Failed Final Voltage Check

[Dhouse7516]

Okay, thanks. Does that mean I should replace the regulator, or could it be a soldering issue?

[Paul Birkeland]

I would plan on replacing the regulator.

[Dhouse7516]

Okay, thanks Paul.

[Dhouse7516]

And, you are correct. I tested and it’s shorted.

[Dhouse7516]

Okay, so I replaced the LM431 and the blown R3, and I'm still failing the shunt test. OB and Kreg B are now back in range, but everything else is high. Any thoughts?

IA: 290
IB: 289
OA: 281
OB: 220
KregA: 6.38
KregB: 3.49

[Paul Birkeland]

everything else is high

IA: 290
IB: 289
OA: 281
OB: 220
KregA: 6.38
KregB: 3.49

The B side of the board is working properly.  The A side likely has a broken wire or poor solder joint that isn't allowing the regulator to function properly.  The pairing of 281V on the 12AU7 plate and 6.38V on the cathode indicates that the current source half on the A side (Q1/Q2, R1, R2, and the LEDs) is working properly, but the 431 regulator half of the board isn't functioning.  Is the Breg to +reg jumper installed?

[Dhouse7516]

This is very helpful, Paul. Thanks. I will go back and look at all of the joints and connections on the 431 half and report back.

[Dhouse7516]

Christ, the RC resistor on the A side just caught fire as I was doing a voltage check. I guess it's time to admit that I am out of my depth and send this in. I will reach out to queen tomorrow to request a repair package.

[Dhouse7516]

Paul, being a glutton for punishment, I am thinking that I might make one more run at this before sending it in. I looked through my spare resistors and I have both 220 ohm 1 watt and 220 ohm 1/2 watt. Which is more appropriate for the RC position on the C4S board? Thanks.

[Paul Joppa]

If Rc blew up, then Cc must have been shorted.

[Dhouse7516]

Thanks! Excellent call. CC is definitely shorted.

[Dhouse7516]

I am assuming that the shorted capacitor is a symptom of the larger issue of excessive voltage on the A side of the board, rather than the cause of the issue. Do you agree?

[Paul Birkeland]

The cap is a 400V rated cap and the Eros doesn't make 400V anywhere in the circuit.  I would expect that cap to still last a few thousand hours at 600V, so excessive voltage seems very unlikely to be an issue.

[Dhouse7516]

Okay, thanks. That makes sense. I will replace it and the RC resistor (assuming a 1 watt 220ohm is in spec?) and see where I’m at.

[Dhouse7516]

Sorry, my mistake. The 220ohm I have is half watt. The 1 watt was 220k.