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Lynx 2 Flex circuit “perfect” position?


Tommy10

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Hi everyone.

Ive read all the forum posts here about D-pad issues but here’s the background...

I’m currently trying to solve a problem of just one button not working on my Lynx II after installing a BennVenn rev6 and new speaker. Everything works perfectly except for the left direction on the d-pad doesn’t work. 

Ive cleaned (with alcohol) the ribbon connector that enters the motherboard and reseated it countless times to try and get the button to work. I’m sure the button was working fine before I opened it up. The only possible visual cause could be a minor kink in the flex circuit that seems to be caused as it sits over a certain bit of plastic on the shell.

A few have said that the flex circuit must be seated “perfectly”. Can anyone define “perfectly” as surely it just sits where it sits without fine adjusting. 

Thanks for any help.

Tom

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I've ran into this before with another Lynx II I serviced over a year ago. Ended up that the d-pad itself on that Lynx had to be in a specific position in order for all the controls to register properly. All the direction were working, but Left was harder to engage that the other directions. I can't recall what the dpad looked like, but ever since that happened, I now take my VIA scribing and boring tool and scratch a T on the inside center area of the d-pad itself to mark which way was up when I removed it. I haven't had it be a problem since.

 

I've also seen I think about 3 different revisions of the Lynx 2 d-pad and they are all just a tiny bit different in the centers. One variant doesn't have any supports from the centers to the L/R/U/D sections, while another did have small supports that went from the center outward. I've even seen one that just had one support coming from the center and went to the bottom or top dpad position as I recall.

 

Have you taken your meter to verify you have continuity from the left trigger portion of the pad to where it connects on the end of the ribbon? Same with the ground points from the left as well?

 

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Thanks Crossbow. I was hoping to contact you as one of your previous posts was on this topic. Regarding marking the d-pad, It never moved in the dismantling process but I’ll keep it in mind. Ive not done a meter test, that’s something I should have thought about. I’m afraid when It comes to ground points you’ve lost me. Electrical diagnostics are a nightmare to me. Perhaps that’s why I’ve hit a wall now.

I’ll update shortly.

 

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What I meant by ground points was that if you look at the flex circuit closely. You will see that one trace is shared by most of the controls and buttons. That is because in most cases, all that happens when you press a button or direction, is that you are completing the circuit to trigger that input to the game system. So to check the ground in this case I was meaning that using a meter in continuity mode, you just probe different parts along that traces to be sure that signal is good on all the directions. Additionally one of the ends of the flex cable where it plugs into the Lynx is where they all terminate.

 

Another thing to be aware of, is the removing and inserting that flex multiple times into the socket on the lynx, will result in the traces wearing off at the end. It only takes a few times to have one of them seemingly just rub all the way through. A trick to correct that, is to use a pair of scissors and trim off about a 1mm from the end. that should bring enough of the carbon coated traces that haven't been scraped on yet by the connecter to essentially provide you with an all new end to insert and go from there.

 

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Another thing here is that there are holes in mylar flex that match up with pegs on the top and I think bottom of the tray frame it sits on to help with alignment. Also tab sections around the function buttons and the dpad section that the flex fits and sits under. 

 

The actual buttons are nothing more than small domes similar to that used on the controllers from the 2600 and 7800 just much smaller and they do wear out with use over time. But my initial guess is that one of the traces from the dpad direction not working is broken within the flex somewhere. Might try holding the flex up to some light and carefully bend it slightly in places (not enough to crease anything!) to see if breaks appear and light begins to shine through. I've had to do similar with 5200 controller flexes when I've had them be flaky. I've not had any success in repairing broken traces given the mylay used melts stupid easy under any iron temps. So I've just had to replace them out when I find a break in them. Also be careful with the flex on the Lynx II in regards to the power LED. It is literally just taped onto the traces that power it and that tape wears out over time. In fact 2 of the new flex I received from Best about 2 years ago, already had flaky LED operation because of the original tape being loose. Just had to reinforce with some kapton tape wrapped around the ends tightly.

 

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Update...

I’ve included a picture which probably explains my problem.

I tested continuity and the circuit is fine in all respects including the d-pad left direction to a point. Its a complete circuit to the transparent part toward the end of the ribbon but not right at the tip. As the picture hopefully shows a few carbon contacts are worn away either through my excessive cleaning or reinserting of the ribbon.

Crossbow, you mentioned I can snip off 1mm to reveal fresh contacts. Is this my next move or is this flex circuit beyond repair?

Thanks.

8F79A04F-F4B6-4584-B434-352F3DAEC4B6.jpeg

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Yes... cut along in as straight a line as you can right at the point where the traces just start to rub off. You can do this maybe two times before you don't have much left to hold onto to insert the cable in easily.

 

Keep in mind this can't really be avoided. After nearly 30 years these carbon traces will scrape off easily and just unplugging the cable from the socket is enough to cause this. Even the replacements from Best will do this if you insert them in and out more than a few times.

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3 hours ago, Nop90 said:

Can a conductive ink pen help to restore the worn edges without haveing to cut the flat?

It might but as I've not used one, I don't know about the durability of the ink once dried. The reason this happens is because the fingers on the inside of the connector are metal of course and it literally scrapes away at the traces until they are completely destroyed on the ends as you see here. Even with new flexes the carbon traces are still just as old so it still happens. When I install LCD upgrades into the Lynx II units, I make sure to NOT lock the ribbon in while testing until I'm finalizing the install and buttoning it up for the last time to help reduce the wear on the cable ends as much as possible.

 

So to get back to your conductive ink. I don't see a harm in trying it, but it isn't likely to last long term either.

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Update...

After snipping off 1mm of ribbon cable I can confirm all buttons are working now. Thanks Crossbow, that was a top tip and really appreciated. 

Seems that the end of the ribbon just needed “refreshing”.

Thanks Nop90 for the conductive pen suggestion but I decided not to go with it but It may well work for anyone else experiencing the same issue as me. 

Thanks again.

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