Channel imbalance + two LEDs on speedball V1.1 large board are unlit

[Pumpkins10]

Long time Crack owner here, had my unit since 2016 with no major issues between then and now.

I recently experienced an extremely loud pop that came from my headphones when i accidentally leaned too far back in my chair and tugged at the jack, and now notice that the left channel is significantly lower in volume than the right. This is consistent with all headphones plugged into the unit, and the headphones that popped are thankfully not imbalanced when plugged into other amplifiers.

Looking at the insides, I immediately see that D1 and D2 on the A side of the large speedball board are not lit when powered on, and the large transistor on the A side is warm but the B side is significantly hotter. Reflowed all the joints to no change.

Here are the voltages on the speedball boards, relative to ground -

Large Board -

0A = 122 V
0B = 116 V
B+ = 197 V

Small Board -

0A = 79 V
1A = 197 V
0B = 76.5 V
1B = 197 V


I dont have access to the user manual anymore so cant recall what other probe points that I might need to get values for, so please let me know any that are needed

Looks immediately to me like voltages are a little low on the B side probe points, but its the LEDs on the A side on the top board that aren't lit. hoping I can get some help and understanding here

[Paul Birkeland]

Can you post some photos of the inside of the amp?

The voltages don't look to be a problem, but it's odd that LEDs would be out with otherwise OK voltages.

[Pumpkins10]

Of course, I've attached some photographs. please excuse my inability to keep the point to point circuit looking nice 😅

[Paul Birkeland]

If I had your kit here for repair, I would replace the 2N2222 and TIP50 transistors.  To do this without a good solder sucker, it's usually easiest to cut the transistors off first, then pull the leads out out of the board when the transistor is gone.  After that, solder braid may be able to suck the remaining solder out of the board so you can get new transistors in.

While doing that, I would be having a hard look at the build to see why that happened.  It's very rare for these parts to just randomly fail on their own.

[Doc B.]

Yeah, my money is on the 2N2222.

[Pumpkins10]

Appreciate the info guys, thanks for helping out.

As I said, didnt happen on its own but as the headphone jack was accidentally yanked on. Nothing other than the LEDs and the A-side TIP50 not getting hot appears out of the ordinary or damaged to me.

While having that good look you mentioned, what would you recommend looking the closest at? bear in mind that my electronics knowledge doesnt extend much further than high school level - I can take measurements but theres not much actual understanding if that makes sense.

what I have been able to discover so far -

All the resistors are measuring as the correct values.
All capacitors are charging when probed in ohms mode and present voltage when in volts mode of the multimeter.
The two unlit diodes are behaving as expected, measurable resistance in one direction and too high to read in the other.
Probing the A-side 2N2222 behaves as expected of an NPN transistor. Between E and C is open, between B and C behaves like a diode, and between B and E behaves like a diode.
The A-side TIP50 behaves exactly the same as above, though this doesnt necesarially indicate that they are operating normally when powered on, right?


Regarding the transistors, would there be any discernable difference if the ones on the A-side are from a different manufacturer? or should I just replace all 4 of them?

[Paul Birkeland]

Just replace the ones on the dead side, I wouldn't replace them all. 

I would just look for loose connections while, untrimmed leads, that kind of stuff.  Yanking on the HP jack shouldn't produce this kind of issue. 

[Doc B.]

  Yanking on the HP jack shouldn't produce this kind of issue.

Unless the chassis was pulled out of the base when it happened and parts got knocked around.