This is topic Strange problem, bulb loosing one pin after several uses in forum 8mm Forum at 8mm Forum.

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Posted by Winbert Hutahaean (Member # 58) on December 02, 2014, 01:20 AM:
I don't know if this only happen to the particular bulb I am using.

This is an USHO 150w 15v bulb that I promoted several years ago here.

EFR projector bulb (150w 15v): USHIO

I put this bulb on Elmo ST-1200. One day the bulb was off, and was thinking the filament had got burnt. But after checking it, it was one pin that had gone. I replaced the pin with the other pin found from a broken bulb. After soldering it the bulb worked again. But since the bulb was too hot, the (tin) solder wire got melted after several reels of use, and the bulb went off again.

So I took a new bulb to replace. Surprise, after several time of use, it happened again. The bulb lose one pin at the same place (the other pin was intact and clean).

So these are the close up pictures:


Below is the place where bulb was sitting:


You can see one place has noticeable a burnt mark. I don't want to put another new bulb just to find the same case is happening.

So do you guys see this often? what do you think is the problem.

I knew Maurice Leakey and Terry Lagler also got this USHIO bulbs from the same seller. Do you experience this too?
Posted by Martin Jones (Member # 1163) on December 02, 2014, 02:39 AM:
Probably nothing to do with the bulb. It's a problem of localised heating..... the PIN is getting overheated because there is bad contact in the lamp-holder.. Not enough to prevent the bulb working, although there may be a slight drop in brightness you may not notice.
The bad contact generating the heat could be either between the pin and the holder OR between the feed wire and the holder contact. The latter is more likely; if the connection is a screw, tighten it.... if crimped, re-crimp it.
Make sure any sign of corrosion or blackening is removed.

A common problem in mains plugs carrying large currents: a loose screw in the plug will heat the pin and burn both the plastic of the plug AND of the socket it is plugged into.
Posted by David Ollerearnshaw (Member # 3296) on December 02, 2014, 04:10 AM:
On my original ST1200 it too did this. On its next service the report of new parts was 1 lamp holder.

If you check the bulb after a few hours use, you may find the pin becoming pitted. That's how mine went.

I think it was caused by poor contact on that one pin, which causes a slight arching/sparking.
Posted by Maurice Leakey (Member # 916) on December 02, 2014, 04:58 AM:
May not be the lamp. I suggest that the lamp holder be replaced as soon as possible. As Martin says, there's a lot of current going through those small pins. 10 amps.
Posted by Steve Klare (Member # 12) on December 02, 2014, 08:28 AM:
Paul Adsett did a post here suggesting doing away with the slip in socket altogether and installing something that grips the lamp pins all the way around: more surface area, lower temperature, less mayhem.

That Awful Elmo Lamp Socket

I did it on my own ST1200HD. The socket was cheap, easy to find, the surgery was pretty simply and I think I got a little brighter picture too.

The one thing I was picky about among the many sockets I found was finding one that explicitly stated it could carry enough current. If I was going to go to all the trouble and wind up with something that was going to fry, I might as well leave things as they were!

My old socket was turning brown on one side like the picture above, so it was time for a change.
Posted by Winbert Hutahaean (Member # 58) on December 02, 2014, 09:00 AM:
Now Steve, since I have to change the socket, I want to upgrade the bulb to 24v 250w (using external transformer), do I need to find a different socket or just the same?

What other thing do I have to be aware of? Is cooling system enough using the current fan installed? Any other suggestion?

Posted by Steve Klare (Member # 12) on December 02, 2014, 09:17 AM:
A 150W bulb operating at 15V needs 10 Amps. A 250W bulb operating at 24V needs about 10.5 Amps. By the time you find a socket that can accommodate the first (with a margin of error), it should do the second too.

I remember the sockets I saw were rated for line voltages (115V etc.) so the 15V/24V thing shouldn't be a problem.

I want to say that a 250W lamp in a 150W projector is pushing it as far as cooling capacity, but then again, I know of an ST-800 (100W lamp) that has been running a 250W lamp with an external transformer for years without melting anything.

I'm sure back when warrantees were in effect, ELMO would have hated the idea, but it isn't exactly like you want to go skiing with rockets strapped to your back or build an atomic reactor in your garage...

All else being equal, I'd do a two bladed shutter just to keep the setup simple. (even though the surgery is worse there...)
Posted by Andrew Woodcock (Member # 3260) on December 02, 2014, 12:25 PM:
I have never had a GS1200 or a Fumeo 9119 etc, but I thought the pin width was different between the 200 / 250w lamps and that of the 150w A1 232? Am I correct, question to anyone who uses both?
(Gx5.3 base vs Gz6.35)
Posted by Steve Klare (Member # 12) on December 02, 2014, 01:01 PM:
You should be able to pull up the specs on the 'net.

An old friend of mine had a Eumig 810D that he had rigged to be switchable between the 250W lamp (with external transformer) and the 100W with the internal one, so I assumed the sockets were the same.
Posted by Andrew Woodcock (Member # 3260) on December 02, 2014, 02:31 PM:
Thanks Steve, I shall look it up on technical specs for each lamp.

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