micro-ATX PSU and A4000D

[bigwall68]

I am sure this question has been asked a ton, so apologies up front.

Just got my hands on my dream amiga, a 4000(rev B), and looking to replace the original PSU.  

I see the adapter to purchase however what watts/volts/amps etc should i be looking for to replace it?

Thank you - Craig

[Pat the Cat]

Depends how many other cards you plan to add to the A4000.

If none, it's not an issue, but.. PPC accelerator, least 300W on the 5V rail. In my opinion. A good 100W safety margin. 040s are most power draw, so if you got 040 PPC, that is greediest combo. 060s and 030s don't need so much.

You can't go wrong fitting bigger watt capacities, so long as they will fit physically.

After accelerators, 24 bit GFX cards larger power draw than most. Video cards generally. Upto 60W per board is a good rule of thumb.

Normal Zorro expansions, whether 16 bit Zorro 2, or 32 bit Zorro 3, usually not an issue with all slots filled. That's what the original PSU was designed for, really.

Bridgeboards are same class, but if you got old ISA cards too, they can draw quite a bit. Maybe 30W per card.

[bigwall68]

Thank you.  What about output amps and volts?

[Pat the Cat]

Compare the new with the old. If values or bigger, not a problem. The tricky part is finding high capacity in that PSU size.

If you fit more W than is needed, it isn't a problem. If less or just the same Watts, can be issue.

Check all rails, some are not used on Amiga. So not important. Import one is +12V and +5V (+12V is used by drives as well, some drives are greedy here). -5V and -12V much less important, they are for things like serial port compatibility.

+5V is the crucial one, and like I said, you can fit more and greedier expansions than CBM thought was ever going to happen.

One thing that can cause an issue is the timer circuit. This came in as part of the PSU wiring. Big box Amigas can bypass with jumpers on the mainboard to set Powerline tick or NTSC/Pal tick. You don't have to have the signals coming in through the power connections, but if they don't, you have to set a jumper or two to get the board booting properly.

I  hope you get some good usage of that A4000. I never owned one, I  thought they were bit ahead of their time, like A3000, only more so. I did own an A3000 for a few years, and somebody else blew up the PSU one day while programming a Pacman clone in AMOS (he was a Pacman fanatic from childhood).

The gentleman sourced everything, did all the work, I just had to figure out the jumpers to get it booting nicely and the matter was resolved. We never did discover the exact cause of PSU failure. Probably old age, or vibration caused by excessive thrash metal music and similar. The main voltage regulators were shot to bits internally, all connections were fine. Just stock 25MHz A3000, no cards in it.