Shunt Regulator A side C4S A end problem

[YUL400]

Hello,
I've just performed Final Voltage Check on the Eros Tape Preamp and Shunt Regulator A side, C4S A end, doesn't light up. OA pad Voltage is 220 volts instead of 170 volts. LEDS are checked. Any idea ?
Thanks.

[Paul Joppa]

Does the same voltage appear at the tube socket to which it is connected? If not, check the solder joints. If so, post the rest of the voltages.

[YUL400]

Exactly the same voltage. OA excepted voltages of Shunt Regulator A side C4S are all OK.

[Paul Joppa]

The problem is probably not in the voltage regulator board, so we need the rest of the voltages. You can start with the 6922 socket voltages if you like, that has a good chance of leading towards the problem.

[YUL400]

Hello,

6922 voltages at C1=220V, C2=100V, C3=103V, C4=7.7V, C5=0, C6=163V, C7=100V, C8=100V, C9=0

Thanks

[YUL400]

Do you want more readings ?

[Paul Joppa]

Do both LEDs on that side fail to light? If so, there is probably a bad solder connection or a reversed LED. You can get more information by measuring the voltage on the LED terminals, but I'd suggest checking visually and re-flowing the LED joints even if they look good. You're going to need magnifier and a strong light!

[YUL400]

I've resoldered both Leds on A end. After I've found one of them melted. They are very fragile components. I've ordered some from Digi-key. Will see with new Leds. I'll keep you updated.

Thanks.

[YUL400]

Problem solved. New diode installed. Many thanks to you Digi-Key Corporation www.digikey.ca for your incredibly fast and professional service. The kind of service excellence that is only found in the aeronautical and / or medical sector. Thumbs up. Thanks to you too Mr Joppa for your help. It's now time for the first try.

[Paul Joppa]

"Problem solved" - my favorite two words!

Congratulations, that one was a little tricky. Glad it's working now.  :^)