Incorrect DC voltage readings on small PC board during Speedball build[resolved]

[mightygrey]

Hi guys, been loving my stock Crack so much I ordered the Speedball kit - just installed the small PC board, and plugged-in for the first round of voltage checks. All four LEDs are lighting-up fine, as are the 6080 / 12AU7 tubes.

My voltage readings are as follows:

OA:      -24 (should be 60-90v)
IA:        48 (should be 170-270v)
B-A/B:  -81 (should be 0v)
IB:        48 (should be 170-270v)
OB:      -24 (should be 60-90v)

These are all far lower, and in some cases negative - can't seem to find any pre-existing threads on the board? I'm in Australia = 240v.

 

[Doc B]

The measurements look like the ground is probably not at 0 volts. It seems odd that everything lights up with those voltages. I'd guess that there is either a miswire somewhere, a disconnected ground somewhere, or you have perhaps been testing with the black test lead connected to a terminal that is not grounded.

 

[Paul Birkeland]

I agree with the grounding issue, and voltages like these would have me looking at the solder joint where the black wires meet at the headphone jack.  If one is loose, you'll have exactly these issues.

-PB

 

[mightygrey]

Thanks Doc and Paul.

I'll take a look at all my black-wire connections and give them all a thorough re-looking at. Is there a chance this may have already been a problem with my stock-build? It's been working fine (well, mighty fine!) thus far, but could there have been a grounding-fault, but still allowed a signal/music to work?

Cheers,

Matty

 

[Doc B]

The only way to know if that problem existed with the original build is if you had taken similar measurements. Best plan now is to reheat the terminal that PB suggests, and remeasure.

 

[Paul Birkeland]

If I'm remembering correctly, your original build toasted the power transformer and had some other issues.  Your current problem is potentially related to existing gremlins.

 

[mightygrey]

Yes that's me alright! I've gone ahead and removed the resistors on the stock build so can't easily test it, but it seemed to be working ok. Will give it another whirl tonight and report back. Cheers guys.

Matty

 

[mightygrey]

If I'm remembering correctly, your original build toasted the power transformer and had some other issues.  Your current problem is potentially related to existing gremlins.

Update: I'm sitting on the couch with HD650's on my head; a pint of Samuel Smith's Taddy Porter in-hand; Smashing Pumpkin's "Siamese Dream" playing; and a grin from ear to ear!

I must level with you guys - I realised to myself that I'd had the black lead of the multimeter clipped to "terminal" 12 on the transformer - not the real "terminal 12", hence my crazy readings. I can only laugh about it now, but I disconnected the board, and basically re-soldered my entire base Crack (probably for the best). Realised after going through the original build manual that "hey...there's another 12 on here" - lo and behold my readings were spot-on, completed the build with flying colours, and voila.

Thanks again for being so responsive and helpful guys - can't tell you how much the personal touch has really added to the experience. Very chuffed with myself right now, and psyching myself up to take-on a pre-amp next.

Cheers, and thanks guys.

Matty