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PICList Thread
'Eprom eraser.'
1998\07\01@063053 by Clewer,Brian

Hi guys,

If you are having trouble getting hold of an eprom eraser tube, try
asking the place that sells the whole box, for a replacement tube for
your home made device.  As far as the germicide bulb goes, I thought
these were the sort that were used on developing photo PCB's (I could be
wrong).  The bulbs you should be clear and not have a white coating
around the outside.

Hope this helps,


1998\07\01@100616 by Peter L. Peres

picon face
Phone your local Philips dealer (lamps etc) and ask for an UV lamp (It's
marked UV-C but never mind that). This is the exact same lamp that fits
some sterilizers and its white version is used in emergency 'portable'
lights. Power rating is 6W.

The lamp is clear see-through and should not cost more than US$12 no
matter where you are and who sells it.

Erasure time is 30 minutes for windowed PICs at 5 mm (1/2 in) from the
tube. This includes a safety margin. The lamp does not get hot worth
mentioning. The ballast coil does, however, so don't use hot stuff to
mount it. FYI a capacitor across the power input leads before the coil and
lamp rated at 400 Vac is a must, it helps ignition with the starter. The
capacitor should be 0.1 uFarad or more.

For some wimpy circuits it is necessary to glue a piece of insulated thin
conductor along the side of the lamp, from aluminum cap to aluminum cap.
The wire should not touch anything except the glass of the lamp (do not
un-insulate). It aids ignition by increasing the electrical field around
the electrodes while the lamp is off. The ignition characteristics improve
spectacularly with this setup.

I'd like to remind do-it-yourselfers that the coil is the most critical
part in a mercury vapor lamp, so do yourself a favor and use the right one
specified for the lamp. The starters for 6 Watt lamps are also special, in
that they are smaller than the usual lamp variety and fire faster. A
normal 'large' starter will work but it will take a long time to start the

Whatever you do, don't look into the running light. Its effect shows much
later and if you experience burning, reddening and dryness in the eyes and
eyelids after using the thing, seek medical help.

The usual way to set up a somewhat safe turn-on circuit, is to use a
micro-switch in series with the lamp. The switch lever protrudes and
either the closing of the lid or putting the lamp face down on a table
(over the chips) closes the circuit. I've built such a lamp inside a metal
cake baking form once. It worked very well. When the lamp is on the table,
face down, the tube glass is 1/2 in above a leaded chip laid on the table.
This also turns on the lamp, via micro-switch. An extra switch is on the
power cord. YOU MUST ground the metal case if using a metal case, using
the 3rd conductor (green-yellow here). Use an extra solid screw to attach
the ground wire.

And of course you get to use this at your own risk, and can't sue me for

hope this helps


(who built several mercury vapor lamps for various purposes, including
EPROM erasure and PCB exposure, including using high pressure mercury
vapor lamps)

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