Crack Voltage Problems [SOLVED]

[Ramblin_Reck]

Hey everyone. I just finished building my Crack and everything seemed to go pretty well until I got to the voltage checkpoint. Most of my voltages were well within the allowable range, however, there were 5 voltages that were well above what they should have been. The voltages were:

    Terminal                         Manual Value                   Actual Value
               

          1                                    75-90                               155
          7                                      100                                153
         A6                                      90                                 155
         B1                                      90                                 155
         B3                                     100                                154

Also, the LED at A8 does not light. I measured the voltage at this terminal and it was around 15 V, much higher than the voltage being seen by the other LED located at A3 (~1.5 V if I remember correctly) so I'm guessing that thing is pretty much toast at this point. Honestly, I don't know a great deal about the circuit but, after looking at it for a bit, I can see how A6, 1, and B1 are all the same. I can also see how B3 and 7 should be the same voltage. I'm not sure, however, whether or not those two sets of terminals relate in any way but I'm kind of assuming all of these terminals deal with the same channel (feel free to correct me if I'm wrong). What I can't figure out is what exactly is happening here or where the best place to look next may be. I would really appreciate any help.

Thanks

[Doc B.]

Those voltages indicate that that half of the tube is not conducting. Start by checking to see if the LED is in backwards.

[Paul Birkeland]

15V at A8 would have me looking really hard for a loose ground wire in the Crack, especially the jumper from the upper to lower deck of the volume pot, and the terminal on the headphone jack that accepts multiple black wires.

Other than that, do both halves of the 12AU7 glow?  If the red wire that connects to A4 and A5 isn't well connected to both, then only half the tube would conduct.

-PB

[Ramblin_Reck]

I really hope this doesn't post 3 separate times but I think I'm having a bit of trouble with the pictures I'm trying to attach actually uploading so I'm going to try without them. If they do end up posting, I'm very sorry.

Anyway, thank you both for your replies. Per your suggestions, I rechecked the orientation of the LED (band toward ground) and made sure once again that both halves of each tube were indeed glowing and found that everything there looked okay. I also looked pretty extensively for any loose ground wires and even tried reflowing a few of them, most notably at the volume pot and headphone jack, and made sure that both A4 and A5 were well connected. Everything here also seems to look fine, yet the problem persists.

[Doc B.]

Have you tried removing the 12AU7 and plugging it back in? A dirty tube pin might create the readings you are seeing.

[Ramblin_Reck]

Yes, the tube has actually been inserted and removed multiple times throughout the process of checking resistances, voltages, and attempting to reflow solder joints. I also make sure that it is fully inserted every time I plug it in. Is there any other method I could use to ensure the pins are clean?

[Paul Birkeland]

Can you carefully measure the voltage at A7?

[Ramblin_Reck]

I'm getting a reading of 0V at A7.

[Paul Birkeland]

Yeah, you probably have a cooked/broken LED then. 

This is actually easier to remedy than replacing the LED, just run a jumper between A3 and A8.  If your T5 pops down where it should be, you can leave the amp like that without harm.

-PB

[Ramblin_Reck]

Okay, I'll see if I can get that done later tonight. I'll post a reply here later on whether or not it solves things. Thanks for the help!

EDIT: I have now soldered the jumper between A8 and A3 and all voltages seem to be within their allowable range. I originally read jumper between A8 and socket ground and noticed a few voltages were below what they should be before noticing that I had been dumb and the circuit needed to pass through that final resistance of the LED for them to be correct so I promptly fixed that and it all seems okay. Thank you both for helping me troubleshoot everything.