digitalFAQ.com Forum

digitalFAQ.com Forum (https://www.digitalfaq.com/forum/)
-   Video Hardware Repair (https://www.digitalfaq.com/forum/vcr-repair/)
-   -   Panasonic AG1970 chroma board recap? (https://www.digitalfaq.com/forum/vcr-repair/12801-panasonic-ag1970-chroma.html)

brandonpaterno 06-01-2022 06:10 PM

Panasonic AG1970 chroma board recap?
 
1 Attachment(s)
Hi !!

I got ahold of a Panasonic AG1970 for virtually nothing. I grabbed it because it's the same model that we use at my college for tape recordings and transfers -- and I figured since it was so cheap I wouldn't mind grabbing it.

I got it home, plugged it in, and at first everything seemed fine. It took tapes, the screen looks bright, and it's quiet. I think the first two times it instantly spit out the tapes but after that I had no problems. I connected the VCR to a TV and to my dismay I noticed the image was extremely broken looking/staticy. I googled the AG1970 and found out that these things like to fail -- perhaps not as much as the AG1980 but they still do fail. I'm new to all this VHS stuff so I don't know what exactly the issue was specifically, all I know was the VHS images were all messed up. The images were semi recognizable, but the colors were very distorted. I discovered that pausing the video made the image look normal.

You may be wondering why I am not including a picture: the issue resolved itself, and now the image is stable and looks fine to me. From my brief research it seems like although the vcr is working, it most likely will fail with continued usage. I was seeing a lot about SMD caps, but when I opened the vcr I couldn't see anything of the sort. The normal electrolytic caps look perfectly fine! However, I could see corrosion on the metal shield on the "VEP03895D" removable board, so I removed the board from the system and unsoldered the metal shield and was presented with a myriad of SMD caps, two with some sort of weird orange gunk coming out the sides. I googled the board and it seems like this is a chroma board.

I figured since the issue corrected itself I should nip the problem in the butt and just replace the smd caps now rather than waiting for the problem to get worse. I know these boards are different than a regular PCB but it seems like the corrosion hasn't eaten through anything... yet! I wrote down what the caps have labeled on them and I'm going to try to find SMD replacements.

I just want to verify that these values are accurate for this board:
4x 47UF 6V
2x 47UF 6V
1x 47UF 16V
1x 4.7UF 25V
This is a picture of the board. I think the values are pretty clear, but I've never done anything with SMD's before besides with a Sega Game Gear a long time ago.
Attachment 15252
If you all have any tips on working with SMD caps, I would love to hear !! I have a heat gun which I can control the temperature of, as well as a controllable soldering iron. Are there any precautions I should take?

Also -- are there any other boards which fail due to leaking electrolytic inside of these machines that I should refresh? I've mostly worked with audio before so I wonder if I should recap the PSU or if I should leave it alone since these vcrs are only about 30 years old.

Thank you !!!

lordsmurf 06-02-2022 03:03 AM

Quote:

extremely broken looking/staticy
This is often bad heads, not bad caps.

In your case, it may have just been clogged heads. Then it became dislodged. That's why it "fixed itself".

hodgey 06-02-2022 05:01 AM

2 Attachment(s)
"Fixing itself" after a bit can also be due to sub-par/failing capacitors working better after warming up a bit, though head clogging is of course also a possibility yeah.

Judging by the service manual, VEP03895D (VEP03895C in the SM, maybe there were multiple revisions) is the sub luminance & chrominance pack, responsible for noise reduction and Y/C separation. So, bad caps there could certainly cause image distortion.

Not very familiar with the 1970, but the relatively popular PAL NV-FS88/FS200 decks are based on the same layout and share like 90% of the parts, and they do have certain caps that go bad on the equivalent board. The specific module (they're called a Hybrid IC typically) in the picture seems to be for Y/C separation or something, and the video signal goes through it both on playback and recording, so if the caps go bad it will cause issues. That module/hybrid IC in particular differs from the PAL equivalents (on the FS88/200 there is a different module in that part where the caps go bad), though I did find this random post about someone replacing caps on the same sub-module on a related japanese deck. Might be easier to replace the caps with new SMD ones though given the space constraints rather than what that person did.

I've replaced some SMD electrolytics on a NV-F77 (the non-svhs top of the line deck from the same lineup as the FS88/FS200, which shares most of the parts except the video circuitry) on a hybrid ic/module:

Attachment 15257Attachment 15258

I just used hand-soldering and solder wick rather than using rework station/hot air, but that might be a better solution, I'm no expert. If you've never worked with SMD electrolytics before it might be a good idea to practice on something else first though.

Another thing that can cause static/noise looking a bit like head clog/massive dropout on these early/mid 90s panasonics (or at least the PAL variants) is bad/cracked solder joins on the video head assembly as shown in this video, so that may also be worth checking if you experience similar symptoms.

Bad Power supply capacitors can also be a thing in decks of this vintage, though that tends to cause more subtle waves or noise on the image due to ripple/instability of the voltage going to the circuitry, or alternatively trouble turning on.

dpalomaki 06-02-2022 08:00 AM

1 Attachment(s)
To my eye, 4 of those caps look to be 10 mdf 16V. See the attached (but some sources might use a different marking scheme).

It makes sense to replace leaking caps.
Caution: it is easy to mess up copper traces if not careful working on SMD caps.
Others that look OK I would apply an in circuit ESR test and only replace if they test bad.

Note that the bad SMD caps came from a specific time period and were rumored to be the byproduct of inept industrial spying: they stole the wrong formula for the electrolyte in the caps. Generally speaking the AG-1970 production runs probably missed most of before that period. The AG-1980 smack dab in it.

brandonpaterno 06-14-2022 01:19 PM

failure !
 
Quote:

Originally Posted by dpalomaki (Post 85057)
...It makes sense to replace leaking caps.
Caution: it is easy to mess up copper traces if not careful working on SMD caps.
Others that look OK I would apply an in circuit ESR test and only replace if they test bad.

And mess up I did! The traces on the 47uf 6v cap in the top left corner of the picture lost the traces. I tried to attach the replacement capacitor up stream, but now the video looks really staticky, worse than before. The colors do not line up at all which tells me that I really messed the thing up :-( Lesson learnt for 13 bucks. If anybody has any knowledge of where to properly attach the 47 uf cap let me know, I was able to see a resistor underneath that seems to be electrically attached through a point in the board which goes from one side to the other. Also, if anyone knows what vcrs have equivalent hybrid IC's let me know. This thing is in really really good shape and the VFD is super bright which tells me this thing was seldom used. It would be a shame to throw it away, let alone part it out.

dpalomaki 06-14-2022 06:21 PM

Do you have the factory service manual? It should show the details of the circuits and board layouts, part numbers, and values.


All times are GMT -5. The time now is 04:57 AM

Site design, images and content © 2002-2024 The Digital FAQ, www.digitalFAQ.com
Forum Software by vBulletin · Copyright © 2024 Jelsoft Enterprises Ltd.