Author Topic: RF service monitor repair.  (Read 2203 times)

0 Members and 1 Guest are viewing this topic.

Offline Radio Tech

  • Frequent Contributor
  • **
  • Posts: 927
  • Country: us
  • KC4UMO Buddy
    • Hobby Forum
RF service monitor repair.
« on: August 23, 2015, 03:54:34 pm »
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
« Last Edit: August 23, 2015, 03:56:10 pm by Radio Tech »
 

Offline Radio Tech

  • Frequent Contributor
  • **
  • Posts: 927
  • Country: us
  • KC4UMO Buddy
    • Hobby Forum
Re: RF service monitor repair.
« Reply #1 on: August 24, 2015, 10:33:17 am »
One night this week I will pull the LCD off the board.  In hope to find some information on it.

Offline Fraser

  • Super Contributor
  • ***
  • Posts: 8414
  • Country: gb
Re: RF service monitor repair.
« Reply #2 on: August 24, 2015, 09:51:36 pm »
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
 

Offline Fraser

  • Super Contributor
  • ***
  • Posts: 8414
  • Country: gb
Re: RF service monitor repair.
« Reply #3 on: August 24, 2015, 09:56:05 pm »
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
 

Offline Radio Tech

  • Frequent Contributor
  • **
  • Posts: 927
  • Country: us
  • KC4UMO Buddy
    • Hobby Forum
Re: RF service monitor repair.
« Reply #4 on: August 25, 2015, 01:32:46 am »
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.

Offline Fraser

  • Super Contributor
  • ***
  • Posts: 8414
  • Country: gb
Re: RF service monitor repair.
« Reply #5 on: August 25, 2015, 01:46:37 am »
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
 

Offline divelectservices

  • Contributor
  • Posts: 38
  • Country: us
Re: RF service monitor repair.
« Reply #6 on: August 25, 2015, 01:54:09 am »
Many moons ago I converted an industrial circuit board with a smashed and unavailable LCD display to 8-Segment LED... just a thought
 

Offline Radio Tech

  • Frequent Contributor
  • **
  • Posts: 927
  • Country: us
  • KC4UMO Buddy
    • Hobby Forum
Re: RF service monitor repair.
« Reply #7 on: August 25, 2015, 09:25:49 am »
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.


Share me

Digg  Facebook  SlashDot  Delicious  Technorati  Twitter  Google  Yahoo
Smf