Disappearing needles.

[newshound]

There won't be if he's had it 25 years!

[The Other Mike]

I know you should know the electrics inside out but it sounds like a partial lamp / electrical failure, maybe a dimmer not working or a split arrangement where the needles are lit at full brightness and the lamps have failed and the rest of the panel is dimmable and the lamps last forever

[Nightjar]

Could you fit electroluminescent tape around the edge of the casing, to light the needles directly, instead of relying upon reflection?

[Dave Plowman (News)]

The only illumination is the back lighting through the instrument face via the numerals - and spill round the sides of the face or through the needle bearing hole. As I said, the case is white, so there will be some. Thing is, the backlit numerals are perfectly normal - it's only the needles which are dim.

[Dave Plowman (News)]

They say a picture tells a thousand words, so perhaps these will.

Both taken only a few minutes ago so almost dark.

This one is taken with flash.

This one with the panel lights on.

[meow2222]

Perhaps you'll only find out by opening the thing up. If that happens, you coudl always have a few sm ultrabright LEDs on hand as a last option if the original system is not practical to fix. Either to fix to the inner side o f the front, or if necessary to glue on to the needles. A few strands of ex traflex loosely twisted would survive plenty of cycles and give about zero resistance to movement. Hopefully you can sort what's there though.

NT

[Dave Plowman (News)]

I think it would be easier to find out what reflective paint was used originally, and re-paint them. ;-)

The actual bulbs are standard items that even Halford sell.

[Adam Aglionby]

I remember getting quoted 80GBP each sometime in late eighties.

OK :-) practical Blue LEDs for which Shuji Nakamura and colleagues have just won the Nobel Prize .

Rememeber any brands? its an anorak interest of mine

Thanks

[Adam Aglionby]

Reflective or photoluminescent, reflectives tend to be glass bead in a binder and fail in patches,

[Adam Aglionby]

Get a spare panel to experiment on, does look like should just be lower lamps below needles

[Dave Plowman (News)]

As regards the smaller instruments, there is one panel light each at the top. The lower ones you're probably seeing are warning lights and nothing to do with the instrument illumination.

[Martin Brown]

Yes. The "Blue" LEDs back then were dim and "blue" in the same sense that the "green" ones were green. True "green" Emerald green came later.

Not really. I do remember lusting after them but at the time as a student they were stratospherically expensive.

[charles]

even red LED weren't cheap when they first appeared (late 60s). 28/- each is what I remember.

[Martin Brown]

I was allowed to buy one if I could find a use for it. It is still there illuminating a gunsight on an 18" telescope at Salford observatory many decades later. Dim as hell compared to modern ones.

The guy who invented them is a bit miffed with the Nobel prize committee and TBH I think he has a point. His was the ground breaking research that made these bespoke bandgap materials possible.

I still recall marvelling at how much brighter they got if you dunked them in LN2 to stiffen the crystal lattice. A trick you can only do three or four times before they disintegrate from thermal shock.

[The Other Mike]

Have you ever changed the lamps, if so and they are the type that is latched with a 90 degree turn into a flex pcb backed by rigid plastic then there are several different wattages and lamp envelopes in the exact same moulded base style. Some will have a light output around 100% higher than others.

[Dave Plowman (News)]

Interesting. There are two sizes of holders across the entire unit - but only one size on the small instrument side. So the same holder for the warning lights and panel illumination. And according to my fiche, they both use the same 1.2w bulb.

However, that doesn't explain how the numerals light up just fine, but not the needles. Since they share the same bulb.

[RJH]

snip

Luminescent paint doesn't just fail all of a sudden, does it? Half lives and all that. 'Energising' the needles with a bright torch should induce a glow, I'd have thought.

And it's a bit of a daft design, if it is luminescent. Light from the instrument or other dash lights obviously wouldn't reach the needles' face - or they'd show up. And if that light doesn't reach them, where's the source? Sunlight's going to be a bit unreliable when they're most needed :-)

Is there an SD1 inner circle you could consult?

Best of luck with it all. My guess would be some sort of secondary lighting circuit, but you seem to have ruled that out.

[Dave Plowman (News)]

I'd say they're probably similar to other Smith's designs. Although the back lighting may have been a first.

Oh yus. Got the same rude comments about aged eyesight as here. ;-) Until I posted the pics.

It just possible the mask which is black on the outer and white on the inner is very dirty, and not doing its job. But I did have the speedo cluster apart fairly recently to sort the trip counter and that was spotless inside.

[Adam Aglionby]

Even when your not a student high end hifi is stratospherically expensive ;-)

Wonder if some high end hifi now comes fitted with a deliberately dim red case, red LED , for retro appeal and ,er, sonic performance...

Nick Holonyak Jr should get some more recognition but Shuji Nakamura pursued a path ,pretty much alone, that had been discounted by many.

It is truly a shame there was no Youtube at the time, but should you ever recreate the experiment , please video it :-)

[Adam Aglionby]

So probably more reassuring that you can`t see the needles ;-)

Should the surround act as a light guide?

Needles look like they are a inverted V shape so will need some light coming from below somehow surely, hard to tell from the pics.

If its an acrylic lightguide it might have yellowed a bit from lamp heat.