the schematic says it's a different value, I put in a 1K. I'm not convinced the schematic I attached is exactly what Im working on here. But changing that resistor did nothing anyway. Does anyone know of a better schematic?
I swapped out U9 which did nothing. U10 is, I think, labeled LU1 and RU1. I attached a photo of the area showing LU1 and R78. As you can see there are a lot of components listed with right and left designations.
There's nothing like that on my posted schematic.
Also, when depressing the 'bridged mono in/on' button, it has no sound out of either side. I'm hoping there is some kind of switching problem. I'm not sure how to proceed from here.
Oh, voltages... There's 80v +/- going to both modules, and for low voltage there's 14v on the L side but 11v on the R side. I wonder why this is happening.
Can anyone help me with this, I'm stumped?

[Jon Snell]

Have you measured the mute voltage on each side and have you signal on the 2.7k resistors feeding the amplifier inputs.

[pontiacpete]

I can find Q1 and Q2 both j112s. There are a couple of 2.7ks that don't seem to be connected to the Fets. But when I measure voltages
on the FETs there's about 11v on the gates. Here's a picture of the area and Q1 and 2

[Jon Snell]

The FETS are on until switched off with the voltages shown on my sawn off schematic. There must be less than zero to allow signal to pass.
Insert a signal into the amplifier, have you any signal on the FETS or differential pairs?

[g1]

Check if this is a better schematic match for your unit.

[pontiacpete]

Thanks G1 your schematic is looking a lot closer to this amp.

Also, There's a signal on R4 where it is connected to Q1.

[nevetslab]

Thanks G1 your schematic is looking a lot closer to this amp.

Also, There's a signal on R4 where it is connected to Q1.

Looking thru my Eden WT800 folder, I don't see the two thermal switches that are on the bottom side of the amp modules' heat sinks (can't be seen without removing the amp modules). One is in series with the output of the amp module, OOR, if memory serves, but not shown on the schematic. I can't recall if the other one is in series with the the AC mains. I don't have an amp here to look at, and all of my photos haven't detailed these.

OH, I remember. The other thermal switch puts the fan into HIGH SPEED MODE, so either module will allow high speed, probably switches in around 55 deg C, maybe less. If the Right Ch module has a bad series-connected thermal switch, there won't be continuity between the output buss on the PCB and Pin 5 on the connector. If it's open, could be the fast-on connector isn't connected to the thermal switch blades anymore. Or, bad crimp?

As for the difference in the low voltage you're calling out....14V on the left module and 11V on the right module. The chassis wiring schematics I have shows the unmute voltage coming from the Preamp Board, and splits to each power amp module by way of a 10k resistor, but, from the Left Unmute feed, there is a 1k resistor to ground, which would seriously alter the balance. So, there appears to be errors on the schematics I have, just to add fuel to the fire.

The unmute voltage comes in on Pin 2 of both power amp harness connectors. I assume this is where you're getting your readings. Still, different on each module or not, it's enough to unmute the FETS's and allow signal to pass to the double differential amp front end of both amp modules.

Assuming you ARE getting signal on both the LEFT and RIGHT amp modules' on the bases of Q3 and Q4, are you getting output signal at the output buss on the PCB, where all emitter resistors are feeding that buss? This is before the output inductor and before the series-connected thermal switch below the PCB.

Another thought, which has shown up in my shop, has been an intermittent Bi-Amp Switch on the front panel. Normal mode is with the button released. I've found that switch pushed in, putting the amp in Bi-Amp mode, and don't get LF on the Left, and only LF on the Right Output. if this switch is involved, it will affect the signal you get on both modules at the output buss, ahead of the harness connector output pin 5.

[pontiacpete]

There’s signal on the base of both Q3 and 4.
No signal on R18 either end of the 39k

[Jon Snell]

You should have lots of +ve DC on Q7 Emitter and lots of -ve DC on Q8 emitter. Almost rail to rail less a volt.

[pontiacpete]

Yes -82v on Q8 and 80v on Q7

[Jon Snell]

If you have signal on Q3 & Q4, there should be signal on the base of both Q7 & Q8, transferring to Q10 & Q11 then to Q12/17 respectively on their emitters.
How far does the signal get?
Check R24 & R25 for slight heat showing they are passing current.

[pontiacpete]

Can I disconnect the other module while work on this? I shorted the differential pair, maybe both of them, trying to compare my signal with the one that's not working.. unbelievable
Anyway I'd like to keep working of this if possible.

[nevetslab]

Can I disconnect the other module while work on this? I shorted the differential pair, maybe both of them, trying to compare my signal with the one that's not working.. unbelievable
Anyway I'd like to keep working of this if possible.

Sure. Just unplug the 6-pin harness connector of the other module. You might want to first discharge the power supply caps before struggling with the connector. You can leave the module mounted.

[pontiacpete]

Ok thanks nevetslab.
So, the signal seems to stop at the bases of Q3 and 4. I’m not seeing anything on the bases of Q7and 8

[Jon Snell]

If there is signal on the bases of Q3 & Q4 check there is signal on the emitters, (should be the same), R10 should have about 78volts DC across it and there should be signal on the collectors.