Help with picoatx on amiga1200 board: the screen goes on and off

[mechy]

It sounds like you may have a bad connection(intermittent) in the power cables, or indeed the 5v rail on the pico psu is not strong enough.  i assume the outside source has the recommended voltage-Does it need to be higher than 12v? to feed it?
Don't go by overall wattage, that assumes all power combined with a certain efficiency(usually something like 70-80%) and doesn't really mean a whole lot.
the amperage output on +5v will be more meaningful.

[mechy]

Thanks for the reply:

Checked the cable...so far no short circuit; tried with the impedance of the cable, and it won't fluctuate, as sign that the copper inside the cable does not have interruptions.

The outside power source is rated 10A (9.79 effective); the pico should use it at 75% probably, so let's say that it should not have problems with anything below 60W. The Amiga with accelerator should use about 15-20W.
Altho I have no way to check for efficiency and quality of the external brick...so can't exclude that it is the problem (I need a different brick and see what happens)

The pico has 2 models, which uses 19V (red connector) and 12V; I have the 12V version (yellow connector); so I think that I am using the correct voltage.

The 5V output ( the ATX connector has 4-5 5V rail, plus the one used to power the peripherals) seems to be around 4.84A, recorded at the ATX connector. Someone said to put together all the 5V rails, except the 5VSB, which output max 1A and must not be used...It may make sense to connect them all to use more power, but the Amiga requires very little current, right?
I don't have the exact requirements for the 5V rail on the amiga; I need to check the original PSU, but is hard to believe that it needs more than 5A.

Strange thou that nobody that uses it has mentioned to put together all the 5V rails...but I suspect that the issue is like you mentioned, an incorrect current on the 5V rail >_<

You are best making 12v from higher voltage(19v) more than likely but alas,you say you don't have that version...I have to guess the 12v version is a buck/boost style. This is purely a guess mind you w/o knowing exact specs of the pico psu. If it does have separate 5v rails they may be right to get enough wattage the +5 rails need to be connected together-again not sure without knowing the whole deal.
In any case 4.84v is very low. i have seen odd behaviour on amigas with under 4.92v. need to find out why/where the loss is-its likely a problem.
the original 5v psu for the A500 is 4.5 amps on the 5v which is usually ok with a accelerator,so probably 25-30w depending on efficiency on the 5v rail easily.. with other expansions more.
Check the external psu for 5v first under full load,if its ok, then you have to suspect the pico psu next. just work your way down the line.

[mechy]

Ignore the 19v remark, its what left over from a badly edited message late at night

I cant believe i misread amps for volts.. i should pay closer attention.

Ok reading the docs,for the 120W pico psu from your link. the max power from the 5v rail is 6amps(with a peak of . Peak is just what they mean  by surge.  With the 1200,accelerator and hdmi converter(assuming it really does pull 1 amp) you are possibly maxed out.


some thoughts:

The hdmi converter is putting you over the top slightly. try running w/o it and see if all is ok. maybe use composite or rgb.

some power supplies share the 3.3/5v rail and need a dummy load on 3.3v to regulate properly. doubtful the case here but the docs do not say its shared or not.

The docs say it will hit overload protection and shutdown at 13 to 13.5v input.. check the 12V psu coming in under load and make sure it doesn't hit 13v+

the docs say:
"At max load, forced air ventilation is required. For fanless operation de-rate the output of the 3.3
and 5V rails by ~20%. Peak load should not exceed 60 seconds."

so, if we de-rate it(i assume you aren't fan cooling it),then you lose 1.2amps of power.. that leaves you with 3.8amps on 5v fanless-less than the stock 500 psu.
There lies the trouble i bet.

I think its a case of you being dangerously close to the max this psu can do. Its not uncommon to find stuff that doesn't match/meet spec exactly, and its never a good idea running a psu at max capacity.  The derating for no fan is likely the problem.

Mech