Teac A-3340 Hum when recording

[AnnieJohnson]

I have recently acquired a Teac A-3340 (4 channel) reel to reel tape recorder.
For now I am only working with 2 channels. However when I connect the headphone, I notice there is a slight hum.
When I want to record something and switch inputs to ‘Source’, then hum increases and become much louder (especially on the left channel)
So to summarise, there is hum on both channels but it is louder on the left channel when input is switched to source. It does sound like mains hum and I was wondering if someone had a similar problem on this deck. I don’t want to start adjusting bias levels or randomly changing capacitors everywhere. The heads are in good condition. The manual indicates that it may also be faulty record amplifier or some record relays. I have some questions and would be grateful for some guidance:

Q1 . I think looking at the mains supply circuit capacitors may be a good starting point to address hum?
Q2. Would faulty record relay still allow recording to be made? I can make recordings on both channels
Q3. What should I look out for in the record amp circuit?

Kind Regards

Annie

 

[The Ghost of FM]

Is the hum still present if you disconnect the deck from all external connections, both inputs and outputs? I ask because its important to learn if the hum is an internal issue with the deck or a ground loop issue with your collective of gear.

Also, is the hum present at the line level output jacks as well? Meaning, if you connect the deck to an external mixer, amp/computer, etc, is the hum audible on that external source too or only through the deck's headphone jack?

It's important to do a basic process of elimination first, to help nail down where the hum is coming from before you start fretting over relays and power supplies.

Cheers!