Motorola PEBL weirdness

[Eric The Viking]

The DC insists on clamshell phones.

Stupidly, a few years ago I got her a pink Motorola PEBL U6. It's not posh, but she was very fond of it.

No surprise: the screen went dark. I bought her another (in maroon - couldn't source pink).

No surprise: the screen went dark on the maroon one.

This time, I found a source of flexi-PCAs for the hinge. Absolute nightmare to fit, but it works, and I could see a crack in the old one when I took it out. The wretched thing has at least four layers to it, and I've never seen such a tortuous route for any cable - it makes vehicle wiring look incredibly easy.

Out of curiosity, I swapped the two screens over. The pink one worked too! So I gaver her back the fixed maroon one, and spent a "happy" couple of hours wiggling a new ribbon into the pink one's hinge.

I put it back together, fitted the battery in and, hey presto!

The screen backlight didn't work. :twisted: :twisted: :twisted: :twisted: :twisted:

You can just about see the display at the right angle, so data is evidently getting through. But there's no backlight.

So I borrowed the working 'phone back. connected the dark screen directly to the body with a fresh ribbon cable (no hinge involved). It works fine. Put the maroon one back with it's correct screen. Tested it; handed it back.

So I now have a proven ribbon cable. I have a proven screen. I plug cable into body of phone. Nowt.
:twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted: :twisted:

It IS heading for the bin at this rate. But before it goes there...

... does anyone know: did Motorola ever use metal hinges to carry current? Did they change their approach around 2007?

I'm running out of ideas: the newer phone was made in 2008 and has fewer bits in it than the 2006 (pink) one that's giving all the trouble. The only other thing I can think of is that the backlight driver transistor has blown up, assuming there is one, or the thing might be fused (can't see one on the PCA).

I don't want to let it beat me, but it's doing a good job of it right now. If you have any ideas, please PLEASE reply. And no, she really REALLY doesn't want a newer phone (I've been instructed).

I'm going out to sharpen some plane irons. About a dozen. I may be some time.

E.

 

[porker]

Eric,
I might be able to find out as I work in mobile phone development. I also work with a couple of ex-Motorola guys. My guess would be that it is very unlikely that it would be designed so that a metal hinge itself will carry any current. I have never seen this arrangement in tear downs. I have only ever seen it done by flexi and these are very fragile components often using a sort of conductive ink rather than "wire" as you have found. They crack easily as you have seen. The other observation is that it is very unlikely that exactly the same components would be used in handsets manufactured two years apart. Part obsolescence is a big issue and models get changed constantly as manufacturers change components. Most of the older backlights used some sort of EL backlight and the high voltages can be a problem as the drivers are not the most reliable parts. Not sure about the spec on this one so it could be LED. I reckon you were lucky to find the flexis and get it working. Do the display modules look identical in both devices? Anyway I will ask around next week.... Please don't hold your breath though as in mobile phone terms this is getting back a bit.

 

[Eric The Viking]

That's very kind.

It's weird: both displays work with the newer main board, but neither work with the older one.
As far as I can tell, the only issue is the backlight. You can move screen+proven flexi PCA across to the old unit and it won't work.

The PCA technology is impressive though. I was involved with tape autoloaders for computers in the 1990s. We had a design that fitted a six-tape cartridge into 5.25" full height form factor. Lots of flexis in the cartridge handling mechanism, but far thicker and stronger than the one in that 'phone, only a single layer usually (to motors or sensors), and not flexing in the same place all the time. Those phone ones are a big ask for the technology!

Never having dismantled one before, I was also rather surprised that it appears to be a parallel bus approach. I would have made the flexi more robust (at the expense of extra components).

I guess they're just not built to last, but it's still pretty impressive.

You can clearly see the cost reduction changes though. The later one has a pair of screws omitted, and what I think must be an RFI suppressing set of fingers omitted from the hinge (that's why I wondered about it being a return path). the aerials are gold plated on the early one, stainless on the later one, but a grounding pad was added to the flexi (I think).

Out of curiosity, do you teardown competitors' products to do component counts, etc.? Our industry used all sorts of devious ways to get kit as soon as it came onto the market, to enable MTBF estimations and so on. I used to use the data. Mind you, our stuff had a design life of something like >100,000h (power-on).

Altogether fascinating, if more than a bit fiddly!

E.