Tape deck started humming after I opened it up

[Simon Loisel]

Hi, this is my first post here at Audiokarma and I am very excited to be a new member!

Here's my issue:
The right channel on my Teac A-4070 began working intermittently. Usually it would be very very quiet and sometimes after I moved the deck it would become fully functional. Today, I opened up the deck to see if any connections were obviously faulty and I did not find anything, but I unplugged and plugged back in several multi-pin jacks inside the machine. Luckily, the right channel is fully functional again.

However, now there is a low hum coming through. The volume of the hum is directly affected by the output volume setting. I am going to open the deck again and look for any disconnected ground wires but I thought I'd post here just incase anyone recognizes this problem and has advice. Thanks!

 

[Simon Loisel]

A few more details: the hum comes through when the tape is both playing and stopped. Also, the hum is louder in 3 3/4 IPS mode than 7 1/2 IPS, which makes me think the issue is the grounding in one of the motors.

 

[polymetric]

Sometimes there are grounding wire(s) connected to the chassis. You might have left one of those loose. It'd be fairly obvious and hard to miss, but it wouldn't hurt to check.

 

[audiojones]

I'd revisit the multi-pin connectors inside the machine again, maybe when you got one pin to make another one lost it's contact. Could try cleaning all of the pins and sockets by spraying some contact cleaner in them and plugging / unplugging the connectors a bunch of times.

This model used a whole bunch of relays IIRC, might need to go through and tap them all, see if any make the hum go away when tapped.

 

[Chip Chester]

There is also probably a shield around the playback heads, which should be grounded. This would likely be thru mechanical connection, but check for wires there, too. You can take a test lead from a known good ground point and selectively ground individual components/assemblies, if you have a service manual that shows that they indeed should be at ground potential... Do this after verifying that other operating equipment around it is not the true cause. (Big transformers in amps, fluorescent light ballasts, etc.) Is it there on headphone monitoring, or just when monitoring thru other equipment?

Chip