[GreenKeys] Model 33 Progress

[drlegendre .]

"Usually I don't like to shotgun the equipment, but I agree.  When something
is not working correctly that has the electrolytic capacitors in it, just
replace them all."

This is generally the approach I take as well, but it's not always
practical or desirable - particularly if it will significantly alter the
original appearance of a piece. And there's still some wisdom in the "if it
ain't broke" concept.

In any event, my comment about ESR meters was in response to you expressing
frustration with the fact that you wished to test the cap, but lacked
access to the correct side of the board.

So if you think the issue is local to the KB, you can verify that by taking
the KB out of the loop, and using the TU the way it's intended - as the TU
on the end of a circuit (that sends known-good data signals). Hook up your
RS-232 / USB to 20mA CL converter (you have one, right?), fire up a
terminal soft and start typing to it.

On Tue, Nov 8, 2016 at 9:09 AM, Brad via GreenKeys <
greenkeys at mailman.qth.net> wrote:

> I did a bit more experimenting last night.  I tried temporarily pulling out
> one contact wire at a time so that it could not make any contact.  One of
> them, once pulled out, caused the type unit to move the carriage with each
> key press.  It also caused some characters that had been wrong to come up
> right.  So I'm back to thinking something to do with the keyboard.
>
> I think I sort of get how it works.. the base of the contact wire touches a
> contact at the bottom.. and then the tops of the contact wires complete or
> break a circuit.  So hitting a key will cause a pattern of connected and
> broken contacts and that I guess is your matrix decoding that tells the
> print unit what to print.
>
> I think contacts are not being made properly.. so some keypresses don't
> generate enough of a signal to produce a letter while others do.  I've
> observed the plastic sliders that control contact sometimes seem like they
> are still leaving gaps up top where contact looks like it should be made.
>
> It moves pretty fast though so its hard to tell.  I am trying to find a
> matrix or something that I can use to somehow check contacts for different
> keys.  I wonder if I can set a key without power and check continuity.. I
> do
> notice that when the machine is running contact wires seem to briefly get
> pulled against the strip.  Don't think they'll do that with no power.
>
> -----Original Message-----
> From: GreenKeys [mailto:greenkeys-bounces at mailman.qth.net] On Behalf Of
> Ralph Mowery
> Sent: Tuesday, November 8, 2016 6:52 AM
> To: greenkeys at mailman.qth.net
> Subject: Re: [GreenKeys] Model 33 Progress
>
>
>
> > -----Original Message-----
> > From: GreenKeys [mailto:greenkeys-bounces at mailman.qth.net] On Behalf
> > Of Jeffrey D Angus
> > Sent: Tuesday, November 08, 2016 4:28 AM
> > To: greenkeys at mailman.qth.net
> > Subject: Re: [GreenKeys] Model 33 Progress
> >
> > On 11/8/2016 12:18 AM, drlegendre . wrote:
> > >
> > > For reference, this is where ESR meters (Capacitor Wizard, the Blue
> > > Meter, etc.) or other so-called "in-circuit cap testers" can come in
> > > very handy.
> > Or...You can not waste your time testing 40-50 year old parts that are
> > known to fail, and that will fail eventually, and just replace them.
> >
> >
> >
> Usually I don't like to shotgun the equipment, but I agree.  When something
> is not working correctly that has the electrolytic capacitors in it, just
> replace them all.  They may not be bad, but could be and if they do go bad
> while working on a problem you will chase things all around.
>
>
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