Large led scrolling sign repair.

Thread Starter

Pingzing

Joined Nov 12, 2019
5
793A830F-4279-40BD-B8CE-F32A4EFAB7B1.jpegHello
I am repairing a large led sign for a local fire fighter it is the old one that used to hang in the station. I have found a faulty transistor, some control boards that where shorting on the main led matrix. The part where i have gotten stuck is i think i have a fault with a shift register but i am unsure on how to test it. And if anybody knows why it is starting from the middle of the matrix i am looking for ideas.
thank you
 

Sensacell

Joined Jun 19, 2012
2,454
The good news is its starting from the middle...

That implies that half is working? You can check the signals on the working side, compare to the non-working side...
 

Thread Starter

Pingzing

Joined Nov 12, 2019
5
The good news is its starting from the middle...

That implies that half is working? You can check the signals on the working side, compare to the non-working side...
Thank you, that makes sense, I had not thought of that with the shift registers.
 

atferrari

Joined Jan 6, 2004
3,489
I have tried but the manufacturer was a small local company who is not around anymore, would you know of a common schematic anywhere?
Sorry, I was stating the obvious. You do not need me doing that.

Could you identify the processor and compare how it deals with both halves?
 

dl324

Joined Mar 30, 2015
9,154
Welcome to AAC!
And if anybody knows why it is starting from the middle of the matrix i am looking for ideas.
Unclear if it's starting from the middle or if it's starting at the beginning of the matrix and doesn't display anything until it gets to the middle.
 

dl324

Joined Mar 30, 2015
9,154
have a video but I am in able to post it as I can only select pictures
That EPROM should have a sticker over the quartz window. EPROMs can be erased by exposure to light of certain wavelengths. It might take weeks to years, but a sticker is cheap insurance.
 

Sensacell

Joined Jun 19, 2012
2,454
Judging by the board, it's probably vintage late 1980's.

These things are always based on modular LED boards that plug together. Lots of troubles can be traced to crappy oxidized connections between modules.

Look and the signals going in and out of each module, try to find what's different between the working and non-working modules.
Note that these things have gotten much cheaper now that it's 2020, don't kill yourself, buy a new one if it's not relatively simple to fix.
 

dendad

Joined Feb 20, 2016
3,084
It looks like the EPROM sticker fell off as it is in the first picture. But do cover it up as flouro lights, and daylight will erase it in time.
You may be able to swap LED modules to see if that moves the fault, but as mentioned above, check the SR signals in and out. Compare boards. And the connections.
As it is pretty old, have a good look for cracked solder joints too.
 

Thread Starter

Pingzing

Joined Nov 12, 2019
5
There are sus looking connections on the board I was looking at replacing the board but my knowledge of programming is limited to arduino, and because it's partly working I thought I would try to repair it first. Is there a replacement board available where i would not have to start from scratch?
 

Sensacell

Joined Jun 19, 2012
2,454
If you got super lucky, you might find another unit to harvest parts from, but nobody will stock ancient replacement boards- there is no money in it.
See my earlier comment- this is a losing proposition unless you find a simple problem that fixes it quick.
 
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