Adjust Panasonic AG-1980/5710 with extended cables?

[MrPete]

As has been discussed here, the Panasonic AG-1980/5710 S-VHS VCR's have a strange design with the main board upside down... making it literally impossible to do service/test adjustments with the board(s) in place.

To make it worse, the necessary cables are too short to pull the board and have everything connected while the main board is right side up!


I'm looking at solutions for this. Obviously it MUST be possible somehow.


The "obvious" solution is to obtain a few extended cables. But that doesn't necessarily work correctly.


Before I go out and do that, I'm hoping to ride on others' coat tails.


HAVE YOU TRIED THIS?


* Did it work?
* Which cables did you extend?
* Any cautions?
* Is there another solution?


Thanks!
Pete

[aramkolt]

Good question - I'm not sure there's much to be gained by adjusting the factory settings per se. The service manual doesn't really tell you to adjust anything that is inaccessible - Most of the boards with adjustments are accessible THROUGH the top main board (they have little holes that allow you to access the potentiometers from above the board, even though the circuit boards are below.

The only one that you really can't adjust is a few trimmers on the TBC board which I believe have to do with individual levels of RGB. Since color is going to vary from tape to tape and is almost never oversaturated, I don't think it makes sense to mess with those. Any users that picky about color can adjust in post and I've always thought the color on AG1980's is richer to begin with than a lot of others, so you have more to work with.

The only "extension" I'd consider putting on the board is the "Y" or luma adjustment for S-Video which is accessible through the main board, but having access to that would allow you to not clip whites and you could vary it depending on the tape if that adjustment was accessible outside of the VCR (without opening the top lid). I've never actually touched it though since there's usually a separate proc amp in the chain - but if you don't trust your automatic gain control on your capture card and you are seeing white clipping, it's a mod I'd consider at least trying - though not for calibration purposes per se since luma can also vary from tape to tape.

It's not too uncommon to measure 120+ IRE whites from commercially made tapes on the recommended JVCs which can be a problem, but I haven't really checked the variability on luma levels from tape to tape on the AG1980 yet, again because there's usually a proc amp in the chain.

[MrPete]

@aramkolt -- THANK YOU! Boy do I feel dumb... "Most of the boards with adjustments are accessible THROUGH the top main board (they have little holes that allow you to access the potentiometers from above the board, even though the circuit boards are below.)"

Now to find a nice strong plastic trimpot tweak tool.

I agree on RGB levels. Unless way out of whack, it's a nit to balance that. (My fave story on that: my wife's family had NEVER seen her parents' wedding photos, because the undeveloped film sat in a hot car glove box throughout their honeymoon. Everything was dingy orange. Yet with modern photo tools, I just touched the wedding dress and called it gray-scale... BOOM: perfect colors throughout )

[MrPete]

BTW, I have on order a nice modern tool for much of this testing: the Owon VDS1022i PC Oscilloscope. Not only is it a US$80 2 channel scope with isolation, very fast refresh and conservatively 25MHz bandwidth... it has hardware video signal triggering. Can choose exactly which video line to see! Should be nice for this project.