Noise, Heat, and Sparks: Oh My!

[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  ;D

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

 

[MrPotatoSalad]

Continuity test (Black/Red probe):
Top:
C/B:.6
E/B:.6
Rest are not connection.

Bottom:
B/C:1.3
C/B:.6
E/B.6
E/C:.6
Rest are no connection.

New:
C/B:.6
E/B:.6
Rest are no connection

 

[MrPotatoSalad]

2N2222 (Black/Red probe):
Top:
C/B:.66
E/B:.66
Rest are no connection.

Bottom:
C/B:.66
E/B:.66
Rest are no connection.

New:
C/B:.66
E/B:.66
Rest are no connection

 

[MrPotatoSalad]

Bottom TIP50 out of board (Black/Red probe):
C/B:.6
E/B:.6
Rest are no connection.

Transistors are fine. Something else is funky.

 

[Paul Birkeland]

Yeah, perhaps you could borrow a camera from a friend this week to nab some decent photos of the PCB?

-PB

 

[MrPotatoSalad]

Yeah, perhaps you could borrow a camera from a friend this week to nab some decent photos of the PCB?

-PB

Could you tell me what to look for on the board for now?

If anything, the top of the board is in better condition than the bottom. I also disconnected the red and black wires so the two parts of the board are completely separate. Took both TIP50s out and they were fine. Only one that changes readings is the bottom one when I put it in the board, but the top is the problem.

 

[Paul Birkeland]

I really don't know what other options there can be.  There aren't a ton of options left for what's wrong, but you have one half of the board that works, one half that doesn't.

One other thing you can do is to flip the board around, so that the "Top" side is facing the other way, then see if the same side of the board continues to give you the same problem.

Beyond that, it's a matter of what's different between the non-working side and the functional side.

-PB

 

[MrPotatoSalad]

Replaced both TIP50s. Same resistance for the TIP50s on board (meaning the good side of the board changed its connectivity again when put in). Everything is opposite by switching the board around.  What is now top LEDs are on. However, the LED closer to center in what is now bottom board is on and lights up immediately. The one towards edge is out. Right small board and A3 LEDs are on. A8 has a very faint glow. Don't know if reflection or just barely on.

T1:20
T2/4/5:70

 

[MrPotatoSalad]

I'll be damned. My webcam takes better close-ups than my phone. Hopefully these work.

And the 2N2222s are not connected either visually or via multimeter.

 

[Paul Birkeland]

First things first, your TIP-50 transistors are not mounted correctly, with those long legs exposed, you're asking for trouble.  They also may be harder to solder in properly like that.

In photo 2, I see what looks like two solder blobs on the 2N2222 touching each other.

In photo 2, I can see that the TIP-50 legs aren't poking through the solder pads, this could really cause some problems.

In photo 4, I can see a similar solder blob on the 2N2222, it would be a good idea to get that off and trim the lead nice and short.

-PB

 

[MrPotatoSalad]

First things first, your TIP-50 transistors are not mounted correctly, with those long legs exposed, you're asking for trouble.  They also may be harder to solder in properly like that.

In photo 2, I see what looks like two solder blobs on the 2N2222 touching each other.

In photo 2, I can see that the TIP-50 legs aren't poking through the solder pads, this could really cause some problems.

In photo 4, I can see a similar solder blob on the 2N2222, it would be a good idea to get that off and trim the lead nice and short.

-PB

2N2222s aren't connected but I will clean it up. Maybe there is a jump in electricity?