Bypassing a video projector's bulb test?

[A.J.]

I'm attempting to bypass the bulb test shut-off function on a
Sharpvision series LCD video projector. The point is to make it
believe that there is a bulb so it won't shut down after finding none
(I'm planning to use an alternate light source). Anyone know of a
quick and cheap way to do this?

The arc voltage seems to jump to about 1500 volts, then level at
around 200V or so (supposedly once the arc is started in the lamp).
I'm thinking a big old VR would trick it if I can match the original
bulb's resistance, but how to get around the initial spike... I know
not.

Any info would be appreciated.

 

[Ian Stirling]

A.J. <ajeromin@ea.com> wrote:

I'm attempting to bypass the bulb test shut-off function on a
Sharpvision series LCD video projector. The point is to make it
believe that there is a bulb so it won't shut down after finding none
(I'm planning to use an alternate light source). Anyone know of a
quick and cheap way to do this?

The arc voltage seems to jump to about 1500 volts, then level at
around 200V or so (supposedly once the arc is started in the lamp).
I'm thinking a big old VR would trick it if I can match the original
bulb's resistance, but how to get around the initial spike... I know
not.

I would simply try connecting a power resistor of Wattage/200V ohms to
it.
The starting spike shouldn't matter, it has no power.

 

[A.J.]

Thanks. I'll give it a try. I guess the worst that could happen is the
resistor will burn up, and maybe a few components inside, and I'll
still be stuck with a dead projector that requires $420 bulbs...

 

[Ian Stirling]

A.J. <ajeromin@ea.com> wrote:

Thanks. I'll give it a try. I guess the worst that could happen is the
resistor will burn up, and maybe a few components inside, and I'll
still be stuck with a dead projector that requires $420 bulbs...

You have investigated other sources of compatible bulbs?
What sort of light are you considering replacing it with.

 

[Rich Grise]

On Fri, 12 Nov 2004 08:07:37 -0800, A.J. wrote:

Thanks. I'll give it a try. I guess the worst that could happen is the
resistor will burn up, and maybe a few components inside, and I'll
still be stuck with a dead projector that requires $420 bulbs...

What's the bulb's _wattage?_ Just use a resistor with that or higher
power rating, and it will not burn.

Probably. ;-)

Good Luck!
Rich

 

[N. Thornton]

ajeromin@ea.com (A.J.) wrote in message news:<95d0836.0411120807.482fc89e@posting.google.com>...

Thanks. I'll give it a try. I guess the worst that could happen is the
resistor will burn up, and maybe a few components inside, and I'll
still be stuck with a dead projector that requires $420 bulbs...

What bulb are you paying $420 for? A bit steep.

Since its an arc bulb you just might be able to put an old fashioned
pair of carbon electrodes in there. Have used those, they make a nice
intense point source, and compared to 420 are very cheap. Arc lights
dont normally run at 200v though, 1 ohm is more typical. Also you need
to motorise the rods, and provide some simple optics to enable regular
realignment during use, making it not a trivial option.

A halogen bulb may be cheaper, but again 200v is not a standard
halogen V either. have you considered putting a $10 mercury bulb in
there? Or is this super high power? or is it condenser optics
requiring a point source?

Always give the details f you want the help.


NT

 

[John Fields]

On 11 Nov 2004 10:55:45 -0800, ajeromin@ea.com (A.J.) wrote:

I'm attempting to bypass the bulb test shut-off function on a
Sharpvision series LCD video projector. The point is to make it
believe that there is a bulb so it won't shut down after finding none
(I'm planning to use an alternate light source). Anyone know of a
quick and cheap way to do this?

The arc voltage seems to jump to about 1500 volts, then level at
around 200V or so (supposedly once the arc is started in the lamp).
I'm thinking a big old VR would trick it if I can match the original
bulb's resistance, but how to get around the initial spike... I know
not.
---

If you can get the maintenance manual/schematic for it, there's gotta
be a place where whatever senses the current flowing through the
lamp/lamp driver is sending that information to whatever needs it to
keep the projector running. That's surely going to be a low voltage
signal which you ought to be able to duplicate with a voltage divider
across the low-voltage supply or a resistor-Zener reference. You
might even be able to work it out by opening up the machine and taking
a look at how the lamp is driven and the "lamp on" signal derived.

--
John Fields