Xenarc 702TSV torn flex cable after custom fit

STI_FFY · 05-01-2009, 03:07 PM

I bought a 702TSV to replace the old Lilli in my Subaru's dashboard. The reason for the replacement was that the old Lilli was never very easy to see, and the touchscreen has started to fail lately. Sometimes touching the screen does not move the pointer at all or moves it to a point very far from where touched.

The 702TSV is incredibly bright and all my testing so far shows it to be far better than the original Lilliput (which was not transreflective).

Of course I had to modify the display to fit it into the double-din opening in my STi's dash. Now the Xenarc LCD panel snaps into the STi dash from behind.

Anyway, after taking it apart many times and putting it back together for intermediate testing, it failed the test yesterday. The colors were all screwed up. I first verified that this affliction applied to all 3 sources - VGA, AVI2 and internal menus. The most likely candidate for this collection of symptoms was the flex cable.

It turns out that in the disassembly process I overstressed the flex cable that connects the controller to the LCD panel. It has a short tear through pins 1-4 of this 50-pin flex cable.

Be careful with that cable! It cannot be replaced apparently. I had to buy a new LCD panel @ $190 plus shipping in order to fix this.

Fortunately for me Xenarc are very good about selling parts.

It's very sad that now I have this perfectly good and very bright LCD panel that cannot be used for want of a few conductors on this cable. If the other end was removable this would be a $10 fix.

I tried to repair this by jumping the gaps with fine wire, but there's no soldering tip on earth thin enough for this job - at least not when wielded by me.

SwiftDeath · 05-01-2009, 03:49 PM

Wow that's rough. I suppose it's good you posted this as it's good to know how strong, or in this case fragile, certain components are.

STI_FFY · 05-01-2009, 06:56 PM

It seems to be very difficult to slide the cable out once the black plastic bail has been lifted on the connector. With no pull tab or block on the cable it is necessary to pull on the cable itself. It is difficult to pull without exerting uneven pressure and one end of the cable will get stressed.

When the new one arrives, I will consider gluing a pull block onto the cable so it will be easier to get it out of that connector when need be.

PaulF · 05-01-2009, 07:17 PM

Have you tried shaving the plastic off of the wires? If you used a knife and shaved the plastic off of the ribbon in that spot, you might get enough room to solder it.

STI_FFY · 05-01-2009, 07:25 PM

The insulation isn't the problem. The spacing between the wires is.

I got the copper exposed using an emery board. I actually managed to bridge pin 1, but when I tried to bridge pin 2, the bridge on pin 1 came undone (the iron touched it briefly). Also the jumper wires are so short that when you touch one end, both come unsoldered and the wire shifts.

I suspect the only way to be successful would be to have several wires spaced the correct distance and solder them all at the same time. I have not yet come up with a way to do this.

I haven't given up. I've thought about taking an old surface-mount chip and using its legs. I'll need to find one with the right spacing and long legs.

colin · 05-01-2009, 07:30 PM

Try using solder paste and a heat gun on very low air pressure on just that spot. The syringes that they provide you with are ridiculously small and with wet enough solder you could fix that for sure. If not, sell it to me for super duper cheap and Ill make it work

STI_FFY · 05-01-2009, 08:47 PM

Quote: Originally Posted by colin

Try using solder paste and a heat gun on very low air pressure on just that spot. The syringes that they provide you with are ridiculously small and with wet enough solder you could fix that for sure. If not, sell it to me for super duper cheap and Ill make it work

I think the problem with that approach would be lack of structural strength. The moment it flexed the solder would crack. You need some wire across the tear for rigidity.

colin · 05-01-2009, 09:00 PM

Well im assuming the black (darker) part doesn't flex? I would just coat that part in epoxy and not let it flex. There's no way that a 1mm difference in where the cable can and can't flex would affect performance. Youd basically just be extending the rigid connector area.

mrbean_phillip · 05-01-2009, 09:49 PM

Would you consider selling that LCD then? I could fix it, and have a need for just an LCD -> will run LVDS onterface off my motherboard to it...

Would appreciate your feedback.

STI_FFY · 05-01-2009, 11:28 PM

Quote: Originally Posted by mrbean_phillip

Would you consider selling that LCD then? I could fix it, and have a need for just an LCD -> will run LVDS onterface off my motherboard to it...

Would appreciate your feedback.

I'm not really interested in selling it. I plan to devise some way to fix it. It may take some time, but there's got to be a way.

nobb · 05-02-2009, 12:14 AM

Have you looked into getting a silver solder pen? I have no experience with them, but it would probably be easier than soldering.

rodweb · 05-02-2009, 02:34 AM

Is the cable plugged in at both ends or is the other end permanently connected?

Perhpas you could be looking for a new cable. There is a seller on eBay called RaidGear (from memory) who I bought a ribbon extender for the buttons on the 706TSA.

mrbean_phillip · 05-02-2009, 03:32 AM

Ah, no worries.

Thx anyway, and goodluck with it

STI_FFY · 05-02-2009, 04:38 PM

Quote: Originally Posted by rodweb

Is the cable plugged in at both ends or is the other end permanently connected?

Perhpas you could be looking for a new cable. There is a seller on eBay called RaidGear (from memory) who I bought a ribbon extender for the buttons on the 706TSA.

I don't think so. I've not taken the backlight/LCD assembly apart yet, but I probably will eventually. The flex cable becomes as wide as the assembly at the top, and disappears into the full width of that assembly. There is a piece of tape over top of the opening through which it passes. I am imagining that the LCD panel (minus the backlight and houusing) has this cable permanently attached to its top edge much as the touch panel does.

Xenarc have removed the ID label from the back of this assembly so I can't tell who manufactured it.

STI_FFY · 05-02-2009, 04:41 PM

Quote: Originally Posted by nobb

Have you looked into getting a silver solder pen? I have no experience with them, but it would probably be easier than soldering.

Although this is an interesting idea, I think it won't work because the tear does not fit perfectly back together. The edges of the tear curl a bit. There is nothing in the gap on which to draw. If I made an epoxy extension of the stiff portion of the flex cable (where the contact fingers reside) to just beyond the tear, I might be able to do this. It's worth considering.

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