Hello! I bought a WM-D6C (serial ~72,000 amorphous head model) earlier this year and it's in really good condition cosmetically. Playback is also very good from what I can tell. The only real problem I've encountered with it is with the recording function. I've tried recording a few different tapes and experience roughly the same result each time—On playback, the tape sounds totally normal for about a minute, but after that the left channel drops out and is very low volume. The right channel continues to record perfectly at full volume, but I can't seem to figure out why the left channel is not the same. Today I tried connecting a battery powered Sony microphone to the mic input and it seemed like when I tapped on the mic and created a spike in the volume, the left channel would return for a moment before dropping out again... pretty weird. Another thing I tested was the Line In port, which I couldn't seem to get any sound from, but I might've been doing something wrong. I don't have a lot of experience repairing electronics like this, but I have most of the tools to try it, so any advice would be much appreciated! Going to try cracking it open and giving it a visual inspection in the meantime, will update this thread if I notice anything out of the ordinary. Thanks in advance for your help!
The spike and momentary return to normal suggests a poor electrical connection somewhere. Things to check are: REC/PB swtich (clean with contact cleaner), REC level pot (these will get damaged if unit was dropped), crack on the PCB near IC302. Regarding LINE IN, what signal have you fed into it ? A mic will not work on line in, as it needs plug-in power (which line in doesn't have) and signal is too low without the mic preamp. LINE IN bypasses the mic preamp (it's right after it), so fact the mic works but line in not is strage and would point to a faulty rec level pot at first glance.
