"Bob Urz" wrote in message ...
Terry Given wrote:
Clarence wrote:
"NSM" wrote in message
"BOB URZ" wrote in message

| Ok, the retrofit application i have has a display about 3/4" wide by
| 4" long. Plastic encased like a laminated card. The EL display
| backlite is dead. Measuring the voltage with my fluke on AC scale
measures
| about 55 volts AC. Is this too low for operation? It seems to be
powered
by a
| sealed step up module

Might be enough - tried 120 VAC on the strip?

The EL is also frequency sensitive, since it IS a losey capacitor. If the
frequency of the 55 Volts was higher than the usual 400HZ it might be
enough. I
have run El's on 50 - 75 V RMS at 1.8KHZ. Higher frequencies tend to
have an effect on the color.

Dont forget the type of fluke may be quite important - the waveform is
in general not sinusoidal, and beware the frequency response of the
meter. "When in doubt, scope it out." I invariably use a scope to see
whats going on, and (where appropriate) a meter for the actual
measurement. I've been caught too many times.....

nowadays I use my trusty HP3400A 10MHz AC thermal RMS meter, which cost
about US$50 - I miss those MIT junkfests on a sunday....

I have never chopped one to pieces, but the contaminant issue sounds
quite feasible. I last designed an EL backlight into a product 4 years
ago - at the time I put a lot of work into ascertaining the lifetime,
which is a strong function of temperature, voltage, frequency, sock
colour etc. IIRC the backlites I was using were rated about 2,000 hours,
and so I got the software to turn off the EL a few minutes after a
keypress. I also designed a decent smps to drive the thing - the asian
prefab EL drivers I looked at all had nasty waveforms, and were
seriously crappy (appalling layout, beating bjts to death etc) as well
as expensive and inconvenient to mount - which dies first, the EL or the
smps.....

Cheers
Terry

2000 hours does not sound like a lot. What are the failure modes on a EL
display? Its not like it has a filament that burns out

Bob

The Phosphor fatigues and dims. Lower stress levels will achieve a longer live
in some phosphors. However abt 5,000 hours is the most I've seen.

The Asian drivers are basically a blocking oscillator, and the wave form is
pretty distorted. However even a modified sine-wave-form will work and it
doesn't affect the life enough to detect in a few hundred units I tested.