Dever 504 MkIV bulb problems

[matthewdwilliams]

Hi there

I have a Devere 504 MkIV which is a fantastic enlarger however I appear to be blowing bulbs after approx 10 hours use.

The bulb installed is a 24v 250w halogen.

Can anyone tell me if there is likely to be a problem with the powersuply or is this normal?

Thanks
Matt

[Peter De Smidt]

It's not normal. If you know how to safely use a voltmeter, you might want to take some readings.

[IanG]

My De Vere 5108 uses the similar bulbs, not identical - 4 24v 300v and they were blowing in pairs, most frequently always the same 2, and the time span suddenly shortening

The problem is oxide film build up on the lamp holder contacts causing monetary arcing as they turn on.

The problem was solved by cleaning the contacts, I just used a small piece 1200 grit wet & dry paper, I tore & folded it over and ran it through the contacts which cured the problem.

Now I'll check the contacts more regularly.

Ian

[Martin Aislabie]

You might have a bad batch of bulbs.

I have had the same buld in my 504Mk4 for over 3 years now.

Cleaning the contacts as Ian suggests is always a good idea.

How are you switching your bulb on & off - my transformer has quite a soft ramp up & down (takes may be more than half a second to get up to full brightness and roughly the same time to go off)

Martin

[ic-racer]

I had an odd problem with one of my power supplies that uses a PWM (Pulse width modulation) circuit driven by a 555 chip. Oxidation of the bulb socked caused a poor contact which caused the feedback loop to ramp up voltage to near 120, then it seemed to spark across and make good contact and blow the bulb before the circuit could ramp back the voltage pulses.

I found a place that sells the sockets and got a new one and have been OK since then.

(The above is an educated guess based on seeing signs of sparking on the bulb terminals. Less likely possibilities were a bad batch of 4 GE bulbs. My replacements have been a different brand.)

[Aled Hughes]

I bought 7 of these for Uni in 1989, the electrics were a nightmare, do you have a black transtab unit? If so never use the focus switch, I taped them all up. When De vere went to the wall, some of the engineers set up their own servicing companies, and for £80 changed a capacitor and modified the circuitry, the then worked perfectly and still do 20 years later. There must be someone out there who still services the units?