Rigol DM3051 multimeter backlight failure

[matt6ft9]

I have a Rigol DM3000 series multimeter where the backlight seems to have failed.  Without the backlight, the LCD is very difficult to see.  But, I am able to go into the menu to the area that turns up and down the backlight intensity, no luck.  The contrast (in the same menu area) adjusts well.

I took the meter apart and pulled out the LCD module.  There are two markings along the edge of the PCB:  “A” and “K”.   I assume this is the anode and cathode marking for the backlight.  Also, there are two beefy (2R2) resistors RB1 and RB2 going to the “K”. 

I put my handheld meter to the diode setting and then held the probes to the A and K pins.  (this will light a typical white LED very faintly)  The backlight does not turn on.  I considered taking the black bezel off, but I have never had luck with getting zebra strips back on 100% operational.  Oh, if you look between the black bezel and the PCB, there is a marking on what I think is the backlight:  “GX-LB11230WS-B”  Google does not get any hits on that.

So, at this point, I’m not really sure what else to try.  I’d hate to lose a nice meter due to defective backlight.

Matt

[Macbeth]

Have you actually measured the voltage going to the backlight? If something sensible is there then it would look like replacing the whole LCD panel is in order.

Looks like a jellybean part rather than a custom display made just for Rigol. It looks the same as the DM3058/68 displays in which case have a look for a 256*64 LCD.

[matt6ft9]

Ok, finally got back to it.  There is an LM324 quad opamp on the LCD PCB.  I used pin 11 as the common connection for the readings.  The Anode side of the backlight measures 24V and the cathode side of the backlight is at 0V. 
The LCD does not seem to be a standard, off the shelf product.  (that I could find)

To me, it looks like there are LED strips on each end of the display.  My next plan is to use a Dremel tool to cut the black metal bezel off the end of the display.  I should then be able to bend down the PCB that contains the white LED’s.  (I thought about bending down the black metal, but I thought that would put too much pressure on the LCD itself)

[wraper]

My next plan is to use a Dremel tool to cut the black metal bezel off the end of the display.  I should then be able to bend down the PCB that contains the white LED’s.  (I thought about bending down the black metal, but I thought that would put too much pressure on the LCD itself)

Are you crazy? Why do you need to destroy the display with dremel? Just bend the metal hooks holding the bezel into straight position, then remove it. You will have an access to the LCD and after removing it, to the backlight. If you destroy the bezel, LCD won't be properly pressed down to the conductive rubber strips and PCB anymore, therefore you'll need to figure out how to undo the damage done (if you won't completely destroy the display in the cutting process  ).
Anyway, you won't be able to remove the backlight without removing the LCD itself first.