My Olivetti M24 was humming away nicely until I switched it off. It then failed to power on again. The PSU is not outputting any voltages on any of its outputs. The technical manual is here https://bitsavers.org/pdf/olivetti/m21_m24/Olivetti_M21_M24_Theory_of_Opera…. The PSU is described from p188 with an outline schematic on p194. The full schematic is on p274. A schematic useful to anyone with the actual board in front of them has been created in the following forum post https://forum.vcfed.org/index.php?t...ower-supply-replacement.1237316/#post…, the schematic is this one: https://forum.vcfed.org/index.php?attachments/m24_psu_schematic-jpg.1252584/.
I have done some verification with the scope but I have reached a point where I am not sure what signals I should expect. I have attached a dummy load on the +12V, +5V and +15V outputs to meet the specs for minimum current.
I see a 20KHz square wave on the inputs to the output transformer T438 (pins 1 and 2). The manual says that the diodes on the output rectify a half wave. I assume these are the ones labelled D134 and D136.
The following image shows the signal on the two diodes marked D134 on the schematic for the 12V output, measured from their anodes to 0V output.
https://rjarratt.wordpress.com/wp-content/uploads/2025/08/diodes-on-12v-out…
For the other two diodes, labelled D136 for the 5V output I get this:
https://rjarratt.wordpress.com/wp-content/uploads/2025/08/diodes-on-5v-outp…
Do these look correct? The peaks seem to be too low to even begin to produce the required output voltage.
Thanks
Rob
M1705
M518
M7741
M8342
M835
M8350
M8360
M8357
M8365
M8366
M837
M839
M841
M847
M849
M860
M8650
M8659-YA
M865
M8652
M8653
M8655
M866
M868
M884
M885
M880//H241 MR8E-EC
Also CR8- an actual DEC card reader interface, dec industrial control
equipment,EMEX paper tape interfaces, and other dec compatible boards
including memory.
Microsoft released WIN 95 on this day 30 years ago. It was a game changer
for the average PC computer user but more important than Windows 3.1? Not
so sure.
Happy computing,
Murray 🙂
Hey all, after a couple years of prep (weekends here and there), I've
finally finished a full coverage video about the Sharp PC-5000.
It's not the most meaningful system in history, but it also shows the
"MS-DOS 2.0 experience" and bubble memory usage.
Various folks around here helped me figure this system out and get some of
the equipment, very much appreciated the willingness-to-help community here.
Video is on YouTube titled as:
Sharp PC-5000 and MS-DOS 2.0 Usage Demonstration (EDLIN, CTTY, MASM, BASIC,
Pascal, WordStar, more!)
Or link...
https://www.youtube.com/watch?v=dHPiomuWDmk
And to those who can't use YouTube for whatever reason, I've started also
uploading over on Rumble as an alternative source:
https://rumble.com/v6ybfky-sharp-pc-5000-and-ms-dos-2.0-usage-demonstration…
I'll be at VCF MW coming up, hoping to pick up another system that I've
been wanting to explore for a long time! Not sure yet it works, but that's
how the hobby goes :)
- Steve (voidstar tech / Xiphod)
There seems to be a LOT more people who don't believe in trimming or
formatting their copies of the messages they are replying to. I see that
kind of obvious disrespect for other readers, and ignored it for a
while. But it is getting worse. Please format/trim when replying.
Marvin
I finally got the missing keyboard and now it is time to try
and revive it.
A couple quick questions.
It has a board in it called IBM PC INTERFACE with the numbers
170-18-165 and CIL18-16 printed on it. It has a 50 pin connector
on the bracket end. If I take it out the machine dies almost
immediately doing the POST. Tried Google with no luck. Anybody
remember what it is?
Next problem. 1701 error. Light on MFM drive flashes 3 slow
and 4 fast continuously. Being as this machine was known to
work when it was last shut down any suggestions? Could it be
a stiction problem and the disk just isn't spinning up? (Can't
tell by listening as the fan is pretty loud. Not bad just louder
than any good disk I have ever heard.)
And then one other not related to a problem. Being an original
PC owned by users and not geeks is it likely that the floppy
controller is one that can handle other formats (like TRS-80)
and maybe even 8"?
And just to wrap it up. What are the chances of finding an
external drive or even a cable that could be made to connect
to an external drive?
Really hoping to get it to run. Would love to see what the
Psychology Department had on it. At least WordPerfect as there
is one of those function key templates taped on the keyboard.
bill
Frank wrote:
> I wasn’t around back then ;) But I think the big problem with
> steam tractors was since they were so heavy they would sink into
> the fields. I don’t think that was an issue really solved until gas
> powered tractors came around.
We're getting off topic but I want to interject that if you want to see operating steam tractors, stationary steam engines, and lots more, get to Mt Pleasant Iowa RIGHT NOW for the annual Old Thresher's Reunion which starts TODAY.
I note that when the Old Thresher's Reunion first started in 1950, the steam tractors being run there were only 40-50 years old, not too dissimilar to how an Apple II or PDP-11 is today.
https://www.youtube.com/watch?v=hs4L2nSqCL4https://www.oldthreshers.org/other-events/steam-school/
Tim N3QE
Interesting for Tesla’s early history, but skip to 49:00 for a nice rack he is putting together with an 11/20.
https://youtu.be/88KHfX_kPIY
He also appears to be on the cctalk list.
I have some 3.5" drives I don't need.
One 350 GB PATA
Three 320 GB SATA
One 500 GB SATA
Yours in exchange for a PDF of a shipping label from
Van Snyder
2229 Shields Street
La Crescenta, CA 91214
Local pickup also OK.
Just say which ones you want. They all have smartctl reports that claim
they passed.
Hi guys,
I'm somewhat sorting my stash of forever laying around parts
and there are 12 pcs from those:
https://www.tiffe.de/images/CII1040.jpg
That are two PNP BJTs in an TO can..and I think they are old.
I've desoldered them years ago. Most of them have an TI logo
printed on top.
I could'nt find any data..can someone help here?
Thx,
Holm
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Goethestrasse 15, 09569 Oederan, USt-Id: DE253710583
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