Tissot LCD - She put up a fight but I was quite insistent

[quietman]

So,

When you're looking through Ebay and spot some fool who's just purchased those dog-looking wrecked LCDs somewhat optimistically - well it might just be me......

I received my two weekend won Broken Tissot LCDs today. From reading on this forum and elsewhere I think they are the Casiotron / Hamilton / Tissot 1976-1977 ones. Both with rough cases that I can refinish nicely, one with broken glass, one missing its original strap and both unashamedly DEAD. I opened them up and one had a nice clean looking Casio branded movement housed in green plastic. I'll post pictures of that one when I've had time to dig inside a little. But the other one looked, um, molested. And a bit grotty. But they are damn fine looking watches. So here it is, Patient A in pictures -

There's a scratch on the front layer of the display. It looks like it is the polariser and printed with the silk screen so I elect to leave it as is.


The gold plating on the battery terminal is delaminating and will have to be removed to prevent any floating flakes becoming Short Circuit hazards.


You can see that the flexi connector has been fiddled with, not refitted properly with one connection missing. Under a loupe it looks pretty bad. The kapton / copper / top have all delaminated and it has been refitted sans kapton. I would describe it generously as 'falling apart'


The front of three PCBs comes away freely as it was designed to -


The remaining two PCBs open out following the removal of four screw - one has a Vbat+ contact under it, another on the long stand-off is longer than the others - don't mix them up later.....


The front display PCB has a clamp holding the sandwich together. Uh oh this looks bowed - crack to the back of the Liquid Crystal element from being screwed down without being lined up properly....


Also, one of the conductive rubber contact strips is shorter than the other and doesn't cover the whole row of contacts on the glass. Damn. But wait....the contacts at one end of each row is connected together by a track-via-track on the underlying PCB (see two photos up....) so its not required and I guess as designed. This seems a bit silly to me - if you refit the rubber strip at the wrong end of the slot then you're U/S.

The remaining two PCBs can be seperated once the flexi connector clamp is removed (the clamp takes the unconnected/broken flexi track with it....) -


When I opened the case up a single strand of wire about 1cm long fell away. Not surprising to have some rubbish in there given the state of the flexi and the display reassembly. Whilst having a really good inspection of the remains I spotted a stray wire coming off a screwed on component next to the battery terminal. I guess this is where that stray piece came from -


There has to be some explanation for this. A nicely designed and assembled module like this has screw-fit components for a reason. I presume that it is select-on test capacitor to trim the quartz to a within the range of the variable capacitor. It is connected to the crystal but I guess that someone saw it next to the battery and perhaps took it for a blown fuse and shorted it out with wire (its a cap so measures DC open circuit...)

Now the diagnosis is complete we are ready to operate. My first fix just reinstated the single missing link on the flexi and cleaned up the switch contacts which seem to be plated onto the outside circumference of the board and got rid off all of that loose gold from the Batt- terminal -


I properly reassembled the front display and carefully refitted the remaining flexi contacts onto their respective pads -


But still dead. So then I changed the Xtal. Still dead. So then I faced reality and figured that the flaky flexi had to go, chopped it and set about reinstating the connections using some kynar. Of course there were lots of handy vias and pads to use well away from the terminals on the top PCB but on the bottom one I had to solder right onto the IC pads. Fortunately I had some top line equipment that was more than up to the job.

The patient on the operating table -


Whole again-


The scars-


Reassembled and now it .... still doesn't work. But the backlight does and wait was that a flicker I saw? Push. Flicker. Push. Flicker. Looks encouraging. There now seems to be a problem with the contacts on the flexi rubber strips. I tinned the pads on the PCB to provide some slightly raised bumps. A few segments there now when recased and I can get more by pushing directly on the glass over the rubber strips on the front face when out of the case. So I stacked some grey PVC tape into strips as adhesive spacers to safely apply a little pressure when cased and attached in the relevant places -


And so she sings once more -




Just need to rub her down with wet and dry, bit of Tcut, bit of Silvo, maybe some Scaryum on her face. But first I need to go and tickle her younger sister.....

MP.

[Old Tom]

Lovely bit of rebuilding!- both modules were actually made by NEC with main clock chip from Hitachi (Casio did not make their own modules till you get up to module 31 and even some past that were still bought in from other sources). Do have a tendency to be very current hungry after the battery has splurged all over them- check the running current, should be less than 5 microamps, more and the board needs cleaning (carefully. No vinegar or other urban myth cleaners!)

[retroleds]

Nice work Mike! The array of colored wire - did you cut a network cable up? THat's one of my go-to consumer items for thin, nice wire...and those USB cables that come with everything today.

the board needs cleaning (carefully. No vinegar or other urban myth cleaners!)

What would you suggest? (I'm personally partial to dissolving those metal salts before rinsing them off....)

[james_stan]

Hmm

You've done this sort of thing before ain't you ? Also some mention of conformal coating in your last post.

Come on, tell us, what's your day job ?

Cheers

JS

[quietman]

Yes I spent some years working in industry. Doing electronics research, design, product development and suchlike. But I gave up the corporate world a few years ago so unfortunately I no longer have access to £20k oscilloscopes or stereo microscopes and clean rooms.

[retroleds]

Don't despair - decent stereoscopes can be had from the Chinese for under $300 and quite sufficient(for this work) oscilloscopes for under a $1000 new.

For those wondering - 'kynar' is a brand of PVC, used extensively for wire coating. So, PVC coated wire.

[quietman]

Yes the kynar wire is sometimes also referred to as 'wire wrap' wire (and yes I'm just about old enough to know what a wire wrap is!) I think it is 30 AWG single core. Its really good for PCB work because it can be bent and holds its shape for complex routings as well as being precise enough for tacking onto pretty much anything. And you can strip it very cleanly with a hot solder loaded iron - sounds dodgy but it works and it saves you buying a new set of small gauge strippers - its very fussy stuff when it comes to being stripped with a tool. Stripping with an iron also means you can tack one end and then cut and strip the other end without tugging on the solder joint or whatever delicate thing you've dabbed it onto. I think people sell small quantities of it on Ebay to cater for those people who hot rod their playstations and such.