Fluke 115 lcd display question

[cv007]

I have a Fluke 115 which works fine, but the lcd viewing angle/contrast is not very good (seems like a somewhat common complaint with these). Usually I turn on the backlight to help out a little.

Disassembled the meter to check it out. After reading the msp430 datasheet and app notes about driving an lcd display, I measured the external voltage divider resistors that are used for the lcd drive voltages (4 voltage levels total, ground is internal it seems). They are 100k resistors along with some unknown value of caps (they are 1uf or less from the looks of them). The measured values are 99k, 94k, 95k (from memory). I also measured the voltages and the values would swing in about a 10mv range.

My question is- at what point do those 'unsymmetrical' voltages start affecting the display contrast? The msp430 app notes seem to indicate that its quite important that those drive voltages are symmetrical and stable, but they don't give any numbers to shoot for. They also show for best contrast (on 'larger' displays/segments- what qualifies as large I'm not sure) to use a low current op-amp in buffer mode for the drive voltages, with high value resistor divider as input.

I'm not sure I want to start more testing unless I'm sure an improvement is possible. Maybe someone with experience driving lcd's can say whether its a waste of time or not. (The Fluke may start squealing if the soldering iron gets close to it- so don't want to upset it unnecessarily)

Thanks.

(I was also hoping to see active serial output on the unpopulated header connector tied to the msp430 serial port- but there is none)

[M0UKD]

I have the same problem with my Fluke 115. I like the meter, but the LCD is not great. Could really do with a contrast adjust in certain lighting conditions and angles. My Fluke 179 is a lot better.

I'd be interested if there is a mod that can be done to increase the LCD contrast.

Here is an example comparing my new 115 to my old 233



Cheers, John.