Useful ATX Power supply modification - UK Vintage Radio Repair and Restoration Discussion Forum

valvekits · 16th Oct 2010, 12:56 pm

My Mac quicksilver computer was out of action the last couple of days. I ended up modifying an ATX power supply to get me up and running again. Whilst trawling the net for a solution I came across this website which is basically about modifying ATX power supplies to get whatever voltage you like.
It's in Italian but I used google translate to get a reasonable understanding.

http://www.chirio.com/switching_power_supply_atx.htm

Eddie

paulsherwin · 16th Oct 2010, 1:09 pm

While not wanting to sound negative, I should remind people that these are safety critical subassemblies and can become dangerous if modified improperly. I'd advise people to leave them alone unless they're confident they know what they're doing.

On the other hand, it's easy to use PC PSUs as cheap 12V and 5V stabilised supplies with only minor wiring modifications.

techiesteve · 16th Oct 2010, 2:33 pm

Eddie, the G4 Quicksilver power supply has always been unreliable. Most problems I've seen were caused by the enameled wire insulation in the +5V and +3.3V output filter toroid cooking and shorting the +5V to +3.3V. Apple declared this PSU vintage some time back, no longer available. Apple can currently only supply PSU's for the last of the Powermac G5's from 2005, and these will soon go vintage. I've seen these simple faults in older Apple PSU's recently. Early PM G4 PSU's containing two vertical smd based boards, change the two conventional electrolytics on each upright board. PM G5 600W as used in dual 2 GHz 2004 models, TOP-249Y (25V supply psu) blown apart, no other damage.

PeterG8BZR · 20th Oct 2010, 9:18 pm

Hi Eddie, I would agree that ATX power supplies can be usefully modified. I needed high current 6v supply (about 20 amps) to power up an old valve BCC mobile phone and it was very simple to modify the psu. It helps that 6v is very close to the normal output voltage. You do have to be careful to maintain a minimum load on most of these units though.

Jason Pero · 21st Oct 2010, 12:50 am

I have done that as well, except I undid all the wires except ground and 12V, traced out whole OCP, OVP circuits and regulation feedback. That helped me to identify the crucial two resistors voltage divider for voltage regulator feedback comparator and recalculate new voltage. Got 15V spot on first try.

That was used to power the toshiba DTR P4 notebook.

Cheers, Wizard

16th Oct 2010, 12:56 pm	#1
valvekits Pentode Join Date: Dec 2008 Location: Nottinghamshire, UK. Posts: 239	Useful ATX Power supply modification My Mac quicksilver computer was out of action the last couple of days. I ended up modifying an ATX power supply to get me up and running again. Whilst trawling the net for a solution I came across this website which is basically about modifying ATX power supplies to get whatever voltage you like. It's in Italian but I used google translate to get a reasonable understanding. http://www.chirio.com/switching_power_supply_atx.htm Eddie

16th Oct 2010, 1:09 pm	#2
paulsherwin Moderator Join Date: Jun 2003 Location: Oxford, UK Posts: 27,967	Re: Useful ATX Power supply modification While not wanting to sound negative, I should remind people that these are safety critical subassemblies and can become dangerous if modified improperly. I'd advise people to leave them alone unless they're confident they know what they're doing. On the other hand, it's easy to use PC PSUs as cheap 12V and 5V stabilised supplies with only minor wiring modifications.

16th Oct 2010, 2:33 pm	#3
techiesteve Pentode Join Date: Aug 2009 Location: Aylesbury, Bucks, UK. Posts: 161	Re: Useful ATX Power supply modification Eddie, the G4 Quicksilver power supply has always been unreliable. Most problems I've seen were caused by the enameled wire insulation in the +5V and +3.3V output filter toroid cooking and shorting the +5V to +3.3V. Apple declared this PSU vintage some time back, no longer available. Apple can currently only supply PSU's for the last of the Powermac G5's from 2005, and these will soon go vintage. I've seen these simple faults in older Apple PSU's recently. Early PM G4 PSU's containing two vertical smd based boards, change the two conventional electrolytics on each upright board. PM G5 600W as used in dual 2 GHz 2004 models, TOP-249Y (25V supply psu) blown apart, no other damage.

20th Oct 2010, 9:18 pm	#4
PeterG8BZR Retired Dormant Member Join Date: Sep 2009 Location: Romsey, Hampshire, UK. Posts: 19	Re: Useful ATX Power supply modification Hi Eddie, I would agree that ATX power supplies can be usefully modified. I needed high current 6v supply (about 20 amps) to power up an old valve BCC mobile phone and it was very simple to modify the psu. It helps that 6v is very close to the normal output voltage. You do have to be careful to maintain a minimum load on most of these units though.

21st Oct 2010, 12:50 am	#5
Jason Pero Retired Dormant Member Join Date: Jul 2010 Location: Kingston, Ontario, Canada. Posts: 51	Re: Useful ATX Power supply modification I have done that as well, except I undid all the wires except ground and 12V, traced out whole OCP, OVP circuits and regulation feedback. That helped me to identify the crucial two resistors voltage divider for voltage regulator feedback comparator and recalculate new voltage. Got 15V spot on first try. That was used to power the toshiba DTR P4 notebook. Cheers, Wizard