exxos's Atari, Amiga & retro forum

I've had some strange graphics glitches running an optimised Blitter code running on my Atari 1040 STE with the original PSU. Interestingly the issue was mainly visible within the first hour after cold starting the machine. At first it wasn't noticable but got worse every minute. However, the problem settled down after about one hour runtime. Replacing the PSU fixed this fortunately. Any ideas what may have been the cause?

Video after about five minutes (original PSU):


Video with the new PSU:


Edit: program added

Bad caps in the PSU. There are a whole bunch of mandatory fixes for various machines listed .. https://www.exxosforum.co.uk/forum/viewt ... =17&t=1585

Cool demo BTW!

exxos wrote: 13 Jul 2020 14:13 Bad caps in the PSU. There are a whole bunch of mandatory fixes for various machines listed .. https://www.exxosforum.co.uk/forum/viewt ... =17&t=1585

Thanks for the link.

The old PSU looks quite ok but I guess that's not important to know that after 30 years the PSU caps need to be replaced, right? ;)

sascha.springer wrote: 13 Jul 2020 14:26 The old PSU looks quite ok but I guess that's not important to know that after 30 years the PSU caps need to be replaced, right? ;)

Probably strange wording: I meant that you have to replace your PSU for sure after 30 years even when the caps look ok!?

Well, I have to add that the issue is not visible while using the Blitter in a regular way so I have had no problems with games or demos which are using the Blitter.

The caps dry out over time, which changes the way they work, so instead of a nice smooth voltage output you'll be getting something very different.

So its definitely a good idea to change them and also relatively cheap and easy.

I think @PhilC is suggesting that you just change the caps in the PSU, you don't need to change the whole PSU.

There are kits in the store for several different ST PSU types but if you have a different PSU version from these I'm sure someone on the forum will be able to confirm what components need to be changed.

I can vouch from personal experience how strange & inconsistent the system can be when the PSU starts to fail...unless you were to change the PSU and keep everything else the same you'd almost never expect the fault to be with the power supply alone.

It can also be the start of a gradual degradation of the PSU performance, so it will potentially begin to show more symptoms the longer you leave it.

Probably the program can be used to check if you have issues with your Atari STE as well so I've attached the program. ;)

sascha.springer wrote: 14 Jul 2020 11:14 Probably the program can be used to check if you have issues with your Atari STE as well so I've attached the program. ;)

Awesome, next time I have a STE on the bench I will leave that running!

sascha.springer wrote: 14 Jul 2020 11:14 Probably the program can be used to check if you have issues with your Atari STE as well so I've attached the program. ;)

@sascha.springer Thanks for that...though in my case the problem system is my original 1040STF from 1987...and the PSU that allowed it to work just fine was borrowed from one of mt STEs... :lol:

The STF worked ok with the original supply...but would then fail to boot if i plugged a dongle into the cartridge port (Notator or Cubase)...until I swapped the PSU & then it booted & ran the programs just fine. :roll:

Since then, the video output from the STF has started to show more noise (with the original PSU) and again is much less evident with the PSU from the STE so I have the recap kit ready to use.

that really strange bad PSU has so visibie impact on the BLiTTER