Fluke PM6669 modding [backlight]

[cprobertson1]

I've recently picked up a Fluke PM6669 while in the US, and after a brief repair at the PSU side I've not got it working!

Granted, it's only the base model with no second channel, so it's limited to 0.1-120MHz but hey-ho, it's still useful!

Lately I've been using it late at night and cursing it's dim LCD screen though, and I've decided I wan't to (try) to mod in a backlight.

I'm thinking adding a row of SMD LEDs around the glass plate on the LCD panel and hoping enough of it will filter out - but figured I might as well do some research first!

Has anybody had any experience adding decent-looking backlights to fairly standard LCD modules?

[bingo600]

https://www.eevblog.com/forum/projects/hp-3457a-lcd-backlight-mod-(also-for-3478a)/msg227880/#msg227880

/Bingo

[cprobertson1]

Ha! Perfect!

When googling around I found a lot of gameboy backlight mods - but wasn't sure how it'd work with a long, relatively thin LCD ony my frequency counter as compared to the roughly square lcd of the gameboy

That's a sneaky idea that onlooker guy had with cutting up ebay LED bulbs - I'll need to remember that one!

My plan was to use a strip of copper-clad FR4 board with some scores across it to break the track into segments and then simply soldering some 0603 LEDs across the scores to make a series strip of LEDs.

Dismantling that LCD Module to change the reflective backing around is going to be nerve-wracking; I'll need to find some other modules to practice on first

Will post pics here of the process and the end result

Will post pictures here once fini

[cprobertson1]

Hmm, I've hit a snag! Actually, two snags, but I sorted one of them already!

The contrast seems a bit off - looks fine when view it from above, but viewing it straight on or from below makes it unbearably pale.

LCD bias looks to be controlled internally from the PCF8576 driver IC, so Im not sure how to fix it! Any suggestions

 I can live with it, but its very, very pale when the backlight is on =/

As a side note, I discovered that if you put the polariser in backwards, it inverts the display, giving a black, opaque background with white, transparent text - which is a surprisingly nice effect! Reminds me of those midas transflective modules!

[cprobertson1]

The plot has thickened! I reckon that by applying a voltage to Pin 12 (V_LCD) (which is currently tied to ground) I can get the PCF8576 to adjust the Bias: can anybody confirm that from the datasheet before I go adjusting anything?