Issue with Low Tide Mod build

[pcborpcp]

Hi there,

I got the Low Tide Modulator pcb along with some other projects. While I could finish the other effects just fine, I came across a problem with the Low Tide. I hope you can help me.

So the issue at hand is that the polarity protection diode (D3) gets fried whenever I power up the circuit.
After the first time, I removed all IC’s and transistors, because the board got really hot. But even without transistors and IC’s connected, the D3 gets fried immediately. I even tried to use a N4001 diode instead of the BAT48. The diode remains to get fried and it gets really hot.

I switched out the DC socket, double and triple checked the polarity of the wiring and the DC plug (center negative) and it’s all correct. I even let a friend look over the build, just to make sure I didn’t miss anything.

Do you have any idea, what the problem might be?
I would really appreciate your support on this.

Thanks

 

[carlinb17]

How are you powering it and can you post pictures?

 

[pcborpcp]

How are you powering it and can you post pictures?

I'm powering it with a universal AC/DC power supply with 1500mA. It works fine with my other pedals. I can take some pictures, but I have to remove the pots first.

 

[zgrav]

sounds like a possible short to ground but this is all theoretical. post detailed pictures of both sides of the board and you may get better feedback.

 

[pcborpcp]

sounds like a possible short to ground but this is all theoretical. post detailed pictures of both sides of the board and you may get better feedback.

Alright, here are some pictures - I hope they're detailed enough.
You will notice the damaged soldering spots for C32, 39, 40, 41. But this happened after the issue occurred. I thought one of the caps might be faulty when the diode got fried, because I forgot to measure them before, so I desoldered them. But I was unable to get the solder to flow again and had to push a needle through the holes to get the caps back in. I know this might be an issue (I measured continuity and it still seems to work though), but it was not the cause of the problem.

 

[zgrav]

are you having the same issue with the board in and out of the enclosure when you are testing it?

 

[pcborpcp]

I didn't put it in an enclosure yet.

 

[zgrav]

FYI -- those jacks might be a problem for you when you put everything in the enclosure.

use your dmm and see what the resistance is between the positive power supply wire and ground (no power applied to board).

 

[pcborpcp]

FYI -- those jacks might be a problem for you when you put everything in the enclosure.

use your dmm and see what the resistance is between the positive power supply wire and ground (no power applied to board).

Thanks, yeah I know. I have to order those slim fit jacks. These are just for testing purpose.

So the DMM reads 08.50 mOhm. Does this help?

 

[zgrav]

the next thing I would suggest is cleaning off your board with Isopropyl alcohol on the solder side. and then post another detailed picture. I understand that you had the problem before you pulled out the parts that look messy on the board, but those places look problematic now. I think you are going to need to use the schematic to make sure the mounting holes for those parts are still connected to the parts shown in the schematic. doing that may also isolate the other issue you are having. other folks may have suggestions too on things to check.

 

[zgrav]

I am sure you realize by now that the low tide is a tricky build where the kind of troubleshooting you were doing can spiral out of control and create more problems than it solves.

 

[pcborpcp]

the next thing I would suggest is cleaning off your board with Isopropyl alcohol on the solder side. and then post another detailed picture. I understand that you had the problem before you pulled out the parts that look messy on the board, but those places look problematic now. I think you are going to need to use the schematic to make sure the mounting holes for those parts are still connected to the parts shown in the schematic. doing that may also isolate the other issue you are having. other folks may have suggestions too on things to check.

Thanks for your help. Believe me, I'm very aware that I've complicated the problem with the pulled caps. I'm very upset that I messed up those spots. I will make bridges between the problematic places and the next connection when possible. Like I said before, I checked continuity between the connections and it seems to be fine. I've attached some more pictures and hope someone else might chime in with another idea.

 

[zgrav]

You now have the diode D3 removed. RIght? What happens when you are powering the circuit now? Anything? If nothing is smoking or heating up, see if you are having any voltage showing up at any of the transistor or IC contacts on the board. The point is to make sure that all of the power is reaching the board through the power diode and not through some other route.

 

[pcborpcp]

You now have the diode D3 removed. RIght? What happens when you are powering the circuit now? Anything? If nothing is smoking or heating up, see if you are having any voltage showing up at any of the transistor or IC contacts on the board. The point is to make sure that all of the power is reaching the board through the power diode and not through some other route.

Yes, D3 is removed. When I power up the circuit, I get 9.22V at the D3 negative side, but nothing anywhere else. Nothing gets hot.
But here's a head scratcher: when i put an LED with a 4k7 resistor in D3, the LED lights up and doesn't get hot. But there's also no voltage on the transistor and IC contacts.

 

[zgrav]

The LED lighting up when in D3 suggests that there is some kind of connection to ground. Which would also explain why there is no voltage showing up in the transistors and ICs.

 

[pcborpcp]

The LED lighting up when in D3 suggests that there is some kind of connection to ground. Which would also explain why there is no voltage showing up in the transistors and ICs.

Do you have any idea where that connection might be?

 

[bowanderror]

I built the LT as well, and it's a complex build to troubleshoot, but well worth the effort. Here is the schematic, which is a critical reference during troubleshooting. Without being able to power up the unit, you'll mostly be looking to find connectivity (the beep setting on your DMM) between components that shouldn't be connected.

A potential problem area is going to be around those capacitors you mentioned:

I can't quite tell from the grainy pics, but there may be solder bridging some traces that were previously under the solder mask (the insulating black stuff that peeled off). This could be grounding a part of the circuit & causing your short.

These pictures look better, but we still can't see much of anything due to the low light. If you have a bright lamp or a well-lit area that you can take photos in, that will increase the contrast & remove the grainy noise from the images. From there we may be able to see where the problem is.

 

[zgrav]

Use your DMM to measure the resistance between the ground pad and the side of D3 that does not connect to the power. What do you get?

If it is no resistance or low resistance. you will need to isolate the unwanted connection to ground The most likely cause would be a solder bridge between two connections on the board, since you seem to have had the problem before you started pulling pieces off of the board. It is also possible though that the damage to the board from removing parts may have created a short to the ground plane in the board that might be harder to diagnose and repair. You can do a visual inspection to see if you have any stray solder bridges between pins that are close together.

 

[bowanderror]

Use your DMM to measure the resistance between the ground pad and the side of D3 that does not connect to the power. What do you get?

If it is no resistance or low resistance. you will need to isolate the unwanted connection to ground The most likely cause would be a solder bridge between two connections on the board, since you seem to have had the problem before you started pulling pieces off of the board. It is also possible though that the damage to the board from removing parts may have created a short to the ground plane in the board that might be harder to diagnose and repair. You can do a visual inspection to see if you have any stray solder bridges between pins that are close together.

I'd do the same at both pads of C39, 40, & 41 as that will help us identify if they are the problem. For electrolytic caps, the the square pad is the (+) side and the round pad is the (-) pad side. You should get a beep (or close to 0 ohms) on the (-) pads as they are connected to ground. On the (+) pads, you should get a resistance of less than ~2.2k ohms on C39/40, and a much higher resistance on C41 (possibly no connection).

 

[pcborpcp]

I can't quite tell from the grainy pics, but there may be solder bridging some traces that were previously under the solder mask (the insulating black stuff that peeled off). This could be grounding a part of the circuit & causing your short.

Yeah sorry, I'm terrible at taking photos. I tried to get a better look at those spots. Just want to reinstate that the short already appeared before I've created that mess. But I know it doesn't help.