need help my A4000 won't start with new A4000 ATX PSU adapter

[Darin]

So wanting to replace my old and trusty original A4000 PSU with A4000 ATX PSU power adapter I purchased a micro-ATX psu that fits nicely into the A4000 PSU chasis BUT....

1-tried connecting micro-ATX and nothing..PSU not starting at all nor A4000 so tried another full size ATX PSU and same thing
2- contacted Amigakit and they told me it was some 'sense' thing with newer PSU's but I had my suspicions
3- tried starting the PSU without connecting to A4000 and voila PSU started up no problem with following voltage readings:
 
Grey -+5.21v
Blue--11.32v
Yellow-+ 12.14v
Red-+5.23v
4- let Amigakit know and they said these readings were fine and adapter was working ok but offered no help as to why it wasn't powering on my A4000

So long story over I turn this mystery over to my fellow amigans and hopefully I'm not the only one in the world this has happened too?&^! :-D  :-P ..how come this kinda luck never happens when I buy a lottery ticket  ;-)  :roll:

Some new ATX PSU's do have the feature where they won't start if there is no current draw on the correct line, the sense line.  But I don't think this is the problem you're running into.  Does your A4000 still start up with the old PSU?  The voltage you're getting on the blue wire does seem a little low.  A problem some people run into is that some ATX PSU's don't allow for the enough current draw and will shutdown if there is more current draw than the PSU wants.  Older machines, Amiga's included, do require more current than some new ATX PSU will provide.

[Darin]

Interesting as I had the same thing happen when I used one of their adaptors on my A3000.  Unfortunately, not only did it not work, but now when I plug in the OLD working original adaptor my 3000 will not boot with that one either.
Dead in the water and I don't know why. (And yes it worked just fine until I tried the adaptor.)

So not sure if the adaptor was the issue or the power supply I tried but one of the 2 appears to have blown my 3000 and I am quite sad...

 

You cannot use the AmigaKit adapter with a modern ATX power supply on an A3000, it won't work.  Modern ATX power supplies do not provide the -5V line that the A3000 requires, and the don't provide the tick signal (though the jumper can be changed to use the internal vsync instead).   I had this confirmed from AmigaKit when I was looking to replace the PSU in one of my A3000's.  I couldn't source a good ATX PSU with the -5V line so I just went with Ian Stedman's ATX adapter, which has been working fine for quite a while now.

Hopefully someone didn't think they could interchange a +5V line for the missing -5V line on the adapter.

[Darin]

http://ianstedman.co.uk/Amiga/amiga_hacks/Amiga_Power_supplies/amiga_power_supplies.html#ATXPSU

Has good info on power supplies.

My A4000 with original PS has a tick signal out. I do not know if J104 selects this as external cpu signal or not.
I would check this jumper to see if it is set to internal.

The A4000 PSU doesn't provide a tick signal like with the A2000 and A3000.  The power connector has 6 pins, +5V, -12V, +12V, Power Good, and 2 GND's. 

J104 is the CPU clock source.  This has to be set properly if you have an accelerator card in the CPU slot.

[Darin]

Interesting as I had the same thing happen when I used one of their adaptors on my A3000.  Unfortunately, not only did it not work, but now when I plug in the OLD working original adaptor my 3000 will not boot with that one either.
Dead in the water and I don't know why. (And yes it worked just fine until I tried the adaptor.)

So not sure if the adaptor was the issue or the power supply I tried but one of the 2 appears to have blown my 3000 and I am quite sad...

 

You cannot use the AmigaKit adapter with a modern ATX power supply on an A3000, it won't work.  Modern ATX power supplies do not provide the -5V line that the A3000 requires, and the don't provide the tick signal (though the jumper can be changed to use the internal vsync instead).   I had this confirmed from AmigaKit when I was looking to replace the PSU in one of my A3000's.  I couldn't source a good ATX PSU with the -5V line so I just went with Ian Stedman's ATX adapter, which has been working fine for quite a while now.

Hopefully someone didn't think they could interchange a +5V line for the missing -5V line on the adapter.

That is interesting as it was a power adaptor specifically labeled for the 3000..  (Or I wouldn't have bought it)
Here is the link to the Amigakit listing: http://amigakit.amiga.store/product_info.php?products_id=1164

Yes, I know, I have the same adapter here that I bought from AmigaKit.  It's specific in that the motherboard connector is for the 3000.  When I was confirming the voltage outputs on the connector before I plugged it in, I noticed there was no connection for the -5v pin. I emailed AmigaKit and they confirmed to me that 1) -5v is required and 2) modern ATX power supplies no longer include the -5v line and I should try to find an older ATX power supply that did include the -5v line.  I did find some old ATX power supplies that did have the -5v line from the late 90's and early 2000's, but most of the voltages weren't in spec any longer.  If you check the pin out for an ATX connector to the lines on the connector on your power supply, you'll notice there is no line for where the -5v pin should be. 

[Darin]

As a general good suggestion that was passed down to me.  Always, always test the voltages on the motherboard power connector before plugging it in to your Amiga to make sure the right voltages are on the right pin.

[Darin]

Yeah, it would be nice if they added to the product page something that says an ATX power supply with a -5V line is needed.   Internally the ATX power supplies have the -5V available, they just don't run the line to the connector any longer as PC motherboards don't use -5V.

A couple things I would try.  Test the pin voltages on the adapter to see what ones match the A3000 power spec by comparing to the original A3000 power supply connector voltages.  Especially what comes out of the -5V pin on the adpater. 

Amiga pin # Description
1                  +VID (this should be +5V)
2                  +5V
3                  +5V
4                  +5V
5                  No connect (or IIRC the A3000 PSU has +5V here, at least it was on mine)
6                  Gnd
7                  Gnd
8                  Gnd
9                  Gnd
10                Gnd
11                -5V
12                +5V_USER
13                TICK
14                -12V
15                +12V

[Darin]

yup mine thankfully still starts up with original PSU

Oh, that's good!   I would try to find an ATX power supply where the blue line for -12V is more in the range of -11.8V to -12.2V.  The -11.32V your getting there may be too low for your A4000.

[Darin]

* -5V is not needed on the Amiga
* always test voltages with a dummy load applied - you can't assume the voltages of an unloaded supply are 'in spec'

Also check the 3.3V Sense wire - apply a dummy load the 3.3V line and also connect it to the Sense wire - more info here: https://reprap.org/wiki/PC_Power_Supply#Voltage_Sensing

I'll disagree on the -5v being needed, as -5v runs though the video slot, the Zorro slots, and the RGB connector. 

I will agree that it is best to test the voltages with a PSU under load.

[Darin]

I should have been more specific.  It's not needed to be supplied by the PSU to the A4000.  If you tell him he needs -5V from his ATX PSU that is wrong.

-5V on the A4000 is generated from -12V on the motherboard.  So it is not needed to be supplied by the ATX PSU he has.

Ah!!  Yeah, there are two topics in this thread...  One is on the A4000 PSU replacement, which yeah totally, the A4000 PSU doesn't supply -5v.  Which makes it much easier to use an ATX PSU with an A4000 as long as the PSU can supply enough current for the A4000.

The other topic that was brought up was an A3000 ATX PSU adapter and how modern ATX PSUs don't supply the -5v that the A3000 needs.  My previous comment was directed at the A3000 and it having -5v from the PSU.