Side expansion does not boot when taking power from A500

[Sim085]

I have an A590 configured to take power from the A500. I had this connected to one unit and it works fine, it works both when I have an SCSI HDD connected and also when I have a CF card connected.

I have tried to connect the A590 to another A500 I have. But with this unit, the hard disk does not want to start. Sometimes it starts but then stops. Never managed to boot.

In both units I am using Kickstart 3.1 and I have tried with both bottom expansion board connected and without.

Also I am using the same Power Supply with both units.

Everything works fine with the second unit, If I use an internal expansion with CF card it boots from this ok. I have another external hard disk (GrandSlam) that is configured to take power from another power supply and again the second unit boots ok from this when I use a second power supply to boot the external hard disk.

Therefore it seems like, while the first A500 is able to provide enough juice to the external hard disk from the side expansion port, the second one is unable to do this, even though in both cases I am using the same power supply, not using any bottom expansion ports, and using same kickstart.

Anyone knows what the issue might be?

[derSammler]

Different revisions of the A500 draw different amount of current. The second one may need more and the PSU can not deliver enough for it and the A590.

[Sim085]

Both have rev8 motherboards, the A500+ one (not the A500 one that came with some unit). This is why I am so confused, the motherboards are identical. The motherboard from which the A590 cannot boot does not even have any battery leak.

Originally Posted by derSammler

Different revisions of the A500 draw different amount of current. The second one may need more and the PSU can not deliver enough for it and the A590.

[Sim085]

Just wanted to add that this is the power supply I am using...
https://uk.rs-online.com/web/p/switc...pplies/6447219

[Sim085]

I used some isopropyl alcohol to clean up the side connector of the second A500+ motherboard. It did not look dirty but I thought it would not hurt.

Now... if the HDD in the side expansion unit is a CF card then it boots ok, but if I change the HDD to a mechanical one it will first show me the Kickstart Insert Floppy Disk screen, and then, after I do a couple of restarts (CTRL+A+A) it boots. It consistently keeps doing this behavior.

The other A500+ boots normally regardless if using the CF or the mechanical HDD.

[derSammler]

Originally Posted by Sim085

Just wanted to add that this is the power supply I am using...
https://uk.rs-online.com/web/p/switc...pplies/6447219

That seems very underpowered to me. 2A on 5V, 4A on 12V, and 500mA on -12V. I would highly recommend getting something that has at least 4.5A on 5V like the later original A500 PSUs have.

//edit: seems like the specs are different depending on where you look. It says 50W on the website, but 60W in the PDF, and there it says 4A on 5V and 2A on 12V. But even 4A is still too low and does not reach what the later A500 PSU delivered (which was a must when setting the A590 to internal power).

Both have rev8 motherboards, the A500+ one (not the A500 one that came with some unit).

Even then, different chips inside may result in 100mA more or less, which, based on that underpowered PSU, can make a big difference.

[Sim085]

Looks like you are right! Have an old A500 Power Supply and using that one the A500 booted from the mechanical hard disk on first attempt!

I will use the original A500 power supply until I get a new modern one.

So 4.5A on the 5V line.
What should be the amps on the 12V and -12V lines?

Originally Posted by derSammler

That seems very underpowered to me. 2A on 5V, 4A on 12V, and 500mA on -12V. I would highly recommend getting something that has at least 4.5A on 5V like the later original A500 PSUs have.
//edit: seems like the specs are different depending on where you look. It says 50W on the website, but 60W in the PDF, and there it says 4A on 5V and 2A on 12V. But even 4A is still too low and does not reach what the later A500 PSU delivered (which was a must when setting the A590 to internal power).


Even then, different chips inside may result in 100mA more or less, which, based on that underpowered PSU, can make a big difference.

[Sim085]

Ok found this guide here: http://www.ianstedman.co.uk/amiga-power-supply-guide/

It says:

+5V : 4.5A
+12V : 1.0A (edited: copy error from my side, wrote -5V instead of +12V, thanks Jope for pointing it out )
-12V : 0.1A

Originally Posted by Sim085

So 4.5A on the 5V line.
What should be the amps on the 12V and -12V lines?

[Jope]

You should have +5, +12, -12.

There is a table near the top of the page, this line is interesting to us:

Type			Part number	+5V current	+12V current	-12V current	Combined power rating
A500 type 2**		312503-03	4.5A		1.0A		0.1A		35.7W

Any replacement PSU should have at least this much. +5 is the most important rail in an Amiga, +12 is used mainly for spinning motors and secondarily as a reference voltage. -12 is only used as a reference voltage.