Decimator debugging

[Zounds!]

I built an ISP Decimator clone using this vero layout:


Based on this schematic: http://1.bp.blogspot.com/-6MIbm-Xv_iA/T_niVO0XcxI/AAAAAAAABuc/0hEt6sjJ5UU/s1600/decscheme.jpg

It passes sound but doesn't gate. The threshold knob just adds some noise and makes my signal quieter. I've been debugging for the past few days: early on it gated momentarily but then the gate seemed to just open after a second. Now it doesn't gate but my voltages look a little better than they did then (but still not great). Go figure.

My only substitutions are a PN2222A for Q4 and resistors soldered in series for R5 and R20.

U7
5.8     3.9
4.9     3.9
4.9     3.9
9.5     0.0
3.9     5.0
3.9     5.1
3.9     7.4

U9
5.8     1.4
7.0     7.4
7.0     4.6
9.5     0.0
7.4     7.4
7.4     7.4
7.4     7.4

U5
7.4     9.5
7.4     7.4
6.7     7.4
0.0     7.4

U8
7.4
7.5
7.4
7.5
4.6
7.4
9.5
7.4

Q1          Q4
E: 3.9     0.0
B: 4.6     0.6
C: 3.9     4.6

For comparison, proper voltages for U8 are here: http://www.diystompboxes.com/smfforum/index.php?topic=99848.msg956249#msg956249
And proper voltage for U5, U7, and U9 are here: http://www.diystompboxes.com/smfforum/index.php?topic=99848.msg956273#msg956273

Some pictures:





I've tried: checking component placement (I've looked over it A LOT!), checking for solder bridges with a magnifying glass/mercilessly cutting between traces with a razor, replacing all ICs and transistors (except U8, as I only have one and they're expensive!), and re-flowed some suspect joints. I opted to post here rather than to just start replacing diodes randomly, as I bet somebody can offer me a more logical clue to work with! Thanks!

[Zounds!]

This one's killing me. At this point I've pulled every component and tested and/or replaced them, double checking placement when I put them back in. I found one cap that was the wrong value (used 2.2uf instead of 10uf for C9) and a few resistors that were about +/- 10% out of spec. Didn't find any placement errors.

Now my signal is very distorted. It gates but I have to hit pretty hard for the gate to open and the threshold pot only has a slight effect (I tried swapping it out). I audioprobed from the input and got clean signal into pin 3 of U5, but it's distorted at pins 1, 6, and 7, and I'm not sure how to follow the circuit past there. 

Here are my current voltages:

U5
8.8   9.5
1.3   2.7
2.4   2.6
0.0   2.6

U7
1.5   1.5
1.5   1.5
1.5   1.4
9.5   0.0
1.1   1.8
1.5   1.8
1.5   2.4
   
U9
1.5   8.9
2.4   2.6
2.3   4.7
9.5   0.0
2.6   2.6
2.6   2.9
2.6   2.6

U8
3.3
2.7
2.6
2.7
0.2
2.6
9.5
2.6

Q1
1.1
1.5
1.5

Q2
0.0
0.6
0.2

I'm worried that the THAT2181C was either DOA when it arrived (ebay seller from China that I've never dealt with otherwise) or that it's been damaged by getting pulled out of the sockets so many times. This one's looking pretty bleak, I know, but I'm hoping someone can help!

[strassercaster]

I built an ISP Decimator clone using this vero layout:


Based on this schematic: http://1.bp.blogspot.com/-6MIbm-Xv_iA/T_niVO0XcxI/AAAAAAAABuc/0hEt6sjJ5UU/s1600/decscheme.jpg

It passes sound but doesn't gate. The threshold knob just adds some noise and makes my signal quieter. I've been debugging for the past few days: early on it gated momentarily but then the gate seemed to just open after a second. Now it doesn't gate but my voltages look a little better than they did then (but still not great). Go figure.

My only substitutions are a PN2222A for Q4 and resistors soldered in series for R5 and R20.
I built this exact same layout. I couldnt get it to do anything but pass signal. i gave up after 2 nights of troubleshooting. My build is correct. I have a feeling this layout has been altered or wasnt verified. the that chip wasnt cheap and took a long time to come. I will watch this post to see if anything good comes from it. I have finished 97 pedals and have three on the bench I couldnt ever get to work this is one of them. There is a new layout at tagboard effects in the request or contributions section. I may try that one. The problem is most if not all noise reduction kills high end eq its a give and take i guess/ I made the same sub as you for the 2222 it shouldnt matter i dont think
U7
5.8     3.9
4.9     3.9
4.9     3.9
9.5     0.0
3.9     5.0
3.9     5.1
3.9     7.4

U9
5.8     1.4
7.0     7.4
7.0     4.6
9.5     0.0
7.4     7.4
7.4     7.4
7.4     7.4

U5
7.4     9.5
7.4     7.4
6.7     7.4
0.0     7.4

U8
7.4
7.5
7.4
7.5
4.6
7.4
9.5
7.4

Q1          Q4
E: 3.9     0.0
B: 4.6     0.6
C: 3.9     4.6

For comparison, proper voltages for U8 are here: http://www.diystompboxes.com/smfforum/index.php?topic=99848.msg956249#msg956249
And proper voltage for U5, U7, and U9 are here: http://www.diystompboxes.com/smfforum/index.php?topic=99848.msg956273#msg956273

Some pictures:





I've tried: checking component placement (I've looked over it A LOT!), checking for solder bridges with a magnifying glass/mercilessly cutting between traces with a razor, replacing all ICs and transistors (except U8, as I only have one and they're expensive!), and re-flowed some suspect joints. I opted to post here rather than to just start replacing diodes randomly, as I bet somebody can offer me a more logical clue to work with! Thanks!

[strassercaster]

hey maybe we can help each other. i just went back and another guy verified it in april of this year. it must be us or a bad THAT chip maybe idk. I did find a couple mistakes in my build maybe I bombed my THAT2181 chip. I am busy with work the next couple days but ill post my voltages on sunday . maybe you can post your chip and transistor voltages as well. I noticed on the tagboard forum there was a thread as well on this build ill go back and look at that thread as well. Mega builds can be mega dissappointing that is for sure

[Zounds!]

Yeah, the layout seems pretty solidly verified, so I think it's definitely an issue with our individual builds. I set this aside and ordered another THAT2181C, as I can't debug much further on my own without knowing for certain that whatever I have as U8 is properly functioning...

[Zounds!]

Update: I plugged in the new THAT2181C and the results are the same as they were. Signal is distorted and I need to strum hard for it to pass, but it is gated. Any thoughts? Wondering if I'll just need to start from scratch with this one 

[jimilee]

Might be time for an audio probe.


Sent from my iPhone using Tapatalk

[Zounds!]

I didn't get very far audioprobing, unfortunately. The schematic is more complicated than the usual overdrives I build and uses some unfamiliar ICs to boot, so I'm not really sure where signal should or should not be. I audioprobed from the input and got clean signal into pin 3 of U5, but it's distorted at pins 1, 6, and 7, and I'm not sure how to follow the circuit past there. 

The schematic I initially posted above is definitely complicating things, as it is the full buffered G-String version of the pedal. This looks to be the simplified version that the vero is based on: http://i262.photobucket.com/albums/ii81/kearns892/DecimatorSchematic11.jpg

[Zounds!]

Bump