Quantcast Panasonic AG-DS840 - bad capacitors? - digitalFAQ Forum
  #1  
02-12-2016, 12:42 PM
Mejnour Mejnour is offline
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Hello,

I have a Panasonic S-VHS AG-DS840 that I never took the time to play with it.

I finally found that when the vcr is "cold" first use of the day, the image take time to stabilize
5-10 minutes, to finally have a stable image.

If I un-power the unit and re-power it right away, it look like the vcr kept it's stored "energy" because when played the image is stable right away.

The longer the vcr is closed, the more time the image take time to stabilize.

Example of image at a cold start

Image stop shaking at 2min08sec
The same sequence few minutes later

I assume that it's bad capacitors problem.

My question is should I change all capacitors? (this vcr have many removable cards; TBC1; TBC2 etc.) with many capacitors
or I may restreint my energy for the big capacitors in the power unit block?

Thanks
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  #2  
02-12-2016, 09:09 PM
dpalomaki dpalomaki is offline
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When I looked the "few minutes later" post had been blocked due to copyright. The unit dates from ~1994, the era of failing SMD capacitors, so that could well be an issue, but there could be other internal, perhaps temperature-related, issues as well.

How long can you turn it off and still have a prompt recovery (seconds rather than minutes). If seconds the problems are likely electronic and if minutes they may be thermal as well.

It is unlikely that all capacitors would need to be replaced - the trick is determining which ones.
One approach is to obtain an in-circuit capacitor tester and check the capacitors, especially the SMDs for high ESR and out of range capacitance values.

Whether or not it is worth trying to fix it is a separate issue and would depend on the history of the unit and issues such as the condition of the heads, transport condition including belts and rubber components, and whether or not tape handling functions work even if video electronics to not play well at this time.
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  #3  
02-12-2016, 09:41 PM
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lordsmurf lordsmurf is offline
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You need to attach samples here, not Youtube.

FYI: I'm not sure who "UMG" is, but that was clearly fair use, and we'd tell them to take a flying leap.

Ideally, actually, you should replace all the caps. When one goes, more are likely more already gone as well. And then others will surely be soon to follow. If you're in the USA (or even Canda), TGrant is the guy to use.

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02-13-2016, 08:56 AM
Mejnour Mejnour is offline
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Sorry the second video have been block for copyright.
Machine have 838hrs Drum, 209hrs Capstan.

I would say that the capacity of recovery is linear with time, the longer it is stopped, the longer it take to come back.
Few seconds stop is not a problem, I have the time to change tape without problem.

I have a capacitance meter but I learned "the hard way" that to have correct reading, you have to unsolder at least one of the capacitor leg, I don't know if I really want to do that

I think this machine have over 100 capacitors

Thanks guys
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02-15-2016, 04:06 PM
dpalomaki dpalomaki is offline
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You can generally testy the ESR (equivalent series resistance) of electrolytics in circuit, at least sufficiently to identify the bad and marginal capacitors that are likely to be causing image issues.

At least within the AG1980 series, the main sites of failing capacitors was on the timer board (display) and the Y/C board that has the analog and digital Y/C circuits. These seem to be the critical locations, and the boards most often talked about. (Not sure how that compares to the inner parts of your unit.) While replacing all is not a bad idea, it may be unnecessary. When recap-ing my AG1980 I found the main issues were with the surface mounted electrolytics - perhaps 20% tested to have high ESR. This traces back to some bad capacitor production after the mid 1990s (attributed by some to stolen industrial secrets that went wrong). Thus the AG1980 (and its vintage) generally has the issues, while the AG1970 (an earlier generation) does not.

The FSM for your unit should include a maintenance schedule that will help assess remaining head and capstan life if that is a concern to you. Electrolytic capacitors used for bypass and ripple filtering usually have a wide tolerance (e.g., +/- 20% and a go/no-go ESR value) so precise component value measurement is not necessary.
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