Quantcast Panasonic AG-1980 white streaks, comet tails? - digitalFAQ Forum
  #1  
12-05-2017, 11:48 AM
NJRoadfan NJRoadfan is offline
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Had to pull my AG-1980 out of the box for an EP tape transfer yesterday. I'm running into the common problem with the output showing comet tails, but its intermittent. Sometimes its bad, other times the machine plays fine..... some tapes are more prone to it then others. Has anyone isolated the cause of this in these decks yet? It is definitely NOT tape dropouts as the tape plays fine on my JVC DVHS deck.

Video heads should be fine, this unit was hardly used before I got it and I really haven't put too many hours on it. Only reference I could find to the problem is possible static build up and discharge in the head assembly, but this deck appears to have a grounding strap for that (unlike the Betamax decks referenced below that need them retrofitted).

http://www.palsite.com/pcat_gndkit.html
http://www.palsite.com/950tech.html#static

Note: The machine isn't showing any of the other problems, my Y/C board seems to be behaving so no color problems.
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  #2  
12-06-2017, 02:24 AM
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lordsmurf lordsmurf is offline
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You have bad caps.

Welcome to the club, we've been waiting for you.

A TGrant $300 fix is in your future, unless you know how to dismantle it, and test all the caps on all the boards.

(From what I was reading, deter isn't fixing them anymore. He fixed my last comets issue, for a few bucks less that TGrant, though the luma is now a shade darker afterwards. I don't think he tested the output color values like Tom does. TBC-3000 when using it anyway.)

It's not the heads.
It's not static charge.
It's caps.

I have yet to hear an explanation of how/why that specific issue happens. Because it does look like head damage. Yet it is not.

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12-06-2017, 04:30 AM
Quasipal Quasipal is offline
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Quote:
Originally Posted by lordsmurf View Post
You have bad caps.

Welcome to the club, we've been waiting for you.

A TGrant $300 fix is in your future, unless you know how to dismantle it, and test all the caps on all the boards.

(From what I was reading, deter isn't fixing them anymore. He fixed my last comets issue, for a few bucks less that TGrant, though the luma is now a shade darker afterwards. I don't think he tested the output color values like Tom does. TBC-3000 when using it anyway.)

It's not the heads.
It's not static charge.
It's caps.

I have yet to hear an explanation of how/why that specific issue happens. Because it does look like head damage. Yet it is not.
The job of capacitors in the video stages is decoupling (DC) and frequency filtering. Simply, the comets (streaks) are caused by clipping of the video signal caused by the capacitors not acting correctly due to drying out. This clipping is the same on screen as when the head gap opens up and the signal is clipped due to the width of the head gap not being able to render the highest frequencies (like when a audio head wears the sound gets muffled - same thing but with video).

Why bother testing capacitors? All are ageing ungracefully so to change the lot gives you peace of mind that there is not a rogue cap waiting to spoil the party after you have it all back together. If you like podcasts, putting one on while you change capacitors is actually quite therapeutic.
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  #4  
12-06-2017, 09:23 AM
NJRoadfan NJRoadfan is offline
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Eh, I have had plenty of bad caps around here

This repair is going to have to wait. Just moved and the project table is covered with boxes.... oh and that whole mortgage thing takes a chunk out of my budget every month. My cap replacement guy might be cheaper, but he wants just the boards, no sending the whole unit.
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ag-1980, comet tails, playback, white streaks

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