Identifying LCD Display - VDO Logic Combi

[JohnW]

No, the control IC has signal lines under it on my board. From what I have seen, the problem in my set up is the LCD (which has deteriorated over years), and in some way (firmware, layout) the aussie LCD is incompatible with my controller.

Unless I can find another LCD, worth a shot, then I will give up and look for an alternative solution.

 

[kellys_eye]

Two possible solutions then:

Since most LCD panels these days are fully integrated devices i.e. have the display and controller on one board and sold as an individual, complete, module.....

1. Find an LCD module (16x1) with the same physical size LCD and strip it down to the LCD 'alone' and see if it will fit your existing board. All LCDs boil down to being these glass substrate things in the end - it's only their final packaging that the user usually sees.

2. Since the LCD controller on your board has in I2C interface, find a 16x1 integrated LCD with an IC2 interface built-in. I know (because I've got a few of them) that 16x2 panels exist but haven't yet come across a 16x1 with I2C interface.

Good luck.

 

[Lomax]

Since I've been dreaming of getting hold of a VDO Logic Combi myself I have been following this thread with interest. These are old and rare units, and LCD issues appear to be common - and often seem to be caused by excessive exposure to sunlight and/or water. I have finally been able to get hold of a 0-2500 version of this instrument, and thought the OP might be interested in seeing some photos from inside my unit, which differs from the OP's in some ways. Most notably, the location of the LCD controller chip is different, and the LCD has red LED backlight diodes instead of the milky (green?) LEDs in the OP's instrument. I suspect there are multiple versions of the "Combi", which might explain the issues the OP is having with his replacement LCD. There's a supplement PDF on the VDO-Marine website (http://www.vdo-marine.de/uploads/tx_documents/Ergaenzung_Logic_Combi-D-GB_01.pdf) which details the addition of two terminals (#3 and #27) to the rear connectors - these are not present on my instrument.

 

[JohnW]

Lomax, Thanks for your update. You seem to have found an immaculate example. How did you come by it? I would kill for another!

Our damage was simply old age and water ingress - I replaced a couple of the buttons some 9 years ago! The LCD damage was already then under way. I think yours is the same as the Aussie one.

 

[Lomax]

JohnW - yes, it is physically in pretty good condition, though the glass is a little scratched. As it happens, there's someone in Germany who is selling NOS bezels for some "Logic" instruments here: http://stores.ebay.de/BBG-Automotive-GmbH?_dmd=2&_nkw=logic - I've ordered new ones for the Combi, Pilot and Compass instruments, but haven't received them yet.

Sadly though, despite being in pretty good condition, my instrument has an electrical fault, or at least I think so. While things like battery voltage and engine hours display correctly I cannot measure any engine parameters. I've hooked up a couple of 100 Ohm and 1k Ohm trim pots to between sensor GND and the fuel and engine temperature sensor inputs but anything other than close to 0 Ohms causes the instrument to display "Failure" on the LCD. Measuring the voltage on the sensor terminals seems to confirm there is a problem, as I'm only seeing <1 volt on any of the them when floating, and this voltage keeps fluctuating. While I could understand if the instrument only sends a voltage down each line at some interval I would expect this to be much higher, something like 5-12 volts. It would be great if you could measure these voltages on your instrument and tell me what they are, which might give me some clues...

 

[Lomax]

As it happens, the "Combi" instrument I bought came with a repeater instrument as well. This is a crippled version which can only be used as a slave, and which has no sensor input terminals (only the top 4-13 terminal strip is present on the rear). I've looked a little closer at this today, in the hope that I might be able to use it for parts (I have no need of a repeater) - but although the PCBs are the same, the repeater (understandably) leaves some ICs unpopulated, and also has a different ROM (obviously). I've attached an animated GIF which alternates between the two boards, in case anyone wants to see the difference (apologies for the crappy flash photography!).

 

[Lomax]

Resurrecting this in the hope that maybe the OP, or someone else on the forum, can help with identifying those LCD panels. I have recently picked up a free VDO Logic "Log" instrument which has a badly water damaged LCD module - it may be fixable, but without a replacement LCD I'll never know...

By the way, I'm pretty sure they're not 16x1 panels but 8x1, and the (8x48?) matrix has no spacing between characters (it can display a continuous bar graph).

 

[twister]

I have a display on my tractor like that on my tractor. I took it apart and cleaned the contacts and it worked a little better but unless you press on the screen it doesn't always work. Is there a grease or something to put on the contacts to make them conduct?.

 

[Lomax]

I have a display on my tractor like that on my tractor. I took it apart and cleaned the contacts and it worked a little better but unless you press on the screen it doesn't always work. Is there a grease or something to put on the contacts to make them conduct?.

You shouldn't use any grease on the zebra strip or LCD panel - just make sure all surfaces are super clean and that the retaining frame keeps the assembly firmly pressed against the PCB. Use isopropyl alcohol or methylated spirits on a soft lint-free cloth. Clean both sides of the zebra strip, the contact surface on the back of the LCD panel and the contact pads on the PCB. The contact pads on the PCB are sometimes coated with a black carbon paste - do not try to remove this! The metal retaining frame has legs which pass through the PCB and twist in place on the opposite side; if you have cleaned everything carefully and the display still only works when you apply pressure then twisting the legs a bit more may fix the problem. If you get no image at all, or the display is garbled, it may be that the LCD is misaligned with the PCB contacts - disassemble, re-adjust and try again (zebra strip alignment is less critical). Should you need to replace the front and/or rear polarizing films, carefully lift one corner with a scalpel blade and apply a drop of WD-40 - this will gradually creep under the film and soften the adhesive, making the films easy to remove.

 

[twister]

Thanks for your answer. I will clean it again, and see what happens.

 

[Externet]

I have many types of displays available if you are in USA. Is there a picture of your needs or some image of the exact VDO item on the web ?

 

[Lomax]

It should be possible to restore discoloured LCD panels by replacing the polarizers (front/rear) - indeed I have successfully changed reflective displays (with no backlight) into backlit "transflective" displays by replacing the opaque rear polarizer with one which lets (some) light through. But when I recently tried to restore the sun-burnt LCD in another VDO Logic series instrument (the "Multifunction" NMEA data instrument) the display came out looking very yellow, and the text which had previously been black had turned blue. I would be interested to hear if anyone here on the forum has any idea what may have caused this?



I had assumed, without testing, that the polarizers were horizontal & vertical, so that's how I fitted the new ones. But after seeing the result I removed them, suspecting I got the orientation wrong, and compared them with the original films (I should have done this first, of course). I found that the original polarizers were indeed oriented at +/- ~45 degree angles so (although they were now ruined by fingerprints & dust) I tried to find a better combination of angles with the new films. But although I was able to get rid of the ghosting around the inactive segments, I could not eliminate the strong colour cast, only change it from yellow to an orangey-red. So my problem doesn't seem to be linked to the orientation of the polarizers.

I found something interesting when comparing old vs new though; the old front polarizer appears to be made up of two layers, one of which had partially peeled during the (somewhat violent) removal. When combined with a piece of the old rear polarizer on the back of the glass, the part of the front polarizer which still has this second layer looks normal - but the part where it's missing exhibits the same colour cast I got with the new films. Conversely, in negative mode the dual layer part shows as black while the single layer portion is blue.



What might this second layer be? Do I need a different type of front polarizer film to get rid of the colour cast?

Edit: It is worth noting that the new films show no sign of any colour cast when looked at without the LCD glass panel in between them. In fact, when compared side by side with the original front polarizer it is impossible to tell new from old - the transmitted light looks 100% identical and neutral.

 

[Lomax]

What might this second layer be? Do I need a different type of front polarizer film to get rid of the colour cast?

I'll answer that myself: it's what's known as a "retardation" film, which is needed on some types of LCD panels (FSTN), or they will show as yellow/blue instead of silver/black. See attached image for the gory details. Anyone know where I can find this type of film?