Troubleshooting a Little Green Scream Machine

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gregsmakercorner

Member
Hi, first post here, this is my third pedal PCB. My first two were Blue Breaker and they worked great first try on power up! I was on a roll.. :)

I have been troubleshooting all evening, checking my soldering, and going down the rabbit hole of checking all components (eg. Pots, resistors, etc). I'm really stumped on this one. I did decide to use LED's (red ones), since they are optional (vs. using the IN4148 diodes).

Here is the issue: the volume and tone pots work as expected. The drive pot doesn't seem to have any effect when I turn it. I confirmed using a multimeter that the A500k pot is operating as expected, and double checked all my soldering- no solder bridges, no cold joints, for the most part an appropriate level of solder everywhere.. I have a lot of soldering experience (other hobbies) but I was also going a little faster on this one, but after careful examination I don't think there is anything that looks off.

The only component I am really suspicious of is the 4558 Op Amp IC. I purchased from Amazon and they all came loose in a box. I haven't gone through thorough testing of it yet.

EDIT: Also.. the first picture does show that the tone knob isn't fully soldered in- I have already fixed that, but just used that same picture. The later 3 pictures are up to date.

Appreciate any ideas/thoughts!!
 

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Your soldering is pretty good for the most part, give the board a good scrub with some isopropyl alcohol and a toothbrush. Reflow the red LED pads, I see a cold joint there which would make sense! There’s a few potential cold joints all around, see if you can touch em up. Take your time.
 
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Nostradoomus said:
Your soldering is pretty good for the most part, give the board a good scrub with some isopropyl alcohol and a toothbrush. Reflow the red LED pads, I see a cold joint there which would make sense! There’s a few potential cold joints all around, see if you can touch em up. Take your time.
Click to expand...

Thanks! I did reflow everything, and have already scrubbed the board down a few times with IPA. There was some tape that I had removed from the bottom of the board which is probably why not everything looks picture perfect. I'll double check the LED soldering, but I'm 99% sure those are good because I tested the LED voltage on the empty holes where the diodes sit. The lower LED lights up, and gives me a voltage of around 1.4, the other one around .8 but it doesn't light up. Those numbers may not be 100% correct and based on memory.
 
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BuddytheReow said:
Test the voltages on your 4558 and transistors and report them back here.
Click to expand...
Here are the results (all tested installed in circuit) with multimeter.

C4558:
VCC+ to VCC- (pin 8 to 4): 1.89
VCC+ to 1IN+ (pin 8 to 3): 2.12
VCC+ to 1IN- (pin 8 to 2): 1.69
VCC+ to 1OUT (pin 8 to 1): 1.38
VCC+ to 2OUT (pin 8 to 7): 1.3
VCC+ to 2IN- (pin 8 to 6): 1.36
VCC+ to 2IN+ (pin 8 to 5): 1.3

Link to the part I ordered.

I noticed it has a 2MHz unity gain guarantee. I found the TI data sheet and it looks like maybe it needs to be 3MHz? I wonder if that could be a problem

Transistors:
B to E: .706
B to C: .711
 
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I was looking at the circuit diagram and I noticed the diodes are facing opposite directions (D1 and D2). I installed the LED's both the same way on the circuit board, with the anode (long leg) on the round pad and the short leg on the square pad, which is the same "convention" as the LED on the top of the board. I believe it is installed properly but I thought I'd mention it. Unfortunately, the PCB in the instructions is a different version (older?) than what I have. I do have 2 spare boards so I've included pictures of an empty one to show what I'm talking about. I *think* the board is correct but I can't tell by looking at the traces. I started checking continuity to see how things are connected and it does seem right from what I can tell, but I haven't taken the time to walk through the circuit and compare.

I did confirm that the diode square pad, and led square pad have continuity, as do the round pads, so the circuit is probably fine and should allow a diode or LED to be swapped as the directions suggest.

1714501209990.png


1714501748767.png
 

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gregsmakercorner said:
Hi, first post here, this is my third pedal PCB. My first two were Blue Breaker and they worked great first try on power up! I was on a roll.. :)

I have been troubleshooting all evening, checking my soldering, and going down the rabbit hole of checking all components (eg. Pots, resistors, etc). I'm really stumped on this one. I did decide to use LED's (red ones), since they are optional (vs. using the IN4148 diodes).

Here is the issue: the volume and tone pots work as expected. The drive pot doesn't seem to have any effect when I turn it. I confirmed using a multimeter that the A500k pot is operating as expected, and double checked all my soldering- no solder bridges, no cold joints, for the most part an appropriate level of solder everywhere.. I have a lot of soldering experience (other hobbies) but I was also going a little faster on this one, but after careful examination I don't think there is anything that looks off.

The only component I am really suspicious of is the 4558 Op Amp IC. I purchased from Amazon and they all came loose in a box. I haven't gone through thorough testing of it yet.

EDIT: Also.. the first picture does show that the tone knob isn't fully soldered in- I have already fixed that, but just used that same picture. The later 3 pictures are up to date.

Appreciate any ideas/thoughts!!
Click to expand...
Pretty sure that 4558 is fake, I don't think they have that 1/2 moon divot.
 
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