Issues with an exxos PSU

[gigi92]

I have a issues with an exxos power supply.
It works well on my STF.
I just installed it on an STE and : to turn on the computer I have to press the reset button after putting the button on on.
Also there is probably a capacitor that whistles towards the power supply
It stops whistling for example if I launch a game or under memtest..... :shock:
With the original allimenation all works perfectly and no whistling.
Anyone have an idea?

[JezC]

Hi,

The reset issue probably means that the capacitors in the reset circuit need to be replaced on the motherboard.

There are suitable replacements in the Exxos store.

The whistling is probably one of the inductors on the power supply - maybe @exxos can confirm but I had something similar and pressing on the inductors with a finger located which one was the source of the noise...

I think it ended up being a matter of a slight tweak on the inductor to sort it (but the load on the power supply changing can also help as you have found).

[Steve]

Please see this thread for the reset capacitor fix: viewtopic.php?f=17&t=2175

[gigi92]

Please see this thread for the reset capacitor fix: viewtopic.php?f=17&t=2175

i will do but why i have not this issues witch origin PSU ?

[JezC]

i will do but why i have not this issues witch origin PSU ?

Without going too deep into the electronics involved in this, it's a lot to do with voltage levels and the rise time for the supply voltage...not to mention that the original Atari design was a bit marginal even when everything was new, so add 30+ years and it's more of a surprise that it still works with any PSU.

[exxos]

As others have said. The PSUs have a slower ramp up time over the original.. I prefer not to slap 10amps as fast as possible into a 30+ year old circuit. Plus if the reset caps were proper value then they wouldn't be an issue. A lot of STEs even with the stock PSU fail to boot even with the original caps. It's why it's in the mandatory fixes as it's a well known issue.

[gigi92]

it's okay I placed the order, (my card also has 74S257 that I'm going to change for the 32Mhz booster).

Do you think that all this will also solve the whistling?