29 Aug
2025
29 Aug
'25
10:07 a.m.
On Fri, Aug 29, 2025 at 3:51 PM Bill Gunshannon via cctalk
<cctalk(a)classiccmp.org> wrote:
[Video cable]
Not in the origiinal IBM version.
Just a comment that I found it interesting. Surprised there
isn't a lot of noise on the screen.
In the original it's quite short. And of course it's a low-impedance
connection, terminated with 75 ohms at the monitor end.
The main 'noise' on the screen is due to the chroma subcarrier which
does appear on solid regions.
Another part of your machine that's been swapped out at some point.
Well I do. To the extent that I bought all the Techrefs from IBM many
years ago and have a shelf of them upstairs. I've also downloaded the
bitsavers ones of course. Along with manuals for literally hundreds of
other machines. Maybe you can find a failed component on your own but
I am stupid enough to need the schematics.
I have never been able to learn how to do anything from a video, for
me it's the most ridiculous way to present such information. And
there's so much misinformation on the web (in all fields) that I
prefer to start from the original manuals rather than somebody's
version of whatever
Sorry, I was just trying to be humorous. I have piles of paper manuals
for most of my computers.
Unfortunately I've seen the results of people following ill-informed
instructions on the web, particularly with audio amplifiers, etc. The
results sometimes end up on my bench and I have a lot more work to do
than if I simply had to find the original fault.
It's
normally yellow and black twisted pair.
Interesting. Not coax. If the floppy
drive is the orginal Qumetrak then there are little
plastic spacers on the screws to fit into the recesses on the drive
chassis casting. One of mine was missing so I milled a replacement
from plastic block
It's TEAC 55. Only one of those spacers was there.
There are some useful manuals on bitsavers. The Technical Reference
for the PC/XT and portablePC gives the motherboard schematic and BIOS
source. The Options and Adapters volume 1 gives the schemaitcs for the
drives and monitor. And volume 2 gives the CGA and floppy controller
schematics (and lots of others).
Pfft. Who needs manuals when you have google and youTube. :-) As for failed components, I have never and
would never waste time trying that on a PC class machine.
I do, particularly on a machine that's not just another random clone,
for example a genuine IBM one. It's as historic as any other classic
computer. And I am much more likely to have the right IC in stock than
the right replacement board.
Now, on a
PDP or VAX.... Still have an oscilloscope.
Just one 'scope?
-tony