Vintage 'bubble' LED displays

[agardiner]

A segment in the display of my Sinclair PDM35 meter has suddenly died. Only a single segment so not a multiplex drive issue. I have seen this before on the micro LED displays that had bubble type magnifiers bonded to them. Certain models of vintage calculator seemed prone to this such as the Commodore models.

I presume this is a failed LED. Or is there some other cause that can be rectified?

[Buzby123]

I've got an ancient 8-digit bubble LED which was working perfectly until last year, when I dropped it on a hard floor !.

Now it's got 1 segment of 1 digit failed. It could be a cracked LED chip, or a bonding wire come loose.

When I can be bothered I'm going to look with a magnifier to see if it is just a bonding wire.

If it is I may try a repair with conductive stuff, but I don't hold out much hope.

YMMV

Cheers,

Buzby

[SiriusHardware]

This happened to the display on my treasured PFM200 frequency meter and in an act of desperation I tried applying heat for a period of several seconds to the common terminal of the display cell with the faulty segment. It worked, but you have to appreciate that this is a risk, as with all LEDs they are sensitive to excessive heat.

Forum member Timbucus ordered some bubble displays from Eastern Europe soem time ago and found that several of them had one or more dead cells or segments, but was able to revive some, not all, of the dead segments by using the same application of heat to the common terminal of the cell with the dead segment in it. You might get lucky.

If you can lay hands on a working, basic TEXET 880 calculator of the same vintage I think the display is electrically and pinout equivalent. They are sometimes offered with one or more broken keys which are more or less unrepairable due to the way they are made, so those ones tend to be more sensibly priced.

[G6Tanuki]

I've got an "Alpha" 3-digit LED DVM from the mid-70s that uses a bubble-type display which has lost a segment; I must try the heating trick to see if it brings it back to life.

[Mark1960]

I wonder if Tim has one where the four digits you need are still working. Is it the same size digits and pcb as the display used on the MK14? It might be hard to find a 4 digit display but you could possibly use 6, 8 or 9. There are a number of different manufacturer part numbers that are pin compatible.

https://www.vintage-radio.net/forum/...145663&page=14

Looks like the display on the NSA15xx might be slightly larger than NSA11xx.

[agardiner]

Thanks all for the information and advice. Thanks Mark1960 for reposting the pinout information of various displays.

So the consensus is that the LED itself is probably innocent. When I have the time, I might try the heat trick to see if it comes back to life, but if not then it would appear that I can substitute for something.

[factory]

With calculators, the batteries can end up destroying the bond wires, if/when the batteries leak, I've seen comments about this elsewhere.

David

[fetteler]

Yeah, I think I've got a calculator where this has happened.

Shame really.

Steve.