svi-738 inner power board

Supporter (2)

07-05-2023, 15:15

Hi im lost with my svi-738 im in the middle of converting it to msx2 and now my screen is black and the inner power board
has lost its -12v it only gives -4.9v what is burned in my power board i already tryed new L296, LM7912 and 1n5822.
Could it be the 1n5819 i dont understand how l296 is controlling the -12v now it gives the 5v to the output pin2 if i understand it correct it should be 12v.
I have two svi-738:s both have the same issue with the inner power board missing -12v.

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By lkpalwa

Expert (118)

08-05-2023, 14:32

do you have a ATX/AT powersupply near by, you could always try to get +12v, -12V and +5V from there and see if you can start the SVI738, if that does work then issue is not the PSU

https://www.smpspowersupply.com/connectors-pinouts.html

By lkpalwa

Expert (118)

08-05-2023, 14:55

if that works, you could always replace the PSU card with a PICO PSU .. see this project

https://blog.troed.se/projects/atari-st-picopsu-replacement/

By cjs

Master (143)

08-05-2023, 15:32

Note that some PSUs have minimum load requirements on some rails. Check the specs on your ATX (or other) PSU to make sure you're meeting these or it may be the PSU rather than the device under test that's causing a test to fail.

You can meet the minimum load requirements by simply hooking up resistors to the appropriate PSU outputs, but remember to check how much current you'll be pulling, calculate the wattage, and make sure you don't exceed the resistors' power limits.

By poiexi

Supporter (2)

08-05-2023, 20:59

Yes i know the atx option but i wanted to repair the original powerboard, the computer works with atx power,
no issues with that, but the easiest fix would be the pico psu thanks for that information.