cable-effect
Member
I've got an odd issue with this build. What does R102 do in this layout? Smelled something hot and low and behold that resistor is torched. Never had anything like this before. Can post photos if needed.
Caesar Chorus
- Thread starter cable-effect
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benny_profane
Well-known member
It’s there to filter out noise that may be on the power input (and, to a certain extent, limit current spikes when power is applied). You most likely have a short somewhere downstream causing too much current to flow through the resistor and exceeding its power rating.
cable-effect
Member
eh là bas ma
Well-known member
On your picture, I notice that the 3PDT pads aren't fully filled with solder. On the board, a lot of soldering joints look like bubble-shaped (could be the angle of the picture, though). I can't say if it's causing some overheating directly, but it should be fixed, I guess.
You'll need a desoldering pump to suck off some of the solder on each pads. Then reflow the pads and add some solder if necessary, to fill the pads. Not too little, not too much.
The trick is to touch simultaneously with your iron, both the component's leg and the pcb pad for 1 or 2 seconds. Then add a bit of solder to fill the pad. Remove the iron going upward, following the component's leg. That's how you get a dome-shaped solder joint.
You don't want to overheat the pcb or heat-sensitive parts, so be quick when reflowing pads (3 or 4 seconds max), and remove all ICs and transistors in the aera.
R102 according to schematics, is part of the power section, directly connected to +9V power input.
Check your power supply, is it a 9V DC power supply with negative center ?
Check continuity, with your multimeter, on all ground points (jacks, pcb, power jack, 3PDT). Are all ground points connected ?
If it's all ok, plug the power supply and check if the board is getting 9V at the pcb 9V pad ?
Then, You'll need to check the power section :
With you multimeter on continuity mod, check all connection to see if everything checks out, and if there aren't any shorts (two components that shouldn't be connected). Vref, Vcc are inner networks, for exemple, all Vref points should be connected and have continuity.
Here is the build doc : https://docs.pedalpcb.com/project/PedalPCB-Caesar.pdf
You'll need a desoldering pump to suck off some of the solder on each pads. Then reflow the pads and add some solder if necessary, to fill the pads. Not too little, not too much.
The trick is to touch simultaneously with your iron, both the component's leg and the pcb pad for 1 or 2 seconds. Then add a bit of solder to fill the pad. Remove the iron going upward, following the component's leg. That's how you get a dome-shaped solder joint.
You don't want to overheat the pcb or heat-sensitive parts, so be quick when reflowing pads (3 or 4 seconds max), and remove all ICs and transistors in the aera.
R102 according to schematics, is part of the power section, directly connected to +9V power input.
Check your power supply, is it a 9V DC power supply with negative center ?
Check continuity, with your multimeter, on all ground points (jacks, pcb, power jack, 3PDT). Are all ground points connected ?
If it's all ok, plug the power supply and check if the board is getting 9V at the pcb 9V pad ?
Then, You'll need to check the power section :
With you multimeter on continuity mod, check all connection to see if everything checks out, and if there aren't any shorts (two components that shouldn't be connected). Vref, Vcc are inner networks, for exemple, all Vref points should be connected and have continuity.
Here is the build doc : https://docs.pedalpcb.com/project/PedalPCB-Caesar.pdf
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cable-effect
Member
Honestly, my solder joints are pretty good. There were a couple that I had reflowed, but if anything there were a couple that needed a bit more solder. My power supply is good. I'm a bit illiterate on schematics, to be honest. Where on the board itself am I looking for the vref's and vcc's? Visually I've looked over the board extensively and I'm not seeing any leads or otherwise that are touching. All my grounds have continuity.
eh là bas ma
Well-known member
You need to follow the schematic : for exemple, Vcc is connected to C100 + side, C101, IC2 pin 8.
So if you want to read voltage on Vcc, you can probe any of these points. There isn't a Vcc pad, you just have, for exemple, the positive side of C100, or the side of C101 that isn't grounded, or pin 8 of IC2. These are Vcc.
To check the power section you just have to do some continuity tests, following schematics.
For exemple, starting from D100, does D100 negative side having continuity with C100 + side ?
Does C100 negative side have continuity with ground ?
Does C100 + side have continuity with one of C101 pad ?
Does the other C101 pad have continuity with ground ?
Does the C101 pad connected to C100 also have continuity with IC2 pin 8 ?
Does IC2 pin 8 also have continuity with one R102 pad , and one of the trimpot pad ?
etc, etc.
benny_profane
Well-known member
You’re looking for a short to a lower potential on the side of r102 labeled ‘1’ in the schematic. It could also be the case that a resistor value somewhere else is incorrect, increasing the current through r102. You’re right that a short to pin 4 of IC2 could cause this, but it’s not the only way.
cable-effect
Member
Thanks for the clarification! That makes sense. Working on this now.
cable-effect
Member
Alright, I've worked my way through this and have not found any issues with continuity. I forgot to mention that neither of the LFO LEDs are illuminated when it's plugged in. I chalked it up to the odd power issue but figure it's worth mentioning, it could somehow lead me down another path.
cable-effect
Member
Alright, I'm absolutely baffled. I ordered a whole separate PCB out of frustration. Long story short just finished the build and have the exact same issue. The only parts I reused were the ICs, the footswitch, and 9v input. Is there any way that a bad IC would cause this? Or does someone have another idea of the issue?
cable-effect
Member
Will do. Gotta check if I have another 4558 later. Looking at the schematic that would be the most likely culprit right?
eh là bas ma
Well-known member
Some clear pictures of both sides of the pcb could be useful.
Some voltage readings could help to see if there's something wrong with your ICs (if leds aren't lighting up, i wonder if there is current coming to them). Here is a link to learn how to write them down correctly :
Are you sure the 9V DC jack is connected correctly to the circuit ? You didn't confuse the terminals ?
If all continuity tests are ok, no suspicious pads, you can also use an audio probe, to follow the signal according to schematics, and see if there is something weird at some point. Audio probe is great to spot something wrong on a circuit when everything else have failed.
If you aren't familiar with schematics, you'll need a picture of the audio path to perform the audio-probing test. You just have to ask if you need it.
Some voltage readings could help to see if there's something wrong with your ICs (if leds aren't lighting up, i wonder if there is current coming to them). Here is a link to learn how to write them down correctly :
DEBUGGING - What to do when it doesn't work
DEBUGGING - What to do when it doesn't work
www.diystompboxes.com
Are you sure the 9V DC jack is connected correctly to the circuit ? You didn't confuse the terminals ?
If all continuity tests are ok, no suspicious pads, you can also use an audio probe, to follow the signal according to schematics, and see if there is something weird at some point. Audio probe is great to spot something wrong on a circuit when everything else have failed.
Misc > Audio Probe : DIY Fever – Building my own guitars, amps and pedals
[DIY Fever] Audio Probe - very simple contraption that helps with debugging audio circuits
diy-fever.com
If you aren't familiar with schematics, you'll need a picture of the audio path to perform the audio-probing test. You just have to ask if you need it.
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Feral Feline
Well-known member
cable-effect
Member
I'm going to try to swap the IC first and see if that solves it. A TL072 should work as a sub for the RC4558 right? If that doesn't work I'll post photos. The 9v input is wired correctly. All values of capacitors and resistors were verified using my multimeter before installation. This is probably my 20th pedal build and only one that to this point has me stumped!
Bio77
Well-known member
If you look at the schematic your problem is somewhere to the right of R102 in the power section, so, anything connected to the 9V net. Something is shorting to ground and causing a big current across the 33R of R102. You can clip one of the leads on your MM to ground and then probe for continuity at components connected to the 9V net, like C104, Q2, R22, D101 etc.. Since the same thing happened twice, maybe you have a batch of bad zeners (D101)?
cable-effect
Member
Yes, if I recall correctly, slightly amplified signal.
cable-effect
Member
Ahhh ok! That's super helpful. Just to verify, a functional 1n4739 is acceptable for D101 right? Is there a way to test them with a MM before I put another potentially bad one in?
Bio77
Well-known member
Test for continuity across D101 first to see if that's the problem, you could check C104 while you are there. With the new zener you can use the diode tester on your MM to confirm it is a functioning diode but I don't understand zener magic completely. E.g., It won't read 9.1 V. Yes, 1N14739 is a 9V zener.
