Thinking of building a (PC) Power Supply. Lightweight advice requested.

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Thread Starter


Joined Feb 24, 2023
It is a Tektronix 420a ps failed. Threw it away: transformer costs more than a news Silgent 2000X
it WAS a high tech switching powersupply with like 4 voltages out (6 or 8 if +- included).

I realize this project might "be back shelf" (not the easiest project for a hobbiest to finish in near term).

I have a used Tek 420a with working PS (dead acquisition board) to work with.

Can I just disconnect and measure the PS with a 50Mhz scope and mimic the results? With a few drawdown tests?

Can I just buy four chinese switching modules (one for each V needed) ($12 ea, say) then "make my build all about cleaning up the signal" so it "looks as good as the other" on the 50Mhz scope? (all four would fit in the 420a easily I think)

Not asking for total instructions. just broad warnings to save me allot of time, if such advice is possible. If my thinking is way out of the ball field.

I'm a little familiar with power supply jargon - but totally unfamiliar with "what is sufficient to prevent frying IC". (signal smoothness, maximum drawdown allowed). I've tried to find lessons on the internet about "what signal clean-ness is required" and "what drawdown is acceptable" for IC chips. I can't find any after long google searches. Obviously it would be too big a job to chart every chip's requirements with no schematics ever released. I need something "more in general".

(tek 420a mess of a 5 slayer board that "supports 8 all voltage all intertwined from early in the In-Out" (with a highly custom transformer and 3 power control chips on a card with "markings removed") (making repair quite awful. i guess that's high tech!)

(I could put the working PS in the 420a and sell it; find an easier project. I'm unsure of how hard a project this is. Making the PS is easy: insuring the power is "potable" I don't know where I can somthing to read up on it - yet)
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Thread Starter


Joined Feb 24, 2023
(I'm aware of too many "concepts" in power module IC mitigation. What I'm looking for is advice or literature on "what the PC power supply output should be" (given so much draw). I understand (modern) PC like to think power supply IC should be linked with the CPU for demand - that supply isn't a one way street. But this is an older PC and if repaired, for personal supervised use.)


Joined Nov 6, 2012
I'm confused .........
Are You considering creating a Power-Supply for a Tektronx-Oscilloscope,
or are You considering creating a Power-Supply for a Desktop-Computer ?

I'm going to guess that it's the Oscilloscope.
If You can obtain a Schematic, there might be some vague hope.

As for figuring out how much Current each separate Power-Supply-Output will need to provide,
I would first count the number of wires coming out of the Power-Supply for each particular Voltage,
then write-down the Gauge of each Wire.
You may have to actually measure the diameter of each Wire to determine it's Gauge.

The Power-Supply needs to be able to create enough current to just barely stress
each individual Wire's Insulation because of the heat generated by the Current.
The Power-Supply needs to maintain near-perfect Voltage-Regulation up to that calculated Current-level,
before going into Current-Limiting-Mode.

There may be a huge wad of Common-Ground-Wires.
Nothing about the performance of the Power-Supply can be gleaned by
counting the number of Ground wires or noting their Gauge.

I would obtain a Meanwell AC-DC SMPS that will comfortably supply the highest Voltage needed
and handle the total calculated Current demands of all the combined Outputs,
then add ~40% to that Current number,
then, for lesser Voltages, add an adequately rated Buck-Converter for each independent Output,
( or an inverting-Buck-Converter for any Negative-Voltages ).

If You know for a fact that the Power-Supply is the problem with this 'Scope,
this will probably get You back in business, ( there are no guarantees ),
but it's probably not worth the effort, time, and expense.

There are plenty of very inexpensive, and very capable 'Scopes available,
so unless you need something extraordinary, just buy a new one.


Joined Jun 3, 2019
Not aware what sort of unit you threw away, but sounds like an awful lot of work to revive an old scope. Oscilloscopes aren't that expensive and you get a brand new one.
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