Acctim alarm clock

[Chris Hogg]

I've recently inherited an Acctim 71243 radio controlled alarm clock like this one

. But it's display is absurdly dim, even in a darkened room. Reading on the Internet, I see it has a blue plasma LED display, but dimness of the display seems a common complaint with this model. I bought it for my late mother some years ago, and I'm sure it used to be brighter, although never brilliant. I read ) "Earlier generation displays (circa 2006 and prior) had phosphors that lost luminosity over time, resulting in gradual decline of absolute image brightness".

Is there any way I can get into the works and increase the brightness, or is it doomed? I suspect the latter!

[Graham.]

That's a backlit LCD display, not an LED. "Plasma" would suggest the back-light isn't LED either, probebly a cold cathode tube or similar.

[Dave Liquorice]

brightness,

How can you tell from that image?

Plasma suggests it's a Vacuum Flouresent Display so no backlight, LCD, or LED.

VFD's do age, as the phosphor "wears out". It might be possible to get some brightness back by raising the filament voltage.

[Brian-Gaff]

Well doomed I fancy. After all its actual changes in the phosphor. I have a scanner radio with similar issues. Not that it bothers me any more but in order to make it bright enough I increased the brightness by changing a resistor inside which was changed to control brightness. The only snag of doing this was a bit of ghostly glow from nearby segments of the display, which I guess is some kind of leakage effect that not allowing the full brightness fixed. I have a pink and blue display on a dab radio which is losing brightness apparently as well, though I have no idea what technology it is using. Brian

[Brian-Gaff]

The ones I'm thinking of are glass units with pins along one edge, and obvious segments inside that would appear to be like little tubes of gas with phosphor on them. If you tap them they actually go ding, not that helps in any way!

Brian

[Chris Hogg]

Thanks for the replies. I am confused (as usual and yet again!). The Amazon link says Plasma LED, but it wouldn't surprise me if whoever wrote the advert had got it wrong, and you and Graham have differing opinions.

FWIW, the clock has battery back-up so that it continues to receive the MSF Anthorn signal and doesn't lose time when the mains is off. When in battery mode, the display is nominally switched off, but you can see the display numbers if you hold the clock at the right angle, silvery ghosts against a black background, and showing the correct time. There's no way of momentarily turning on back-light illumination, so the numbers stay as silvery ghosts until plugged into a mains supply, but viewing them through polaroid glasses suggests they are polarised, as rotating the glasses makes them disappear and then reappear, IYSWIM.

Does any of that help in deciding their technology? AIUI, the polaroid effect suggests some sort of LCD. But do plasma displays also use polarised light?

[Graham.]

Yes it seems I was wrong. Google sent me to a PDF of the instruction manual that described it as an LCD, but I see now it wasn't a 71243.

They probebly reckoned that "Plasma LED" would sell better than VFD, and what's more they could argue it's not a lie, as each segment is a (thermionic) diode and it emits light!

[Dave Plowman (News)]

Plasma displays were common before LEDs got bright enough for daytime use. The OBC on my 30 year old Rover SD1 has one. That still works just fine - but of course won't have had the same hours of use as a clock.

[Chris Hogg]

I still have in use a Heathkit digital alarm clock* which I assembled over forty years ago (before I got married, so I know the minimum time span!). It's still going strong, although with only two displays, hh.mm rather than hh.mm.ss, because one of the Beckman displays** gave up on me, and I found the continually changing seconds digit was mildly annoying anyway so didn't bother to replace it. Although I doubt the display would be classified as 'plasma' these days, even if it ever could have been.

• like this, with red-orange neon display as here rather than the later blue-green display

** like these or

[Harry Bloomfield]

Chris Hogg was thinking very hard :

I know exactly the type of back light you mean, I have similar with the same dimness issue on an old Tandy/Realistic scanning receiver. It uses a film technology, inserted behind LCD and all suffer the same issue. You can get replacements, which can be carefully cut to size, but is it worth it. The best fix is to add some high brightness tiny LED's along the edge of the display, if you can.

[Dave Liquorice]

Not unless they have polarised filter in front of them but they don't need it. Also I wouldn't expect to see ghosts of the actual changing time on a VFD display with the clock in backup mode.

I'll switch my money to LCD. B-)

[Chris Hogg]

Thanks Harry; sounds like that's what it is. Whatever it is, it doesn't look as though there's an easy fix, so it's heading for the 'small electricals' skip at our recycling centre.