The various models on the schematic:
The display board:
This uses 7106 drivers to drive the LCD - as used in every budget multimeter. Cheap, reliable, no problem at all.
The keyboard:
Just buttons!
The keyboard2:
This uses a 4520 binary counter to cycle through independant, series and parallel (via relays). Nothing too complex, I've used the 4520 before.
The adjust board:
Standard power supply circuitry - relays to select the transformer tap, a rectifier, smoothing caps and a few beefy transistors (15A each) to regulate the voltage. No problem.
The control board:
This is where the fun starts
. Looking at the various parts:
Top left:
A simple power supply for the parts on this board - giving 5v, 8v and -5v.
Top right:
This isn't too bad either. It looks at the current voltage, then decides what transformer taps need energising, and switches them. Not too bad.
Bottom left:
Getting a little more complex here - this debounces and decodes the switches using schmitt triggers and more 4520s, to control a X9C103WS digipot - simple up and down variation of resistance. 4066 switches are used to enable/disable the output of the digipot.
Bottom right:
The output from the digitpot feeds into a few opamps, which mix the constant current mode settings with the constant voltage controls.
I appriciate that this sin't the simplest power supply out there - but it is much better than my current one, which has a big ATMEGA48 - I have no idea what it's programmed to do. I feed that troubleshooting this power supply would be possible - although there's a lot of it, the schematic is made of simple elements. In addition, there are two power supplies - if one has problems, you can compare voltages with the working side.
As for SMD, I'm fine working with it - nearly all my own projects are SMD (down to 0.5mm pitch).
I feel that I'd have a better shot at fixing a complex power supply
with a schematic then a simpler one
without. My current broken power supply has chips with unreadable part numbers - I don't have a hope!