Clueless about A500 problem

[zonaps2]

Hi,
I have this A500 rev6A (512k + 512k trap door, 1.3KS) that I've recently discovered has some issues.
The machine runs fine most of the games/programs, but it "hangs" on a couple of programs.
It doesn't give any guru meditation error, it doesn't reboot, it just freezes, for example in SYSINFO (see attachments).

I've discovered a similar behavior on FA18-Interceptor. The game loads fine, but it makes a HUGE PAUSE on  the "SELECT YOUR FLIGHT LOCATION" screen.
Eventually the game starts, and I say eventually because it takes like 20 min and it has a frame rate of about 1 frame per minute (Yeah, that slow!).

Also the machine is still responsive (VERY slow), if I press F1 the selection screen reboots.

On SYSINFO the disk activity led stays on forever and the mouse locks, on Interceptor there's no disk activity.

I've tried removing the 512k trapdoor with the same result.
I've tried different floppies.
I've tried even loading from a gotek.
I've tried different versions of Interceptor (I have the original disk, but I've tried other cracked adf's as well just in case.
I've tried switching PAL/NTSC modes

The problem persist.
I've tried re seating the custom chips with no luck.
Could this be a chip RAM issue?

I'm clueless about this, some help narrowing down the problem would be very much appreciated!
Thanks in advance.

[Castellen]

Eventually the game starts, and I say eventually because it takes like 20 min and it has a frame rate of about 1 frame per minute

Sounds symptomatic of a hardware timer problem, and this function is performed in both CIAs.  Try exchanging U7 and U8 (they're the same part, both 8520) and see if you notice any change in system operation.  If so, you'll need to work out which 8520 has the problem and replace it.

Also check timer input signals into the 8520s.  U7 pin 19 should have either 50/60Hz depending if it's PAL/NTSC.  U8 pin 19 should be about 15kHz.

[zonaps2]

Well, I've swapped the CIA's, now I have a gray screen, machine doesn't boot anymore.
I swapped the CIA's again to their original position and the gray screen keeps showing.

After seeing this I removed both CIA sockets and placed new ones, the gray screen keeps showing.

So, is it possible that after swapping the CIA's some other chip got damaged because of a bad CIA?

[Castellen]

Well, I've swapped the CIA's, now I have a gray screen, machine doesn't boot anymore.

That (or usually stuck on the white screen) can happen when one of the the hardware timers in U7 isn't working.  But can be caused by various other things too.

I swapped the CIA's again to their original position and the gray screen keeps showing.

There's possibly some intermittent problem that has been introduced when flexing the main board.  The most common intermittent issue is with IC socket contacts.  Try removing then re-inserting all of the socketed dual in-line ICs which is often an easy fix.  See if you have any change.

Failing that, the hardware should be working enough to run one of the debugging tools available, John Hurtell's DiagROM would be useful at that point.  You'll need a copy of it in a physical ROM.

There's nothing definitive yet to say if you have a failed CIA or not.

[zonaps2]

Thank you Castellen for your guidance, I've ordered a couple of CIA's.
Both CIA sockets were replaced. Also I've ordered an Agnus socket, it looks rusty.
Also I've re inserted all the socketed IC.

That DiagROM looks very useful!, I don't have an eprom burner, I've just emailed the guy, maybe e can sell me a programmed one.

Thanks!

[zonaps2]

Upon replacing both CIA's with new chips the machine is working great again.
Thanks Castellen for your help!