DewDude wrote:
Hi all,

I recently acquired an Onkyo TA-207 cassette deck which was in mint
condition and worked flawlessly at first. I'm guessing since I've
given it more use in the last 3 weeks than it's previous owner
probably has in the last 9 years, I noticed that a strange
harmonic-like electical hum had developed. So, after moving the unit
to several locations finally setting it inside a farraday cage and
was unable to remove the noise, it was apparent it was sourced inside
the unit. After a few minutes I discovered the VFD was the culprit,
creating this electronic hum when turned on (this unit has option of
turning the VFD on and off and selecting brightness), and increasing
when the brightness was turned on. I listened to this unit quite a
bit when I got it and it did not have this problem. I've noticed it's
gotten louder over maybe the last week. Now, a few things I've
noticed about this. The noise is not present on tapes I've recorded
when the VFD was on. I verified this in other tape decks. It's also
getting in somewhere in the tape pre-amp circuit, becuase if I turn
Dolby on, the noise is greatly reduced.

I'm not sure what exactly I can do aside from creating a shield around
as much of the VFD as possible, but even then that might not work. I'm
sure this thing was engineered so the VFD wouldn't interfere, and
being made in 1991, it's completely possible that the sudden shock of
use might of caused a componet or two to start breaking down, perhaps
a resistor that's going to ground for shielding has failed...although
it's hard to see a small resisitor like that fail.

I haven't yet obtained a service manual or schematic...so if anyone
out there has one they might be able to dig up for me, i'd appreciate
it, but any other advice would be helpful too.

I'd suspect bad capacitors in the power supply, and / or loose ground
connections.

Mark Z.