A3000D mATX Picasso II black screen problem

[Brosol]

I bought a Seasonic SFX 250W MicroATX power supply

http://cgi.ebay.ca/Seasonic-SFX-250W...82146562211063

and a atx to A3000D adapter cable from amigamaniac

I tested the setup and it worked fine with native Amiga graphics modes. I got distracted and didn't do testing with Picasso II installed. I didn't think there would be any problems so I forged ahead to mod the mATX PSU to fit inside the original A3000 PSU case.

Everything seem to work OK until I tested the Picasso II. All Picasso II screen modes show up as black. I could hear the relay switch modes and the PII shows up in SysInfo/Scout, tried different monitors but still a black screen. (Yes I made sure to set jumper J350 to 2-3)

So undid the mods and connected the old PSU back, J350 to 1-2 and tested again with the PII working again.

So is there a problem getting mATX PSU to work properly with A3000 & Picasso II....other Zorro cards? It seems OK with native GFX modes but I want to use my PII.

Anybody successful in getting such a setup working?

Thanks

[coze]

I wonder if it has something to do with the -5v missing on the ATX PSU.

[vk3heg]

The psu doesn't list -5 volts on the spec label.
The wiring loom also looks like it's missing the (normally) white psu cable lead for -5v.

Pin 18 on atx psu's is the -5 volts line, a lot of "newer" atx psu's dont have this line.


http://www.ianstedman.co.uk/Amiga/am...SU_to_an_A3000

[Brosol]

I will keep the atx adapter cable for now and will look for that -5V line feature the next time I try to do a ATX mod. Pity it fit perfectly inside the old A3000 PSU case using the original AC socket and push button switch. It looked good.

It would be nice if Amiga shops like AmiKit or Veselia had some A3000D PSU replacements or compatible mATX PSU for modding.

Thanks

[vk3heg]

Just keep on searching, they do exist, as I have one in my A4000.

(I didn't keep the org. psu housing though)

Hey Brosol!

You happened to purchase the PSU out of our eBay store.

Sorry to hear about the -5V requirement; if I had known the application I would have been able to warn you about the potential issue for modification.

Do you happen to know the -5V current draw? Would it be possible to strap an LM7905 to the -12V line and give yourself the necessary voltage? Although there may be other concerns over using a linear regulator, the real dilemma is probably that the -12V is only 800mA to begin with.

We have an inverting DC converter which could be an alternative solution; both should be small enough to mount inside the sidewall of the PSU (which could serve dual purpose as a heatsink).

It may just be easier to grab another mATX PSU, but given as this one seems to fit perfectly...

Jeff
Noodlehed Electronics

[rkauer]

Negative rails in any power supply is very weak, they are used only for voltage reference.

A LM7905 or even a small LM79C05 will suffice, even without heatsink attached.

[Brosol]

vk3heg, I wanted to use the original A3K PSU case because of size constraints. Also if possible I wanted to avoid cutting up the A3K case to fit a ATX PSU. The A3000 is my baby and I wanted to keep her good looks.

rkauer....LM7905? I must admit I don't know enough electronics to add such a mod to mATX to supply the -5V voltage line. I basically just tinker and assemble stuff....I would need easy to follow, with pictures tutorial to do such a mod.

noodlehed....Yes I should have mention the application. I just didn't know there would be issues. I don't know the current draw....I'm guessing it would be the same as A4000 setup with a graphics card.

I found to my delight that by turning the Seasonic mATX pcb sideways it fits and aligned with the pcb mount screw holes of the A3000 PSU case. I also replaced the old PSU fan with a blue LED fan ....it looked cool.

If you offer a compatible a ATX PSU with the same or smaller pcb dimensions and watts...or parts & instructions tutorial on how to mod the Seasonic that would be great.

[rkauer]

Look for a mini-ATX PSU with 200W or more and do the LM79L05 hack on the -12V line (use it to feed the negative voltage regulator).

Seek for the 7905 datasheet on the internet will show you how you can hook one to the A3000 hacked PSU.

rkauer stated that the -12v and -5v lines are used as voltage references in which case any LM7905 should do the trick. use -12v line as your input, tie the grounds together, add your 2 capacitors and you should be fine.

If you have trouble finding a schematic try googling LM78xx, the hookup is the same except your input is the negative supply rail. Good luck!

Did someone build this? I need to replace my A3k PSU and it's very hard to find a new ATX PSU with -5V

[Brosol]

I am now using a DURO 400W ATX power supply PCB inside the A3000 PSU case. It has -5V line that my Picasso II needed to function correctly.

http://cgi.ebay.ca/Duro-400W-Power-S...item2c53277dcc

You might find something cheap at a pc recyling depot, swap meets, local garage/yard sales from people getting rid of their old pc junk. Bring a multimeter to test.

[rkauer]

Or just use a negative regulator as the 79L05 (needs to be the "L" version) and hook it to the -12V line: presto! A -5V regulated signal line.