Dirtbag Biasing/Chip issues

[Zerstorte Zelle]

Finished a build of a V3205 Dirtbag deluxe a few days ago and for a bit there everything was sounding good. I was quite impressed with the quality and did prefer it over my diamond memory lane 2 (if you can believe it, the repeats blend better.)

All gravy until...

The effect doesn't do anything one day. LED lit, volume responding but no repeats and certainly no lovely lovely oscillation or feedback. Thinking maybe some of my off board wiring ( pots jacks switch ) were to blame i redid all of it taking the utmost care. Plug it back in get the probe out and what I found is this.

IC4 Pin 3 Biases in and I have repeats. I can hear some noise in the background...hiss and what not but nothing crazy.

Moving on to IC5 Pin 3 and the only thing audible is a really high pitched whistle. Upon checking Pin 7 there is signal and it sounds like a slightly lower fidelity version of IC4 Pin 3. I imagine that means that everything is cool until that point.

What's the deal? do I have a dead chip or something worse?

Thoughts?

ZZ

[madbean]

Did you try re-biasing the second BBD? It sounds like it's just not passing delay. Since you have input on pin7 and no output, I say either a bias or possibly bad IC. Are the voltages on pin5 and pin1 the same as the first BBD that is working?

[Zerstorte Zelle]

here are the voltages per pin. Measured in Vdc.

IC4 pin voltages

1 - .002
2 - 4.69
3 - 5.94
4 - 5.96
5 - 8.11
6 - 4.68
7 - 5.75
8 - 7.85

IC5 pin voltages

1 - .002
2 - 4.69
3 - 4.47
4 - 4.46
5 - 8.12
6 - 4.68
7 - 2.852
8 - 7.86


IC5 pin 7 the problem? Bad chip? I tried biasing the whole thing a few times and no dice. thoughts?

ZZ

[madbean]

Yeah, pin7 on IC5 seems like it's low. Gain1 and Bias2 are somewhat interactive, but, you should be able to dial in the delay signal with the gain mostly off and then just working on Bias2 (you should be audio probing either pins 3 or 4 of IC5 when you do this).

If you are still not getting delay signal, then I would look real carefully at your solder connections on IC5 and confirm you have the correct values for the two trimmers (100k) and the values for R29 and R28.

Let us know what you find.

[Zerstorte Zelle]

Tried fiddling with the trimmers some more and nothing yet. R28 and R29 seem correct. Within .05 of their respective values. Im also probing on the chip at both 3 and 4. Trimmers looking good as well.

I'll have to throw it back on the bench tomorrow to recheck the soldering. would a good alternate test be to swap the chips and check again? i thought about it but also have to wait on that.

ZZ

[madbean]

Try taking the two BBD's out and put the second one in place of 1C4 to see if it passes delay there. That would at least tell you whether or not the actual chip is not wonky.

I'll try and come up with some more suggestions.

[Zerstorte Zelle]

Chips swapped and now I'm not able to get anything to happen on IC4 so...one bad chip. I tried all gain and bias trimmers adjustment and even wound up on their extremes. nothing anywhere.

When i replaced the chips to their previous orientation they worked as before. IC4 biased up and IC5 not able to be biased to pass delay.

So bad chip yeah? I guess it just slowly failed.

ZZ

[jkokura]

Sounds like. Where did you get it? You might be able to get a replacement depending on the reason it failed.

Jacob

[Zerstorte Zelle]

got the cool audio chips from mammoth.

[Scruffie]

They're static sensitive, coulda been damaged during installation if you didn't take precaution or if mammoth don't from them. So it could be you or the supplier... or just plain bad luck, I have had one dodgy cool audio BBD before.

[madbean]

Really sorry to here that. At least you seem to have zeroed in on the problem.

[Zerstorte Zelle]

so it could have failed post boxing due to static ? i know they did not show up in an anti static bag. oh well back to the order form.

After all of the 'bean builds ive done thus far this was the first one that failed. At least it appears that the whole populated board isn't scrap.

Thanks all for the help,

Best,

ZZ

[Zerstorte Zelle]

well this is interesting ( or sad depending. )

replacement cool audio chip showed up today and i popped 'er in. Sadly now neither chip will bias and i have a really crazy screaching at the pins with no delay and nothing at the input.

both IC 4 and 5.

Help?

ZZ

[Zerstorte Zelle]

anybody?

[Zerstorte Zelle]

Finally got on the meter today with some spare time here:

IC 1

4.74
4.75
4.74
0
9.40
4.74
4.77
4.70

IC 2

1.798
8.0
6.36
1.8
9.41
1.795
1.796
.019
1.797
7.04
1.799
1.801
0
1.795
1.795
1.219

IC 3

4.73
4.74
4.74
9.40
.001
4.74
4.74
4.74

IC 4

0
4.34
4.96
4.97
7.98
4.75
4.31
8.12

IC 5

0
4.34
4.65
4.67
7.87
2.68
4.31
8.12

IC 6

2.682
2.684
2.702
0
9.42
4.82
4.79
4.77

IC 7

.644
4.90
4.6 - 5.1 flux.
0
9.4
4.6-5.1 flux
4.90
4.89

IC 8

7.99
8.02
8.02
9.40
.001
4.73
4.74
4.74

IC 9

5.03
4.24
4.27
9.39
9.39
0
9.37
5.06
0
4.32
4.29
0
0


any thoughts?