SUNKING PROBLEM

[madbean]

This is a real stumper. I'm sending you an email as a follow-up.

[Klinq58]

Well, I guess I am glad I am not the only one stumped. If you sent an email, I did not recieve it as yet. I wonder if it is possible that I have a bad batch of TLO72's. I had a number of them floating around that I have tried. I have also wondered if something could be bridged under an IC socket where I can't see. Thanks for all your help so far.

[rhinson]

hello there,  i just built 2 sunkings and am experiencing almost exactly the same problem on both builds.   they use the same parts.  the problem sounds very close to this one with the problem around the voltages on ic2, pins 1 and 7 are off and they will vary as you rotate the gain pot with the sum of both always being in the 9v range  (at the extreme pin1 will be 11v and pin7 - 2v or so, at the other extreme pin 1 will be maybe 7v and pin7 around 2)  the differential makes the pot have a lot of crackling noise.    the other voltages on the ic are as they should be.  i swapped ic's, pumps, etc. but no dice.  i also built one of these on a board i etched from the bajaman layout and did not have this problem---both voltages were around 4.5v and stayed steady with no change/crackle with rotation of the gain pot (same parts used).   i'm thinking perhaps this might be a bad batch of boards with some trace short somewhere.    any ideas would be very helpful----i hate to toss 2 boards full of parts.   perhaps brian could look at a sample board from his last batch and see if there's anything obvious to him pad wise, etc.     thanks very much.     rh

[madbean]

I'll check into this and report back.