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-   -   Bringing a Sony C7 Betamax back to life (https://www.vintage-radio.net/forum/showthread.php?t=180162)

monaro0162 15th May 2021 1:55 pm

Bringing a Sony C7 Betamax back to life
 
5 Attachment(s)
Hello,

I recently acquired a matching pair of Sony C7 UB Betamax video recorders, they are from around 1980 I believe. I've had success in getting a Sony VO2630 umatic and a number of Panasonic VHS machines fully working in the past, and thought that it was about time I added Betamax to the collection!

Both C7's were completely dead on arrival. I found a couple of open circuit capacitors in the power supply, so I did a complete recap and the power supply is now working.

Next was the dead clock/timer and display. It had multiple problems of corroded ribbon cable connections and pcb tracks, stuck buttons and gummed up switches. Repairing the ribbon cable and pcb tracks was a horrible job, but it's now working and able to power up the main unit. The clock runs but time display is not quite right, I may have missed one of the connections, but I can come back to that later.

On loading a cassette its pulls the tape out and wraps it around the head, but on eject there is no movement of the reels to pull the tape back into the cassette, so it gets tangled up. Nor am I seeing any spinning of the video drum, but mechanically it feels perfectly free. Looking at the belts underneath they all feel very loose and will obviously need replacement.

The rest of the electronics seem to be working it is passing a video source signal through, the picture is fine, and even the UHF tuner works. Mechanically it all seems fine inside, grease still present on what I can see of the mechanism.

I'm optimistic that I can get this C7 running again.... but how on earth do you change the belts..it doesn't look easy.

Any advice (other than chuck it in the bin!) appreciated :)

hillsrob 15th May 2021 4:37 pm

Re: Bringing a Sony C7 Betamax back to life
 
Good luck with it. I always wanted a C7 back in the late 70s early 80s. I ended up with a C6 which I still have in the loft to restore at some point. There was something space age about those edge mounted touch buttons. :)

monaro0162 28th May 2021 11:42 am

Re: Bringing a Sony C7 Betamax back to life
 
5 Attachment(s)
Hi all,

I made some progress on both machines. Both power supplies recapped and working, although I've only managed to get one of the clock display working so far. I removed all of the programming buttons as most of them had stuck and I didn't wan't that confusing the timer. I changed the belts on machine 1, it now loads much faster than it did before, but doesn't spin the head drum.

They both power up now, but are in different states of not working! I've listed what each machine does in the photos:

Can anybody advise what I should be checking next? Could the power supplies going bad have damaged one of the control boards?

hamid_1 28th May 2021 2:24 pm

Re: Bringing a Sony C7 Betamax back to life
 
I'm guessing a bit here, but the one with the rewind LED lit and the end alarm sounding, could have a faulty tape end sensor or its associated circuitry. Unlike VHS, Betamax tapes have a foil strip at the beginning and the end. The end sensors are coils. When the foil passes by the pick-up coil, it changes the coil's inductance and that triggers the tape end sequence (the alarm sounds, then it rewinds after a few seconds).

As for the second one, it sounds like it has not detected the presence of a tape - there's a switch in the cassette compartment which may be dirty and not operating.

If the power supply was just dead before you repaired it, then it shouldn't have damaged anything. You can always unplug a board and swap it with the same one in the other machine, then see if the same fault has moved along with the board. If it does, then you know that board is faulty, otherwise it could be another board or something else like a motor, switch or sensor.

The C7 was a very complex machine. I believe it had 3 microprocessors in total. Tracing logic faults is rather difficult.

monaro0162 28th May 2021 6:02 pm

Re: Bringing a Sony C7 Betamax back to life
 
4 Attachment(s)
I got machine 2 going, ironically the one I haven't yet changed the belts on! The logic is working fine now, the stuck led has gone away. It was a gummed up mechanism that pulls the tape out of the cassette on load.. wasn't returning to the corrrect 'park' position after eject. Also there was a similar issue with one of the position sensors on the loading ring next to the motor on the top left hand side.

It now loads and plays, although the picture is a mess. It isn't maintaining servo lock, as far as I can tell, I can hear the head drum hunting, and the picture rolls with colour coming in and out. I'll change the belts next ... and am assuming that I'm going to need to recap the servo circuitry?

Snarf81 31st May 2021 2:36 pm

Re: Bringing a Sony C7 Betamax back to life
 
Change C11 (0.47uf) and C41 (0.33uf) on the AS3 board and your troubles will disappear!

monaro0162 5th Jun 2021 7:53 pm

Re: Bringing a Sony C7 Betamax back to life
 
Quote:

Originally Posted by Snarf81 (Post 1379251)
Change C11 (0.47uf) and C41 (0.33uf) on the AS3 board and your troubles will disappear!

Thank you!

I changed bot of these capacitors and the tracking problem is fixed, the picture is stable vertically, colour is stable, and I'm able to sweep the tracking so that i get noise bars at the top or the bottom of the video image. But ... the image 'tearing' problem remains (as in pic 4 previously) Is this a signal processing problem that could suggest further capacitor replacement is required, or a mechanical problem .. worn heads?

Snarf81 6th Jun 2021 1:44 pm

Re: Bringing a Sony C7 Betamax back to life
 
No worries, glad to have helped.
Have you got multiple tapes? If so, find one to record something on and see if the picture is tearing on that recording. If so then it probably is worn heads.


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