dead TT motherboard repair attempt

[jookie]

I did not test this on my TT, but I find it plausible that a missing SCSI DCU might cause a bus error while TOS is trying to boot from SCSI.

We'll see if that's the case once the DCU arrives from UK to my place... I'll let you know.

[czietz]

In case you have a way to program custom TOS ROMs for your TT, there's another approach you might be interested in trying: EmuTOS (512k ROM version, of course). EmuTOS gives much better error messages than Atari TOS's bombs which might help pinpoint misbehaving hardware. Also, EmuTOS can be custom-built to not use use certain hardware, such as e.g. SCSI.

[jookie]

In case you have a way to program custom TOS ROMs for your TT, there's another approach you might be interested in trying: EmuTOS (512k ROM version, of course). EmuTOS gives much better error messages than Atari TOS's bombs which might help pinpoint misbehaving hardware. Also, EmuTOS can be custom-built to not use use certain hardware, such as e.g. SCSI.

Thank you for the tip, that sounds great. Unfortunately 27C010 EPROMs are now harder to get and I don't have a working EPROM burner... But I'm thinking of changing the TOS to english as the current EPROMs have 'NETH-FR' on them (Netherlands / French?), which are not languages I speak ;) If I'll get my hands on EPROMs and burner, I'll try the EmuTOS, too.

[jookie]

I've added the MCP100-475 supervisory circuit (4.75V threshold voltage) on the PG (power good) line, removed the pull-up to 5V from that PG line, now the TT starts to boot after power on without manual reset button push.

The DCU (UA01) arrived today, I've soldered it on the motherboard, now the TT boots to desktop without 2 bombs. I didn't test the floppy, ACSI and SCSI yet, so that will follow, but at least it turns on and boots to desktop (when bought from eBay, there was no activity, and 5 chips blocked the machine start). I'm waiting for LMC1992 (U816) to arrive to push it into socket and check if that fixes the DMA sound (which couldn't go through the original soldered LMC1992).

tt_tos.jpg

[exxos]

I've added the MCP100-475 supervisory circuit (4.75V threshold voltage) on the PG (power good) line, removed the pull-up to 5V from that PG line, now the TT starts to boot after power on without manual reset button push.

Sounds like the reset circuit needs a recap. Same problem happens on the STE etc. I even suggest using higher values to allow the PSU to power up fully before reset happens.

[jookie]

Sounds like the reset circuit needs a recap. Same problem happens on the STE etc. I even suggest using higher values to allow the PSU to power up fully before reset happens.

Thank you for the info, I will look into that, too.

[rubber_jonnie]

I've added the MCP100-475 supervisory circuit (4.75V threshold voltage) on the PG (power good) line, removed the pull-up to 5V from that PG line, now the TT starts to boot after power on without manual reset button push.

The DCU (UA01) arrived today, I've soldered it on the motherboard, now the TT boots to desktop without 2 bombs. I didn't test the floppy, ACSI and SCSI yet, so that will follow, but at least it turns on and boots to desktop (when bought from eBay, there was no activity, and 5 chips blocked the machine start). I'm waiting for LMC1992 (U816) to arrive to push it into socket and check if that fixes the DMA sound (which couldn't go through the original soldered LMC1992).


tt_tos.jpg

Excellent work sir.

[jookie]

Excellent work sir.

Thank you :)

I've also just managed to complete a side quest - extending the 2 MB ST RAM on a card to 8 MB ST RAM...

Removing 2 MB chips from the RAM card - 1 hour with a soldering iron

desolder0.jpg

Removing 8 MB chips from SIMM from eBay - 5 minutes with a paint removing hot air pistol

desolder1.png

Soldering 8 MB chips to RAM card - 1 hour 40 minutes

solder.png

TT memory test on boot (the RAM was also tested via RAM test on diagnostic cartridge).

boot.png

[stephen_usher]

:dualthumbup:

[Icky]

That's a nicer solution for the SMT boards. The through hole is a pain to desolder and clean up but Lyxman's ram board add-on works well.

Great work :)