8mm Forum: Bell & howell TQ Bulb prob

This is topic Bell & howell TQ Bulb prob in forum 16mm Forum at 8mm Forum.

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Posted by Tom Photiou (Member # 130) on October 27, 2005, 04:45 PM:

I used my Tq (green) B&H some time ago. About 18month to be exact. It has a new bulb fitted which had been use for one feature. I took it out tonight and lo and behold everything works fine exept the bulb will not work. The actual bulb itself is fine.
Can anyone tell me if these suffer in this way?
The contacts are good and clean. The filament is fine. Its a classic case of working perfect last time i used it and now this. I dont wish to buy another bulb just yet as i'm 99.9% sure its not the bulb itself. [Confused]

Posted by John Whittle (Member # 22) on October 28, 2005, 09:14 PM:

Here is where a few quick checks with a meter will tell the story. See if you read continunity across the lamp terminals with it out of the projector. If so then the problem is deeper and not the lamp. Check the terminals inside the projector for corrosion. It's also possible that the switch may have gone bad. Even low voltage lamps put a heavy amperage on the switch contacts. You should be able to read voltage at the lamp terminals inside the machine with your meter with the machine one and the lamp switch to the on position and no lamp installed.

Be careful, but if there is no voltage on the lamp socket, then it's between the line in, transformer and switch(es). If there is voltage present, then you may have resistance from corrosion.

John

Posted by Tom Photiou (Member # 130) on October 29, 2005, 05:17 AM:

Thank you John.
I shall these suggestions. [Wink]

Posted by Tom Photiou (Member # 130) on October 29, 2005, 10:09 AM:

[Mad]

John, If your there or anyone,Today i checked the bulb with a multi-metre and the resistance within the bulb was 1 mega ohm suggesting that the bulb is good. (as mentioned, i used this bulb once only so far)however, when the metre was put into the contacts onlt 13volts appears to be measured. Hope i tested it ok, one pin was put into 1 pin and the other was earthed onto the body.
We also tried one in each of the two pins and this read 0 [Confused]

Wierd as when the pins were tested individualy they both read 13volts each, it only read 0 if the two pins were placed one each into the projectors bulb plugs. (sorry if i sound dopy but electronics are not my normal game)

Posted by Jan Bister (Member # 332) on October 29, 2005, 11:28 AM:

That would suggest that there is voltage on BOTH pins and the differential between the pins is indeed zero. That doesn't necessarily mean, however, that there is no voltage on the pins, as you've already seen: they both measure 13V against ground.
Very weird indeed. But you can be sure it's a wiring problem, most likely a short circuit of some kind that lets current bypass the bulb entirely, thus it doesn't light up.

Posted by Tom Photiou (Member # 130) on October 29, 2005, 01:16 PM:

can a faulty buld cause this sort of prob even yho the filament is fine?

Posted by Jan Bister (Member # 332) on October 29, 2005, 11:27 PM:

No, I doubt it could...

Posted by John Whittle (Member # 22) on October 31, 2005, 08:56 AM:

quote:
onlt 13volts appears to be measured. Hope i tested it ok, one pin was put into 1 pin and the other was earthed onto the body.

There is a problem there. The voltage on lamp should be 22-24 volts. You should read 22-24 from one pin to a known earth and 0 volts on the other. The fact you're reading 13 volts is strange and you need to look at the lamp wiring schematic for clues. Normally these projectors use autotransformers which aren't really dual winding transformers but single winding with a take off point for the lower voltage. A low AC line in will produce this problem or it could be a high resistance on a switch, but now you need to trace the voltage thru the machine.

The lamp should read 1-3 ohms, not megohms. But maybe you just misread the scale.

John

Posted by Jan Bister (Member # 332) on October 31, 2005, 09:12 AM:

I need to pay more attention - I didn't even catch the things John did. Nice job [Eek!]

Posted by Tom Photiou (Member # 130) on November 01, 2005, 12:24 PM:

Thanks John, looks like i'm going to have to contact an electrician localy if i can. The machine is very good and in good condition, trouble is i got FOC so i dont want to pay out too much dosh on it.
Thanks for your help, i'll let you know how i get on. Aint it weird, i put a new bulb in it, watch three parts of Cromwell, store the machine and now this. [Confused]

Posted by David Park (Member # 123) on November 09, 2005, 10:54 AM:

Surprised you haven't a spare lamp to try.
I would suggest you get one, it would show if a projector fault or not, allways a good idea to have a spare anyway.

Posted by Tom Photiou (Member # 130) on November 09, 2005, 12:26 PM:

very true, always have one for 8mm, [Embarrassed]

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