26 Apr
2008
26 Apr
'08
10:01 a.m.
Date: Fri, 25 Apr 2008 22:39:29 +0100 (BST)
From: (Tony Duell)
Did very early machines have AC fans? All the later
ones certainly had 12V
DC ones that would be independant of mains frequency, but an AC fan would
run slower on 50Hz and could cause the machine to overheat. Was it really
that marginal (Acutally, given it's the IBM PC [1], I could beleive it
was).
Yes, they did, but the fans were rated for 50-60 Hz operation and
impedance-protected. With the factory, what 62-watt?, PSU, I don't
think it was possible to stuff the thing full enough of drives and
cards to make it overheat (remember too, that there were only 5
slots) to make it overheat. Wasn't the (black) PSU on the original
PC fitted with red tamper-telltales stuck on along the edge of the
PSU clamshell? I can't remember exactly, but I think it was.
As this was an IBM product, I fully expected that there would have
been some provision for changing the AC input voltage. Certainly
other personal computers of the time had the feature, and this wasn't
supposed to be a product from "Fred's Personal Computer and Aluminum
Storm Door Company". One expected a high level of engineering from
IBM.
[1] When I got my first IBM PC-family machine (a 5160), I took it to
bits
(what a suprise) and sat down with the TechRef. Every few minutes I'd
exclaim 'They did WHAT???' as I found aother it of misdesign...
I never understood the design that featured a complete lack of a
clear airpath between the plug-in-cards. They must not have been
expecting very much expansion.
The MDA card was the most bewildering experience to work through--
circuit traces headed off to nowhere, ICs that seemed to perform no
function. Perhaps it was designed for graphics operation originally
and not completed and rushed to market.
Similarly, one suspects that the printer port must originally have
been intended as a full bidirectional design and then changed at the
last minute--on both the MDA and the printer adapter, all the
necessary circuitry was present for bidirectional operation. Cutting
and jumpering a single trace was all that was needed.
All in all, for as long as the 5150 was in the rumor mill, one would
have expected a better thought-through design from IBM.
Some aspects were pretty good--the original keyboard was very good;
the casework with rolled edges was also notable, although the case
design itself was questionable (particularly in mounting/unmounting
disk drives). Many Taiwanese vendors improved on the case design by
incorporating a hinged lid; I don't know if that met with Part 15
requirements, but it was very convenient.
Cheers,
Chuck
26 Apr
26 Apr
10:34 a.m.
Chuck Guzis wrote:
Date: Fri, 25 Apr 2008 22:39:29 +0100 (BST)
From: (Tony Duell)
63W, I think - close! I did try and add a hard disk to my 5150 once, but the
supply just didn't have enough guts to spin up any of the spare drives that I
had. (which probably implies that maxing out the system would just result in
the PSU shutting down rather than going into some kind of overheat condition)
Did very early machines have AC fans? All the
later ones certainly had 12V
DC ones that would be independant of mains frequency, but an AC fan would
run slower on 50Hz and could cause the machine to overheat. Was it really
that marginal (Acutally, given it's the IBM PC [1], I could beleive it
was).
Yes, they did, but the fans were rated for 50-60 Hz operation and
impedance-protected. With the factory, what 62-watt?, PSU, I don't
think it was possible to stuff the thing full enough of drives and
cards to make it overheat slots) to make it overheat. Wasn't the (black)
PSU on the original
PC fitted with red tamper-telltales stuck on along the edge of the
PSU clamshell? I can't remember exactly, but I think it was.
Not sure; mine had the silver PSU and I don't remember any stickers on that
one (but then it wouldn't surprise me if IBM UK had* different procedures to
IBM US)
* or whoever was responsible for any changes in the UK market
As this was an IBM product, I fully expected that
there would have
been some provision for changing the AC input voltage. Certainly
other personal computers of the time had the feature, and this wasn't
supposed to be a product from "Fred's Personal Computer and Aluminum
Storm Door Company". One expected a high level of engineering from
IBM.
Trying (misguidedly) to control the market by saying which countries which
machines could be used in seemed right up IBM's street, though (probably not
the case these days; as a company they seem a lot more flexible than they used
to be)
IBM seemed to be in a state of "maximum revenue, minimum effort" when it came
to the PC, though.
[1] When I got my first IBM PC-family machine (a
5160), I took it to
bits
(what a suprise) and sat down with the TechRef. Every few minutes I'd
exclaim 'They did WHAT???' as I found aother it of misdesign...
I never understood the design that featured a complete lack of a
clear airpath between the plug-in-cards. They must not have been
expecting very much expansion.
I don't get that, either. With 64KB max on the motherboard, how could they
*not* think people would expand the machines? (Particularly given that it was
safe to assume most people would also have a video card and FDC)
Maybe the assumption was that the amount of metal in the chassis and case
shell would act like some form of big heatsink, and dissipate heat that way.
I'm sure that IBM, being who they are, *did* test airflow and heatsink
characteristics, though (unlike what seemed to happen with the Apple /// :-)
The MDA card was the most bewildering experience to
work through--
circuit traces headed off to nowhere, ICs that seemed to perform no
function. Perhaps it was designed for graphics operation originally
and not completed and rushed to market.
What might have happened is that it was a board designed for something else
entirely, and in a different context - and that someone did a bodge-job when
it came to 'porting' it to the PC. I've seen it happen with other vendors when
products evolve but still share some common ancestral circuitry.
(After what Guy said about the System/23 roots, maybe various bits were lifted
from there?)
Similarly, one suspects that the printer port must
originally have
been intended as a full bidirectional design and then changed at the
last minute--on both the MDA and the printer adapter, all the
necessary circuitry was present for bidirectional operation. Cutting
and jumpering a single trace was all that was needed.
That one's always seemed weird. I assume IBM didn't want the headache of
people blowing ports by using them for non-printer things - plus it wouldn't
surprise me if they had the idea to produce a proper lab or I/O interface for
that kind of functionality (at high extra expense to the buyer, of course) and
this just never materialised.
Some aspects were pretty good--the original keyboard
was very good;
the casework with rolled edges was also notable
Agreed. PCB construction / soldering all seemed to be high quality, too. It's
just the design decisions when it came to the schematics and choice of
components that seemed rather insane.
, although the case
design itself was questionable (particularly in mounting/unmounting
disk drives).
Y'know, I've forgotten exactly what they were like, now. I do think that the
half-height drives just weren't readily available when the 5150 came about,
which would explain the lack of mounting options.
What really puzzles me is that it wasn't a backplane design - putting the CPU
and (basic) memory logic on the motherboard seemed a little odd, given that a
backplane would have given more card slots and more future upgrade
flexibility. It must have been obvious that memory and CPU technology would
improve, and that the number of expansion slots wasn't anything to write home
about.
cheers
Jules
2:31 p.m.
On Saturday 26 April 2008 13:34, Jules Richardson wrote:
They sure did that every time I tried it. :-)
They had to change, in order to survive.
(Snip)
Yes, they did,
but the fans were rated for 50-60 Hz operation and
impedance-protected. With the factory, what 62-watt?, PSU, I don't
think it was possible to stuff the thing full enough of drives and
cards to make it overheat
63W, I think - close! I did try and add a hard disk to my 5150 once, but
the supply just didn't have enough guts to spin up any of the spare drives
that I had. (which probably implies that maxing out the system would just
result in the PSU shutting down rather than going into some kind of
overheat condition) As this was an
IBM product, I fully expected that there would have
been some provision for changing the AC input voltage. Certainly
other personal computers of the time had the feature, and this wasn't
supposed to be a product from "Fred's Personal Computer and Aluminum
Storm Door Company". One expected a high level of engineering from
IBM.
Trying (misguidedly) to control the market by saying which countries which
machines could be used in seemed right up IBM's street, though (probably
not the case these days; as a company they seem a lot more flexible than
they used to be) What really puzzles me is that it wasn't a
backplane design - putting the
CPU and (basic) memory logic on the motherboard seemed a little odd, given
that a backplane would have given more card slots and more future upgrade
flexibility. It must have been obvious that memory and CPU technology would
improve, and that the number of expansion slots wasn't anything to write
home about.
Zenith did that with their XT-class machines, although it wasn't until much
later on (not all that long ago, when I was scrapping usable bits out of a
couple of machines that had been left out in the weather :-) that I realized
that the slots in those were different heights!
I'm sure somebody else did backplane-style boxes too, but that's all that's
coming to mind at the moment.
--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, ?a critter that can
be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin
12:17 p.m.
On Sat, 26 Apr 2008, Chuck Guzis wrote:
Yes, they did, but the fans were rated for 50-60 Hz
operation and
impedance-protected. With the factory, what 62-watt?, PSU, I don't
think it was possible to stuff the thing full enough of drives and
cards to make it overheat (remember too, that there were only 5
slots) to make it overheat. Wasn't the (black) PSU on the original
PC fitted with red tamper-telltales stuck on along the edge of the
PSU clamshell? I can't remember exactly, but I think it was.
63.5? W
Mine didn't. Just tamper-proof torx with a black PS case and white
switch.
As this was an IBM product, I fully expected that
there would have been
some provision for changing the AC input voltage. Certainly other
personal computers of the time had the feature, and this wasn't supposed
to be a product from "Fred's Personal Computer and Aluminum Storm Door
Company". One expected a high level of engineering from IBM.
Harrumph. We don't even have storm doors around here. It's a matter of
making screen doors, or expanding into other markets.
I never understood the design that featured a complete
lack of a
clear airpath between the plug-in-cards. They must not have been
expecting very much expansion.
They thought that cassette BASIC would remain a popular configuration.
All in all, for as long as the 5150 was in the rumor
mill, one would
have expected a better thought-through design from IBM.
An awful lot of the rumors were based on, "well, of course it will
be . . .", "only a moron would make a machine that isn't CP/M"
"Only a moron would make it not be Apple compatible", . . .
"How can it NOT have a 68000?"
Only somebody who doesn't know IBM could make predictions like those.
1:32 p.m.
Date: Fri, 25 Apr 2008 22:39:29 +0100 (BST)
From: (Tony Duell)
Sure, but the fan would turn slower on 50Hz mains. I doubt that would
cause the machine to overheat, but it's the only logical (as opposed to
marketing) explanaition I can think of for voiding the warranty.
Did very early machines have AC fans? All the
later ones certainly had 12V
DC ones that would be independant of mains frequency, but an AC fan would
run slower on 50Hz and could cause the machine to overheat. Was it really
that marginal (Acutally, given it's the IBM PC [1], I could beleive it
was).
Yes, they did, but the fans were rated for 50-60 Hz operation and
impedance-protected. With the factory, what 62-watt?, PSU, I don't think it was possible to stuff the thing full enough
of drives and
cards to make it overheat (remember too, that there were only 5
slots) to make it overheat. Wasn't the (black) PSU on the original
PC fitted with red tamper-telltales stuck on along the edge of the
PSU clamshell? I can't remember exactly, but I think it was.
Later PSUs had tamperproof Torx screws on them, and the IBM service info
implies the PSU should be replaced 'for safety reasons' if there's any
evidence of tampering. Needless to say I've taken IBM PSUs apart and put
them back together with the original screws...
As this was an IBM product, I fully expected that
there would have
been some provision for changing the AC input voltage. Certainly
I've only seen the UK-supplied units, but they have an internal soldered
link that is fitted for 115V nad open for 230V. Why it wasn't a rear
panel switch I don't know (it was on the PC/AT and the Portable [1] of
course)
[1] Whcih make a lot of sence given that that machine was intended to be
moved around. On the other hand, it's not as nice as the HP Integral
supply which contians a little circuit, the purpose of which is to short
out the mains (triac and low value resistor) to blow the fuse if the
machineis set for 115V and plugged into a 230V supply...
The IBM PC and XT supplies I've seen are clarely Zeniths. They are
unueual in that they have a mains-frequency transfortmer for the startup
supply and unlike many small SMPSU cannot be run from a DC input.
other personal computers of the time had the feature,
and this wasn't
supposed to be a product from "Fred's Personal Computer and Aluminum
Storm Door Company". One expected a high level of engineering from
IBM.
In the same way that I used to expect a high level of engineering from
HP, but look what they're turning out now :-( :-(
Similarly, one suspects that the printer port must
originally have
been intended as a full bidirectional design and then changed at the
last minute--on both the MDA and the printer adapter, all the
necessary circuitry was present for bidirectional operation. Cutting
and jumpering a single trace was all that was needed.
On the printer adapter (althohgh not the MDA card), there was actually a
set of solkder pads for this cut-and-jumper mod. They are not documetned
in the Techref, I have no idea why not
-tony
2:21 p.m.
On Saturday 26 April 2008 13:01, Chuck Guzis wrote:
Some aspects were pretty good--the original keyboard
was very good;
the casework with rolled edges was also notable, although the case
design itself was questionable (particularly in mounting/unmounting
disk drives). Many Taiwanese vendors improved on the case design by
incorporating a hinged lid; I don't know if that met with Part 15
requirements, but it was very convenient.
I don't remember Taiwanese vendors doing that, but I do remember a case of
that sort available from Jameco, I think it was. I have a machine in such a
case somewhere around here.
--
Member of the toughest, meanest, deadliest, most unrelenting -- and
ablest -- form of life in this section of space, ?a critter that can
be killed but can't be tamed. ?--Robert A. Heinlein, "The Puppet Masters"
-
Information is more dangerous than cannon to a society ruled by lies. --James
M Dakin
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