Amiga 3000 replacement power supply

[chfriend]

Can anyone who has had to replace their 3000 power supply point me to a currently available ATX model that will either fit or can be easily transplanted?  I've got a refurbed Dell that is almost the same size but no -5v :-(

[danbeaver]

http://www.ebay.com/itm/Flex-ATX-Power-Supply-for-HP-Slimline-P-N-5188-7520-AC-BEL-PC6012-PC6034-PSU-PS-/251388865838?pt=PCA_UPS&hash=item3a87f1ad2e

[amigakit]

We stock the Amiga 3000 ATX PSU adapter:

http://amigakit.leamancomputing.com/catalog/product_info.php?products_id=1164

[chfriend]

Unfortunately neither of those options help unless the converter has a voltage converter circuit on it. No -5v on that supply either. Does anyone have a link to a known good circuit for +5 to -5v?

[mechy]

Unfortunately neither of those options help unless the converter has a voltage converter circuit on it. No -5v on that supply either. Does anyone have a link to a known good circuit for +5 to -5v?

I don't have a circuit, but i have done this using a 7905( i think!) regulator and some filter caps long ago. the -5 needs very little amperage. The input will be +12,not +5 though, you can't go from +5 to -5 since there are losses etc(one exception may be a dc to dc converter).It doesnt make the cleanest -5v,but seemed to work ok.
I think you would be better off finding a proper full atx psu with -5,which is a bit harder these days.

Have you considered fixing the original 3000 psu?

[chfriend]

I don't have a circuit, but i have done this using a 7905( i think!) regulator and some filter caps long ago. the -5 needs very little amperage. The input will be +12,not +5 though, you can't go from +5 to -5 since there are losses etc(one exception may be a dc to dc converter).It doesnt make the cleanest -5v,but seemed to work ok.
I think you would be better off finding a proper full atx psu with -5,which is a bit harder these days.

Have you considered fixing the original 3000 psu?

I have but don't know where to start. I've looked at other threads but they were for nonfunctional supplies. In this case, it's working and putting out correct voltage, at least with low demand. My guess is as I add demand it starts to drift out of tolerance. With just the mb, floppy and he attached it seems to work except for an occasional wobbly screen from Amber until it warms up. If I wanted to do a complete rebuild what components would I need to replace?

[AmmoJammo]

You can't regulated a positive voltage to a negative voltage easily.

You can however regulate the -12volt down to -5volts, simply using a 7905 regulator, and a few capacitors.

[danbeaver]

V=ir where "r" is not a capacitor, but a resistor; hence a change in resistance changes the voltage.

[mechy]

You can't regulated a positive voltage to a negative voltage easily.

You can however regulate the -12volt down to -5volts, simply using a 7905 regulator, and a few capacitors.

oops, you are right, my memory is worse than ever!.

[mechy]

I have but don't know where to start. I've looked at other threads but they were for nonfunctional supplies. In this case, it's working and putting out correct voltage, at least with low demand. My guess is as I add demand it starts to drift out of tolerance. With just the mb, floppy and he attached it seems to work except for an occasional wobbly screen from Amber until it warms up. If I wanted to do a complete rebuild what components would I need to replace?

Just a guess but since the psu is working, its more than likely bad capacitors. You might consider replacing them all. be sure to use low ESR types where needed.

I guess you have reseated the amber chip(checked for clean pins/socket) and also the adjustment pot for the flicker fixer could need adjustment.

[chfriend]

Just a guess but since the psu is working, its more than likely bad capacitors. You might consider replacing them all. be sure to use low ESR types where needed.

I guess you have reseated the amber chip(checked for clean pins/socket) and also the adjustment pot for the flicker fixer could need adjustment.

Adjusting the pot does clean it up faster, but eventually it clears up.  I've also noticed that when I have everything hooked up and it does work, any additional power draw (say, trying to use the floppy drive), will make the system flake out completely and not start back up for several minutes.  

I'll order the caps, it sounds like the logical place to start for now and after opening the power supply open one of the 10v 3300uF caps looks like the vent on the top is slightly expanding compared to the two next to it.

[chfriend]

I just found this power supply:
http://www.amazon.com/Solid-Gear-320-Watts-Supply-SDGR-FLEX320/dp/B00A8ZZXFE/ref=sr_1_1?s=electronics&ie=UTF8&qid=1409531109&sr=1-1&keywords=SDGR-FLEX320

With these specs
ATX Connector  20+4 pin, x1
                                                         P4-12V 4 pin single
                                                         Molex 4 pin  x2
                                                         SATA 15 pin x2
                                                         Floppy 4 pin x1

Dimension 3(1/8)"wx1(7/16)" tallx6"deep
                                                         
DC OUTPUT
                                       12V 17A
                                       +5V 14A
                                       -5V 0.1A
                                       -12v 0.3A
                                       3.3V 11A
                                       +5VSB                                                           2.0A

The original A3000 power supply has a rating of 17.25A +5v, .75A +5vusr, .75A +VID.  Will 14A of +5v be enough?

[chfriend]

I replaced all of the filter caps in the power supply yesterday and the 3000 appears to be working again, it fact, the Amber output is alot cleaner than is has even been since I got this machine.

However, I still do have a problem with my Cybergraphics 64 card occasionally producing a ghosted pink image.  Wiggling the card seems to fix this.  I'm thinking it's either a Buster problem (reseating Buster fixed it once) or a problem with the daughter card.

[danbeaver]

There may be just a wee, rare outside chance (perhaps one in a million) that when you "wiggle" the card it improves on a dirty contact in the card slot; I wouldn't go as far as saying that cleaning the card slot with a toothbrush and forced air along with cleaning the card contacts with an eraser followed by wiping with alcohol would help, but after changing the power supply and completely recapping the motherboard, you might give it a try.