RF service monitor repair.

[Radio Tech]

I posted a tear down on this a while back.
https://www.eevblog.com/forum/repair/com-ser-laboratories-tear-down-possible-repair/msg393803/#msg393803


Things have slowed down here quite a bit so I have some time to put into this old bit of gear.
One part that has me stumped is the LCD display.  It is shot but I need to get that part fixed first so I can carry on with rest of the repair.  I have searched everywhere I can think of to find a replacement.  So looks like I am going to have to retrofit something. No, the LCD is not powered on. This is how it looks since it went bad.



This is where I could use a little guidance. How would be the best way to tackle this?
I know this is not worth the effort to restore. But was my first real service monitor I purchased many years ago. The schematics are very poorly done.

Links to schematics:
http://gokarters.com/smf/index.php?topic=1736.0

[Radio Tech]

One night this week I will pull the LCD off the board.  In hope to find some information on it.

[Fraser]

I suspect that it's am 8 digit LCD panel that may be replaced by a pair if 4 digit panels. Not usually a major problem

I have seen 8 digit panels and they used to be sold by Farnell. You may get lucky on eBay ?

Aurora

[Fraser]

I do have some LCD panels for the Lowe H150 receiver but they aren't cheap and are IIRC 5 digit. I may also have some 3 1/2 panels.  Sadly no 4 digit panels.

Aurora

[Radio Tech]

Thanks Aurora for the reply.
In all hope when I get the old unit out I can see more of what I need. I did find  a few on the bay but will not know till I see the back side.
Really hoping that once the LCD is repaired I can see more of what is going on in the unit. I can not detect any signal out and with out a display cannot detect signal input.

I have found out that he unit was made by a fly by night company. But the quality of it was not bad, just no support.

[Fraser]

Just a side note.... The failure that the display is showing can be caused by dc bias damage to the crystal lattice. That is to say, the AC  backplane signal fails and a DC state exists between segment and backplane. Such a situation causes the segment to become stuck in one polarity. In your case, the segment on condition. The display is sadly ruined by such a failure.

It would be worth checking that the LCD backplane ac oscillator is running before fitting a new display.

Aurora

[divelectservices]

Many moons ago I converted an industrial circuit board with a smashed and unavailable LCD display to 8-Segment LED... just a thought

[Radio Tech]

Just a side note.... The failure that the display is showing can be caused by dc bias damage to the crystal lattice. That is to say, the AC  backplane signal fails and a DC state exists between segment and backplane. Such a situation causes the segment to become stuck in one polarity. In your case, the segment on condition. The display is sadly ruined by such a failure.

It would be worth checking that the LCD backplane ac oscillator is running before fitting a new display.

Aurora

Yes I agree, something went terribly wrong to cause this.  And could be what is causing the other failures throughout the macine. I need to start with finfing what supply rails are working properly then go from there.  Thanks

Many moons ago I converted an industrial circuit board with a smashed and unavailable LCD display to 8-Segment LED... just a thought

Well that is a good thought, noted... Thanks


I am attaching what I think is the board that drives the disply. It is a bit confusing how the block diagram says one thin and the actual schematics are listed by somethng else.