ebay power supply

[ecat]

probing 400v at any time is not a good idea imo!

Anyway, that daughter board is a nightmare, everything is way to small and the board would be trouble to remove: I think I have the comparator outputs to the 2 optos, via 2 transistors so looks good :) The bad news is all the fun gubbins for this is behind the capacitor bank making it almost totally inaccessible :(

Undeterred, lol, I moved on to the inputs to the daughter board and here I may have hit the jackpot... maybe.. The op voltage is divided down by a factor of ten and fed to the daughter board. Yay. These dividers are on the main board and not surface mount. Yay. The bad news is there are two voltage dividers and I have no idea what the second one is for, then again I have no idea which of the 2 we need anyway.

Divider 1 feeds op div 10 (measured) to daughter board pin 12
Divider 2 feeds op div 10 (measured) to daughter board pin 8

You should be able to trace the resistors I'm talking about from these pin numbers.

If I'm right about the lm224 equivalents then pin 12 feeds to a unity gain op amp, pin 8 feeds to a different opamp that actually 'does stuff'. I've no idea what it does but it's not unity gain.

So, why two dividers and two opamps ? 1 to catch the default 42.9v and the other for the variable feature? I don't know. Do I need to change both? I don't know.

These boards were not made for easy disassembly so I've measured the divider resistors in circuit, of course the values measured this way do not match the values required for a div 10 series pair. Ho-hum. One resistor in each pair is big and easy to see - they are not quite under the heatsink and just behind the output coils, I can't see a ref number now the thing is back together :( -, so if you have reasonable colour vision perhaps you can let me know the value?

Anyway, before I risk life and limb by snatching the soldering iron from the coals (should be hot enough by now) I'd like your opinion on which of the two possible modifications would be most suitable...

1) Configure the psu so the variable range works over, say 43v to 47v (ish)
2) Configure the psu so the 'non-regulated' voltage can be set to XXv and the variable input can be ignored.


I'm off to try and find a zener...