Bc780xlt display

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2WAYMAN

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5-6-12 0010 HOURS EDT
Hello all...........
We have a few BC780XLT units in great shape except for the fact that the displays, although fully lit, show no characters any longer. I had previously asked Uniden for replacement part cost(s) and they told me that no replacements were available.
Does anyone have a workaround fix for these displays, perhaps changing out a few components to make it functional once again? The radios in question are in immaculate condition and it is a shame that the displays have gone invisible.
We have performed some repair procedures on similar displays on Motorola portables and mobiles and given them new life.
All assistance will be gratefully appreciated.
73's!
 

sjlamb

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Have you checked for poor connection on the cable that connects the display PCB/Display Module to the main board. I would be surprised if the actual LCD Display Module is the culprit. Especially since you have the same symptoms on multiple units. While an LCD module can go bad, it is not a common failure.

You could also check to see if there is a ceramic resonator or crystal that drives the LCD and see if it is running (oscillating).
 
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kruser

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There was a thread I read here somewhere a year or so back that claimed the 780's are prone to LCD failure.
I questioned that myself as mine was still displaying fine when I read that.
The thread mentioned that many are failing by fading away.

As popular as the 780's are for military air monitoring, I think there would be a lot of talk of LCD failure if the thread I read were true.

Since I read that over a year ago, mine is slowly starting to fade out as well. Mine is still readable but with much less contrast.
It's as if the contrast is slowly changing. So maybe there really is an aging problem with the LCD module that is surfacing as these old but great models age more and more.

I've not attempted too check anything yet but the oscillator for the LCD is a likely culprit as sjlamb mentioned.
I think the display module (LCD) is soldered to its driver and oscillator board so the chance of a bad cable connection would be ruled out. At least that is what I remember as I was going to check into changing out the backlight LED's but stopped when I found that everything was soldered. Or was that another radio? Heck, I don't remember for sure but I'm pretty sure the LCD module is hard soldered in place in the 780XLT.
 

timewave

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Hope this message from the UnidenBC780XLT Yahoo Group helps.
-------------------------------------------------------------------------------------------------------------------
Display not working (and no Audio) FIXED !

I Have fixed the display problem on the 780 without requiring the Service
Manual, but by using a schematic..

The 9 Volt cct that powers the display's LCD graphics (NOT the backlight, which
runs on 12 vdc) WAS NOT working. If your LCD graphics are out AND you do not get
any signal audio (you may still hear audio hiss or "screaching" though)....the
Zener diode that supplies the reference for the 9 volt cct is likly burnt out.
This Zener diode D27 is a UDZ10. It's a small surface mounted chip, close to the Q2
transistor. This diode is a 10 volt zener (not 9v, as it goes through a
resistor) UDZ10 zener. Any suitable sub should work.

Hope this helps anyone with LCD display problems/ NO RF audio problems.

Greg
VA3VFO
---------------------------------------------------------------------------------------------------------------------
Take care.
Lew
 

2WAYMAN

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5-7-12 9 PM EDT
Thanks "timewave" for that information. Out 780's with full display illumination and NO graphics, which faded out over time DO have all other functions working, they receive well and have full audio. Therefore, could this diode still be our culprit???
73's!
 

pro92b

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5-7-12 9 PM EDT
Thanks "timewave" for that information. Out 780's with full display illumination and NO graphics, which faded out over time DO have all other functions working, they receive well and have full audio. Therefore, could this diode still be our culprit???
73's!
The diode is probably not the problem. Here is a procedure originally published by Steve Donnell that might work.

Code:
I've just noticed that the screen on my UBC780XLT is fading... I can barely
make out the text! I've searched the archives and haven't come across any
postings on the issue. Has anybody else experienced this and if so, how have
you corrected it?
 
Fading of the LCD display is an all too common problem with these radios. One
fix I initially came up with, that we previously posted here and more fully
documented in our Scanning USA column (Aug '04), was to provide a means of
adjusting the contrast of the LCD display characters.
 
This can be easily done by swapping out a fixed value resistor with a trim
pot. To do this, take a look at the rear (from inside the 780) of the board
that makes up the front panel. Near the middle, you will see several surface
mounted components. Most of these are capacitors, are tan in color, and have
no markings on them. One will (likely) be green, and have the numbers "822"
marked on it. This is an 8.2K ohm resistor.
 
Replace that resistor with a trim pot having a 10K value, along with a 500
(470 is ok) Ohm resistor in series. If you wish, after you adjust the pot for
the best contrast setting, you can  replace the pot with a single resistor
that closely matches the new value. If you elect to keep the pot and resistor,
you will likely want to anchor them down with a bit of hot glue or epoxy. This
is important  because merely soldering the pot/res to the tiny pads of the
original resistor will not hold them in place very well. Even simply adjusting
the pot can produce enough stress to tear the components from the board.
 
A further update to this was that we found it necessary to adjust the contrast
setting, with increasingly lower resistance value settings. I then installed a
.05uF capacitor between ground and the solder pad of the original resistor
which is closest to the Vol/Sq controls. Since then, 6 mo ago, with the 780 in
daily use, we have had no further issues with the LCD contrast.
Evidently just changing the resistor did not fix the problem permanently and the display continued to degrade with time. The capacitor addition is supposed to stabilize the display and prevent further degradation. I doubt if the capacitor value is critical and a 0.1uF would probably work as well.

Pay attention to component mounting and use glue as recommended or you could destroy the board.
 

kruser

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Great info pro92b. I assume this 8.2 k resistor is in a part of the circuit that fixes the displays oscillator. I think I have a schematic so that should help me figure it out. I'd like to mount my pot so it is accessible externally somehow as long as doing that does not introduce noise. I'd use shielded wire and also add the capacitor.
I was thinking of a pot mounted internally but near the case that would be accessiblethrough a tiny hole just large enough for an alignment tool.
I have times where my viewing angle changes a lot and having an adjustable contrast would be a blessing in addition to fixing the low contrast.

Thanks for sharing this info. Sounds like a simple project for tomorrow evening. If it does not help then nothing gained, nothing lost!

If this works, I think I'll find the same circuit in the old Pro-2004 - 2006 radios and ad it on those as well. They always bugged me even when new as they had a tighter viewing area than the 780 did. With all my radios, it is hard to get them all positioned so the LCD's display with decent contrast.
Some LCD modules seem to have a much wider viewing area over others.
 

2WAYMAN

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Bc780xlt display fix

5-9-12 0038 HOURS EDT
Thanks pro92b and kruser for the info. I will definitely try this out. However, if anyone has already performed this "fix" what value resistor did you eventually arrive at to use as the "permanent" replacement (along with the 1.0 uF capacitor) for the original 8.2k resistor??????? Or is this something that will be different for each and every one of the BC780XLT radios I need to retrofit???
Also, kruser, if you did find that schematic I would really appreciate a copy of it- would you please send a fcopy to me via PM?
Thanks again and 73's!
 

pro92b

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The resistor setting will be different for each radio, thus the need for adjustability. The schematic is attached below.
 

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2WAYMAN

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5-12-12 9 PM EDT
Hey guys.....Just finished 'surgery' on one of my BC780XLT displays per pro92b's wonderful article first published apparently by Steve Donnell and Scanning USA. Did what the man said and it works great!!!
Used a Rat Shack linear taper trim pot 10K and a 470ohm 1/4 watt resistor and connected them via some very strong mini stranded Motorola portable repair wire with heat proof insulation. I knocked off the resistor marked 822 and added some solder to make the pads somewhat bigger. My suggestion to anyone is to remove the front panel of the radio to enable getting to the spots on the board easier- it was a bear trying to reach those little pads even with a magnifying glass! LOL!!
I left 4" wire tails that long so as to enable using the pot and resistor and not put any strain on their attachments to the board. After adjusting the contrast, I found that I would need a 460 ohm resistor to get the best contrast. I decided to try a 330 ohm 1/4 watt resistor I had also picked up at RS today, and voila! the display is as good as when the unit was fresh out of the box!! I then used the .1uF disc capacitor I had also picked up at RS. The only question was which leg of same was the + SIDE as they don't mark them. I don't believe this to be a critical point as it is working now and I'd rather not mess it up. The last thing I did was cover the bare resistor leads, etc, with heat shrink tubing and wire tied the excess wire to the white wire bundle going from the board to the display leaving a little slack .
Thanks again for all the kind assistance.
To anyone with a faded or completely faded BC780XLT scanner, you can have this great radio back in shape within an hour. Beats using a $500 radio as a doorstop!!
73's !
 

davedaver1

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Quite awhile ago, I had this issue and sent if off to Uniden for repair. It's still working fine, I wonder what their fix was. It seems the display is changing value in some way and the pot replacement changes how it's driven, so I guess they probably replaced the display itself. I wonder if putting the cap in would be a bit of insurance, though I don't what it's doing to prevent display degradation.
 

kruser

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Hey guys.....I then used the .1uF disc capacitor I had also picked up at RS. The only question was which leg of same was the + SIDE as they don't mark them. I don't believe this to be a critical point as it is working now and I'd rather not mess it up.73's !
The capacitor you used is a ceramic disc capacitor and will not have a polarity so either dircetion is fine.
The schematic that pro92b posted shows a cap already in place to ground on one side of the 8.2 k resistor so I assume you added the new cap on the other side of your new control?

I'm going to do this simple mod today and will report back with my results!
 

2WAYMAN

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5-13-12 1530 hours edt
Hello KRUSER..............
It was still working fine this AM!!! :) Thanks for the info re. the cap I used. I just followed what the original directions on the post from pro92b (originally written and published apparently by Steve Donnell.) My capacitor is on the solder pad CLOSEST to the on/off vol. and squelch pots on the front of the radio and the other side goes to ground ( used one of the big blobs of solder along the bottom edge of the display -there are about 4-5 of them along there). I think to answer davedaver1's reply is that as the unit ages (mine were in unmarked cars hidden in the hot glove compartments and I think that may have been partially to blame) is that the 8.2K resistor is just too much to allow the lcd driver to oscillate. I went through all the stuff with the pot and 470 ohm resistor last night and after measuring the reading as 462 ohms, I thought what the heck, if just the 470 ohm resistor would work and give you a nice dark contrast, I would try a 330 ohm RatShack resistor and voila, it was even darker! I may be wrong, but it appears that as the unit get older, you need to lessen the resistance to the lcd portion of the display. I do suggest you remove the front cover/frame, and three connectors to make it easier to remove the 822 resistor and solder to those darn little pads!! Good luck and let me know!
73'S
 

kruser

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Mine worked fantastic!
I ended up with a total of 14.4 K ohms. 10K for the control and two 2.2k ohm resistors.
12.2k was not quite enough for my viewing angle so I added an additional 2.2k and that did the trick.
If I were to measure it, I'd guess somewhere near 13k ohms is what I needed.
My board was also different than the schematic pro92b posted. The circuit was the same but all the resistor values were lower values on my board with the exception of the contrast resistor. It was 8.2k like shown on the schematic.
My 780 is well above eye level so I needed the high resistance to give me a good display.
I left my control mounted out the rear so I can adjust it if I ever move the radio below eye level. I tested that and even with the control set to its lowest resistance, the 4.4k of resistors still allow the unlit segments to display so I'm sure I could have used much higher value resistors so the total could not drop below maybe 8k but that is OK. I'm happy with it and I can now read the thing just fine without standing up!


Thanks to all that posted info on this as it does work and helped bunches in my case.
 

2WAYMAN

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Bc780xlt display contrast

5-13-12 2200 HOURS EDT
Hi Kruser...........
Glad to hear your 780 display also has been resurrected! Amazing how you needed 14.4K of resistance and I was able to use one 330 ohm resistor. Pro92B was right again! He said each radio would require a different value to make it work. In any case great news!
73's
 
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