ZVEX Super Duper - Diag help

[beneharris]

Hi guys, I'm stumped.

First off, here is the schematic that is closest to what I have here:

https://www.pcbway.com/project/shareproject/ZVEX_Super_Duper_2_in_1.html


One transistor is just not biasing properly.

Side 1 is the one I am having issues with. It is sputtering like it is starved for voltage - which as you'll see, it is. I have pulled all the resistors up near it and they have all measured fine. I thought maybe the transistor had failed, so I replaced it, and the voltages are the same.

Here are the voltages I am getting. They are taken with the gain controls (C5K) down:

Side 1
D - 4.8v
G - 1.64v
S - 4.1v

Side 2
D - 7.2v
G - 2.69v
S - 1.83v

I have 9 volts at the front side of both 5k1 resistors, but then the voltage drop across the 5k1 resistors coming from the power rail is:

Side 1 - 4.33v

Side 2 - 1.93v

I have tested the diodes and they seem to have a reasonable voltage drop across all of them.

It is just not making any sense to me. What else could be causing this voltage discrepancy.

[mauman]

I think we need some photos of your build.  Is this a PCB?  Vero?  Perf board?  There's definitely a problem with the power/bias for Q1.

[beneharris]

I think we need some photos of your build.  Is this a PCB?  Vero?  Perf board?  There's definitely a problem with the power/bias for Q1.

It is an original pedal. Nevermind the resistor on the back of the board, it doesn't go there. It's a pita to get it where it goes, so for testing I slapped it on back.


I'm doing this from my phone, so if the link doesn't work I'll upload them when I get to work in the morning. Home system is shut down for the night.

https://imgur.com/a/twHHJX8

[Govmnt_Lacky]

Are the transistors installed properly? According to the silkscreen, it looks like they are reversed. (No idea if you substituted)

[beneharris]

I thought that too, but that's how they were when I opened it up. I only ever pulled the one out. And the one I didn't pull, that is the side that works fine.

[Govmnt_Lacky]

I thought that too, but that's how they were when I opened it up. I only ever pulled the one out. And the one I didn't pull, that is the side that works fine.

Might be worth another look when compared to the transistors installed and the schematic.

[beneharris]

I thought that too, but that's how they were when I opened it up. I only ever pulled the one out. And the one I didn't pull, that is the side that works fine.

Might be worth another look when compared to the transistors installed and the schematic.

I'll definitely double check it. But a week or two ago when I ordered new transistors I remember checking the pinout and it was correct, but the silk screen was wrong.

I'm about ready to breadboard this and see if I can duplicate the issue. I know I'm missing something stupid.

[beneharris]

I found this talkbass for sale post and it's got a gut shot, and the transistors are installed the same direction.

https://www.talkbass.com/threads/zvex-super-duper-2-in-1-sa-special-edition.1411791/

[Govmnt_Lacky]

I found this talkbass for sale post and it's got a gut shot, and the transistors are installed the same direction.

https://www.talkbass.com/threads/zvex-super-duper-2-in-1-sa-special-edition.1411791/

I see one picture of the guts and I cannot tell which direction they are in. Regardless, it only takes a second to verify if they are in correctly by using a pinout and the schematic.

[beneharris]

I found this talkbass for sale post and it's got a gut shot, and the transistors are installed the same direction.

https://www.talkbass.com/threads/zvex-super-duper-2-in-1-sa-special-edition.1411791/

I see one picture of the guts and I cannot tell which direction they are in. Regardless, it only takes a second to verify if they are in correctly by using a pinout and the schematic.

Yup, I'll do that again tonight just to be sure, and I'll report in.

[beneharris]

I found this talkbass for sale post and it's got a gut shot, and the transistors are installed the same direction.

https://www.talkbass.com/threads/zvex-super-duper-2-in-1-sa-special-edition.1411791/

I see one picture of the guts and I cannot tell which direction they are in. Regardless, it only takes a second to verify if they are in correctly by using a pinout and the schematic.

Yup, I'll do that again tonight just to be sure, and I'll report in.

Well I'll be damned. I diagnosed the transistor correctly then installed the bitch backwards. Great catch, I'm a moron.

Thanks for the help!

[Govmnt_Lacky]

Well I'll be damned. I diagnosed the transistor correctly then installed the bitch backwards. Great catch, I'm a moron.

Thanks for the help!

It has happened to all of us at some time. Glad you got it sorted!

[jimilee]

Well I'll be damned. I diagnosed the transistor correctly then installed the bitch backwards. Great catch, I'm a moron.

Thanks for the help!

It has happened to all of us at some time. Glad you got it sorted!

It still happens to some of us.


Sent from my iPhone using Tapatalk

[madbean]

I found this talkbass for sale post and it's got a gut shot, and the transistors are installed the same direction.

https://www.talkbass.com/threads/zvex-super-duper-2-in-1-sa-special-edition.1411791/

I see one picture of the guts and I cannot tell which direction they are in. Regardless, it only takes a second to verify if they are in correctly by using a pinout and the schematic.

Yup, I'll do that again tonight just to be sure, and I'll report in.

Well I'll be damned. I diagnosed the transistor correctly then installed the bitch backwards. Great catch, I'm a moron.

Thanks for the help!

Couple weeks ago I spent nearly an hour trying to debug a simple buffer on the breadboard. I had the jacks plugged in backwards.