Atari ST520FM Boot problem.

[Stana]

Hi guy's. I need a bit of help. My st on power up accesses the disk and then bombs out with 8 bombs before gettingbto the desktop. This is a privilage violation. I suspect it's a tos error or bad rom chip. Can anyone confirm this or is there another reason why it would bomb out whilst booting? I have searched this forum but not found a solution to the 8 bombs.
Any help greatly appreciated.

[stephen_usher]

What version of TOS is your machine running and do you have a floppy disk in the drive?

If you have a disk in the drive try powering on without one.

[Stana]

The TOS version is 1.02. I tried with both disk in and out. The drive accesses the disk then gives 8 bombs. I would like to confirm that it is the rom before buying a new set. I am awaiting a diagnostic cartridge to see if that sheds light on the fault.

[stephen_usher]

From first look at the symptoms it's more likely to be either RAM or your custom chips need reseating in their sockets and the sockets cleaning with contact cleaner, more probably the latter.

[Stana]

I have cleaned and reseated all the socketed chips several times. It did boot up and I used YAART to test the ram. it was on for about 2 hours then crashed. When rebooted it went to a black screen with a white border and no disk activity. I then took the chips back out cleaned and refitted. It now accsses the disk but crashes with 8 bombs. Will the diagnostic cartridge boot up or will it not work if the desktop does not come up?

[stephen_usher]

The diagnostic cartridge only needs about 16 bytes at the beginning of the ROM, the CPU, the MMU and serial chip to start up and give information over the serial port. More needs to work for the video to display, but as you're video is usually being initialised it should be able to give you on-screen info.

Given that cleaning and reseating changed the symptoms I'd definitely say that it's bad sockets.

[Stana]

I will give them another go tomorrow. Hopefully the cartridge comes and might have more news.

[stephen_usher]

It may be a good idea to tweak the socket pins slightly to give them a stronger contact and run a fibre glass pen over the chip contacts.

[Stana]

Hi. The diagnostic cartridge came today and found my problem. On testing the roms it found H0 and H2 have checksum errors. Sonew rom ordered from the shop. Hopefully that sorts it.
Thanks all for the help.

[rubber_jonnie]

The diag cart often shows checksum errors for ROMs and it doesn't necessarily indicate they are faulty, but an upgrade to TOS 1.04 is generally a good thing, and I'm presuming that is what you've ordered.

TBH I've fixed a lot of machines and the only machines I've had with a ROM that were genuinely faulty were an Acorn Electron and a C128.

I've never had ST ROMs go bad at all, and as @stephen_usher said, a proper clean of the sockets and chip legs, plus a tweak of the PLCC sockets would be useful. I'd add a scoosh of contact cleaner too, it helps the contacts get clean and stay clean, plus helps by making insertion and removal easier.

If it fixes it great, but I wouldn't be surprised if it doesn't. I guess what I'm saying is look more closely at the chips and sockets while you wait, it may pay dividends.

BTW a black screen/white border usually indicates a RAM issue.