LDC backlight identification and repair for Fluke Phillips PM 2812

[ErwinsCat]

I'm trying to repair the backlight for a Fluke Phillips PM 2812 power supply (and perhaps convert it to a benchtop power supply) the backlight uses a 130 volt AC. I checked the backlight circuit and it producing the voltage for the backlight element. I couldn't find any information regarding the backlight component. I don't know what kind of light it is I don't think it's a LED light and sure it's not an incandescent light either. I doubted I can find the exact model and technology light for it but wondering can I mod another king of flat LCD backlight for it? the plastic tabs that holding the display board and the LDC is very fragile and very tight. I already broke 2 tabs. so I like to get it to fix and never going back to it if possible.  any bits of help is appreciated
Al

[srb1954]

I'm trying to repair the backlight for a Fluke Phillips PM 2812 power supply (and perhaps convert it to a benchtop power supply) the backlight uses a 130 volt AC. I checked the backlight circuit and it producing the voltage for the backlight element. I couldn't find any information regarding the backlight component. I don't know what kind of light it is I don't think it's a LED light and sure it's not an incandescent light either. I doubted I can find the exact model and technology light for it but wondering can I mod another king of flat LCD backlight for it? the plastic tabs that holding the display board and the LDC is very fragile and very tight. I already broke 2 tabs. so I like to get it to fix and never going back to it if possible.  any bits of help is appreciated
Al

The PM281x series uses electroluminescent panels for the LCD backlight. Compared to LED backlight panels they are quite thin so it may be difficult to retrofit an LED backlight.

These are still fairly readily available on the usual auction sites although you might have to search around a bit to find one of the appropriate size. Some suppliers claim that their panels can be cut to size but I would be a bit dubious about that as electroluminescent panels are sensitive to moisture absorption. If you did cut one down to size you would have to ensure that the cut edges are well sealed.

It would be advisable to get the panel along with the recommended driver module  just in case the existing driver in the PM2811 is not compatible.

[ErwinsCat]

Hi mate!
Thank you for reply, I have a second question I forget in the original post, the existing panel seems to melt into circuit board, wondering if that is the way they applied and If yes, can I remove it by hair dryer?
Thanks
Al

[srb1954]

Hi mate!
Thank you for reply, I have a second question I forget in the original post, the existing panel seems to melt into circuit board, wondering if that is the way they applied and If yes, can I remove it by hair dryer?
Thanks
Al

Sorry, I don't know how the panel is fixed in place. The service manual doesn't offer any guidance either.

[ErwinsCat]

Update,
I managed to remove the panel, it was glued to the board I used hot air and it removed easy. I couldn't find suitable backlight yet but found a post online someone replace a backlight with a modified iphone backlight, I'm going to give it a go while I'm looking for suitable replacement EL panel.

[Audiorepair]

A lot of keyboards/audio eqiupment uses such backlights, you might do well to search there.

e.g.
https://www.backlight4you.com/EL-Panels/EL-Replacements:::46_130.html?language=en



But don't buy oversize and cut it down.
As a previous poster suggested, doesn't work for long.

[Gertjan]

Did anyone successfully succeeded in removing the front panel PCB of the PM2811 / PM2812?

The backlight of my PM2811 is broken, but the front panel PCB seems to be stuck (glued?) to the LCD...


IMG_0077  PM2811 front panel PCB stuck to LCD-2000pix.jpg

I was able to free the PCB from the plastic tabs / clips holding it, but now it seems to be stuck to the LCD panel....
I am pulling with a hook though the holes for the tabs in the PCB with a lot of force, but it won't budge. I am pulling with so much force that I am afraid of breaking the LCD panel...

regards, Gertjan

[Gertjan]

Answering my own question 

In the end I was able to remove the front PCB from the front panel:


IMG 1553  PM2811 - Display and backlight removed-2000pix.jpg

The key was using a lot of warmth and be patient.
My idea was to warm up the entire front assembly, to soften up whatever was sticky inside.

I placed the front panel on a PCB pre-heater, set to 60....70 degrees Celsius, to warm up the assembly. Take care to set temperature not too high to avoid deforming the plastic front panel. Let the front panel warm up for at least 10 minutes, to make sure the entire assembly is warmed up.
Then add extra heat to the back of the PCB, near the display, with a hot air soldering gun, set to 70...90 degrees Celsius.

Start prying and pulling on the PCB with a hook. I used a hook used by dentists, pulling on the edges, and in the holes in the PCB around the display, beside the plastic hooks. (point the hook away from the display, to avoid damaging the PCB traces, use the photos in ErwinsCat's start post for guidance)
First object was to unhook al the plastic hooks by pulling away the PCB just a bit.

Then start to pull the PCB gradually further away from the front. This was the easiest on the PCB edges that are away from the display.
You can also push on the display window to help. But be careful, the LCD is made of glass....
At some point, the LCD became un-stuck, and removing the PCB was easy after that.
This whole procedure took me the best part of one hour.


IMG 1555  PM2811 - Display and backlight, backs-2000pix.jpg

Regards, Gertjan.

[Gertjan]

I finished the replacement of the worn out electroluminescent backlight of the LCD dfisplay on my Philips PM2811.

It was not easy to find a replacement EL panel with the correct size. But following the lead of Audiorepair a few posts above I found backlight4you.
There i found this panel: EL-Panel, pink-white, 19.5mm x 222mm, laminated. This panel has the correct with, but is too long.

Fortunately you can cut an EL panel to size, just using a sharp pair of scissors. The catch is that these EL panels are very sensitive to moisture. so you have to seal the cut very well. I used 2 layers of Kapton tape. The outer layer is overlapping the first layer, thus creating a double seal.

The original panel, and the panel cut to size:


IMG 1630  PM2811 - original and cut panel-2000pix.jpg

The  leaflet accompanying the panel warns that you have to be very careful soldering the panel contacts.
First I applied a fresh blob of solder (with fresh flux) to the PCB pads where the panel connects.
Then I mounted the EL panel using double sided tape.
And lastly, while pressing the contacts down with a piece of metal, I soldered the panel pins very quickly. Just heat the solder blob, and the panel pin will slide into the molten solder. Done in under a second! That piece of metal is used to dissipate the heat from the contact pins, so the contacts at the panel side will stay cooler.

The replacement panel, mounted on the front PCB:


IMG 1632  PM2811 - new panel mounted on front PCB-2000pix.jpg

Now the repair is done, but before re-mounting the PCB in the front panel it is a good idea to check if all is fine.
So connect the front PCB to the PM2811, and see if the backlight is working. You do not want a second pass on removing that hard to remove front PCB  .

The result, My PM2811 has a new lease of life:


IMG 1641  PM2811 - with new backlight panel-2000pix.jpg

The display is more blue than original. But it is very easy to read, and actually I like the colour  .

Regards, Gertjan.

[Roehrenonkel]

Hi all,
 
sorry for hijacking, but the display of my PM2813 (in fact at the moment it's a 2812) is dim too. |-(
Has someone a service-manual that covers the power-modules as well?
I'd like to fix the third channel, that broke because of overvoltage.