Amiga 1200 freezing

[Nebulizer32]

Last Christmas, after being hidden away for 26 years at my parents place, I got my old Amiga 1200 back. With an old composite cable connected to the TV, I started it up. To my surprise, it still worked. It still booted from the hard drive to Workbench. Suddenly I was taken back to 1994, when I was 15 years old. All the files that I had worked with then, were still there. Text files with letters to friends that we exchanged via disk, notes for school work. Logs from BBS sessions. I looked through several demos and diskmags, which I have not seen in years. I continued playing on a quarter-century old saved game session of Settlers. My image collection of Erika Eleniak was still there. But after a while, the machine froze completely. It was a recurring problem. After anywhere from one minute to an hour, the machine stopped completely. I thought it was because the machine needed to be recapped. I therefore sent it in to get it fixed. At the same time, I bought some upgrades. Indivision flickerfixer, 8 MB memory upgrade, CF card IDE disk.

Now that I have got it back from recapping, I have tried to get the machine set up again. But I still struggle with the machine freezing. I think there might be something wrong with the hardware. When I start the machine and double-click on the workbench icon, the machine freezes completely. The mouse pointer is frozen and the floppy disk drive stops clicking. This happens maybe 3 out of 4 times, otherwise it works fine. A very few times, the machine has unfrozen after a couple of seconds. When using the CLI, starting prgrams from the disk always works fine. I have seen on this forum that others have had similar problems, without finding a solution.

I can work in Dopus without the machine crashing. Some demos and games also work just fine without anything happening. I even managed to play Settlers for an hour and a half without the machine crashing. But usualy, when I run a game or demo, the machine stops completely after a few seconds. When that happens, soft reset does not help. The machine must be completely shut down for half a minute before it will start again.

I downloaded the "Amiga Test Kit" to see if it could diagnose what is wrong. But I struggle with that program crashing as well. I was hoping it could be the old hard drive that was causing problems. Therefore, I disconnected all of the external components from the computer. I removed the hard drive, memory expansion, flicker fixer, and started the Test kit from disk. What happens then, is that I can sometimes run all the tests without anything being reported wrong. But most of the time, the program crashes at a random point when I press any function key to start a test. This happens seemingly to all tests in the test kit. When I then restart the machine, the app will then crash when loading. Could the cause be that some of the chips are broken? I reckon that it is the same reason that Test-kit is crashing that causes the machine to crash in the other occations? The errors I get in the test kit, all has the same error code: "Exception # 1a (26: Level 2 IRQ)". Also the SSP value is always 0003fffe in the stack dump. The other values seems to be different for each crash.

Example of error message from "Amiga Test Kit":

Amiga Test Kit v1.16 (build: Nov 26 2020 10:54:18)

Exception #1a (26: Level 2 IRQ) at PC 00002796:
    d0: 000f72b8 d1: 00000031 d2: 0003fa0e d3: 0003fac4
    d4: 00000000 d5: 00000000 d6: 00007aea d7: 00000000
    a0: 0003fa84 a1: 0003falc a2: 00000139 a3: 0000217c
    a4: 0000846a a5: 000009d0 a6: 0003fa74 a7: 0003f9bc
    sr: 0004 ssp: 0003fffe usp: 0003f9bc

Stack Trace:
0003f9bc: 0000 0030 0000 0007 0000 7bd4 0000 bb4a
0003f9cc: 0000 7aea 0000 0000 0000 09d0 0000 82a4
0003f9dc: 0000 846a 0003 fbb0 0003 fbaa ffff ff0e
0003f9ec: 0001 41bc 0003 fa70 0003 0000 0000 Faab
0003f9fc: 0003 002c 0003 falc 0003 fa84 070a 0003
0003fa0c: fa24 0002 0003 fac4 2e87 2e78 0040 0031

Anyone who can help me further? Does the "26: Level 2 IRQ" indicate that some specific chip is broken and needs to be replaced?

[modrobert]

In order to find the problem by process of elimination, does it work without freezing if you remove the 8MB memory upgrade (RAM card)?

Originally Posted by Nebulizer32

My image collection of Erika Eleniak was still there.

This is awesome.

[Nebulizer32]

Unfortunately, the machine also crashes when I disconnect the memory extension. I run the Amiga Test Kit from a floppy disk that I created with the adf image. Only the floppy disk drive and the keyboard is connected to the main board.

It might seem that the machine is actually a bit more stable when I have connected the memory expansion. I do not know if it's just my imagination, but it feels like the time between the freezes is a bit longer with the memorycard installed.

I have ordered a new power supply, but I'm not particularly optimistic that it will help with the problem.

[Nebulizer32]

I have tried to find the source of the seemingly random "Level 2 Interrupt", as reported by the Amiga Test Kit. Based on the Amiga OS documentation, there are 7 levels of interrupts. Level 2 is raised from "External Int2 & CIAA". The documentation says that "The 8520s (also called CIAs) are Amiga peripheral interface adapter chips that generate the INT2 and INT6 interrupts".

I found an "Interrupt Signals map for A1200 rev 2B", where "Odd CIA U7" is marked with INT2, together with "Expansion P1". Since I dont have any expansions connected, is it plausible that it is the U7 chip that is broken?

Or could it be something other, related to timing issues on the main card? My card is rev 2B, manufactured by Commodore, bought in March 1994. I have checked if the E123C and E125C resistors are present, and they are not.