On 29/08/2025 07:35, Wayne S via cctalk wrote:
Your schematics are not accessable unless you’re a vcf member.
The rigol outputs look like there no rectification going on as there’s both a
positive and negative going wave.
Where did you attach the scope probes?
And can you make the schematic available to the genetic public?
Wayne,
Try my copy...
https://1drv.ms/i/c/277a0739f125010e/EU8NYVbyy-tIoCBgfquJi5cBfht4wVlyBjAkdgapnBbOwA?e=7LhE9K
Dave
Sent from my iPhone
On Aug 28, 2025, at 23:26, Robert Jarratt via cctalk <[email protected]>
wrote:
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_Operation_Nov84.pdf.
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-1299248,
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-output.png
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-output.png
Do these look correct? The peaks seem to be too low to even begin to produce
the required output voltage.
Thanks
Rob
