Voltage Problems with Speedball [solved]

[ejdelo]

Hello,

When I turned on my Crack the tubes lit up, but none of the LEDs lit up at all. So after seeing that, I went to go measure the voltages of the stated terminals in the manual and... no terminal got any voltage except for terminal 21. The voltage of terminal 21 measured around 200ish.

However, I noticed that after I had powered down the amp the voltage of terminal 21 did not move at all. I waited for a while and it still didn't move. So I carefully grabbed a screwdriver and touched the terminal to ground it and a spark came flying, and then the voltage died out after that.

I thought it might have be a ground issue and so I checked out this thread: http://bottlehead.com/smf/index.php/topic,4812.0.html
I measured the resistances through that grounding path and it all seemed to check out fine.

At this point I'm a little lost and unsure of why the only terminal that is getting voltage is terminal 21. And also the fact that the voltage on terminal 21 does not dissipate when I turn off the amp.

[Paul Birkeland]

Did you build the amp stock before you put the Speedball in?  This functionality is part of the stock circuit, and the amp shouldn't have worked pre-Speedball.

There are black wires from 20 to 14 and 14 to 12.  Be sure these are all in place.  Give them a tug at each end with your pliers to see if they pop out.

The 270 Ohm resistors should also be checked.

At least one of these connections is loose, or the 270K resistor across 12 and 13 is missing.  (But since you have the Speedball installed, it should draw this voltage down very quickly)

-PB

[ejdelo]

I built the amp stock before the Speedball and it worked fine. There didn't seem to be any issue with it at all and the sound came out clear. The black wires from 20 to 14 and 14 to 12 seem sturdy and they didn't pop out at all when I tugged at them with my pliers. And the 270k ohm resistor connected to terminal 12 and 13 seems fine. At terminal 13 it climbs to 270k ohms, but at a very slow pace.

[Paul Birkeland]

How about the two 270 Ohm resistors?

If you get voltage on one side of the 270 Ohm resistor that runs across the power transformer, you should also get DC voltage on the other side of it.

[ejdelo]

I also just tried tugging at the two 270 ohm resistors and they don't have any give to them either. I'm not sure why voltage is only coming across on the right side at terminal 21. Here are some pictures just in case you see anything wrong in these. If you need any other pictures I can try my best to take some.

http://imgur.com/SvAeFou,w4rciyl,9JGeOfz,CyxXCxk,SQnjOxO#0

[Paul Birkeland]

Tug at the black wires as well that follow the 270 Ohm resistors, and tug at the 270K resistor.

Also check the resistance of each 270 Ohm resistor with your meter.

-PB

[ejdelo]

Hmm, well it seems like I'm getting closer and closer. After actually measuring the 270 ohm resistors I found that one did not give a reading. The 270 ohm resistor connected from terminal 13 to terminal 15 measured 270 ohms correctly. However, the 270 ohm resistor connected from terminal 15 to terminal 21 was not giving a reading at all.

I guess that might explain why I was not getting voltage across on the other side and also why no other terminal except 21 got voltage. Might also explain why the voltage was not dying off on that terminal even when I hit the off switch. I'll try to find another 5W 270 ohm wirewound resistor to replace it and report back my results. And thank you for your help so far and for your patience!

[ejdelo]

So I just replaced the resistor today and the kit is in a little better condition now. The voltage on terminal 21 seems to be correctly dying out as after I power down the amp there are no sparks flying from it when I touch it with a screwdriver to make sure its properly grounded.

Now my problem seems to be with the LEDs now. If I plug in the amp and power it on then all the LEDs on the big PCB light up very brightly, but on the small PCBs it's a different story. On the left PCB the LEDs are very very dim and on the right PCB one LED is slightly lit and the other seems to be completely off. Also the LED on A3 does not light up at all, but  the LED on A8 lights up very brightly. Sound seems to come through on the right channel, and on the left channel no sound comes through except for a distinct hum or buzzing noise.

[Paul Birkeland]

Please post the voltages that you have now.

-PB

(Terminals 1-10 are enough)

[ejdelo]

Here are my voltages:

Terminal   Expected   Actual
1                75-90        70
2                  170        175
3                    0           0
4                  170        176
5                75-90        0
6                    0           0
7                  100         0
8                    0           0
9                  100         0
10                  0           0

[Paul Birkeland]

With the 6080 still out, swap your small PC boards and see if the voltage follows a board or stays put.

0V on 5 is generally caused by a cold solder joint on the center leg of the MJE-350 feeding that terminal.

-PB

[ejdelo]

So I swapped the PCBs like you said and.... it worked! It sounds so beautiful... I am at a loss for words. I can't thank you enough for your help as without it I probably would have been here for weeks on end. Well for now I'll have to keep the message short since this thing is so addicting. 

[Paul Birkeland]

Enjoy the amp!

If you find that this issue returns, try hitting those center legs on the MJE-350 transistors.