Fostex 280 weird chirping record

Hi All,

I'm fixing a Fostex 280 cassette recorder. It had a broken (melted) belt which I replaced and gummed up supply and takeup bearings, which I cleaned and lubricated.

When I record a test tone into it, it records, but along with the tone is a rhythmic chirping, it sort of has a galloping rhythm. It is on all 4 tracks. When I record without an input no chirping.  If I record with the pitch control all the way up and playback at that same speed, the chirping is a faster rhythm but the same pitch.

What is going on? It seems particularly odd that it doesn't record without an input.

Sam

The fact that interval of the chirping changes, but the frequency doesn't makes me think it could be a tach pulse or something in the motor control circuit.

Hmmmm.....Does the chirping coincide with the tape counter?

samgraysound said:

... but along with the tone is a rhythmic chirping, it sort of has a galloping rhythm.

Click to expand...

This may or may not apply, but back in the day when I was fixing consumer stuff, cassette decks that had been sitting for years would sometimes do something similar, a squeal modulated by motor boating, or something equally wacky. It was always oxidized contact(s) in the board mounted changeover slide switch from playback to record mode.

A good shot of Cramolin and working the switch 50 times usually took care of it.

Gene

TheJames said:

The fact that interval of the chirping changes, but the frequency doesn't makes me think it could be a tach pulse or something in the motor control circuit.

Hmmmm.....Does the chirping coincide with the tape counter?

Click to expand...

No it doesn't appear to correlate to the counter. Maybe chirping isn't the right word. Sort of a burbling. It is rhythmic but also kind of inconsistent.

Gene Pink said:

This may or may not apply, but back in the day when I was fixing consumer stuff, cassette decks that had been sitting for years would sometimes do something similar, a squeal modulated by motor boating, or something equally wacky. It was always oxidized contact(s) in the board mounted changeover slide switch from playback to record mode.

A good shot of Cramolin and working the switch 50 times usually took care of it.

Gene

Click to expand...

Thanks for the idea. This unit doesn't have a mechanical switch in that way. It looks like the record and transport controls are all front panel push-buttons that controls logic circuitry

The pitch of the noise changes with the oscillator frequency.