RF service monitor repair. - Page 1
Forum section: electronics / repair

author: Radio Tech
author_rank: Frequent Contributor
timestamp: August 23, 2015, 03:54:34 pm
content: I posted a tear down on this a while back.https://www.eevblog.com/forum/repair/com-ser-laboratories-tear-down-possible-repair/msg393803/#msg393803Things 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

author: Radio Tech
author_rank: Frequent Contributor
timestamp: August 24, 2015, 10:33:17 am
content: One night this week I will pull the LCD off the board. In hope to find some information on it.

author: Fraser
author_rank: Super Contributor
timestamp: August 24, 2015, 09:51:36 pm
content: 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 problemI have seen 8 digit panels and they used to be sold by Farnell. You may get lucky on eBay ?Aurora

author: Fraser
author_rank: Super Contributor
timestamp: August 24, 2015, 09:56:05 pm
content: 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

author: Radio Tech
author_rank: Frequent Contributor
timestamp: August 25, 2015, 01:32:46 am
content: 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.

author: Fraser
author_rank: Super Contributor
timestamp: August 25, 2015, 01:46:37 am
content: 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

author: divelectservices
author_rank: Contributor
timestamp: August 25, 2015, 01:54:09 am
content: Many moons ago I converted an industrial circuit board with a smashed and unavailable LCD display to 8-Segment LED... just a thought

author: Radio Tech
author_rank: Frequent Contributor
timestamp: August 25, 2015, 09:25:49 am
content: Quote from: Aurora on August 25, 2015, 01:46:37 amYes 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. ThanksQuote from: divelectservices on August 25, 2015, 01:54:09 amWell that is a good thought, noted... ThanksI 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.