Speedball voltage issues...

[onelivewire]

Hey all,
just finished my crack a few days ago, no problems. Decided to speedball today, and I've run into some issues. The A3 LED no longer lights up, and the D1 LED on the right-side board does not light up. I got odd voltage readings, so I rechecked and resoldered nearly all the new contacts. I did have an arc from 3U to 2U occur while taking readings, but the readings did not appear to be affected afterwards, and the components (at least, the LEDs) seemed to all function the same as before. Tubes are both glowing fine. Here are the voltage readings I'm getting.

1 -108
2 0
3 -185
4 0
5 0

6 -185
7 -76
8 -185
9 -125
10 -185

11 -185
12 -185
13 -185
14 19
15 -185

19 -59
20 -185

a1 -174
a2 -185
a3 -185
a4 -185
a6 -108
a7 -185
a8 -185
a9 -185

b1 -108
b2 0
b3 -76
b4 -174
b5 0
b6 0
b7 -185
b8 -185

I plugged in some cheap headphones after verifying there wouldn't be a spike in the headphone output, and the right channel worked fine. The left just had a very low buzzing sound.

Any suggestions would be much appreciated. The voltage readings look very odd to me...
Thanks in advance for any help!

-e

[Paul Birkeland]

1 -108
2 0
3 -185
4 0
5 0

Can you double check that?  3 is connected to the chassis plate, so having 184V there makes little sense.

[onelivewire]

That's what I thought - I just 2x checked it, and trying both 3U or the chassis plate would give me -188V. I'm gonna keep checking connections.

[Grainger49]

You obviously have an open ground connection.  Look at the sticky in the Crack folder for my post tracing the ground path with your meter.

[onelivewire]

Thanks much! I retraced the ground and found one of the headphone jack lugs may have had a bad connection. Fixed that, and here are the new readings. I should note that the LED at A8 went off while I was testing, and seemed to have shorted to A9. So, LED A3, A8, and D1 on the rightmost of the boards, are off. I made sure to re-test voltages after this. Target voltages are bracketed.

1 183 [75]
2 188
3 0
4 188
5 0 [75]

6 0
7 181 [100]
8 0
9 59 [100]
10 0

11 0
12 0
13 185
14 0
15 205

19 89

20 0 [206]

a1 0 [75]
a2 0
a3 1
a4 0
a5 0
a6 184 [75]
a7 0
a8 15 [1.56]
a9 0

b1 185 [75]
b2 0 [170]
b3 181 [100]
b4 0 [75]
b5 188
b6 60 [100]
b7 0
b8 0

[Paul Birkeland]

Next, check that the transistors are in their proper locations, especially the 2N2907's and 2N2222's.

-PB

[onelivewire]

Alright, just went over all the transistors. Checking it over, the 2N2907s are on the A/B boards, the 2N2222s are on the large board, all with proper tabs. The TIP-50s are oriented properly, as they must in order to fit, and the MJE350s have the written sides facing out, which should be correct, I believe.

[Paul Birkeland]

I'd post up some pics if you can.  The focus should be on the front two PC boards, as their proper operation is a prerequisite for everything else. 

You can also trade the "O" pad wires on the two green boards (or swap the boards) to see what kind of results you get.

Having 0V on the "O" pad (which feeds pin 5) generally indicates a bad solder joint on the center leg of the MJE5731A, or no voltage making it to the "I" pad on that board. 

-PB

[onelivewire]

Aha! The center pin on the right board did it. All of the LEDs on the small board are lighting now, with only the A8 LED out. A number of voltages have been corrected, denoted below with asterisks. Thanks so much for this help by the way! I'll try to find a camera to get some pics.

1 183 [75]
2 188
3 0
4 188
5 78*

6 0
7 181 [100]
8 0
9 110*
10 0

11 0
12 0
13 185
14 0
15 205

19 89

20 0 [206]

a1 77.9*
a2 0
a3 1.5
a4 0
a5 0
a6 184 [75]
a7 0
a8 15 [1.56]
a9 0

b1 185 [75]
b2 186*
b3 181 [100]
b4 77.9*
b5 188
b6 110*
b7 0
b8 0

[Paul Birkeland]

Ah, excellent, things are snapping into place.  To be 100% sure it's the LED, you can switch the wires leaving the "O" pads on the small PC boards to ensure that the same LED stays dim.

We are also removing the voltage checks on the 9 pin socket that tend to lead to shorts during testing.

-PB

[onelivewire]

YES! Thank you. I swapping the boards kept the same LED out, so I swapped it for a new one and all are going great! I remeasured my voltages, and now the only ones which seem off are:

19 - reads 89, should be 0
20 - reads 0, should be 206

This is incredible help. Seriously

[Paul Birkeland]

We had to rebuild the Crack manual a bit and it looks like the voltages got transposed.  I'll alert Josh to patch this up.

-PB

[JamieMcC]

I had a similar reading with the voltages at terminals 19 and 20. Check the speedball correction note in the sticky section of the Crack thread.

http://www.bottlehead.com/smf/index.php/topic,1398.0.html

[onelivewire]

Wonderful. This thing sounds beautiful. I can't thank you all enough