Replacing LCD display - eh?!

We have a rowing machine at home, which has a small built-in computer
thingy with a small LCD display, which unfortunately has got smashed.
Although I know sweet FA about electronics, I decided to dismantle the
computer to see if the screen was a readily replacable standard item.
Extracted the computer from the machine - it just comprises a circuit
board about 1" x 2" screwed to a casing, and below the circuit board is
the offending screen, about 1.5" x 3".
So I unscrew the PCB and lift it off, expecting there to be some form of
wires connecting it to the LCD display. But no, there isn't - absolutely
no evidence of any physical connection to the display whatsoever.
The display drops out of the casing and I can see it comprises 2 thin
sheets of glass (the front one being smashed), with a silvery-white,
non-conductive sheet covering the back. No markings of any description.
So...
First - how on earth does the display work? Induction from the PCB or
something? Is what I'm seeing 'normal'?
Second - presumably these displays will typically be bespoke to whatever
equipment they come from? Or not...? (you'll have gathered it's not
possible to obtain one from the original manufacturer of the rowing
machine).
Thanks
David
Reply to
Lobster
Common connection methods include flat foil ribbon cables, and direct contact along the edges of the lcd (which yours probably has) - you should be able to see corresponding contact pads on the pcb.
These displays are usually bespoke, options are live without it or find a donor rowing machine that's bust in some other way.
Reply to
dom
That's what I thought - but I swear to God there's absolutely *nothing* there... no wires, no possible way to connect them, nada...
David
Reply to
Lobster
sometimes they use a zebra strip of which is just a small block of silicone "rubber" with alternate conducting/insulating layers
formatting link
Reply to
Andy Burns
In message , Lobster wrote
The connecting strip is conductive.
There are some contacts on the printed circuit board with matching contacts on the display. The two items are joined with what looks like a small strip of foam rubber. This strip is made a multi-layer sandwich (running length wise) of an insulator , an electrical conductor, an insulator, a conductor etc. The pitch of the conducting bits is much finer than the pitch of the connectors on the board and display so no matter how the strip is aligned it is guaranteed that there is least one conducting path between the contacts on the board and on the display, and with at least one insulating area between any two contacts. It is a cheap and effective way of manufacture for a one off assembly process. The strips are not designed to be reused but in practice you can probably dismantle and reassemble the cheap ones used in your equipment 10s of times without too much problem.
These strips come with conductive layers being made of carbon, silver or gold with the precious metal ones having a lower resistance. The ones in your device will be the low cost carbon type and if you measure the resistance of the foam between the shorter sides you will probable find a resistance of a few ohms (maybe the low 10s of ohms)
They will be bespoke items.
Reply to
Alan
just mounts. Very odd - they just look like homegenous blocks or rubber to me: can't see any conductors running through them. However, there are some incredibly faint striations on the glass where these strips touch, which must be contacts, and I can now see that there are 2 rows of 13, what must be contacts on the base of the PCB which must match up.
Am I right in thinking that providing the PCB is registered accurately versus the LCD display (which it is, via screws in the casing) that the position of these zebra strips isn't crucial providing they cover the area where the contacts are? Although it looks a bit academic now as I can't see any chance of replacing the display. :-(
Thanks David
Reply to
Lobster
the conductors are strips of carbon impregnated rubber
yes the pitch of the zebra strip is finer than the pcb/lcd contacts, so long as it is roughly in the right place it'll work
bound to be a custom part.
Reply to
Andy Burns
Did you happen to notice two strip of rubber like material between display and PCB? These are conductive, in than there are multiple tracks linking the front to the rear.
Very unlikely you will be able to find anything to replace it. Most are now custom units.
Reply to
Harry Bloomfield
In message , Lobster writes
yes, a fairly standard way of connecting an LCD display
Where were you thinking of getting the correct LCD display from ?
or did you think that they are all the same ?
Reply to
geoff
In message , Lobster writes
No, generally they use conductive rubber strips called (generically) Zebra strip because they're stripey. I'd suspect they fell out, are still in the case or attached to either the PCB or the display.
Highly unlikely to be off the shelf but find somewhere to post pics of it, you never know...
Reply to
Clint Sharp
No they wont..LCD factories have HUGE investments in auto plant, and churn out a few standard sizes in massive quantities.
Sadly these are seldom sold in any kind of retail market.
You are probably reduced to getting it off the machine manufacturer, or finding an indentical unit from something else.
Reply to
The Natural Philosopher
In article The Natural Philosopher wrote:
While this is probably true for a standard matrix like a computer monitor or TV I don't think it applies for the smaller displays on other devices such as the OP's rowing machine. These often have faint outlines of all the icons and digits visible on the screen even when the power is off. I imagine these are all custom devices with the relevant graphic elements embedded into the display. I expect this makes for much simpler logic circuitry in the control system and the extra tooling cost when the panels are bought in the tens of thousands will be relatively low.
Reply to
Mike Clarke
In article , Mike Clarke writes:
I worked for a company which had some custom LCD panels manufacturered back in the 1990's. At that time, you had a choice of using about 3 different types of display, and looking around, that still seems to be the case today. The most basic is a 2 line by 40 character display (and variations, but the chip they use always assumes it's driving a 2 line by 40 character display even where there are fewer characters displayed, or a bigger display with multiple display chips, or is it 2 x 20 -- I forget now).
The second type is a graphic display made of pixels from which you can create your own characters, glyphs, pictures, etc. I've never used one of those, but I expect they're like the character displays in that there are just a few similar driver chips with a reasonably common interface. These first two are common off-the-shelf parts with equivalents from many manufacturers.
The third type is where you have the display areas custom manufacturered to your own image specifications. We supplied the image layout, and it was etched (don't know the details of the process). ISTR a laser etch was done for a couple of prototypes and some other process for the bulk manufacture. The units are supplied with the zebra strip and a connection board pre-assembled -- reliable assembly of the display with the zebra strip is a specialist job. Usually the connection board has the driver chip(s) on it too.
Reply to
Andrew Gabriel
In message , The Natural Philosopher writes
Of course they will
Do you think that the same display would be used for an exercise machine as a CH programmer, for one CH programmer as another, for a GPS as a TV remote?
I don't think so
And ... ?
Reply to
geoff
As well as millions of specials. It's all done on big sheets for most of the process so having lots of different designs is no big deal. Consumer products like this will almost always use a custom LCD with whatever icons & other display layout etc. they want. Tooling costs for this type of LCD are trivial (£ mid-hundreds to very low thousands) compared to things like plastic mouldings.
Reply to
Mike Harrison

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