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Circuit Specialists triple power supply teardown

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I recently received a triple power supply ordered from Circuit Specialists.
It's 0-30V at 0-3amp X 2 and a 5v @3amp supply:

While I'm guessing it's one of the Mastech variants, I was looking for
a supply with LED displays, not LCD, because I find the LEDs to be
much more readable, especially at funny angles to the faceplate.

One of the things I liked about this supply, is that the current and
voltage are color coded.  While I like shiny things as much as the
next fellow, I can tell at a glance if I'm looking at voltage or current.
The voltages are green and the current is red.  Simple!

Let's look at the front panel.  It's the usual assortment of 4 displays, color
coded as I mentioned, each with current and voltage controls.
In the center is a mode switch which allows each supply to run
independently, or in parallel for 0-30v up to 6 amps, or in series
to run as 0-60v up to 3 amps.  Neat!

OK, let's see how well the voltage displays measure compared to my
Fluke 87-V.  First we have the left and right supplies:

and now the non-adjustable 5V supply.  Hmm, maybe I can find some
adjustments inside to tweak things, not that they are very far off.

Switching to amps, let's short out the supplies and see how the readings match.
Here are the left and the right:

So far so good, next I'll have to pop the cover off and see what we've got
inside.  I'd do that in another post.


Good stuff. Once you calibrate these power supplies once I've found they typically stay in good calibration for quite a while. There should definitely be some pots in there to adjust. I don't understand why they don't calibrate them better before shipping out though. Maybe too much time spent sitting in a warehouse...

I've now opened up the power supply and I was completely wrong about the
manufacturer.  This supply is made by Atten, and it an OEM version of

Let's peek inside.  First the overview.  Big transformer, several PCB with pass
transistors mounted on heatsinks with a cooling fan.  The front panel consists
of 2 PCBs, a display board and an output and pot board.


The power PCBs look pretty straightforward, relays to select taps on the transformer
and a bunch of analog circuitry.  No part looks unobtainable, good if we need to
repair this.



But what's this?  Look in the upper left corner of the last image.  Something
look amiss?  Well it's this:


Yes, a bridge rectifier has been twisted almost 90 degrees.  This should have
been fixed by QA.  In fact, I couldn't let this go by and I fixed it myself.

Finally, the front panel boards.  Again, nothing too exotic.  The displays
are driven by the ubiquitous ICL7137 variants.



Time for more testing.  First we have a series of overshoot tests.
The first diagram is the fixed 5 volt output.  Doesn't look bad at all.
The next two diagrams are at 3.3v and 12v.  Also looks quite good.

The final two measure noise.  The first is the 5v fixed output, showing
about 20mv of noise.  The second is an adjustable set to 3.3v.  This
is much quieter, about 7mv of noise.

All in all, this seems to be a nice power supply. 


sorry i am interrupting here, but qurious... why some PSU use those big big transformer, and other use none, just some descreet IC or big opamp/transistor/amplifier only? what the difference in term of efficiency and whats the pro and con?


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