i Just picked up a used teac 144 portastudio and there is a hum (sounds like when a guitar cable isn’t properly connected) when it’s in the “tape cue” setting (sound goes away in “remix” setting). It also causes the VU meters for channel 1 and/or 2 to bounce around even without any input. This symptom is intermittent and sometimes goes away after it warms up. Is this a common problem with these old units? Some notes: - All tracks/channels record & playback - hum doesn’t record to tape It seems like a bad ground connection somewhere, visually everything looked okay inside, how can I test this? Also, would a blown component (cap, resistor, etc) cause a ground issue or am I mainly looking for a bad wire/solder joint? Lots of questions, I’m a noob and it’s been a while since high school tech class. Thanks!