Failed Final Voltage Check
- Thread starter Dhouse7516
- Start date
Dhouse7516
New member
Excellent. Thanks, and will do.
Dhouse7516
New member
So this is strange. I tested the new resistor before installing and it passed at 2.49k ohms. After I installed and soldered it to the board, the resistance check at the leads (on both sides of the board) is failing. I’m getting readings of 10-11 ohms (not K ohms). When I test the R3 on the A side at the leads I am getting 2.49k ohms. Does this suggest any obvious issues to you?
Dhouse7516
New member
The most obvious issue to me is that I might suck at soldering PCB boards.
That would most likely be a shorted 431 regulator.
Dhouse7516
New member
Okay, thanks. Does that mean I should replace the regulator, or could it be a soldering issue?
I would plan on replacing the regulator.
Dhouse7516
New member
Okay, thanks Paul.
Dhouse7516
New member
And, you are correct. I tested and it’s shorted.
Dhouse7516
New member
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
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 said:
Dhouse7516
New member
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
New member
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
New member
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
Moderator
If Rc blew up, then Cc must have been shorted.
Dhouse7516
New member
Thanks! Excellent call. CC is definitely shorted.
Dhouse7516
New member
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?
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
New member
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
New member
Sorry, my mistake. The 220ohm I have is half watt. The 1 watt was 220k.
