Strange ambient constant noise and intermittent loud pop noises/bursts occur only in Tape mode, and only in Right channel.
(noise volume changes with volume adjustment).
When using Mono mode, the 2 channels are mixed - this can confuse to think the issue is common to both cahnnels as it gives identical sound in both speakers - so I am using the Stereo mode which isolated the problem to R-ch only:
Engaging the Record bar makes it silent, but upon releasing, all the above noises fade-in and come back.
There are some 100+ e-caps in the main board, but I'd like to pinpoint the offending caps or components rather than tediously recapping only to find no change.
So far, ALL the caps pulled/swapped were in spec and ESR.
Actions taken to no affect:
1) Tapehead demag
2) Mode switch cleaned (Tape/Radio/Line-in)
3) Volume pot cleaned (which took away crackles DURING volume adjusting, not related to issue)
4) Rec bar sprayed with DeOxit D5 (not sure it penetrates enough tho...)
Note, the noises occur without a mech movement, so pretty sure the rec bar isn't to blame here.
5) Tapehead wires, GND connection and misc interconnections/jumpers verified as good
6) R-ch path e-caps and BJT transistors replaced up to mode switch (see highlighted audio path in pic)
Any suggestions appreciated.
(can post the whole Sanyo M9994K Service Manual pdf, if needed)
R-ch audio path highlighted.jpg 111.54K 5 downloads