> On Aug 28, 2017, at 7:49 AM, Rob Jarratt via cctalk <cctalk@classiccmp.org>
> wrote:
>
> My recently acquired DECstation 5000/240 has had a PSU failure. After
> replacing a couple of small capacitors with high ESR, I have been doing some
> basic checks to see which stages are working. My first step has been to
> check the output of the input rectifier, which has two large capacitors to
> smooth the output, they are each rated at 200V. When I check the rectifier
> output with a basic DMM I measure about 136V on the AC range, and a voltage
> ranging around 160-170 on the DC range.
>
>
>
> I know that some PSUs double the voltage here, and the presence of two large
> capacitors would suggest that happens here too. ...
Can you work out the schematic, at least the critical part: transformer,
rectifiers, capacitors? There are lots of ways to arrange the components. A
couple of arrangements with two capacitors are doublers, but it's certainly
possible to have something else. It all depends on the details.
Ham radio references (ARRL Handbook, equivalent publication from RSGB) will
show power supply structures and show all these schemes clearly.
paul
