-----Original Message-----
From: Tony Duell <ard_at_p850ug1.demon.co.uk>
To: Discussion re-collecting of classic computers
<classiccmp_at_u.washington.edu>
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 _at_10amp and 24vac @0.5amp secondary 120 vac_at_1amp/240 vac_at_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_at_leading.net
Received on Sun Mar 21 1999 - 14:37:36 GMT