Sony VO-4800 not threading up

[MX70]

I have a Sony VO-4800 that I've owned for almost 30 years, and has operated flawlessly, on the occasions I have set it up ( mainly for powering my DXC-M3 and DXC-1820). I've never even had the top off it in all that time.

But today it would not try to thread up.

The head drum spins up, capstan spins, but no movement at the threading ring.

I can manually move the ring into full threaded position, then the machine will play, wind, fast wind, record as normal.

Ejecting the cassette, it unthreads without a hitch, and cassette pops up.

I'm not that familiar with the mechanics of this machine , and unfortunately don't have a manual (yet) , but I am thinking a switch is dirty, or broken ( don't know how that happens , no one uses this unit except myself), but I thought I would ask anyone familiar with this machine if they have any ideas.

I do want to get this machine up and running again as I use it for my two cameras mentioned above, plus I do actually use it for recording on artistic projects.

Many thanks for any help!

Max

[Electronic M]

There's probably a threading motor I would try applying 6V DC to it and see it runs and moves the threading mech. If so the next thing to look for is a switch in the mech that senses the tape is down if that switch is bad it won't thread.... Beyond that get the manual and follow voltages there will probably be a bad transistor somewhere.

[MX70]

Thanks , Tom

I checked out those things yesterday and it seems I’ll have to find the service manual and start tracing the circuits.

Unless anyone out there knows which transistor would be the culprit, if that’s what it is…

Max

[MX70]

Okayyyy…

About 20 minutes after my last post, I started playing around with the VO4800, and I put a cassette in, and it sat there, heads spinning etc. then it made a gear-grinding noise , like it is slowly engaging drive to threading ring (or something) , then suddenly it threaded up. It now will play, wind etc.
Tried it a couple more times , same thing , it will sit for about 30 seconds then threads up. Probably stiff mechanism (or bad belt (?)). I will get in there to go on a fact-finding mission in the next while or so to see what’s what.

Thanks again

Max

[ARC Tech-109]

On the right hand side under the three blue connectors is the threader motor & gear assy, you can undo the three screws and lift it straight out. Under the threading ring are a number of "cams" or grooves that are used to move the various arms along the way, the ring can be removed and this will allow you to get after the stiff grease that's holding everything up along the way. Do not force the gear to move as these are actually quite fragile and are easily broken, a strong threading motor will break them and they're difficult to find.
I've had a number of the 4800's over the years and they're good decks. just take your time and numerous photos so you have an assembly record.

I like your Sony in your avatar, I had an AV8650 years ago that came out of a school auction for $20 along with the later video rover with the plastic body camera of which I don't recall the model number of.

[centralradio]

I have one here but cant remember how the loading drive is setup.I would check the motor .idler tire,belts in that area..