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Old 29th Mar 2023, 5:49 pm   #1
collisr
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Default Shibaden SV700 Open Reel VTR - Wobbly picture?

Hi everyone,

What are your thoughts on this query?

I have a late 60s open reel VTR - a Shibaden SV700. Have cleaned the mechanics and replaced the sole capstan belt. Powered up, voltages look okay as per labelled PSU outputs. I get a strong but wobbly picture (see YT video)

Shibaden 700 test

I have not yet replaced any electronic components. Is this a "recap" the servo board task? If so, I assume I am targeting the electrolytic caps? Many are odd sizes like 500uF, 200uF. How accurate will I need to be with the Farad rating. i.e. if I use 470uF and 220uF (with same or slightly greater voltage rating as originals) will I be okay?

As always, any advice much appreciated.

Rob
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Old 29th Mar 2023, 7:00 pm   #2
TIMTAPE
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Default Re: Shibaden SV700 Open Reel VTR - Wobbly picture?

I'm not an expert in VCR's but replacing any faulty electro's sounds makes sense. If they're not in a timing critical role I imagine nominally close capacitance as you mention would do.

I'd also check mechanicals especially where the frequency of picture or sound oscillation matches the rotational speed of say capstan shaft, pinch roller.

Interestingly in one short shot, the picture seems stable but the time code wobbles. Baked into the videotape?

Of course the horizontally stretched display (widescreen instead of the tape's 4:3) only exaggerates any horizontal errors.
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Old 29th Mar 2023, 7:12 pm   #3
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Default Re: Shibaden SV700 Open Reel VTR - Wobbly picture?

I'm not convinced there is a fault The video from the SV700 will have mechanical timing errors that in today's VTRs would be fixed by a timebase corrector.

The Shib would have replayed into a CRT TV possibly with a flywheel sync line scan circuit. I don't think the flat screen TV you are using can cope... Try an old monitor/TV
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Old 29th Mar 2023, 11:25 pm   #4
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Default Re: Shibaden SV700 Open Reel VTR - Wobbly picture?

I have used these machines as both an operator and a repairer but a long time ago and I cannot remember seeing this effect before. I think Brian is on the right track by suggesting using a monitor that the vtr was designed to be used with such as one using a crt and flywheel sync. My gut feeling is capstan stability. The other thing to check is the full model number of the machine,the postscript tells you what system the machine was designed for and also check the spec of the tape. Is it a CCIR tape on a NTSC machine or vice versa. The wobble of the complete picture exhibits the effect we used to call hunting which was an attempt by the servos to compensate for a mismatch in specifications. Very interesting problem. Peter.
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Old 30th Mar 2023, 12:19 am   #5
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Default Re: Shibaden SV700 Open Reel VTR - Wobbly picture?

Could be a backtension issue; perhaps the tape has gone a bit 'sticky'.
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Old 30th Mar 2023, 3:17 am   #6
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Default Re: Shibaden SV700 Open Reel VTR - Wobbly picture?

Quote:
Originally Posted by peterpixel View Post
.. My gut feeling is capstan stability...
I thought the same. I couldnt hear any audio on the YT. Having the audio playing, especially music should give an idea of tape speed stability. The opening shot of the countdown clock often carried a test tone which could be useful in diagnosis.

Last edited by TIMTAPE; 30th Mar 2023 at 3:46 am.
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Old 30th Mar 2023, 3:19 am   #7
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Default Re: Shibaden SV700 Open Reel VTR - Wobbly picture?

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Could be a backtension issue; perhaps the tape has gone a bit 'sticky'.
There were definitely some early Sticky Shed tapes in that format and era, not least Sony EIAJ 1/2" tapes. But the oscillation is regular. A tape on the verge of sticking may be exacerbating the problem but it doesnt explain the regularity of oscillation.
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Old 30th Mar 2023, 9:41 am   #8
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Default Re: Shibaden SV700 Open Reel VTR - Wobbly picture?

The last thing you need with a mechanical VTR is flywheel sync - that would only make matters worse. We seem to have forgotten that when VCRs came about, we had to shorten the time constant of flywheel sync circuits in domestic TV sets. Professional monitors showed up timing errors quite badly and I remember some (EV?) had a switch to shorten it.

Brian of course, may remember RINSE

Last edited by Cathovisor; 30th Mar 2023 at 9:54 am.
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Old 30th Mar 2023, 10:16 am   #9
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Default Re: Shibaden SV700 Open Reel VTR - Wobbly picture?

Quote:
Originally Posted by Cathovisor View Post
The last thing you need with a mechanical VTR is flywheel sync - that would only make matters worse. We seem to have forgotten that when VCRs came about, we had to shorten the time constant of flywheel sync circuits in domestic TV sets. Professional monitors showed up timing errors quite badly and I remember some (EV?) had a switch to shorten it.

Brian of course, may remember RINSE
+1
Long sync time constants were useful in difficult receiving conditions of noisy but stable broadcast signals. In these conditions, the noise is disturbing the sync of a short time constant PLL, resulting in disturbances of vertical lines.
On the contrary pictures read from a VTR are normally free of noise since they are local but the sync is not very stable, which requires a short time constant in order for the PLL to "follow" this unstabilty.
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Old 30th Mar 2023, 12:57 pm   #10
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Default Re: Shibaden SV700 Open Reel VTR - Wobbly picture?

thanks for all the replies. An update:

Here is a capture of the same tape (a Scotch guardsman series which I have not known to go sticky) made through a G2 MTSC Time base corrector into a Sony DVCAM/Firewire machine

Update on previous video

This one has sound and although the "wobble" isn't as pronounced you can clearly hear wow and flutter on the audio.

I tend to agree with the comments that say this is down to the tape servo aka capstan subsystem. Could it be the pinch roller (it looks okay). Would the servo PCB control the capstan speed - hence back to the 55yo elcos?

I am no expert in tracking down electronics faults so any advice would be much appreciated.

Rob


(oh - and tried multiple tapes - all similar results)
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Old 30th Mar 2023, 1:25 pm   #11
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Default Re: Shibaden SV700 Open Reel VTR - Wobbly picture?

Thanks for redoing it this time with sound! As hoped there is a test tone at the programme head. The audio wobble frequency seems to coincide with the horizontal picture wobble. This time you havent included a shot of the capstan and pinch roller so hard to visually correlate but my guess is the speed wobble is at the capstan shaft but possibly at the pinch roller. I'd draw a half circle mark on the top of the shaft to easier observe any correlation between the picture and audio wobble with the capstan shaft rotation rate.

The spectrograph of the audio tone (it seems a little shy of 1000 Hz) shows the frequency of the modulation at about 7.5 Hz. Ideally the line should be a straight line.

The error in the audio tone is way above what should be expected for such a machine so I'd expect dynamic tape speed error is the cause of the picture problem.

Interestingly throughout the sample recording is a constant high frequency buzz consistent with interference from sparking at a motor commutator and brushes. Perhaps the motor itself needs some attention.

This seems like a good off air recording, showing how well these early small video recorders could do both in picture and sound. I wonder if this recording is available elsewhere or if this is the only surviving copy?
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Old 30th Mar 2023, 1:38 pm   #12
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Default Re: Shibaden SV700 Open Reel VTR - Wobbly picture?

Hello Rob,

You mention that the capstan belt has been replaced. The original belts were really firm and if the replacement is a bit 'stretchy' that is the effect you would get.

Best wishes,

Tony.
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Old 30th Mar 2023, 2:11 pm   #13
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Default Re: Shibaden SV700 Open Reel VTR - Wobbly picture?

Agree with Tony. Had this symptoms once on a Beta.

Another thing could be a deformed pinch roller or lack of lubrication of the capstan shaft/bearing.
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Old 30th Mar 2023, 2:46 pm   #14
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Default Re: Shibaden SV700 Open Reel VTR - Wobbly picture?

Thanks all.

So is the collective view this is a mechanical issue and not associated with caps in the servo board? (I ask because the only time I have seen anything similar is on a Sony C7 betamax where the Sanyo caps on the servo board caused the issue)

I do have a spare "junker" - I will try and swap over the pinch roller and maybe the capstan motor. The "replacement" belt is indeed very thick and reasonably tight but was a complete guess as the original had turned to goo.

More updates next week.

Thanks again

Rob

btw - I have checked and the BBC have this recording that I am using as a test,
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Old 30th Mar 2023, 3:04 pm   #15
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Default Re: Shibaden SV700 Open Reel VTR - Wobbly picture?

Do you know if this tape was recorded on this VTR, if yes then as others have said recheck drive belt and pinch roller. If not then the errors might well be recorded in, try and find another tape. But beware during that 1/2" open reel era there were many different formats. From memory the shibaden helical slope was opposite to Sony's.
I had a Sony ACE2100 which was similar to your Shibaden, the capstan stability was never great but not as bad as yours, which is certainly cyclic. The Sony's capstan phase / speed was governed by comparing control track pulses with replayed vertical sync using a ramp & sample servo. The resulting error voltage was used to slow the (nominally) fast running capstan motor via dynamic braking. Not sure if your Shibaden uses the same arrangment, but if it does might be worth checking time constants etc around the ramp & sample circuit.
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Old 30th Mar 2023, 3:08 pm   #16
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Default Re: Shibaden SV700 Open Reel VTR - Wobbly picture?

Quote:
Originally Posted by collisr View Post
...btw - I have checked and the BBC have this recording that I am using as a test...
In the world of archived recordings it's not just whether there is another copy but which is the best or most complete copy that has survived. Sometimes they can pick the best sections from both. Due to cost issues a lot of original videotaped programmes from that era were erased/overwritten. 16mm film copies never looked or sounded as good as the original pro videotape recordings. I dont know any more on this one but possibly your copy has better quality picture or sound or both than the BBC's copy. Maybe they'd still be interested in it for that reason.
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Old 30th Mar 2023, 3:24 pm   #17
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Default Re: Shibaden SV700 Open Reel VTR - Wobbly picture?

FYI

Managed to find the attached in the service manual.
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Old 30th Mar 2023, 9:48 pm   #18
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Default Re: Shibaden SV700 Open Reel VTR - Wobbly picture?

Quote:
Originally Posted by TIMTAPE View Post
This seems like a good off air recording, showing how well these early small video recorders could do both in picture and sound. I wonder if this recording is available elsewhere or if this is the only surviving copy?
It's not off-air because of the presence of the VT clock and the BITC.

In pre-VHS and other cassette format days, Shibaden recorders were used to provide "off-line" recordings at Television Centre for producers and editors to review their programmes - think of them as "rushes". The machines themselves were repaired and kept in what was colloquially known as "The Shib Shed" in the basement at TC. These machines are not broadcast quality.

This is what you are looking at here: if you look up "Stokowski Conducts" on BBC Genome you'll see that it was transmitted on BBC2 in 1969.

Last edited by Cathovisor; 30th Mar 2023 at 9:54 pm.
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Old 31st Mar 2023, 12:11 am   #19
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Default Re: Shibaden SV700 Open Reel VTR - Wobbly picture?

Quote:
Originally Posted by TIMTAPE View Post
This seems like a good off air recording, showing how well these early small video recorders could do both in picture and sound. I wonder if this recording is available elsewhere or if this is the only surviving copy?
Quote:
Originally Posted by Cathovisor View Post
It's not off-air because of the presence of the VT clock and the BITC.
Thanks for that. I meant in terms of picture quality. The video cameras which came with such recorders were much smaller, cheaper and well below broadcast camera quality of the day. But a recording of a good signal, whether direct as you say (thanks), or off air, looked pretty reasonable, as here, and it would look and sound even better after the tape was expertly cleaned, played back optimally, and without the YT data compression.

Quote:
Originally Posted by Cathovisor View Post
These machines are not broadcast quality.
I know and didnt say they are. I said that this recording, even though below broadcast quality (so were Quads if we want to be fussy) is possibly better quality than whatever BBC copies survive.

Last edited by TIMTAPE; 31st Mar 2023 at 12:34 am.
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Old 31st Mar 2023, 4:41 am   #20
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Default Re: Shibaden SV700 Open Reel VTR - Wobbly picture?

It seems I neednt have bothered! Here is the 1969 Stokowski concert free on YT in early BBC colour, albeit with some strange intermittent chroma gain boosts, a movement jerkiness and a distinct lack of audio bottom end. DVD available.

https://youtu.be/W3-33Dh0jxQ

But assuming speed here is correct, Rob's Shibaden playback is running slow, possibly related to the wow/flutter issue.

Last edited by TIMTAPE; 31st Mar 2023 at 4:56 am.
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