I'm helping a friend restore an old Gates Dualux console full of 5215A preamps, I'm stripping the cards down and replacing all caps and resistors.
The problem I'm having is upon testing with the restored cards there is some serious motorboating happening. I've tested with two different known working power supplies and the problem is still there (and I tested with an un-restored card with no problems, so it would seem that the PSU is not at fault).
When I remove the feedback circuit the problem goes away. I've tried reducing feedback by upping R1 to 100k and lowering C4 as low as .1 but the motorboating is persistent. Since the original caps seem to have a shield I tried mounting C4 under the board, but no change.
I'm wondering if anyone (Doug?) has any experience with this happening with Gates preamp cards, or any other type for that matter.
Thanks,
Paul
The problem I'm having is upon testing with the restored cards there is some serious motorboating happening. I've tested with two different known working power supplies and the problem is still there (and I tested with an un-restored card with no problems, so it would seem that the PSU is not at fault).
When I remove the feedback circuit the problem goes away. I've tried reducing feedback by upping R1 to 100k and lowering C4 as low as .1 but the motorboating is persistent. Since the original caps seem to have a shield I tried mounting C4 under the board, but no change.
I'm wondering if anyone (Doug?) has any experience with this happening with Gates preamp cards, or any other type for that matter.
Thanks,
Paul