No sound after some minutes - HV Voltage Issues

[ambd1]

Hi all,

I recently completed the Moreplay Upgrade Kit. I´m hoping you can help me figure out what's going on.

After completing the upgrade PCB installation I performed all the voltage tests from the manual and everything passed. I then finished the Claymore board installation and powered it on. On the first power on, I had sound on one channel only. I moved the RCA cables around and briefly got sound on both channels for about 3-4 minutes, then both channels went completely silent and haven't come back since. The tubes are still glowing normally.

This is what I could verify.

• All signal path wiring continuity checks: passed
• Component orientations (Q2A/B/C, ZD1-ZD4): visually verified correct
• LM1085 and MJE5731A position are correct
• White wire continuity from 16U to Plate B and 6U to Plate C: confirmed
• D1A and D2A: lit
• D1B and D2B: not lit

Voltage measurements

• A2 to A7: 6.28V
• B2 to B7: 6.25V
• Terminal 21: 303V
• Terminal 23: 0V
• +HV on PCB: 303V
• -HV on PCB: 0V
• B+ Reg TP: 3V (expected 175-180V)
• Terminal 6U: -0.5V (expected 120-140V)
• Terminal 16U: -0.5V (expected 120-140V)
• Plate B on PCB: spikes to 30V for ~2 seconds then collapses to 1.66V
• Plate C on PCB: spikes to 30V for ~2 seconds then collapses to 1.35V
• 2.2uf capacitor in the PCB: spikes to 30V for ~2 seconds then collapses to 3V
• Note: when preamp is powered off, voltages slowly rise back up to 14-20V then gradually discharge

I think that the HV is arriving correctly at the board but something in the shunt regulator section is not working. I've done my best to check everything I can think of. I could remove the PCB board and verify the

Could this be a failed Q2A (MJE5731A)? Or is there something else I should be looking at?

Thank you!

Alan B

 

[Paul Birkeland]

Can you post some build photos?

A Q2A failure will only happen from some other issue that caused it to fail in the first place, so even if you find an open transistor there (they almost always fail shorted, which isn't what you have), then you'd have to keep digging to figure out what caused that problem in the first place.

I'd be more inclined to think that there's something like a marginal solder joint at work.

 

[ambd1]

Can you post some build photos?

A Q2A failure will only happen from some other issue that caused it to fail in the first place, so even if you find an open transistor there (they almost always fail shorted, which isn't what you have), then you'd have to keep digging to figure out what caused that problem in the first place.

I'd be more inclined to think that there's something like a marginal solder joint at work.

Thanks for your help, Paul.

I did reflow just now (before the photos) all that is listed below:

• HV- and HV+ pad on PCB
• Ground pad on PCB
• Plate B pad on PCB
• Plate C pad on PCB
• AC input pads (+AC-) on PCB
• ZD1, ZD2, ZD3, ZD4 — both legs each
• R2A — both legs
• T6 chassis terminal
• T16 chassis terminal

After reflowing, B+ Reg TP remained unchanged at ~3V.