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
I' plan on arriving there between 1 and 2 Friday afternoon. If there is
anything else you want me to bring please email me off list today.
If you have any US/ foreign coins/currency I'm interested in trading or
buying them.
Thanks, Paul
Folks,
The Northwest Computer Museum in Leigh, Lancashire is having a jumble
sale this coming Saturday.
https://www.facebook.com/events/leigh-spinners-mill/tech-jumble-sale/129448…
They have said I can have a table as well so I will be bringing along
some of my /junk /oops surplus bits and bobs.
I will have floppy disks, floppy disk drives, disk drives, keyboards,
bits of Sun SPARC station, RS232 leads, PCI cards..
.. all "as seen" , most for donations to the Museum...
Dave
Time to clean out my basement.
These are going to e-waste unless somebody wants them:
Compaq Presario SR1010NX. Don't know whether it works.
HP desktop box with MB and PS, no DVD, not working.
Dell power supplies for data center clusters: 4 × N750P-50. 1 × PS-
2521-1D
2 × CC8823 power supplies for network switches (don't know the
manufacturer; 3Com?)
3 × Ultrium fiber-channel tape drives. and a few cartridges
PowerOne switching power supply Model SPM5A2M6G1K, 1 × 48VDC @ 5A, 3 ×
12VDC @ 10A, 1 × 5 VDC @ 150A.
Local pick-up in La Crescenta, CA is OK.
Time to clean out my basement.
These are going to e-waste unless somebody wants them:
Compaq Presario SR1010NX. Don't know whether it works.
HP desktop box with MB and PS, no DVD, not working.
Dell power supplies for data center clusters: 4 × N750P-50. 1 × PS-
2521-1D
3 × Ultrium fiber-channel tape drives. and a few cartridges
PowerOne switching power supply Model SPM5A2M6G1K, 1 × 48VDC @ 5A, 3 ×
12VDC @ 10A, 1 × 5 VDC @ 150A.
Local pick-up in La Crescenta, CA is OK.
Some months back I started working on a Philips P3800 computer, there
was a long discussion here about the power switch and its unusual
cylinder lock. At least one person was interested enough in the lock
to say they would like to see it with a view to making a key
At the time I didn't want to post the lock anywhere as I could have
been left with a incomplete and unrepairable machine.
Other projects, some of them classic-computer related got in the way.
but over the last few days I've gone back to the P3800 and have made a
spindle to effectively replace this lock and allow the power switch to
be knob-operated (security is not an issue in my workshop :-)). Thus I
could manage without the lock if I have to.
So if the offer is still open I would consider posting the lock
somewhere (preferably in .uk)
Obviously it's 'work on it as and when you feel like it'. There's a
lot of electronics for me to work on, and I'll probably take many
months to sort that out.
-tony
Just relaying a message here, for those who maybe don't requent the VCF
forum itself.
A 1st-post person says he's original owner of a Datapoint 2200, and is
looking to find a good owner (museum) for it. Not sure where he is
presently located, but the CRT of this DP needs attention - and I'm fairly
useless in that department.
In the Genre|Others section.
https://forum.vcfed.org/index.php?threads/new-datapoint-2200-owner.1244800/…
May be a pre "A" or "B" version, since it has the original tape decks at
top? In any case, likely a pre-1974 model for sure.
-Steve
I read that B. Gates has released 'BASIC for 6502 Microprocessor - Version
1.1' that has 6955 lines of assembly language code. I would say this
qualifies as a major event in the classic computing world.
Happy computing!
Murray 🙂
This might be the wrong list to ask, but here's the question:
I have a Compaq Presario gathering dust in my garage.
Does anybody want it?
Shipping might cost more than its value, but local pickup is OK with
me.
Van Snyder
La Crescenta, CA
