Officepot Posted September 20, 2023 Share Posted September 20, 2023 Hello! I have an Atari 520ST that when using the original power supply, came on and worked as intended, than after about 10 minutes, the screen would start getting interference more and more till the computer would finally totally turn off. I started by recapping the power supply but this did not remedy the issue. I then ran into this forum post https://forum.atari-home.de/index.php/topic,14645.20.html Yes it is in German I am sorry I used google translate. Where they used a CISCO ADP-30RB to make a replacement power supply. Here is a PDF the OP of that forum post provides https://forum.atari-home.de/index.php?action=dlattach;topic=14645.0;attach=22673. The PDF really just talks you through how to make the CISCO supply work. The power supply provides 5V @ 3 A, 12V @ 2A, and -12V @ 0.2A. So I purchased one of these CISCO ADP-30RB power supplies and it did not work. When plugged into my ST520 board the CISCO would throttle down to less than a volt on both the 5V line and +-12V lines. I know that this power supply has a ROF line which stands for Remote On/Off (this pin has to be tied to ground for the power supply to supply power). Well is how I understood it but yet again mine didn't work so what do I know... So I am not sure if I got a bad power supply or if there is something wrong with my 520ST? I then tried a switching power supply I had out of an arcade cabinet. The switching power supply provides 5V @ 15A. I read in another post that the 520ST only needs the +-12V lines for hard drives and other interfacing so it should turn on with just the 5V line? Someone please confirm that. So when I plug this switching power supply into my board it does the same thing. It throttles down to almost nothing/turns itself off. I am starting to worry that my 520ST is somehow bricked/has a short or want to know if someone can point out where I have gone wrong along the way? All in all my question is what did I do wrong with the CISCO? If someone on another forum said they got theirs to work, is there something potentially wrong with my 520ST? I am at a loss on where to go next. Quote Link to comment https://forums.atariage.com/topic/355020-atari-520st-power-supply/ Share on other sites More sharing options...
snarkdluG Posted September 20, 2023 Share Posted September 20, 2023 Sounds like your PSU functions normally when there is a short on the motherboard. Detatch PSU and measure resistance between 5V and GND on motherboard. Also between 12V and GND on motherboard. See if you can find something that have failed/looks strange on the motherboard with your eyes. Quote Link to comment https://forums.atariage.com/topic/355020-atari-520st-power-supply/#findComment-5319891 Share on other sites More sharing options...
TGB1718 Posted September 20, 2023 Share Posted September 20, 2023 8 hours ago, Officepot said: I read in another post that the 520ST only needs the +-12V lines for hard drives and other interfacing so it should turn on with just the 5V line? Someone please confirm that. The +12V is needed for the Floppy drive if it's internal only, both +12V and -12V are used for the RS232 line. So just to test you only really need the +5VDC. You can always test the power supplies if you have something like a 10W 10 Ohm resistor across the 5V line and maybe a 10W 30 Ohm resistor across the +12V line Quote Link to comment https://forums.atariage.com/topic/355020-atari-520st-power-supply/#findComment-5319971 Share on other sites More sharing options...
Officepot Posted September 20, 2023 Author Share Posted September 20, 2023 7 hours ago, snarkdluG said: Sounds like your PSU functions normally when there is a short on the motherboard. Detatch PSU and measure resistance between 5V and GND on motherboard. Also between 12V and GND on motherboard. See if you can find something that have failed/looks strange on the motherboard with your eyes. When measuring between 5 V and Ground I see open with a multi-meter. I did notice that after I had just attempted to turn on the ST I measured again and found 20 Ohm between 5V and Ground. Quote Link to comment https://forums.atariage.com/topic/355020-atari-520st-power-supply/#findComment-5319996 Share on other sites More sharing options...
TGB1718 Posted September 20, 2023 Share Posted September 20, 2023 That could just be residual voltage across a capacitor, if you keep the meter there does it increase back to "open" ? Quote Link to comment https://forums.atariage.com/topic/355020-atari-520st-power-supply/#findComment-5320014 Share on other sites More sharing options...
Officepot Posted September 20, 2023 Author Share Posted September 20, 2023 3 hours ago, TGB1718 said: That could just be residual voltage across a capacitor, if you keep the meter there does it increase back to "open" ? that is correct, it does eventually go back open Quote Link to comment https://forums.atariage.com/topic/355020-atari-520st-power-supply/#findComment-5320115 Share on other sites More sharing options...
Officepot Posted September 22, 2023 Author Share Posted September 22, 2023 For a final update I have finally realized my mistake... the diagram found at the original pdf link I posted is "from the computer view" and not from the connector view. I assumed this was the connector view and was wrong... I had been mirroring the correct pinout like an idiot and after putting the pins where they actually should be it works great! Funny how that works. I plan on putting a gotek into the original floppy drive I have and trying out some games soon on the 520ST! Quote Link to comment https://forums.atariage.com/topic/355020-atari-520st-power-supply/#findComment-5321067 Share on other sites More sharing options...
+DarkLord Posted September 24, 2023 Share Posted September 24, 2023 It happens - I do things like that far more often than I care to admit. Congratulations on getting it working though. Now go and enjoy the results of your labor...! Quote Link to comment https://forums.atariage.com/topic/355020-atari-520st-power-supply/#findComment-5322264 Share on other sites More sharing options...
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