Resistance Issues [solved]

[onelivewire]

After installing some Dayton film caps in my crack's output, I thought I may as well replace the stock pot with a PEC pot. After a week with the Dayton's sounding amazing, I went to change out the pot. After the install my headphones shocked me on plugin. After turning off, I flipped it over and noticed that a speedball washer had come loose. I put it back into place, but wondered if it had shorted anything, as my PEC pot tested exactly as my stock pot, and swapping between the new and old pot made no change. I've resoldered just about every joint on here, in an effort to get a proper ground path (http://bottlehead.com/smf/index.php?topic=4812.0), to no avail. I should note that my fuse is intact and basically gets a 0 ohm reading.

Here are my resistance readings with the black test lead on both the chassis and on terminal 12. I've only listed the ones which appeard out-of-spec.

Black Test Lead on Chassis
3: 0 ohms
6: -3 Mohms
7: -1.7 Mohms and dropping
9: 0 ohms
10: -3 Mohms
12: -3 Mohms
13: -3 Mohms
14: -3 Mohms
20: -3 Mohms
22: 0

RCA Center Pin
Right: -2.9 Mohms
L: ok

————

Black Test Lead on Terminal 12
3: 7.3 Mohms
6: 0 ohms
7: 3.9 Mohms
8: 5.5 Mohms
9: 5.6 Mohms
10: 0 ohms
13: 14Mohm and dropping
22: 18.7 Mohm and going up

RCA Ground Lug: 19 Mohm and going up
RCA Center Pin
Right: ok
Left: 19.8 Mohm and going up

————

I'm not sure what to make of these readings, and any help would really be much appreciated!! It's been a few weeks since I was able to get around to sitting down and testing all these, and I've been missing my Crack so much!

[Paul Birkeland]

After the install my headphones shocked me on plugin. After turning off, I flipped it over and noticed that a speedball washer had come loose.

Which washer came loose?

How did your headphones shock you? 

The resistance readings at terminals 6 and 10 are the important ones for bleeding the charge off those 100uF Daytons.  The resistance reading at terminal 10 tells us that you might have a 2.49K resistor on the headphone jack that's loose or not soldered well on one end.

[onelivewire]

The washer on speedball board A came loose, I believe I had removed it to rerun wire from the bottom lug on the headphone jack (bottom lug when upside down, so the one closest to the chassis) to the top left lug of the PEC pot, as the previous wire did not make the run.
When I was testing the amp out after changing the pot, I was using a cheap pair of headphones I had lying around, and grabbed a 1/4" to 1/8" adapter. It was holding this that shocked me.

After resoldering the points on the headphone jack which you had mentioned, these are my readings.

Black Test Lead on Chassis
6: 2 Mohms
7: no readings
9: 0 ohms
10: 1.9 Mohms
12: 1.9 Mohms
13: 1.9 Mohms
14: 2 Mohms
20: 2.1 Mohms

RCA Center Pin
Right: 2.3 Mohms
L: ok

————

Black Test Lead on Terminal 12
3: -1.4 Mohms
6: 0 ohms
7: 25.3 Mohms
8: 11.7 Mohms
9: 12 Mohms
10: 0 ohms
13: 300 kohm and dropping
22: 12 Mohm and going up

RCA Ground Lug: 12 Mohm and going up
RCA Center Pin
Right: ok
Left: 13 Mohm and going up

Thanks so much for the help!

[Paul Birkeland]

Black Test Lead on Chassis
6: 2 Mohms
Black Test Lead on Terminal 12
6: 0 ohms

This would suggest a ground interruption in the circuit, or terminal 3 isn't touching the chassis.

I'm guessing that you have performed the shorting mod stickied on this forum?

-PB

[onelivewire]

Alright, I think I have the ground path fixed with some soldering. My reading between 12 and the chassis is now 0 ohms. I do have the mod installed to keep startup voltage down.

Here are my readings now, they appear consistent regardless of whether the chassis is used as grounding or terminal 12. I feel like maybe the resistors on the headphone jack are not working, they don’t seem to be providing any resistance across them.

6: 0 ohms
7: No reading
9: 50 ohm
10: 0 ohm
13: 270k and droppiung
B3: no readings
B6: 61 ohm

[onelivewire]

I removed the startup voltage mod and tested the headphone jack resistors as just fine. No issues with their resistance. My readings are now (those now reading properly bolded)

6: 2490 ohm
7: 3 Mohm
9: 19 ohm
10: 2485 ohm
13: .8 Mohm and dropping
B3: 3 Mohm and rising
B6: 19 ohm

[Paul Birkeland]

It looks like you're good to go. 

-PB

[onelivewire]

Really? I just want to double check that my readings for 7, 9, 13, B3 and B6 are alright. Should B3 and B6 not be similar? 7 and 9?

[Paul Birkeland]

Is 9 really 19/50 Ohms?  Your meter will have a tough time reading that terminal with the Speedball installed, which is part of why we don't provide a resistance check in that manual.

-PB

[onelivewire]

Rereading from terminal 12 to terminal 9 this morning, I got a value of 126.5 ohms, without touching anything other than the terminals. Terminal 7 is still giving me 3 Mohm resistances.

[Paul Birkeland]

Was the washer that came loose on the transistor/heatsink junction?

If so, check it against the manual, as I believe the tip 50 is making metal to metal contact with the heatsink.

[onelivewire]

Aha! It appears the plastic inserts that keep the screws from touching the transistors were put in facing the wrong direction. After fixing this, my readings are:

6: 2490 ohm
7: 3.6 Mohm and rising
9: 2.5 Mohm and rising
10: 2485 ohm
13: 6 Mohm and dropping
B3: 3.6 Mohm and rising
B6: 2.5 Mohm and rising

I'm liking the looks of this!

[Paul Birkeland]

Yeah, you can give it power now.

-PB

[onelivewire]

Oh my. And once again, this thing is sounding absolutely gorgeous with the t1's... I can't thank you enough!