SWTPc 6800, common format (sharable?) repair journal? - test-drb@ccmp.vtda.org

21 Mar 1999

-----Original Message-----
From: Tony Duell &lt;ard(a)p850ug1.demon.co.uk&gt;
To: Discussion re-collecting of classic computers
&lt;classiccmp(a)u.washington.edu&gt;
Date: Sunday, March 21, 1999 2:44 PM
Subject: Re: SWTPc 6800, common format (sharable?) repair journal?

...
 > First issue:  Power system is missing the
transformer.  I do have the MP-P,
...
   the filter
cap, and the rectifier bridge. 
MP-P? 
(Power supply) it's the fused board that I'm guessing puts the power on the
buss.

...
 >
> I found a nice ad in Kilobaud issue #2 on the inside cover that gave values:
...
 > 10amp, 25amp rectifier bridge, and 91000mfd
computer grade filter cap. My
> nighttime reading this evening shall be "Building Power Supplies",
Archer,
...
   cat 62-5025. 
;) 
 From those components, I think it must be a linear
PSU (or at least a mains frequency transformer).

What secondary voltages do you need? What currents? 
The transformer T1 from specs lists at:

    7.25vac @10amp and 24vac @0.5amp secondary 120 vac@1amp/240 vac(a)0.5amp
primary, power transformer.

...
 One way to work those out is to determine what voltages
you need across
the smoothing caps and then divide by sqrt(2). For the currents, multiply
the maximum load current by sqrt(2) and add a bit for safety.

Now work out the total power (sum of current*voltage of course). That'll
give you an idea of the VA rating of the transformer you need. 
I will spend some time to more understand those last two paragraphs...

...
 The transformer might be a standard part, or it might
have been custom.
If the latter, in the UK you can get 'transformer kits' - core + bobbin
with pre-wound mains primary. You wind the appropriate secondaries (the
kit instructions tell you how many turns you need for 1V output) and
assemble the core laminations. 
I'd definately buy one if still in production but I definately want to make
a power supply (probably for the sym *if* that one can also not be bought.
;)

...
 > First question:  The baud lines on both busses
(110,150,300,600,1200) caugt
...
 > my eye and that ad above states: "Crystal
controlled oscillator( 1,7971 )
> provides the clock signal for the processor (before?) and is divided down by
...
 > the MC14411 (both on MP-A2  GK) to provide the
various baud rate outputs for
...
   the interface
circuts.  Full buffering on all data and address busses..."
 Does that mean that all these cards are serial? 
I doubt it. More likely they just bussed some useful clock frequencies
over the backplane. Then all the serial cards (using 6850s?) could use
them for the baud rate clocks. Saves putting a crystal + divider on each
serial port card. 
...

> reports and make some kind of open reference.  I sure would find it usefull.
...
 > (read that as alot of things to repair. :))    I
imagine alot of you have
> encounters in repairland...   It would be nice to have alot of this stuff in
...

I seem to get ever more things to repair... (and not all of them are
classic computers...) 
i would imagine. ;)

...
   a prolog
predicate database for pattern searches. 
-tony

- Mike: dogas(a)leading.net