Falcon white screen won’t boot but tests ok w/diag cart

[Nethak]

Hello.

I have a Falcon that once worked, but after being stored it only shows a white screen at boot with no logo, memory test, floppy activity, etc. It has TOS 4.04, 16MB memory board, and a power supply with new capacitors and proper voltage output.

When I insert Exxos’ diagnostic cartridge, however, it runs diagnostics just fine - the screen comes alive and timing/RAM/audio diagnostics pass with no obvious failures. The short blitter test does seem to hang (unless I’m just impatient).

Looking at the system startup order of operations in the troubleshooting guide, I’m not sure where my system is going wrong.

Has anyone seen this before or might have any ideas of where to start?

Thank you.

PS- I am a pro with a multimeter, but a novice with the cheap Amazon scope I have. I also have another working falcon and, mostly out of desperation vs actual troubleshooting, I’ve already tried swapping socketed parts (and even installing a DFB1X!) but nothing changes. Also, the previous owner installed sockets for the Ajax chip and the two MC6850P chips, so it’s seen work in its day…

[Badwolf]

Hello.

I have a Falcon that once worked, but after being stored it only shows a white screen at boot with no logo, memory test, floppy activity, etc. It has TOS 4.04, 16MB memory board, and a power supply with new capacitors and proper voltage output.

When I insert Exxos’ diagnostic cartridge, however, it runs diagnostics just fine

Sounds like you may be missing the bus grant jumper on the expansion header.

When you open up the case there are two rows of parallel pin headers towards the bottom left side, straddling the CPU.

The bottom (smaller) one should have a jumper on the top of its two subrows between the pin fifth from the right and sixth from the right. If you look at that pin header set straight down, you'll see a white line on the board indicating its position.

Check that a) it's there and b) it's clean and making contact.

BW

PS:

I’ve already tried swapping socketed parts (and even installing a DFB1X!) but nothing changes.

DFB1X would not require that jumper (and need you to remove it, actually), so if that didn't work it's possibly something else, or a bad connection. Obviously make sure the jumper was correct reseated after removing DFB1X!

Does the diag cart work with DFB1X installed?

[Nethak]

Thank you for the response! Apologies for the delay in mine.

With the DFB1X card, the machine doesn't boot/black screen and it won't load the diag cart. Without the DFB1X card, and with or without the bus grant jumper, the diag cart comes up without issue and when removed, just a white screen. I can certainly try another jumper/check the connection.

[Badwolf]

Thank you for the response! Apologies for the delay in mine.

With the DFB1X card, the machine doesn't boot/black screen and it won't load the diag cart. Without the DFB1X card, and with or without the bus grant jumper, the diag cart comes up without issue and when removed, just a white screen. I can certainly try another jumper/check the connection.

Could be as simple as that, yes. I spent an afternoon scratching my head once as a jumper was dirty and not making good contact!

Diag cart will boot nicely without that jumper, but TOS needs it very early in the boot process.

If DFB1X is black and TOS won't boot with that jumper, then it's possible the whole expansion connector is dirty and needs a good dose of contact cleaner.

BW

[Nethak]

Thank you. I replaced the jumper on the header with another (original one seemed loose) and replaced the NVRAM chip and it now boots to a desktop. Unfortunately I did both at once, so I’m not sure what fixed my issue.

Now that it “boots,” my issue is the floppy disk/hard disk icons do not appear and the floppy and IDE drive are not being recognized even though they do work on another Falcon I have, so I know they’re ok. I decided to take a parts cannon approach and replace the Ajax and SDMA(!), but my problems persists. Even by itself, the floppy isn’t recognized. Diag cart says not ready or some such error when I try read test. Speed test actually works and says speed is ok lol.

I will search the forum and see if anyone else has had issues with drive icons not appearing. I’m down testing the floppy cable? I might also try booting from SCSI to see if any storage works at all.

Thanks.