Noise, Heat, and Sparks: Oh My!

[MrPotatoSalad]

Also, is it of any concern if I had the large board out and replaced it with the 10W resistors but sill had the smaller boards in and got hardly any power in the left ear. If the small boards are fine, should they work as replacements for the stock resistors on T1/2 and T4/5?

[MrPotatoSalad]

Small boards out gives:
1:61
2:70
4:72
5:20

All lights on at first (of course bottom board strong), but then the light on A3 goes out after a few seconds of glowing. Issue is definitely the main board as you said.

[MrPotatoSalad]

Large board out gives:
1:80
2:178
3:178
4:79

All LEDs on. Rest of voltages check OK for the Speedball manual. Some are a bit higher, but only 10% or so.

Sound is also OK. No distortions or noticeable issues vs the stock Crack.

[Paul Birkeland]

Yeah, with the big board out and the 3K/10W resistors in, the amp should work.

Beyond a problem on the big PC board, can you triple check the wiring hookup of the board itself?  Depending on how your amp is wired, wiring one of the "O" pads to 6 or 10 accidentally could also cause your problem.

-PB

[MrPotatoSalad]

Checked the four wires going into the large board and they are all in the correct place. Only thing I can think of is that one of the capacitors or wires is shorting T6/7 or T9/10, but then there should be some obvious voltage differences with the 3K/10W in, right?

[Paul Birkeland]

If one of the capacitors was shorted, the corresponding 2.49K resistor on the headphone jack would explode. 

With the 3K/10W resistors in, your power supply voltage should pop back up, and you should have ~100V at 7 and 9.

-PB

[MrPotatoSalad]

If one of the capacitors was shorted, the corresponding 2.49K resistor on the headphone jack would explode. 

Good to know 

Yes, my voltages were around 108V for T7/9, so the issue is the large board. Could there be anything wrong with the large PC board itself? Like I said, I am getting different resistances when I compare the same points on the top versus bottom. All resistors check out, so there must be a short in the path.

And what I did with the heatsink lug is fine, correct? All lugs should have connectivity to each other.

[Paul Birkeland]

Yeah, the heatsink lugs isn't too much of an issue.

Yes, there is a short in there somewhere, and we have narrowed it down to one half.

You can measure between pairs of transistor legs on that half to see if you can identify a shorted transistor in the path.

Beyond that, replacing the big PC board might be the easiest option.

-PB

[MrPotatoSalad]

My voltages on T1 is 82 V and on T5 is 78 V. Is this an issue.

I replaced the 5W 270ohm resistor over the transformer, but kept the other resistor on T13/15 in, which has a resistance of 290 ohm. Will replacing this resistor help?

[MrPotatoSalad]

Resistance discrepancies:

Top TIP50 Base/Collector: infinite
Bottom: Jumps around 2K ohm

Top 2N222 Collector/Emmiter:9M
Bottom:infinite

Top TIP50 emmitter/31.6ohm joint closer to end of board:9M
Bottom:infinite
Same for TIP50 emitter to 2N222 emitter.

Hopefully that's enough.

[Paul Birkeland]

My voltages on T1 is 82 V and on T5 is 78 V. Is this an issue.

The manual specifies 75-90V.

I replaced the 5W 270ohm resistor over the transformer, but kept the other resistor on T13/15 in, which has a resistance of 290 ohm. Will replacing this resistor help?

290 Ohms is within the tolerance of the part.  This is not where your problem is, we are already quite certain that your problem is on the top half of the large Speedball PC board.

-PB

[Paul Birkeland]

Resistance discrepancies:

Top TIP50 Base/Collector: infinite
Bottom: Jumps around 2K ohm

Top 2N222 Collector/Emmiter:9M
Bottom:infinite

Top TIP50 emmitter/31.6ohm joint closer to end of board:9M
Bottom:infinite
Same for TIP50 emitter to 2N222 emitter.

Hopefully that's enough.

None of these are showing shorts, but you don't have all the measurements.  Each transistor should be measured for:
collector/emitter resistance
collector/base resistance
emitter/base resistance

-PB

[MrPotatoSalad]

The manual specifies 75-90V.290 Ohms is within the tolerance of the part.  This is not where your problem is, we are already quite certain that your problem is on the top half of the large Speedball PC board.

-PB

I get that, I'm just seeing if there should be any other issues that reduce problems down the line.

[MrPotatoSalad]

None of these are showing shorts, but you don't have all the measurements.  Each transistor should be measured for:
collector/emitter resistance
collector/base resistance
emitter/base resistance

-PB

Yes, I measured everything, I only put down discrepancies though. The rest were either infinite or ~15M and dependent on whether the red or black probe was attached (switching from 15M to infinite when probes were switched). I'll measure them if you like.

[Paul Birkeland]

When they blow, they blow shut, so you would measure between two legs and see something very close to 0 Ohms.
  If your meter has a continuity beep, that is the setting to use to check for this.

-PB