design fault on WMS / Bally display driver board - (REV 6 only)

[beaky]

I have come across a revision of the wpc dot matrix driver board that won't work on some "CHERRY" brand displays due to not enough voltage on pin1 on the ribbon cable going to the display (display enable)

It is revision 6

After several hours of comparing it with a later revision side by side, powered up and each display board hooked up to a booted cpu board and using an oscilloscope I came to the conclusion that the circuit can not provide enough voltage on pin 1 to enable some displays.

I also replaced all I.C.s that have anything to do with that part of the circuit in case I missed any faults with the test equipment.

it can only produce 4.3 volts on pin 1 where the other display driver boards (4 in total) all had around 4.8 volts DC.

It did work perfectly fine on a "VISHAY / DALE" brand display.

has any one else come across something like this and if so is there are any documentation on hardware mods that can be done to over come this (I just don't have the time to play around my self at the moment)? 

[Marty Machine]

It sounds more the case that the display in question is actually pulling down the 4.8v down to 4.3v, loaded down from a slightly flakey driver chip on the display unit that won't work?

4.8v is concerning too, i'd expect 5v-5.25v instead.

MM.

[beaky]

those voltages are with the display disconnected.

and how do you get 5v to 5.25v when you only have a 5v regulated supply running into the circuit? you would have to be running 5.25v and above and have absolutely no voltage drop at all through the entire circuit.

I have 5 display driver boards here at the moment and all of them except the one in question has an output of 4.8v on pin 1 with or without a display connected and they are all being tested with 5.0 volt at the 5 volt input.

[pinmadd]

Yes Beaky, I have struck this, had to put cherry display in another pin that could run it   

[Marty Machine]

Didn't realise the supply input voltage was so low, perhaps a mod or addition to provide at least 6-7 volts INTO the driver board will yield a decent 5v to the display and make it work?
Isn't there a 12volt rail on the matrix board that could feed a (added) 7805 regulator to give a solid 5v to the display?

I know you said you have no time to experiment, but it's inevitable, as there's no alternative fix besides installing Cherry displays.

my 2cents.

[beaky]

good idea. (6 to 7 volts in) would definitely  fix the problem. but i don't have the time
I will just put a note with it when i send it back to the customer, so they know it needs a certain display 

 

[beaky]

Yes Beaky, I have struck this, had to put cherry display in another pin that could run it  

thanks for letting me know, looks like some one stuffed up when they were doing a fix up to the previous revision   Imagine the look on the persons face when some one told him "you know that new revision that you did, well it won't work with certain displays and we have several thousand in stock" 

[Marty Machine]

This almost calls for an addon regulator-mod/board to ensure those pinnies will run all displays in future