Panasonic AG-DS840 bad capacitors?

[Mejnour]

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

[dpalomaki]

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.

[lordsmurf]

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.

[Mejnour]

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

[dpalomaki]

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.

[Sunbittern]

Sorry to bump this old thread but I think I'm having the exact same problem with my AG-DS840 - did you find out which capacitors, board, or general area of the deck was the issue?

I can't see the original videos posted but when I first turned my deck on the picture was complete gibberish (although I did get sound):

Screenshot 2024-11-23 181347.jpg

After the deck warmed up for a while, and I turned it on and off a few times, I get grainy black and white video through the monitor composite output:

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Interestingly the TBC menu overlay text is clear when I turn that on:

Screenshot 2024-11-24 124628.jpg

I opened the deck up and took a peek inside, and pulled out some of the internal boards and looked at them, but there's no obvious leaking or bulging capacitors that I can see. So I guess I will need to figure out how to measure the capacitors individually and determine if they're bad (this will be new to me - I'm more of a software guy than hardware).

[dpalomaki]

Bad or weak caps may not leak or bulge; that is a worst case behavior. In my experience they look normal more often than not. (Just like AA batteries they may die well before they leak.)

That the system performance gradually improves when on can mean weak caps are reforming when power is applied.

Measuring caps while in the circuit is not precise but often can identify failing/failed caps. An ESR meter, as discussed above, is one tool that can be used for this. While it is not a 100% guarantee test it works in many cases. They are NOT expensive as test equipment goes. Always power off the system and let it sit for a bit so charge on caps can bleed off.

Your grainy monitor photo is consistent with failing caps. In the case of the AG-1980 these were mainly on the Y/C board. That is a good place to start. Many folks replace ALL of the SMD electrolytic caps on the Y/C board since they account for most of the bad caps that degrade the image.

The on screen VCR menu text is likely added after the Y/C board.