Calibrating your timer?

[megzdad81]

After spending a long weekend lith printing, not understanding what I was doing wrong sheet after sheet, I caught my Omega D5 power supply/timer gradually reducing the time on its own between 5 and 10 seconds per exposure!

Since it's also the voltage stabilizer life is going to get interesting.

I have 2 other timers, but never considered calibrating any. I even use one to determine best lens shutter speeds.
My bad!

Anyone know about repairing this problem? I'm sure a replacement unit will be more th.an the enlarger.

 

[Nicholas Lindan]

Omega D5 power supply/timer gradually reducing the time on its own between 5 and 10 seconds per exposure ... Anyone know about repairing this problem?

The problem with your timer is drift - calibrating it won't cure the problem.

If your timer has two rotary switches to set the time then it is probably similar to the one shown in this schematic:

http://www.jollinger.com/photo/cam-coll/manuals/enlargers/omega/chromegatrol-schema.jpg

The drift in time is probably due to an old & leaky (current and/or goo) electrolytic capacitor at C1 in the schematic.

Most old electronic equipment can be brought back to life just by wholesale replacement of all the electrolytics.

It looks like your timer has two: C1 - 22uF/15V - the capacitor used for timing; and C2 - 300uF/50V - the power supply filter capacitor.

A good place to buy replacements is Digikey. Two suggested replacements are
http://www.digikey.com/product-detail/en/20SEP22M%2BTSS/P16389CT-ND/4204287
http://www.digikey.com/product-detail/en/EEU-FR1H331LB/P15377CT-ND/3072257

The timing accuracy will probably be a bit off, but the x1 and x0.1 times should still match. I would advise leaving the trimpots that adjust timing alone as absolute accuracy isn't important - heck the speed of the paper varies up to 1/2 a stop (40% in time) from box to box. If you do want to reset the absolute accuracy then you will then have to adjust the two trimpots that calibrate the timer: R6 for x1 and R8 for x0.1.

 

[BradS]

Thanks!