The board in question is under the mirror box floor, inside. What's the
phrase? If it ain't broke....................
John
________________________________
Camtech, Olympus Service since 1977.
21 South La. Huntington NY 11743
631-424-2121 http://www.zuiko.com
Free Olympus Manuals: 1-800-221-3000
--------------------------------------------------------------
----- Original Message -----
From: Dirk Wright <wright@xxxxxxxxxxxx>
To: <olympus@xxxxxxxxxxxxxxx>
Sent: Friday, December 03, 1999 5:00 AM
Subject: Re: [OM] OM-2S and reciprocity failure
>
> >For example we can estimate the current output from the photocell by
> looking
> >at the integration capacitor used
> >and knowing the integrator output voltage swing can be no more than
> >approximately 2V or so. The capacitor is
> >470pF. At 120seconds exposure time this implies a photo detector
> current of
> >very approximately 10pA (!0^ -11 A) and hence
> >total board leakage must be less than this. (dV/dt = i/C) This
> implies
> >board leakage resistances of hundreds of Giga Ohms and Mosfet
> >gate leakage currents at pA levels. In practise for non ceramic boards
> this
> >is almost impossible so guard ring techniques
> > and/or conformal coating is probably necessary. The OM2N has a
> slightly
> >larger
> >capacitor (680 pF) which eases the requirement a little but not much.
> >
>
> yeah, I understand. From your description, the circuit sounds like an
> electrometer type of circuit, where the input impedance of the ampifier
> is extremely high in order to detect very small currents. You are
> exactly correct in saying that stray capacitance and leakage through
> the circuit board is critical for proper functioning of the circuit.
>
> >The Olympus OM2 service manual for example says :
> >
> >" The shutter amplifier (M circuit board) requires very high
> insulation
> >resistance on its every part, and must be kept free from dust, smudges
> etc."
>
> Where is this board located in the OM2n? is it in the bottom of the
> camera, under the cover plate? If so, I need to clean mine, since it
> had a thin film of oil on it. I don't know how important this is
> because oil has a very high resistance value, which is one of the
> reasons it's used in power transformers, etc. What should I use to
> clean it? Should I remove it from the camera in order to clean it? I
> think denatured alcohol is a pretty strong degreaser, but I don't want
> it to get into other parts of the camera I suppose a Q tip full of d.a.
> would be ok, followed by a squirt of canned air?
>
> Be seeing you.
>
>
> Dirk Wright
>
> < This message was delivered via the Olympus Mailing List >
> < For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
> < Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
>
< This message was delivered via the Olympus Mailing List >
< For questions, mailto:owner-olympus@xxxxxxxxxxxxxxx >
< Web Page: http://Zuiko.sls.bc.ca/swright/olympuslist.html >
|