DO NOT TRY TO DO THIS MOD !!! IF YOU ARE NOT AWARE OF THE SHOCK RISK !!!
I got two old PC powersupplies for free, to be used for this test..
are named DTK Computer model PTP-2008. 200 Watt Output.
+13.5V 14Amp cont. 20 A for 20 sec.
The external 230 Volt AC power
ON/OFF switch is removed and bypassed.
Old unused outputs are removed. Over
voltage protection changed to only protect one output at 16 V,
regulating resistor net changed to only monitor a single output,
Do it like this:
Cut: white, orange, blue, and yellow wires as close as
possible to the pcb.
Cut: all plugs away in the other end of the black and
red wires, parallel all red and black wires..
Desolder: Fan wires, L1, L3,
L4, R25, R26, R27, R29, R50, R51, R52, R61, R66, D10, D16, D17, C29, C28,
Mount a 680 Ohm 1/4 Watt at R50 location.
Mount solderpins in the
holes for R26, R61 and Fan connection.
This is a fast part-drawn schematic that
only covers what I wanted to know.
Mount 13.5 K Ohm at the solderpins at R26.
(13.5 Volt output adjust point)
Mount 15 V Zener and 100 Ohm in
series in the ZD1 holes. (Over voltage protection)
If two or more
powersupplies needs to be paralled, then cut R30,
now it is possible to enter
constant current mode opperation without shutting down.
This is also needed
if your load (or radio) has big capasitors in parallel with the power supply
Orange wire connects unused cap
to the new 13.5 Volt output (old +5 Output).
Transformer low voltage outputs
and 12 volt output vindings are connected to the high current
The fan is reverse mounted so
that it will blow cold air into the heatsinks and transformer.
The NTC is
glued with epoxy to the heatsink with the powerdiode,
The fan controller is
changed so that the fan starts to rotate at +40 C on the heatsink,
temperature goes further up, the fan will rotate faster.
Mount potentiometer 47 K at R61
solderpoints. (adjust to fan start at 40 C then change to normal resistor)
Output ripple is under 5mV pp at 20 Amp. (0 - 100 Mhz)
I have tested it
with my HF VHF and UHF rig, and could not hear any more noise than
Output power has been tested with 14 Amps cont. for one hour, no
problem at all !!
Efficiency at full max load is 60 %
This mod done April 2002 by me OZ2CPU.
Dont ask for schematics or any more
info. All I have is here on this page..
Idea to this mod was found here:
If you want to know more about switchmode converters get the "bible"
Switchmode power supply handbook by Keith Billings. From McGraw-Hill
Company ISBN: 0-07-006719-8