Why is this display dim and whining?

[WHaThEFLuX]

Back with another weird display issue, just wondering if anyone can shed some light on the source of the problem.....

I was sent multiple displays that function correctly but the lower half is not as illuminated as the top half. My first thought was that the displays themselves are just old and dying, but I noticed that all of them are "dim" in the same spots and produce a loud whine when powered.

When you look at the video you might think the lower half of the display is not that dim, but when the tinted case is attached the characters on the lower line are barely visible.

I figured the whine was coming from the big cap, but replacing it did nothing. After switching it out with a radial cap I had lying around, I discovered that the whine is definitely not coming from the cap but the display itself.

I also received one "good" display for comparison, it's much brighter with no whining noise at all, however the display does hum a bit.

My question is:

Are these just bad displays or is some component on the board fried causing them to be dim and whine? These displays are ancient looking 95 pin glass monsters that belong in a museum so replacing them is out of the question, I just figured I'd let the experts take a crack at it before I ditch the project!



Video of whine:

http://vid1138.photobucket.com/album...psasoyga3c.mp4

[eccerr0r]

Re: Why is this display dim and whining?

<pet peeve> it's a horizontal device, take pictures and movies of it in landscape mode!!!</pet peeve>

That's a vacuum fluorescent display - and is a vacuum tube. It needs to generate a "high" voltage to jump the vacuum, it uses a switching psu with an inductor, and likely that's what's whining. Now why it's whining - probably due to age, vacuum leak from the glass, ...

[WHaThEFLuX]

Re: Why is this display dim and whining?

I did the best I could with one arm, my apologies......

So there is most likely no way for me to brighten up the lower line on the display? Where are the psu and inductor located, on the board or within the display?

[eccerr0r]

Re: Why is this display dim and whining?

Power supply/inductor is usually on the board outside of the glass somewhere on the module... It may use a charge pump, but these should be quiet unless something's loose...

If it got dim over time, likely there's not much that can be done except overdriving the heater element and squeeze the last bit of life out of them before they dim to darkness forever... They look pretty readable on the movie, I'd just leave it.

[WHaThEFLuX]

Re: Why is this display dim and whining?

I see, I don't see anything that resembles a psu/inductor but I'll take your word for it.

Thanks for taking an interest, I really appreciate it, one last question.....if I did want to experiment with overdriving the heater element, how would I go about accomplishing that?

[R_J]

Re: Why is this display dim and whining?

It should have a dc/dc converter somewhere on it suppying around 25-30 volts, that converter sometimes supplies the a/c for the filament also. maybe it's between the board and the display, I suspect its output is no longer filtered and is too low.
I suspect the whining is from the dc/dc converter trying to charge its output cap (which is now open) similar to the charging in a photo flash, but the cap never gets charged so you here it whining. that raw a/c compunent would also effect the display

[budm]

Re: Why is this display dim and whining?

There is small inductor to the left of number 3 switch counting from the left.

[stj]

Re: Why is this display dim and whining?

i want to see the other side of the board.

[WHaThEFLuX]

Re: Why is this display dim and whining?

Not much to see on the other side unfortunately, all the goodies are in between the display and the board facing up into the display.....

I was able to charge the filaments and improve the display brightness a decent amount, I'll post the pics in a minute, big thanks to eccerr0r for the suggestion!

[WHaThEFLuX]

Re: Why is this display dim and whining?

Charging the filaments:




Not perfect but a big improvement, even with the tinted case:

[goontron]

Re: Why is this display dim and whining?

that .331 is an inductor....

[WHaThEFLuX]

Re: Why is this display dim and whining?

What's all the fuss about the inductor? Could replacing it potentially fix the issue?

The inductor is definitely not the source of the whine, it sounds like it's coming from underneath the display where all of the elusive ICs are.

If I had to take a guess, I'd say R_J's theory sounds the most plausible. I'd rather not remove the 95 pin display to find out, but if it must be done I'm up for the challenge.

[budm]

Re: Why is this display dim and whining?

The inductor is part of the Voltage booster circuit that take the low input Voltahe and produces that 30V for the display, think of the display as vacuum tube which needs high Voltage to operate.
http://www.explainthatstuff.com/how-...lays-work.html
https://www.noritake-elec.com/techno.../vfd-operation

[WHaThEFLuX]

Re: Why is this display dim and whining?

Ok bud I gotcha, thanks for the links!

So would it be worth it to remove/check/replace that inductor before trying to remove the display?

[budm]

Re: Why is this display dim and whining?

The problem may not be the inductor but the circuit that is related to drive the inductor.

[WHaThEFLuX]

Re: Why is this display dim and whining?

Attempted to remove the display, got frustrated because I'm handicapped at the moment, so I decided to sacrifice the display since this particular board was
water damaged, and out came the dremel:

[WHaThEFLuX]

Re: Why is this display dim and whining?

I'm starting to feel like I should give up on this one, unless there's anything else to tinker around with.....

The good news is that I came across a newer revision of the board and display, one that has access to everything, the bad news is that it's water damaged and completely dead.

Anything I can try?

[WHaThEFLuX]

Re: Why is this display dim and whining?

I've already tried replacing the component that was in the toasty area but still no power. It's a MC33063A switching regulator: https://www.onsemi.com/pub/Collateral/MC34063A-D.PDF

[R_J]

Re: Why is this display dim and whining?

You could clean that white corrosion off the ic etc. use some alcohol or something similar and an old toothbrush, you never know it might start to work.

[budm]

Re: Why is this display dim and whining?

I've already tried replacing the component that was in the toasty area but still no power. It's a MC33063A switching regulator: https://www.onsemi.com/pub/Collateral/MC34063A-D.PDF

Page 5 of the spec sheet shows app notes for 28V boost converter.