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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc.

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Old 11th Dec 2018, 10:24 pm   #1
jamesperrett
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Default Sony C6 Fault Finding

While I'm fairly experienced with general electronics and audio, this is my first attempt at working on a video recorder...

I borrowed a Sony SL-C6 from a friend in the hope that I could replay some digital audio PCM encoded tapes using a PCM701 encoder/decoder. Unfortunately it hadn't been used for a while and some of the belts were no longer doing their job. I haven't been able to find a set of C6 belts at a reasonable price so have bought a selection of similar sized belts from CPC and have replaced the capstan belt, the forward belt and the threading belt. I bought a recent looking, sealed Sony tape to test and it will now load a tape and play and record after a fashion. However there are still problems which prevent the PCM encoder from reading the data for more than a fraction of a second every so often. Unfortunately I don't have any already recorded Betamax tapes that I'd be willing to try so can't find a way of isolating whether the problem is on the record or playback side.

I've recorded a few seconds of the input signal (with silent audio) going through the recorder and put it up at
https://drive.google.com/file/d/1-6v...ew?usp=sharing

while the output looks like
https://drive.google.com/file/d/1R7I...ew?usp=sharing

The last couple of seconds are silent so should look like the input file above. The decoder managed to extract a little bit of audio near the start but was mute for most of the time.

I've tried cleaning the ACE head - there was a little bit of dirt on there but it didn't make any difference. The tape itself doesn't appear creased but it sounds a bit like the speed of something is changing cyclically - possibly in time with the change in the horizontal shift seen in the second video. I have a copy of the service manual and have seen the pages on the C6 at the PALSite but I think I need a little guidance as to what to look at next. Could it be a tape tension issue and, if so, what do I need to adjust to change the tape tension? The PALSite C6 page mentions servo issues and suggests adjusting a couple of potentiometers but I'm loathe to start adjusting things without being a little more sure of what the issue really is.

Does anyone have any idea about where I should look next?

Many thanks,

James.
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Old 11th Dec 2018, 10:51 pm   #2
Red to black
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Default Re: Sony C6 Fault Finding

Search on this forum for Sony C5/6/7 problems, myself and others have posted component references in the past for cyclical mistracking/capstan servo faults for these machines, There are two capacitors on the servo board of the C6 in particular that are of note.
I am fairly busy right now but if you get no joy searching on here I will look up old notes for you when I get back home,
Ps. I am not sure the SL-C6 had PCM facilities the SL-C9 had an adaptor at some point.
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Old 12th Dec 2018, 12:22 am   #3
jamesperrett
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Default Re: Sony C6 Fault Finding

Would those servo board capacitors be the C7 and C8 mentioned near the top of

https://www.palsite.com/slc6tech.html

I realise that the C6 may not be the ideal partner for the PCM701 PCM adaptor but it happened to be easily available so I thought it worth trying. I'll have a bit more of a dig around for previous posts.
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Old 12th Dec 2018, 1:59 am   #4
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Default Re: Sony C6 Fault Finding

Almost all SLC6 machines will these days need the capstan and drum servos to be set up as well as having the infamously dodgy low value capacitors replaced. These are electrolytic types in the SLC6 whereas the SLC7 had mylar ones in the same circuit.

There was a switch on the machines that were specifically intended for use with the PCM701... this disabled the drop out compensator when in PCM mode.
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Old 14th Dec 2018, 2:35 pm   #5
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Default Re: Sony C6 Fault Finding

Replace all light blue Sanyo capacitors, on the servo board.
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Old 14th Dec 2018, 2:39 pm   #6
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Default Re: Sony C6 Fault Finding

Those tants on the servo board,two are very notrious CRed??)
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Old 31st Jan 2019, 12:00 am   #7
jamesperrett
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Default Re: Sony C6 Fault Finding

Quote:
Originally Posted by DangerMan View Post
Almost all SLC6 machines will these days need the capstan and drum servos to be set up as well as having the infamously dodgy low value capacitors replaced.
I've just had a chance to get back to this and replaced the 0.22uF capacitors in the capstan servo circuit as well as the 0.1uF capacitor (C43) in the head drum servo circuit. Things have improved but it still isn't right and I can still hear the head drum speed changing in both record and playback. I was looking for a setup procedure for the servo circuits in the service manual but couldn't see one so I was wondering whether anyone could point to the setup procedure or is it a case of gently adjusting the pots and seeing if there is any improvement?

I saw mention on PALSite of having the machine hanging off the side of a table while making the adjustments from underneath - is that the right way to do it or could the machine be used on its side? I'm trying to work out how I could attach scope probes to check the signals if it had to be kept horizontal.

Many thanks,

James.
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Old 31st Jan 2019, 2:46 pm   #8
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Default Re: Sony C6 Fault Finding

Apart from the mentioned cap replacements, I'd go through the machine mechanically and as a learning exercise as VCR's are somewhat different from audio tape machines. It might be a good idea to obtain a book on general VCR service, or specific to the C6.

I'd also source a known good pre recorded Beta cassette. As well as the picture, the linear sound track can also give useful information from any wow and flutter present as to the stability of the machine's tape drive.

Looking at the output sample there's what looks like the basic PCM pattern but overlaid with a lot of noise. Could this be as simple as dirty video heads or poor back tension? Again, a pre recorded Beta tape would be a good way of checking the VCR's picture and linear sound performance before attempting to play the PCM tape.

I have 5 working Beta machines, three Sony and two Sanyo, for transferring customers' tapes and am able to service and repair them. I've found repair and service of VCR's challenging at times but rewarding.
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