Again things have slowed down but a few goodies were found: A Rockwell
AIM65 4k computer inside what looks like a large calculator case that is
black and grey in color, has a onboard thermal printer using calculator
size paper, not tested yet, free; also got 6 R6500 mb's some are marked as
being bad all free; a Mac IIcx missing HD and memory simms for free; a
working Mac SE/30 without KB and mouse for $15; a Victor 386sx/20 laptop
broken screen with power adapter for free. Other manuals gotten at thrift
stores and some software that's been the week. Keep Computing - John
Tony Duell quoted me as having written:
>> On the subject of BBC video problems, it occurs to me that the BBC micro
>> does scrolling by moving the pointer to the start of the screen (under
>> some conditions?). If you can get it to do this, and see how the
>> display behaves, you may be able to determine easily if it's an
>> addressing problem.
>
> Is this going to tell you very much?
>
> The BBC _does_ use hardware scrolling (it changes the start-of-memory
> register in the 6845), but as the screen is a contiguous array of bytes,
> all that a scroll does is effectively increment that pointer by the
> number of bytes/line of characters (= 640 bytes in mode 0, etc) and then
> clear the new bytes displayed on the bottom line.
>
> So the new line 0 will be the old line 1, etc, but there are no other
> changes. A given byte on the screen is displayed in the same relative
> position to other given bytes on the screen. In mode 0, &3281 is still the
> second dot row of a character in the far left column. Of course if the
> text goes all over the place on a hardware scroll then you can be
> virtually certain that the 6845 is playing up.
What I meant was that addressing problem _external_ to 6845 generally
means that the fault will occur at the same _memory_ address. So that
type of scrolling means the fault will scroll up the screen, appearing
at the same place in the _text_ every time. Won't it?
If the screen line length were an integer power of two, a fault in the
bottom few address lines would appear at the same place on every line.
Fortunately the BBC micro is 80 characters per line, so you will see
things recurring on a slant. This slanted line of fault should move up
the screen as it scrolls.
Something to try, anyway. I am a firm believer in non-invasive tests!
Philip.
Sam Ismail <dastar(a)wco.com> wrote:
> First stop: Computer Recycling Center
[list elided]
Hmph. I stopped by weekend before last (14 Feb) and it looked like
they'd been cleaned out. Even the bookshelves were mostly empty.
Probably for the best though, given how far behind I am with other
stuff that needs doing.
> Corvus Systems Hard Drive unit - I believe this goes with the rest of the
> Corvus Concepts computer. It has several connectors on the back labeled
> "Processor", "Drive"...it also has one labeled "VCR" and a video IN and
> OUT jack. McFrank, this is so you can backup to a VCR right?
Yep, that's what it's for (although the hard drive could have been
used with about a half-dozen different kinds of systems, not just the
Concept). I'm not sure whether the jacks imply the presence of
whatever you actually need to do the backup or whether there is
additional hardware or software required (this is one of those
things that I know I need to figure out some day when I get all
those manuals in front of me at once).
-Frank McConnell
<> The Intellec MCS8i and the PDP11 (obviously, since all I/O is memory
<> mapped) do allow you to access I/O devices directly from the panel.
<
<...and the front panel on the Altair 8800b.
The 8008 does not have memory mapped IO, there are distinct IO
instructions. It's not to say MM/io is not done. The PDP-11 memory
and devices are the same things and there are no specialized IO
instructions.
The altair...(8800 and 8800a) from the front pannel there is no way to
interrogate an port mapped IO device or write to it. You must do it with
a little code.
Allison
On Mon, 23 Feb 1998 20:14:09 +0000 (GMT), Tony Duell
<ard(a)p850ug1.demon.co.uk> wrote:
>>I have a text file somewhere explaining how to make a functional copy of
>>this unit using more modern parts (LEDs and ULN2803 driver chips, I
>>think) if anybody wants it.
If you can put your hands on that text file, I'd be interested in it.
Thanks!
-------------------------------------------------
Rich Cini/WUGNET
<nospam_rcini(a)msn.com> (remove nospam_ to use)
- ClubWin Charter Member (6)
- MCP Windows 95/Windows Networking
Tony's comment, below... about the only equipment needed to repair... was
helpful.
So, as I have an Altair, a BBC, a KIM, a Sorcerer and various other beasties
awaiting ressurection, and having little (well, OK... no) electronics
experience, starting at square 1...
a) What should I be looking for in a logic probe. Any recommended models
(say, <$100)
b) Ditto for multimeter.
c) Where can I find a brain? :)
Actually, the Altair will be my first task. I'm thinking of #1 taking out
all the boards. Good idea?
I have it firing up and basically behaving, but some LEDs don't light when
they should, but are definitely able to light when they want to.
A
>Hmm... I've yet to find a classic computer fault that could not be
>tracked down using 3 things - a logic probe, a multimeter (DMM/VOM) and
>a _brain_. On the grounds that my brain isn't that good, I sometimes have
>to use other test equipment, but when I finally do track down the
>problem, I generally realise that the symptoms were obvious from the
>start if only I'd realised what they meant.
allisonp(a)world.std.com (Allison J Parent) wrote:
> [....] IO however while it would be nice to
> interogate or write to devices could leave the cpu "out of sync" since
> all IO is done from the accumulator.
You say that like there's something wrong with it.
Well, there could be, I suppose, if your hardware is such that reading
its registers changes them, and the operator doesn't realize this.
Was the latter really considered a problem in those days? Or was it
just that as a result it wasn't real useful to have the front panel do
that? (Or was it just the additional cost of having the front panel
do that?)
-Frank McConnell
<The only things I know about this board is that it's a SCSI controller, a
<it's BIG. It's about 10"x12", has an 86-pin edge connectr on the bottom,
<two 50-pin edge connectors on the top, and uses eight 2651 SCSI chips. It
<labeled "DATASTREAM ASSY 100716 REV A". Does anyone have any idea what
<this is for?
<TIA
Sounds more like an 8 port serial board! The 2651 is a USART type device.
The 50 pin connectors might be board to pannel connector cabling.
Allison
Anthony Clifton - Wirehead said:
>I see this problem alot at hamfests. You can't blame them. They want
>to bring what will sell and they're most likely to not have to carry
>back home. They perceive no value to ancient computers so they assume
>nobody else will either.
I have 2' x 3' white board taped to the little rolling cart I take with me.
On the board, I write down all the stuff I'm looking for that day.
=========================================
Doug Coward dcoward(a)pressstart.com
Senior Software Engineer
Press Start Inc.
Sunnyvale,CA
Curator
Museum of Personal Computing Machinery
http://www.best.com/~dcoward/museum
=========================================
Does anybody have any information on a North Star Horizon? I may be
acquiring one of these soon but don't know much about it except that
it has wooden side panels and used to support a half-dozen terminals.
Is it a S-100 bus?
Thanks for any help-
Marty Mintzell
