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Repair of King luminescent / gas discharge displays, and LED replacements

We have a KR87 ADF where the display has gone blank. Or not quite — no numbers are visible on the display, but there is a glow around a few points at the bottom of the panel. Should I assume this is a display panel problem or could it be the driver circuitry?

ESKC (Uppsala/Sundbro), Sweden

If a part is working, it is probably not a cracked display panel.

I have the KR87MM, if you need it. I believe the driver chips are still available. I would just clean up the connections and change all the chips driving the display.

Administrator
Shoreham EGKA, United Kingdom

Peter wrote:

I have the KR87MM, if you need it.

Got it, thanks. Very useful.

ESKC (Uppsala/Sundbro), Sweden

I read somewhere that the LED replacements mentioned further back are no longer available, due to some legal / certification issue. May be EASA-reg only. Worth a check. I wonder if @simon is still out there?

Administrator
Shoreham EGKA, United Kingdom

Bevan Aviation in the US fits LED or LCD replacements.

Highly recommended to me by a colleague out there who sells avionics. Apparently the repair is not obviously visible.

If you are Euro-reg then you need a dual release 8130-3 and I have a contact for generating these, too.

Administrator
Shoreham EGKA, United Kingdom

Any idea of price for the repair?

Posts moved to existing thread.

@bathman I suggest contacting them with details.

One UK company which used to offer the LED replacements was charging best part of 1k, but they were paying another company down the road to print off an EASA-1 form.

Administrator
Shoreham EGKA, United Kingdom

Peter wrote:

If you are Euro-reg then you need a dual release 8130-3 and I have a contact for generating these, too.

If you have an ELA1/2 aircraft (includes non-complex — in the EASA sense — airplanes with an MTOM of at most 2000 kg) you can do without a dual release 8130-3 or EASA form 1, according to item (c) of the following paragraph in part-21:

21.A.307 Release of parts and appliances for installation
A part or appliance shall be eligible for installation in a type-certificated product when it is in a condition for safe operation, and it is:
(a) accompanied by an authorised release certificate (EASA Form 1), certifying that the item was manufactured in conformity to approved design data and is
marked in accordance with Subpart Q; or
(b) a standard part; or
(c) in the case of ELA1 or ELA2 aircraft, a part or appliance that is:
(1) not life-limited, nor part of the primary structure, nor part of the flight controls;
(2) manufatured in conformity to applicable design;
(3) marked in accordance with Subpart Q;
(4) identified for installation in the specific aircraft;
(5) to be installed in an aircraft for which the owner has verified compliance with the conditions 1 through 4 and has accepted responsibility for this compliance

This is also supported by part-ML:

ML.A.501 Classification and installation
(a) Unless otherwise specified in Subpart F of Annex I (Part-M), Annex II (Part-145), Annex Vd (Part- CAO) to this Regulation and Annex I (Part-21) to Regulation (EU) No 748/2012, component may be fitted only if all of the following conditions are met:
(i) it is in a satisfactory condition;
(ii) has been appropriately released to service using an EASA Form 1 as set out in Appendix II of Annex I (Part-M), or equivalent;
(iii) has been marked in accordance with Subpart Q of Annex I (Part-21) to Regulation (EU) No 748/2012.

I know what you’re going to say, but my avionics shop has no problem with this. In fact they’re the ones who made me aware of this possibility when we had difficulty getting a dual release 8130-3 for a replacement piece of avionics.

ESKC (Uppsala/Sundbro), Sweden

Indeed; that’s the “dynamite” clause which “almost everyone” pretends doesn’t exist

However I doubt it covers user repairs. I am fairly sure that it isn’t possible to get a partial display failure on these (eg. a decimal point not working) and the cause to be the display. After all, the whole thing is just some bits of metal in an evacuated chamber.

I have just been playing with some old bits, one of them a KDI572 with some duff display elements, and the same display worked perfectly in another KDI572.

So it has to be the driver chip(s). They contain high voltage transistors so probably don’t last for ever. OTOH one can find the circuit boards very cheaply, from dead avionics, and a transplant isn’t hard. You just can’t do the repair legally.

It could also be the contacts but they are not difficult to access and clean, or just move around a bit to test them.

I also don’t see a mechanism for these displays wearing out. Maybe they do, like fluorescent tubes wear out, but I would not expect it to be just some parts of it.

Administrator
Shoreham EGKA, United Kingdom

Peter wrote:

am fairly sure that it isn’t possible to get a partial display failure on these (eg. a decimal point not working) and the cause to be the display

Partial failures aren’t that uncommon. The cause often is (sort of) the display – it’s the connector at the bottom. You can fix them “off the books” by dissasembling it and cleaning the connectors. Our old Narco radio was notorious for it.

The displays will wear out too – cold cathode displays are subject to sputtering, but it’ll take many years for this to be a problem as they are usually designed with this in mind (e.g. gas fill, the old nixie tubes would have a small amount of mercury which extended the lifetime about a hundredfold), and they are also multiplexed (so all the digits aren’t on all the time, they rely on your persistence of vision, as the electronics cycles around them).

Last Edited by alioth at 18 Jan 16:07
Andreas IOM
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