From: lasner@watsun.cc.columbia.edu (Charles Lasner)
Subject: Re: What I've got and what I'd like to have
Reply-To: lasner@watsun.cc.columbia.edu (Charles Lasner)
Organization: Columbia University
Date: Mon, 16 Nov 1992 07:59:42 GMT

In article <1992Nov16.022626.22158@news.uiowa.edu> jones@pyrite.cs.uiowa.edu (Douglas W. Jones,201H MLH,3193350740,3193382879) writes:
>	I have originals of the schematics and maintenance manual.
>> I have three extra M8650 current loop interface boards.
>	I have a pile of these too -- but note, the 8650 can do RS232
>	as well as current loop!  You can hook modern terminals to
>	them at up to 2400 baud, and even faster if you use jumpers
>	to points not advertised in the manual.  Read the extended
>	comments in the board schematics for the M8650 to find out
>	how to make the RS232 cable and how to jumper for higher
>	speeds.
The M8650 is current loop at 110 baud if the crystal is 14.418 Mhz.  To make
it do the other rates, you have to change the crystal or even the whole
oscillator circuit to 19.6608 MHz, which is a fairly standard rate.  Then
the lowest baud rate is 150, not 110 baud.  The schematics show that the 
original card was designated to go up to 1200 baud only using a set of
neatly arranged split-lug jumpers, where one side of all of them is in
common.  Basically, you are picking off the proper divide-down output intio
the next stage, etc.  Then there was an ECO to add 2400 baud using another
similar pair, but located some distance from the 150,300,600,1200 jumpers.
But, if yo look at the schematic, there is the common run near the chip in
the upper right hand corner of the card, and pins on that chip are for
even faster outputs such as 4800, 9600, 19,200, 38,400, etc. and they
only need a short jumper, although not "neat" or "official".

You can also use the current-loop output for speeds faster than 110 baud,
but only if you remove (at least one end of) an electrolytic capacitor
being uses as a filter for the "dirty" input data of the tty commutator.
When removed, the rate can easily go to 9600 baud current-loop if needed.
On the KL8-JA card, a routine jumper change implements the same mod, but
you have to unsolder it here.

Also, note that the KL8E can go faster than the KL8-JA!  
Whether it's current-loop or RS-232 depends on the cable plugged in.  There
is a short designated current-loop connector that ends with a flat Mate'N'Lok
connector to a DEC current-loop terminal, and it has a jumper to enable the
current loop input on the module.  If it's RS-232, then you have to use the
BC01V or BC05C cables which implement an alternate jumper for the RS-232
input convertor.  The outputs are both driven so there is no need for an
output control jumper.

>> I'd be interested in a
>> source for ASR-33 ribbons and paper.
>	I think it's a standard kind of cloth ribbon.  If worse comes
>	to worse, the width of the ribbon is exactly standard, so al
>	you have to do is wind a ribbon from whatever kind of spool
>	you get onto the ASR33 spool.

It's a standard ribbon for a rather ancient standard typewriter.

>> And all of the plastic associated with the air filters in the
>> desktop case has deteriorated,
>	Strip out the bad filters.  If your air is dirty enough to
>	need filtering, go to a furnace store and look at the filter
>	media they have to offer.  I've seen some "plastic" furnace
>	filter material that's not too different from the DEC stuff,
>	but thicker.  I assume it'd work well enough if you can get
>	it to fit in the path of the airflow.  I've got a rack-mount
>	system with no air filters (at least, none remaning) inside
>	the rack.  The top-of-rack fan still has a filter, though,
>	but just about anything can be stuffed there.

That urethane foam can be deadly when it flakes apart; better to vacuum it
all away, and go bare, but air conditioner filter is essentially the same
stuff, with perhaps a different "weave" and effective density, etc.

cjl
Newsgroups: alt.sys.pdp8