Troubleshooting LCD (alphanum) display problem

Hi,

I have a NAVITEK LAN/cable tester (for want of a better name).

It includes a two line alphanumeric (plus icons) display to present prompts and results to the user.

The display has developed faults -- similar to "dropped pixels". I'm trying to figure out the best way to sort out where the problem might lie -- in the display connection *or* in the (serial) interface to the display PCB.

And, of course, ideas as to how it might be repaired. While the device wasn't inexpensive ($500), it's long obsolete so probably not worth sending it in for service (I will contact the manufacturer just to see how outrageous their service prices are :> ).

OTOH, it's *really* handy when I need it.

I.e., fixed it would be wonderful. Even "as is", it has some value (though it requires patience to determine what the display is saying as the prompts cycle by).

I suspect the first step would be to see if the individual "displays" (prompts?) are consistent each time they appear or if they exhibit some variation.

Then, determine if there are any patterns in the faults.

Finally, mechanically stress the device to see if these patterns change.

Any other things I might want to try or observe?

Thx,

--don

Reply to
Don Y
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Yes. Make sure it has fresh batteries. I know.... I'm sure you checked. But how many times.....

Could it be the LCD display itself? If it's just a character LCD, you may find one off-the-shelf to replace it, and should be relatively inexpensive, especially if it is the 14 or 16-pin parallel variety, and not the more expensive serial types. Do a little research first to make sure the line addressing (cursor placement) is the same between the broken and replacement LCD display. I've seen LCD's that assign weird starting addresses for the cursor positions, which vary by line, and sometimes, in the middle of a line.

If the LCD is a graphic type, my "guess" is the display is bad, since a few bad pixels here and there should cause "that much" readability issues for you.

Best of luck.

-mpm

Reply to
mpm

When you have the device open, look at the display module and see if there is a model number on the display. I did this on a ocd ii that has display problems. Then looked for that model number on the internet and got a file with all the specifications for the display model. And an address in China that sell the display modules for something like $3 plus shipping.

Dan

Reply to
dcaster

Opened a brand new lithium 9V just before my post (after seeing the problem with the *installed* battery, previously)

That is my current thinking. But, I will have to drag out a movie camera to capture the various displays (it cycles through various displays every second or two as it runs its tests -- no way to "pause" it anywhere but at the start of the test sequence). Then, I can look to see if certain pixels are missing in *all* characters in a particular display position -- or, just a particular character (i.e., the font may be defective, assuming pixels are being transferred to the display instead of characters)

There doesn't *seem* to be any change in any *particular* "display". I just haven't been able to correlate those deficiencies with *other* "displays"

The "display board" interfaces to the "processor board" via an

8-pin connector fabricated similar to the way LCD glass mates to an elastomeric connector (i.e., just "touching" surfaces, not "engaging" pins) [this complicates troubleshooting as opening the package causes the display board to lose its connection to the main board -- I'd have to find some suitable vias and attach pigtails]

So, I suspect the display interface is serial -- it doesn't make sense to interpose a serializer to a parallel display.

The display has icons as well as the graphic area for the 2 lines of text so I imagine this might complicate locating a COTS replacement.

If this is indeed the case, then being able to objectively review images of the various "screens"/displays should allow me to verify those pixels are, indeed, dead. Given that the missing pixels don't seem to change (e.g., when flexing the device), any other result would suggest a defect in the data being sent *to* the display (i.e., font defined in rom)

Reply to
Don Y

Yes: Open it up and see if the LCD contacts the circuit board or a sub-module via the usual two rubber strips. They look like thin mechnical buffers but in reality they contain contact fibers. Over time this can dry out a bit and then some segments lose contact between LCD glass and the board below. This is also true in most stand-alone LCD modules except that you often can't see the rubbers because they are behind a thin aluminum frame. Such conducting rubber strips can be bought.

A typical sign is that when you have the unit apart and then gently press on the glass sides where the strips are the fault pattern changes. But not always.

Of course there's always a chance that something else happened, like on one of our large atomic wall clocks: One fine days the leading "1" had vanished. So it would show 1:00 instead of 11:00. Opened it up but turned out the driver was shot. Since that was under a blob of tar that was the end of the clock.

--
Regards, Joerg

http://www.analogconsultants.com/
Reply to
Joerg

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text -

Understood. Therefore - Add mechanical possibilities to your list of things to investigate.

As to the display, do not rule out that it could still be a power supply issue. It is still possible that the rest of the device is sending display data and/or commands to the LCD before it has had a chance to exit its Power-On-Reset - typically several hundred milliseconds, at least. If so, the display will very likely behave as you have described.

Not so easy to fix, or troubleshoot, unfortunately - especially if you have a custom LCD.

One idea: If the processor has a way to pause it (like a reset on a 8051 device), I suppose you could try holding the processor in reset while the rest of the device powers up. Give the LCD a few seconds, THEN let the processor go and see if that "fixes" it. It might at least help narrow down the problem. It could also very easily end up being a complete waste of time!! :(

-mpm

Reply to
mpm

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