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TOPIC: Speedometer illumation

Speedometer illumation 4 years 4 months ago #392

  • kielyp
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Hi to all,
I wonder if anyone can help or advise with speedo illumination problem on ZB.
Speedo doesn't illuminate when panel light and pilot is on.
I have checked the obvious and removed/replaced the 6w bulb fitted behind and at base of speedo. Bulb is working ok and can be seen to be lighting behind wooden dash but does not seem to illuminate anything ? Certainly not the speedo itself.
I cannot see any other speedo bulbs to replace ? All other instruments illuminate
( green ) as they should.
Can anyone help ? Many thanks

Further to above and thanks to an old posting of Paddy Reardon and others, I now know that the bulb behind speedo is not intended to illuminate the speedo directly.
I believe it is intended to provide ultra violet light ( through black glass ) thereby causing fluorescent paint of speedo numerals to glow green.
It appears the fluorescent paint has deteriorated over the last 56 years !!
After shining bright torch on speedo, it will glow dimly for about 30 seconds.
Last Edit: 4 years 4 months ago by kielyp. Reason: further knowledge of cause of problem
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Speedometer illumation 4 years 4 months ago #393

  • gruntie
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Junk the black filter and replace the bulb with a 12v UV LED. All will glow as it should.
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Speedometer illumation 4 years 4 months ago #394

  • kielyp
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I will do that. Thank you very much, and a happy New Year to you and all.
Pat Kiely
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Speedometer illumation 4 years 4 months ago #395

  • clacksman
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Gruntie is correct. I made up a set of three High brightness UV LEDs connected in parallel and mounted in a curved strip of alloy inside the curved black glass. This gave enough brightness with the black glass still in situ. The advantage of keeping the black glass is that it cuts out the stray visible frequencies of light produced by the UV LEDs, making the glow from the fluorescent paint more dramatic.
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Speedometer illumation 4 years 4 months ago #396

  • kielyp
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Hello clacksman, and thank you very much for your reply, I really appreciate it.
Could you possibly elaborate on how you went about the job ?
What type of alloy strip did you use and how did you mount it within the speedo ? Also how did you mount the LEDs to the alloy strip, and adapt the electrical connection ?
The only UV LEDs I can source online are in Australia, and have 5mm wedge connections.
Thanks again, and regards from a stormy Emerald Isle.
Pat
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Speedometer illumation 4 years 4 months ago #397

  • clacksman
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Its a bit late to reply properly tonight. I will put something together tomorrow and get back to you.

Andy
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