12 Jul
2011
12 Jul
'11
8:14 p.m.
Same old problem I need a decent camera to capture. I think I have
found the chinese camera
that the expensive fiche scanner uses, its 200$ in the states and over
400? in the UK and I just got raped for car insurance.
Ive tried emailing the chineses supplier and am waiting for a reply
http://www.tucsen.com/ProductView.asp?id=44
A black and white version could be even better
Dave Caroline
On Tue, Jul 12, 2011 at 8:56 PM, Jarratt RMA
<robert.jarratt at ntlworld.com> wrote:
Ooooohhh, a result! Thanks. Don't suppose you know
if there is a PDF
of the new printset, I could really do with at least the input
assembly and the bias and interface board drawings.
Thanks!
Rob
On 12/07/2011, Dave Caroline <dave.thearchivist at gmail.com> wrote:
there are two designs of the relay assembly on
the H7140 fiche here,
the old ones parts list has a
Resistor (R1) 3 ohm 5% 7 W ?13-14848-00
the new one has a sub assembly on that with thermistor listed as
Thermistor 7.0 10% dec part number 13-17198-00
Dave Caroline
On Tue, Jul 12, 2011 at 7:33 PM, Jarratt RMA
<robert.jarratt at ntlworld.com> wrote:
Actually I am not sure it does make sense, but
then I am not an
electronics
expert, so I may have this wrong.
This resistor is not in parallel with the coil, but connected across the
terminals of the relay, ie the terminals the relay is designed to short
when
it is switched on. The resistor is supposed to limit the current going to
the big electrolytic smoothing capacitors that come right after the bridge
rectifier and provide enough power for the circuitry to check that the
mains
is "OK" and then switch on the relay when the capacitors have charged up
and
connect them directly to the bridge rectifier instead of via the inrush
limiter.
I hope that makes sense.
I still need to know what the spec of these components is so I can find
replacements.
Regards
Rob
On 12 July 2011 15:03, dwight elvey <dkelvey at hotmail.com> wrote:
Hi
?I think you are talking about a dampenning resistor. This is
placed in parallel with the coil.
?The resistance is usually equal to or somewhat larger than
the coils resistance.
?Coils like to keep current flowing and don't like having the
current source broken quickly. The voltage would go up
until something arced or broke down.
?The choice of resistor would be determined by how quickly
one wanted the relay to release.
?Although, counter intuitive, a smaller value of resistance
would prolong the time for the relay to release. A higher
value would cause the release to be sooner.
?The higher value resistor would also create a higher voltage
across the resistor.
?At the instance the drive is removed, the same current that
was running through the coil is now running through the
resistor at that instant.
?This voltage adds to the source voltage and is the voltage
that the transistor ( if from a transistor ) has to hold off.
If the source voltage was 12V and it was an equal value
resistor, the transistor would have to take 24V when the
relay was turned off.
?Make sense?
Dwight
> From: robert.jarratt at ntlworld.com
>
> I used the wrong term I think, inrush limiter is the right one.
>
> Rob
>
> > -----Original Message-----
> > From: cctalk-bounces at classiccmp.org [mailto:cctalk-
> > bounces at classiccmp.org] On Behalf Of Rob Jarratt
> > Sent: 12 July 2011 04:10
> > To: General Discussion: On-Topic and Off-Topic Posts
> > Subject: Identifying the Surge Suppression Resistor in PDP11 H7140
> > PSU
> >
> > Work is continuing on repairing the H7140 PSU from my PDP11/24.
> >
> > Now it seems that the surge suppression resistor across the relay has
> failed.
> > This resistor is marked as R1 on the printset (p66 and p69) but
actually
> is two
> > components connected in series. The parts list on p71 of the printset
> lists a
> > 3ohm 7W 5% resistor, but it is not 100% clear if this is supposed to
> > be
> the
> > surge suppression resistor, although it does seem likely.
> > The thing is I measured the resistance of the two resistors
(in-circuit),
> one was
> > open circuit and clearly the failed component, the other measured
10ohms,
> it
> > might be failing too I suppose.
> >
> > The two resistors are marked KCC 13-17198-00 8234. I have not been
> > able
to
> > find any information on them, so I can't verify the spec and I don't
know
> what
> > to replace them with. Does anyone have any information on these
resistors?
> >
> > Thanks
> >
> > Rob
>