Author Topic: Is this a fuse (from a projector lamp power supply)  (Read 2326 times)

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Offline ElektroQuark

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Is this a fuse (from a projector lamp power supply)
« on: May 21, 2017, 10:15:16 am »
Hi,

My projector stopped working in the middle of a movie. It's an Optoma HD80.
If I try to start it, it tries to boot starting fans but i have a second fans stop and system powers off without any fault LED lighted.

The HVPS of the lamp has this:



As the label, it looks like a fuse. It's open.
In the back of the PCB the pins of the fuse are conected by a series of 2.2M resistors:



Is it really a fuse?

If so, any advice at buying/changing it?
« Last Edit: May 21, 2017, 10:22:15 am by EdoNork »
 

Online PA0PBZ

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Re: Is this a fuse (from a projector lamp power supply)
« Reply #1 on: May 21, 2017, 10:29:00 am »
Looks like a spark gap to me.
Keyboard error: Press F1 to continue.
 

Offline cowana

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Re: Is this a fuse (from a projector lamp power supply)
« Reply #2 on: May 21, 2017, 10:50:22 am »
I'd go with an 800V GDT (Gas Discharge Tube)
 

Offline ElektroQuark

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Re: Is this a fuse (from a projector lamp power supply)
« Reply #3 on: May 21, 2017, 11:03:55 am »
Can it be a TVS?

Offline wraper

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Offline Gyro

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Re: Is this a fuse (from a projector lamp power supply)
« Reply #5 on: May 21, 2017, 11:17:37 am »
TVSs are semiconductor devices. That one is specifically a gas discharge tube, it will have much higher peak current capability (arc discharge).
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Offline ElektroQuark

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Re: Is this a fuse (from a projector lamp power supply)
« Reply #6 on: May 21, 2017, 11:47:18 am »
So it's OK to see it as an open circuit with the meter.

Offline Gyro

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Re: Is this a fuse (from a projector lamp power supply)
« Reply #7 on: May 21, 2017, 12:25:29 pm »
Yes, if out of circuit. Your meter probably can't resolve the 22Meg resistor chain on the back, although there should be other circuit elements too.
Chris

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Offline bktemp

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Re: Is this a fuse (from a projector lamp power supply)
« Reply #8 on: May 21, 2017, 12:27:18 pm »
The spark gaps in projectors are used for igniting the lamp:
A capacitor gets charged until the threshold voltage is reached and the sparkgap fires, discharging the capacitor into the ignition transformer for generating many kV for igniting the HID lamp.
That's why it is called a switching spark gap  (unlike other spark gaps, designed for overvoltage protection).

When the projector stopped working while it was on, I doubt the spark gap is the problem, because it is only necessary for starting the lamp.

Did you check for other faults?
I had a projector that didn't power up. After debugging the power supply without success I found the lamp door interlock switch broken off its mounting bracket, therefore it disabled the lamp power supply.
 


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