Traynor YGM-4 No Output

[Sleet]

An idled project has now gotten my attention. I have a Traynor YGM-4 which stopped working sometime ago. Here are the symptoms and some of my attempts to troubleshoot.

Problem: No output. No sound to the speakers or when hooked up to an external speaker.

Visual observations: Amp appears to power up with all tubes glowing. No obvious burnt or loose components. I did try "chop-sticking" while powered up with no obvious findings.

I've attached a PDF file with the Voltage readings from the tube pins:

I am able to inject a signal and do some tracing with my scope, but I thought I would start with the obvious possibilities.

Thanks.

[g1]

Are you sure you have the correct schematic revision for your amp? You are missing most of the supply voltage for the power tubes and PI tube, but for that version of schematic, I don't see how that could happen yet still have proper voltages at other preamp tubes.
Any sign of any mods?

Post some pics of the insides if you can.

[nosaj]

See if there is one on the lid of the amp.
nosaj

[g1]

Some of the other voltages are a bit wonky as well. Suggest checking meter battery and redo those voltages making sure to really dig in with the probes.

[Sleet]

Here are some pictures. The schematic I posted came from the inside of lid so it should be accurate. I've seen other schematics that don't quite match up show more in the way of voltages. My meter battery just recently died, sot there is a fresh battery in there. I agree that some of the numbers look weird.

[Enzo]

OK, so you have good B+ on the power tube plates and WAAAYY low on the screens. Is R40 OK? You are dropping 400v across it instead of 10v.. Schematic says 470 OHMS, any chance it has a 470k resistor there or something?

[Sleet]

Enzo,
I went and measured R40 and it read 465 ohms. You can see it one of the pictures I previously posted.

[Helmholtz]

Do you really have only 45V at the EL84 plates (pins 7)?
What is the B+ at the OT CT?

Also EL84 cathodes (pins 3) should be at 0V according to schematic.
With cathodes at 38V and grids at 0V it looks like cathode bias, i.e.wrong schematic.

[Sleet]

I went back and measured pin 7 on both output tubes and found 460V and for the red wire (center tap) also 460V. My mistake.

[Helmholtz]

I went back and measured pin 7 on both output tubes and found 460V and for the red wire (center tap) also 460V. My mistake.

Now that makes much more sense (though voltages are way too high for EL84s).

Can you see a cathode (power) resistor and bypass ecap connected to EL84 cathodes (pin 3)?

[Sleet]

No cap or resistor. On my amp Pin 3 from each power tube is connected by a jumper. However It's shown on the schematic but it also shows the jumper connected to ground.

[g1]

You need to recheck all the voltages on your voltage chart. At least all the plate and cathode voltages.

[Sleet]

I've been a bit confused (ahem) with the schematic and the tube locations on the chassis. My voltage measurement chart needs to be reworked again to reflect proper designations for the preamp tube pinouts.

[Helmholtz]

No cap or resistor. On my amp Pin 3 from each power tube is connected by a jumper. However It's shown on the schematic but it also shows the jumper connected to ground.

Ok, but then you can't have 38VDC there.

Also your negative grid bias (pins 2) is missing.
You should not insert power tubes until the biasing is verified.

[Sleet]

I remeasured all of the voltages of the tube pins. My first several attempts were done in error not having recorded the readings for the proper tube location designations. With the help of the tube layout chart I believe I have it correct now. I have uploaded the latest readings and where the locations of the tubes are in the chassis. I also noted what appears to be an open disk capacitor on the chassis picture.