Capacitor spark/pop when volt testing

[adlehman]

Hi y'all,

When completing final voltage checks on my Stereomour II, I got to testing terminal 34 and 35, where the 100uf 450v capacitor is connected. When I attached the red lead to terminal 34, it sparked and popped. After that, the terminal gave me no power reading. All of my measurements leading up to that point were correct.

I believe I had shorted the capacitor, but why/how? The fuse is not blown, btw.

Would the logical next step be to replace the capacitor and see what happens?

I have attached pictures of my build for reference. I am still learning about electronics, so thank you for any help and guidance anyone may have. Appreciate ya!

[kgoss]

Not related to your question but it looks like you are missing one ceramic resistor on one hum pot

[adlehman]

Whoops, I'm on it!

Thank you!

[Paul Birkeland]

I would imagine the 130 Ohm 2W resistor leading to that terminal blew, likely from the hot end of the cap being briefly shorted to electrical ground.  You can measure each of the 130 ohm resistors while they are still soldered into the amp to check them, just be sure the amp is off.

[adlehman]

I'll check that today and report back, thank you, Paul!

[adlehman]

Paul, I think you are right.

That resistor is giving me no reading now.

Is there anything I should keep in mind as I replace that resistor to make sure I don't have the same outcome?

Again, apologies if I am missing something obvious, still new to this!

[Paul Birkeland]

You probably accidentally touched your probe to multiple terminals.  You can just measure pin 2 on each 4 pin socket instead, and they'll be around 350V or so.

[adlehman]

Got it, thank you! Once everything is swapped out and cleaned up I will report back.