Schemo for a SPI 230G AT psu

Does anyone have a schematic for a 230W AT psu by SPI (Sparkle Power, Inc.)? I believe the model # is SPI-230-G or '-235-G. I have one of these and want to mod it for either +13.8VDC, or +/-20V for some chip-amps I want to test. It looks like a very good design, made with good quality components, and decent build quality. It even has pots for current-limit adjust and V(out) adjust! I changed out most of the semis for some new, unused Motorola parts I had lying around (TL494, MJE13009, MBR1100, 1N4004, 2N3904, 2N3906, LM393, etc.).

I have searched the entire forum and have found no info on this particular mod. Help! :bigeyes: Thanks,

Hey Alex,

Yeah, I'm thinkin' about it. I have been spending the last 8 weeks re-creating the pc board pattern in Express PCB. Variations would include:
1) a DC-input to power a CPU from +12V
2) Bi-polar output for a chipamp
3) +13.8V out for powering radios, amps, EQs, and other signal-processing stuff.

Since I'm going with option #2, I can live with the P-B Drive, 'cuz I know it works. I'm not changing the primary side (except for upgrading the MJE13007s to '13009's, and 330mF/200V mains caps from the cheap 85 degree Centigrade units to Panasonic 105C Low-ESR TS-series cans), or the PWM chip. I want to change only the output section, which means the output sensing scheme, over-voltage and over-current protection.

I doubt I'll do anything to the existing psu's pc board I have, but I DO want to re-do it in the software so I won't have to hack up an otherwise good board. About the only thing I could do with the existing board is change it for the +13.8V-only output.
yeah you're right : with this board you could only get 13,8V without huge'll have to make a new pcb for your entire project.

do you have any idea how i could suppress the free running startup ?

my ideas :
suppress the 1 turn on the gate drive x former (shunt it)
suppress the two 330K C-B resistors in power stage
feed an auxiliary voltage of about 15-20V for TL494

what's your opinion about this ?

I'm a little reticent to start changing the operating points of the high-voltage stuff. Aside from upgrading (as opposed to outright changing) the components, the circuit on the primary side is set up so that the Royer Oscillator (as it is called) will enable the TL494 to start. W/O this setup, the PWM would never get power, and the circuit would never start.

If you want to change over to MOSFETs, the drive circuitry will be simpler, even with a drive xfmr, but will require a major re-work of the drive section. Since the Self-oscillating start-up would now be disabled, you would have to provide a separate dedicated power supply for the'494. The whole idea of this feature was so there wouldn't have to be a separate supply (which would add expense, and eliminate the capability of the PSU from operating off 330VDC).

So, back to my original question, Anyone have a schematic for the SPI-230G?