OT:Kenmore range display diming?

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Paul Hovnanian     mailto:Paul@Hovnanian.com
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Keep your gnosis out of my business!

[snip]

My range has a nice blue burner status display. And if the power goes out, you can still light it with a match.

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Paul Hovnanian     mailto:Paul@Hovnanian.com
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professor; n, One who talks in someone else's sleep.

Yup, that reference is what I recalled... that VFDs use filament-based electron emission, to cause phosphors to fluoresce. They aren't all that different from CRTs in that regard. I did recall they were prone to aging due to filament wear-out (less emission) and apparently they can suffer from phosphor wear-out as well.

The "gas-filled tubes" being referred to are, I think, Nixie tubes, which are basically neon bulbs with pretensions of grandeur :-) and don't use any phosphors or filaments as far as I've ever heard.

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From all the equipment I've worked on, it's the phosphor that burns out.

The filament usually doesn't wear out. It's like the filament in a light bulb except that it isn't even driven into a red glow so it'll usually live forever (unlike the phosphor). When the phosphor gets tired you can increase the filament voltage a bit. At some point the filament strings start to glow and you'll see several faint dark red lines across the display. That causes more electrons to be emitted, more brightness. But the filament must be driven from an AC source, otherwise there can be uneven brightness across the display, especially if it isn't very highly muxed.

[...]

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Regards, Joerg

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Couldn't he just take it down to the corner drug store and use their tube tester to see if it's weak? Of course, he would need a flux capacitor ... :-)

Ed

And a time machine. Plus probably a DeSoto Club Coupe if it is a few blocks away.

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We use 16-segment VFs in several of our products [1]. Most of these are powered up 24/7. After 10 years or more of operation, they look fine. Lots of clocks and microwave ovens and DVD players use VFs and they seem to hold up very well.

We used DC filament drive, 24 volts on the grids/anodes, and it looked fine.

John

[1] except that NORITAKE has EOLd the glass. We just did a PC board that uses an Atmel processor and an LCD, as a drop-in for the old VF display board. It intercepts the SPI 16-segment+grid drive scan, converts back to ASCII, and drives the LCD. Nuisance, but avoids bashing the code on a bunch of products. Pity... the VFs looked great.

On a sunny day (Wed, 29 Sep 2010 11:11:34 -0700) it happened John Larkin wrote in :

Did you check teh competition?

Noritake used to be great- local office, great service etc. 8-(

24V non-muxed? That's a lot, then you should be able to read the numbers from Sutro Tower :-)

DC on the filaments is probably ok but if you look closely you'll probably see a slight brightness variance from left to right. IOW, the display sees 2-3V or whatever you filament voltage is less on one side. This is why people either drive it switch-mode or use a 60Hz transformer tap if there is one.

That is sad. VFDs look so much nicer, don't have a reading angle problem and are just plain easier to read. Very much so for people who need to wear reading glasses. But VFDs are power hogs because of the filament.

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From this thread I gather that there are concern. John wrote EOL, you write "used to be". Are they throttling back something?

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They closed their local office and moved everything back to Chicago to save money with cheap labor. ;-)

No, the 8 characters are multiplexed. I meant that I used DC on the filament. In theory that tapers the character brightness, but at 24 volts on the anodes and maybe 3 volts on the filament, it didn't show.

I was going to do a 9-phase mux, 8 characters displayed, with PWM filament drive during the 9th time slot. But it wasn't necessary.

The new LCD looks mushy compared to the old VFDs. But between the tube going obsolete, and the driver availability getting iffy, we gave up on the VFs.

John

One possibility, if a VFD, is that charge has built up on the glass and attracted a lot of dust to cover the actual display unit. If you can get it apart, then it may just need simple cleaning. I have seen this on some units used in dusty conditions. Presumably the range gets a lot of fumes from cooking.

Jon

Jon Elson wrote in news:M5CdnfWIpa0NXz7RnZ2dnUVZ snipped-for-privacy@giganews.com:

I did pull out the display and clean it. There are no visible signs of damage, mind you that doesn't mean anything if a cap is drying out it wouldn't show anyways.

It seems to have two Pcb's press fit and notched to the back of the display one on top of the other. One of those things were if you try to take the pcb out you are likely going to damage the whole thing. So I made a command decision to use it until it is completely unreadable then try to disassemble and replace the cap. That and I'm to dam lazy to disassemble half the stove to change a cap right now ;-)

Is it typical for VFD's to only dim in one area or do they usually fade uniformly? I'm asking because the clock part is fine it's just the top right corner where the temp is displayed in orange whereas the clock is green.

Dunno about that. The VFD segments, from a microwave made in 1883 I dismantled recently, showed a browning or dulling of the most used time digits, suggesting the phosphor degrades over time, like the CRT TVs do.

Actual cause of the microwave's demise was that the controls became erratic and the processor was sometimes going silly. Quite solidly built, made in Japan.

Grant.

Unless the grid digit select is leaking away for top right? They work like valves (tubes) common cathode is the heated horizontal wires, grid to select which 'digit', anodes for the segment pattern under each grid.

Something like that.

Grant.

Sounds like quite a valuable antique. Steam powered?

Best regards, Spehro Pefhany

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