Old LCD display - Page 1
Forum section: electronics / testgear

author: electronics-whiz
author_rank: Regular Contributor
timestamp: December 13, 2014, 03:55:14 pm
content: I got an old stereo i tried to fix for a friend, but nothing i can find is wrong with. It has one of those LCD like displays, but has the grid lines, looks like those old style displays. Dave mentioned something about it takes like 300V to run these. Where does that come from? It has a big power transformer i would like to reuse, i just don't know if that would have the 300V output. The display seems to just connect to an IC, and a few small SMD passive things.Also if i wanted to reuse the display how do they work?

author: electronics-whiz
author_rank: Regular Contributor
timestamp: December 13, 2014, 04:10:05 pm
content: Sorry wrong section feel free to move.

author: SeanB
author_rank: Super Contributor
timestamp: December 13, 2014, 04:17:00 pm
content: Vacuum flourescent display, it runs of typically 30V with a heater of 3VAC as power. Your transformer will likely have a 20VAC winding and a 3VAC centre tapped winding in it to drive the display.

author: Macbeth
author_rank: Super Contributor
timestamp: December 13, 2014, 05:30:26 pm
content: LCD is nothing at all like VFD, and certainly doesn't need 300V. I can only imagine that kind of voltage being half wave rectified to run Nixies. Is the OP smoking crack?

author: electronics-whiz
author_rank: Regular Contributor
timestamp: December 13, 2014, 06:42:09 pm
content: I saw Dave working on something with a VFD and said something like you don't want to go poking around with this on because there's 300V there. Usually when i watch it's like 1AM so maybe i was tired and misunderstood, or he was referring to something else on the same board.

author: miguelvp
author_rank: Super Contributor
timestamp: December 13, 2014, 06:47:00 pm
content: Without pictures we don't know if you have a VFD or an LCD or what else, brand model of the stereo will help as well.

author: electronics-whiz
author_rank: Regular Contributor
timestamp: December 13, 2014, 08:11:02 pm
content: I'm pretty sure it's a VFD as I've never seen an LCD like this. It's thick, has a glass stub off one end, and fine wires across the top. I put 3V DC across the heater I assume are the fine wires on the top, and connected -30V to one and +30V to some of the leads nothing happened though.

author: electronics-whiz
author_rank: Regular Contributor
timestamp: December 13, 2014, 08:12:37 pm
content: It has a label, goggling it showed nothing of any use. Futaba P/N 212141 10-bt-167gk

author: helius
author_rank: Super Contributor
timestamp: December 13, 2014, 08:59:26 pm
content: Futaba is a VFD manufacturer. You probably won't find a datasheet, as most VFD made for consumer electronics used customized designs. But that doesn't matter, since they all work the sameexceptfor chip-in-glass types with integral drivers. (which are identifiable by having less than 10 pins.)An application note with basic description of the VFD components and driver circuitry is at this page from Noritake:http://www.noritake-itron.com/subpages/applicnotese/vfdoperapn.htm60 V is really excessive, you only need about 12V to make them illuminate. With a dual-output DC supply, strap the supply for -3V and +12V common referenced, put the 3V across the filament, and connect the +12V to one of the grids. then probe the same +12V to any of the anode pins. Like this: