Also, if I power on the machine with the probe on _INT3 most of time the screen remains white. More rarely it shows "Software failure" like in the attached picture.

That sounds suspicious.  Since _INT3 is actively driven by a low impedance output from U2, connecting a scope probe (typically 10M Ohm impedance) shouldn't make any difference.  Sounds a lot like _INT3 might be open-circuit/floating, but if you've confirmed continuity, then the problem may lay elsewhere.  It's also possible that some of the graphics operations use DMA modes, so perhaps pay attention to the DMAL signal.  That should have activity all of the time (groups of 4 x active high strobes), as generated by U3.

and removed Paula to check traces under the chip (some of them were "blacky") I putted all back and powered on the A600 with some ugly glitches on the half-down screen like in attached pictures.

I gather the A600 was originally working correctly (no graphics display issues) before you did anything.  And it was OK after replacing the capacitors?  But the problems appeared immediately after reworking U3/Paula?  If so, it's very likely that the fault is a direct result of an issue you've introduced; such as a solder short between two lines, intermittent/unsoldered joint, damaged PCB track/pad, etc.  As opposed to reverse engineering the system by forum posts to track down a potentially very complex issue, my suggestion would be to very carefully go over everything you've done (again), inspect the entire board for a stray blob of solder, etc.

I don't know what your rework process was (i.e. temperature control, etc), hence there could be a possibility that U3 has been damaged.  Though I'd be looking for a connection issue or short between lines to begin with.

I checked around Denise, there where some blacky traces but nothing so bad.
I checked the continuity from CPU/Angus/Paula for _INT3, IPL1-2-3 and they seems good.
I checked also the _INT3 with the oscilloscope and the active (low) signal is present just during bootup but rarely when the floppy animation runs. Most of when the floppy is "full out" and the screen looks good. In the rest of the time it is always high level. Also, if I power on the machine with the probe on _INT3 most of time the screen remains white. More rarely it shows "Software failure" like in the attached picture.
I forgot to mention before (just because I just reinserted the original Kickstart ROM to do checks) that after sometimes (randomly) the screen screws up, like in attached picture.

Thanks all.

These comprise of the full colour preview and excerpts of our Amiga Future issue 178 (January/February 2026) which can also be viewed online on the Amiga Future website.

Some of the interesting articles in this issue are:

Interview Bjørn "Dr. Awesome" Lynne
Show Report Amiga 40 Mönchengladbach
Beyound the Screen: Temple of Apshai
Knowledge 11: Chunky-Buffer
Special: 40 Years Amiga Part 5
Demoscene
Preview Software Manager
Review Freak Out
Review Phantom Leap
Review Hyper Sports Port
Review Callback
Review Yeet
Review AmiBrixx
Review AmigaOS 4.1 Update 3
Review FrameThrower
Review Retro-Printer

Of course there's actually so MUCH more in the magazine.

Needless to say you will often get other versions of software, some of which were commercially available, as well as some of the latest try-outs or freely released software applications and games for, hopefully, every Amiga variant of Operating system, so that's Amiga 'Classic', OS4, MorphOS, and AROS, including some PD software for these systems, all on the Readers' cover CD.

A detailed description of the varied content and excerpts of our current issue can be found at: https://www.amigafuture.de/app.php/kb/index?c=13

The Amiga Future magazine is available both as an English and German printed magazine - each issue is printed in FULL COLOUR - directly available from our magazine editorial office and from various other Amiga dealers.

Important Notice!

All our Amiga Future subscribers should check that both your current postal and email addresses for you are correct  that has been supplied by you to us.
The Amiga Future gets packed and shipped a few days prior to its actual release date. So, we need any change/correction to your address to be passed to us before we dispatch it, and in any case as soon as possible.
Bear in mind that: Usually requests to forward on mail will not be handled with such mail items, i.e. magazines!

We also ask that you check that your subscription fee(s) are current and up to date, i.e. already been paid, as some, in fact quite a few, subscription fees are still not currently fully paid.

Preview: https://www.amigafuture.de/app.php/kb/index?c=13
Orders: https://www.amigashop.org

http://25.amigafuture.de
https://www.amigafuture.de
http://www.apc-tcp.de

Anyone found a version Christmas Fire & Ice that doesn't have the music stutter?

Sometimes multi-layer ceramic capacitors can go resistive if they've been subject to physical stress (cracking) or contamination such as corrosion damage from capacitor electrolyte.  It's not uncommon for this kind of fault.  If the capacitor appears damaged/corroded or it there's any sign of heating, it should be replaced.

The valid clue here is that the 'insert disk' animation is getting screwed up.  The fact that the rest of the graphics mainly appear to be drawn OK suggest that the graphics output hardware (U4, U12, etc) is likely OK.

I'm not sure exactly how the disk animation works at the software level, but in hardware it relies on the level 3 interrupt (_INT3 on the schematic).  This is generated by U2/Agnus, which gets passed to the interrupt handler U3/Paula; presumably the software is relying on the interrupt to move the disk image data between different areas of memory to create the animation, not sure.  Based on the clues in the screen photo, something about this interrupt is broken.

While viewing the 'insert disk' screen, monitor what's happening with _INT3.  The line should be inactive all the time (high), and only strobes active (low) while the disk is 'moving', with an active duration of around 200nSec.  Make sure this signal is arriving at U3/Paula pin 20.  If that appears to be OK, there's possibly something broken with the interrupt priority level lines from U3/Paula and the 68000, so check continuity of the three IPL lines between U1 and U3.