stuck screws on LCD clamps

[james_stan]

Hi all

A couple of weeks ago I picked up cheap a Rotary Demand LCD which I think (according to DWL) has a Hitachi module.
Anyhow it looks well built and after cleaning the battery hatch it responded to a new battery !

BUT if the left hand digit segments are activated (e.g. in Chrono mode) then all segments dim to almost nothing
The same happens if the clock counts to more than 9:59. So I was trying to disassemble more for further
cleaning (maybe clear a short) but fell at the first hurdle. The screws securing the LCD clamps (that I think also hold
the module together) are stuck fast with a kind of thread lock resin like you use in car mechanics - it's red too.

Has anyone seen this before and have a method for removal ? I sharpened a screwdriver to scrape the screw
head slots which I think are now clean but I don't want to be too brutal with the resin that has been set
around the screws for fear of damaging something.

Cheers

JS

[Kasper]

thats not easy...you can try to make it abit warm..but watch out not to damage the lcd.

[bruce wegmann]

Yes, I see this all the time on the screws that attach the bracelet to the case on Pulsar P2s. It's called Lok-Tite. Many feared the screw would gradually un-screw over time, and the bracelet would come apart, and the watch would fall off their wrist, probably while they were scuba-diving. So, to prevent that, many jewellers would put a small drop of Lok-Tite onto the screw head, which would work its' way down into the threads, and freeze the screw in position, permanently. Lok-Tite is a good product, designed for that purpose (it's actually a variant of the instant adhesives that are so notorious for bonding fingers together on contact) and that's exactly what it does. Plus, this glue has had 35+ years to cure. Try applying a drop of penetrating oil on each screw, and let it sit for a few hours. Lok-Tite is also soluble in acetone, but I have never tried using this on an LCD module, so that carries unknown risks. So far, I have not encountered screws so firmly bonded they could not be freed by this method. After extraction, I use a razor blade to remove any trace of adhesive from the threads.

[quietman]

I pulled one of these modules apart a few months ago - from an Accurist watch - I think these modules appeared in quite a few brands watches. I assume its the same type from your description.

In the one I took apart the offending red gloop was dabbed onto the screw head rather being a true threadlock. A kind of waxy plastic and can be cut/pushed away with a midget screwdriver. Make sure you get it all out of the slot (screwdriver + Xacto blade) or you'll mash the head. The you should be able to turn them pretty easily. I didn't use any heat or solvents.

One thing you should be wary of once you get the screws turning is that this whole assembly is a sandwich with the contacts made to the chassis plate by about ten little springs. Seperate carefully or you'll be mudering some springbars with your side-cutters.

Last warning - the 'mirror' is a somewhat apologetic little flimsy thing. You can see in the DWL picture that this one is a little wrinkled from its years. Be particularly careful with it......

[james_stan]

Hi Guys

Thanks for the replies.Indeed I thought it was loctite too but on mine it's gone rock-hard - presumably due to the extended curing time as mentioned. Acetone - that's nail varnish remover isn't it ? Might try some drops from a feather.

@quietman - yes I believe it's the exact same watch as the Accurist -thanks for the warning regarding the springs. Is
it best to separate the halves with the face upwards in that case - assuming I get that far? Also this mirror has also wrinkled already 'twas like it on arrival

JS

[quietman]

I don't think there's a better or worse orientation for pulling it apart. Putting it back together's the tricky bit.

Most threadlocks are Acrylic formulations (about the only thing they have in common with super-glue....other than being made by, amongst others, the Loctite company....) - so anything that attacks acrylic would help. But I don't think this is threadlock per se. Threadlock works down in the thread - anaerobic curing etc etc. Normally applied to the thread and not the head. What you have is a blob on the screw head - as I recall it hadn't wicked down into the threads on the Accurist module. Usually used for anti-tamper but perhaps it was also used for 'headlocking' back then? And it could still be acrylic.

Acetone will attack many plastics. I personnally wouldn't put the stuff anywhere near an LCD module. It [i][b]could[/b][/i] attack the plastic chassis and even the PCB substrates. Even the fumes [i][b]could[/b][/i] cloud your polymer LC polarisers.....

My Accurist was very dead so I didn't think too carefully about undoing those screws. Just scraped the screw-head clean, turned the screws and watched the little springs go ballistic........

[james_stan]

Hi All

Ok (bravely) chipped away the red gunk an got the piece apart, swabbed the tracks ( a few suspect bits of debris) with vinegar and then distilled water and finally isopropyl to dry out. Noticed that on reverse side of the ceramic circuit board (non component side) one pad appeared to be missing - corroded ?
(@Quietman do you have a phot of your circuit for reference ?) noted that the springs are to create contacts form the main PCB to the QC and alarm circuit - some black rubber 'pegs are also present one of which fell out - not sure of there purpose maybe also conductive. Also ther is a small green circuit with a wire wound componnent on it - speaker driver ?

Reassembled an tried battery - hmm - clock works but only visible at an angle and VERY dim - still one missing segment. Suspect poor power +ve or -ve connections to LCD panel - other thoughts ?

All teh best

JS