Hookup your scope across the 5v and gnd on J254 and see what the trace looks like. Also do +12 v. And -12v on j100 That will tell you if one rail is bad. You should have not much ripple. If there is a lot, trace that voltage rail back.
Sent from my iPhone > On Aug 29, 2025, at 14:42, Rob Jarratt <[email protected]> wrote: > > There are different labels on different schematics because the official > schematic uses numbers that are not marked on the board, the other numbers > are actually marked on the board. If you look at the marked up JPG then they > are D15/16 etc, if you look at the schematic in the technical manual they are > D134/136 etc. It is quite confusing! > > Thanks > > Rob > >> -----Original Message----- >> From: Scott Baker via cctalk <[email protected]> >> Sent: 29 August 2025 20:10 >> To: General Discussion: On-Topic and Off-Topic Posts <[email protected]> >> Cc: Wayne S <[email protected]>; Robert Jarratt >> <[email protected]>; Scott Baker <[email protected]> >> Subject: [cctalk] Re: Repairing an Olivetti M24 PSU >> >> I'm confused -- maybe I misread-- the original post says D134/D136 and the >> most recent post says D15/D16 and D18/D19. Which diodes do the >> oscilloscope traces go with? >> >> Scott >> >>> On Fri, Aug 29, 2025 at 10:36 AM Robert Jarratt via cctalk < >>> [email protected]> wrote: >>> >>> Sorry about the schematic, it is here >>> https://rjarratt.wordpress.com/wp- >> content/uploads/2025/08/m24_psu_sche >>> matic-marked-up.jpg but it is just a marked up version of the >>> schematic that is already on BitSavers. >>> >>> I attached the probes to the anodes of the diodes marked D15/D16 and >>> D18/D19 in the marked up schematic and to the GND output. >>> >>> Thanks >>> >>> Rob >>> >>>> -----Original Message----- >>>> From: Wayne S <[email protected]> >>>> Sent: 29 August 2025 07:36 >>>> To: General Discussion: On-Topic and Off-Topic Posts < >>> [email protected]> >>>> Cc: Robert Jarratt <[email protected]> >>>> Subject: Re: [cctalk] Repairing an Olivetti M24 PSU >>>> >>>> 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? >>>> >>>> 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_o >>>> f_O peration_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-o >>>>> n- >>>> 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 >>> >
