[pure-silver] Re: ELC bulbs failing in D2 Dichro Head
----- Original Message ----- From: "Georges Giralt" <georges.giralt@xxxxxxx> 
To: <pure-silver@xxxxxxxxxxxxx>
Sent: Wednesday, January 16, 2008 2:56 AM
Subject: [pure-silver] Re: ELC bulbs failing in D2 Dichro Head 



Selon J Stewart <jrstewart8@xxxxxxxxxxx>:
Folks, can anyone help me troubleshoot reasons why my lamps are blowing out within a few seconds of turning on my Dichro II color head (on a D2). I'm using the standard D2 power supply with stabilizer. The stabilizer fuse is intact. The power cord is plugged into a surge protector via the timer. My 
house has always had a stable power supply.
The bulb elements are breaking. The problem began immediately. A bulb I had been using for a couple years fractured. When I put a new one in, it burned out within seconds. I repeated this with a new bulb and the same thing happened. One bulb actually broke the reflector in the process, but I'm not 
sure it was caused by the same problem.
I have a voltmeter to check current to the socket if you can help me understand what I might be looking for in isolating the cause. 

Thanks in advance.

Jim

Hi Jim !
If IRC the ELC is 24 V. As the power supply is stabilized, it could be that it went south and deliver way above the 24 volts needed. This is easy to check, and 
will not need a bulb.
Put the leads of the tester into the lamp socket and turn the enlarger on. You will get either 0 V (if the stabilized output stage use the bulb as a polarizing device) or a voltage. If it is above 24 V you've got the culprit. Be sure to check with DC and AC voltages (you may have an AC voltage mixed with the 
DC output, the sum of the two being above the 24 V).
If this gives you hte impression that the power suply works fine, check for the bulb base. These sockets use small diameter pins and oxydize quickly causing 
spikes and sometimes sparks.
Sometimes this make the lamp burn. Change for a high fgrade one (go to the lighting store the biggest you can find in your town) and plan to change this 
socket once in a while..;
Hope this will help !

--
In general I agree with this. I don't know what sort of regulator is used in these power supplies but it sounds like the regulation element has shorted or opened (which depends on whether it is in series or parallel with the lamp) causing the voltage to become very high. A clue is whether the bulb flashes as it burns out. A voltmeter will tell you what the open circuit voltage at the socket is. It should be very close to the lamp voltage. It may be somewhat higher if the regulator requires a minimum load (the lamp) to regulate. If the voltage is very high you will need to find the circuit diagram to determine what the regulating element is. Since lamps are failing instantaneously its unlikely that its the socket or the lamp pins, the lamps are just being blown out by high voltage. 

---
Richard Knoppow
Los Angeles, CA, USA
dickburk@xxxxxxxxxxxxx 
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