madbeanpedals::forum

General => Open Discussion => Topic started by: Hack_Black on May 30, 2020, 09:57:37 PM

Title: Fried Bias Pot?
Post by: Hack_Black on May 30, 2020, 09:57:37 PM
Ok, now I'm working on a BYOC Germanium Boost. If a trim pot gets fried, does it usually act as a short or open between terminals? The voltage at the trans base is staying the same with bias pot adjustment (it reads full battery voltage - 7.5 volts).

I bought it on Reverb from the guy who built it for cheap. Fixing it is more challenging than I expected.
Title: Re: Fried Bias Pot?
Post by: Hack_Black on May 30, 2020, 10:14:46 PM
Does this question make any sense?
Title: Re: Fried Bias Pot?
Post by: somnif on May 30, 2020, 10:20:17 PM
Given how a pot is constructed, I'd imagine a damaged/broken one to go open circuit (like blowing a track off a board). I could be wrong though, things can break in odd ways.

Have any pics of the board? Perhaps someone here can spot something.
Title: Re: Fried Bias Pot?
Post by: Hack_Black on May 30, 2020, 10:28:03 PM
Maybe I will post a pic, but it is so sloppy. It's ugly too. Guy painted it to be a green mixed with gold color, but I doubt it turned out like he wanted. I don't want it to look like my work, LOL but guess it doesn't matter. Before I got into it the DC jack didn't work and it would cut in and out on battery. It's got torn traces and everything.
Title: Re: Fried Bias Pot?
Post by: Hack_Black on May 30, 2020, 11:07:46 PM
Well, here's proof I didn't build it. And I'm not claiming to be a solder jockey either. I'll post circuit pics next.

(https://i.imgur.com/IQyWwSJ.jpg)
Title: Re: Fried Bias Pot?
Post by: Hack_Black on May 30, 2020, 11:12:54 PM
(https://i.imgur.com/OhELKKP.jpg)
Title: Re: Fried Bias Pot?
Post by: Hack_Black on May 30, 2020, 11:16:18 PM
(https://i.imgur.com/UKC3uFe.jpg)
Title: Re: Fried Bias Pot?
Post by: Hack_Black on May 30, 2020, 11:21:17 PM
Why would there be +7.5 volts (that is all the battery power) at the base of the transistor socket?
Title: Re: Fried Bias Pot?
Post by: somnif on May 31, 2020, 01:13:49 AM
Ok, first dumb question, is anything shorting out against the back of the pot?
Title: Re: Fried Bias Pot?
Post by: Hack_Black on May 31, 2020, 02:42:22 AM
Thanks for the reply. I don't think so. When it was in the box it was. But I've been working on it with just the guitar in/out jacks installed in the box since this adventure started. I'm giving it a break for tonight.

I thought I burned something up by overheating with soldering iron, but it appears that isn't the case.

I have an unused Mad Bean Rangemaster board. But I don't have a non-boardmount pot. I'm not sure what my next approach will be tomorrow. I really need to get a better soldering iron.
Title: Re: Fried Bias Pot?
Post by: lars on May 31, 2020, 04:36:46 AM
What transistor came with the pedal? In the pictures, I don't see one.
Title: Re: Fried Bias Pot?
Post by: Hack_Black on May 31, 2020, 04:02:28 PM
Quote from: lars on May 31, 2020, 04:36:46 AM
What transistor came with the pedal? In the pictures, I don't see one.

I took it out while soldering. It's an OC76. The center lug of the volume pot was intermittent. The traces were torn off. I had to scrape the board to expose a trace and solder the lug to it on the component side. I thought I was going to burn stuff up soldering so I took the transistor out.

I'll start working on it again here in a little bit.
Title: Re: Fried Bias Pot?
Post by: lars on May 31, 2020, 05:11:49 PM
I did notice there are three purple wires going to the output jack, whereas in the BYOC instructions, it only shows two. It looks like the DC input jack in your pictures is being grounded to the output jack. I would suggest changing it to match how BYOC wired things up in their build document. It can be very easy to mess up the grounding scheme with PNP transistors. Your pedal should be running positive ground.
Title: Re: Fried Bias Pot?
Post by: jimilee on May 31, 2020, 05:55:45 PM
Quote from: Hack_Black on May 31, 2020, 04:02:28 PM
Quote from: lars on May 31, 2020, 04:36:46 AM
What transistor came with the pedal? In the pictures, I don't see one.

I took it out while soldering. It's an OC76. The center lug of the volume pot was intermittent. The traces were torn off. I had to scrape the board to expose a trace and solder the lug to it on the component side. I thought I was going to burn stuff up soldering so I took the transistor out.

I'll start working on it again here in a little bit.
For future reference, you could just run a jumper to the next component in line.
Quote from: lars on May 31, 2020, 05:11:49 PM
I did notice there are three purple wires going to the output jack, whereas in the BYOC instructions, it only shows two. It looks like the DC input jack in your pictures is being grounded to the output jack. I would suggest changing it to match how BYOC wired things up in their build document. It can be very easy to mess up the grounding scheme with PNP transistors. Your pedal should be running positive ground.
That is weird, the input and output jacks were reversed. the stereo jack should to the input. And that's only if a battery was going to be used.
Title: Re: Fried Bias Pot?
Post by: Hack_Black on May 31, 2020, 06:04:48 PM
Thank you for the replies. I chose this forum because some can get so snarky.

I did have to run a jumper instead of trying to use the trace.

Sound is getting through now and the volume and toggle is having an effect, BUT the signal is very weak. The bypass signal is louder.

I'm going to re-check the wiring again. Thanks!
Title: Re: Fried Bias Pot?
Post by: jimilee on May 31, 2020, 08:58:51 PM
Quote from: Hack_Black on May 31, 2020, 06:04:48 PM
Thank you for the replies. I chose this forum because some can get so snarky.

I did have to run a jumper instead of trying to use the trace.

Sound is getting through now and the volume and toggle is having an effect, BUT the signal is very weak. The bypass signal is louder.

I'm going to re-check the wiring again. Thanks!
I know what you're saying, we're all about learning in these parts.

The input and output jacks need to be desired. The stereo goes on the input. If you're not going to use a battery, I'd leave the the third solder lug empty.


Sent from my iPhone using Tapatalk
Title: Re: Fried Bias Pot?
Post by: Hack_Black on May 31, 2020, 09:34:19 PM
It's working.
Title: Re: Fried Bias Pot?
Post by: Hack_Black on May 31, 2020, 09:39:19 PM
Quote from: jimilee on May 31, 2020, 08:58:51 PM
Quote from: Hack_Black on May 31, 2020, 06:04:48 PM
Thank you for the replies. I chose this forum because some can get so snarky.

I did have to run a jumper instead of trying to use the trace.

Sound is getting through now and the volume and toggle is having an effect, BUT the signal is very weak. The bypass signal is louder.

I'm going to re-check the wiring again. Thanks!
I know what you're saying, we're all about learning in these parts.

The input and output jacks need to be desired. The stereo goes on the input. If you're not going to use a battery, I'd leave the the third solder lug empty.


Sent from my iPhone using Tapatalk

I missed your post. I'm wondering if the wiring looks weird because it's designed to run a PNP with a negative tip supply, so a standard DC 9v adapter can be used. Anyway, I'm so confused right now I honestly can't tell you what fixed it. Ha ha. If I think of it later I'll post. Thanks!