Dim VFD on my Pioneer RX-370 - Page 1
Forum section: electronics / general

author: sonnytiger
author_rank: Frequent Contributor
timestamp: August 13, 2013, 09:52:45 pm
content: The system is as old as me so, its acceptable that the display is getting a little dim, but it is annoying to try and read, any suggestions as to how to brighten it up? The only feasible way seems to be to up the filament voltage, but how would I do this? separate supply? change a resistor that might be keeping the voltage at bay?

author: Stonent
author_rank: Super Contributor
timestamp: August 13, 2013, 10:58:44 pm
content: Wasn't sure if you had seen this recent posting:https://www.eevblog.com/forum/chat/vacuum-fluorescent-display-rejuvenation/

author: David_AVD
author_rank: Super Contributor
timestamp: August 13, 2013, 11:14:23 pm
content: I don't have a manual for that model, but sometimes the issue with a dull VFD is low Vee (bad caps in PSU) or low heater voltage (also bad caps). I would check these first before assuming the VFD is low in emission.

author: sonnytiger
author_rank: Frequent Contributor
timestamp: August 13, 2013, 11:19:53 pm
content: Thanks! My issue seems to be oxidized filaments, as there is uniform dimness and when other segments light others dim as if there were a lack of electrons.

author: David_AVD
author_rank: Super Contributor
timestamp: August 13, 2013, 11:27:48 pm
content: I've repaired VCRs (way back when!) and amplifiers before where the issue was definitely the capacitors, so thought it worth mentioning.

author: sonnytiger
author_rank: Frequent Contributor
timestamp: August 14, 2013, 03:24:57 pm
content: Ok I will take a look at the caps then, thanks!

author: mzacharias
author_rank: Frequent Contributor
timestamp: August 18, 2013, 12:11:53 pm
content: These models leave the main power supply caps charged up; even if unplugged they don't bleed off. Do bleed off the big caps before you do anything else.Sometimes there is just a film that has built up on inside of the display lens and a simple cleaning will restore VFD brightness.

author: sonnytiger
author_rank: Frequent Contributor
timestamp: August 18, 2013, 05:27:37 pm
content: right got it, thanks!

author: sonnytiger
author_rank: Frequent Contributor
timestamp: August 18, 2013, 06:07:29 pm
content: Caps all appear to be good and there is no dirt on the filter. What are my options now? I can't really see an easy way of modifying voltages.

author: David_AVD
author_rank: Super Contributor
timestamp: August 18, 2013, 10:37:45 pm
content: Have you asked Pioneer spares for a price on the part?

author: envisionelec
author_rank: Frequent Contributor
timestamp: August 18, 2013, 11:52:21 pm
content: Quote from: sonnytiger on August 18, 2013, 06:07:29 pmYou don't modify the voltages, just remove the display and crank the voltage up on the filament as explained. Read the thread posted above, again.

author: sonnytiger
author_rank: Frequent Contributor
timestamp: August 19, 2013, 02:10:16 pm
content: Right crank the voltage on the filament, but the display would be very difficult to get back in, would I be able to boost the voltage for a few seconds in circuit? or would there be a cap in he way or something. Or maybe its ac right off the transformer....

author: sonnytiger
author_rank: Frequent Contributor
timestamp: August 19, 2013, 02:17:05 pm
content: So after examining the board I can do it in circuit: There is only one cap on the ground plane and it is rated 50V. no problem. Just gotta get an lm317 set up

author: sonnytiger
author_rank: Frequent Contributor
timestamp: August 19, 2013, 03:18:53 pm
content: Okay I used 12v to get it orangey-yellow hot, best I could do and it made a big difference. Still kind of patchy though, I'm thinking getting it hotter would fix that?

author: envisionelec
author_rank: Frequent Contributor
timestamp: August 20, 2013, 02:44:47 am
content: Quote from: sonnytiger on August 19, 2013, 03:18:53 pmMaybe. You can get them to nearly white hot for a second or two max. The issue is that the filament deposits impurities on the local grid that makes up the segments, dimming them. You may never be able rid the display of those dim patches.I wouldn't leave it in circuit. At least desolder or clip the leads to the display...

author: sonnytiger
author_rank: Frequent Contributor
timestamp: August 20, 2013, 01:42:49 pm
content: Hmmm maybe i am just better off leaving it alone haha. If i get bored in the future i will dick around some more. Thanks for the help guys!