Thank you. Yesterday I re-flowed all the solder on each surface mounted PLCC chip due to some very odd infrequent issues. Do you think it is possible that you could sometimes have a dry solder joint on one of these chips legs? Well, anything is possible... Although there are so many sources of prob...

I'm not currently sure if it's the left one or right one, but you could measure connections from one and other to some known chips to tell them apart. Both are C300581 chips. You can measure pins PD0-PD7, if they are connected to UA02 (== 5380 SCSI chip, which is on the right on MB), then that chip ...

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. Yes, that's what I've thought, and as I could swap my through hole (THT) RAM with this SMD RAM with a friend (for a price of upgrading one of his 2 MB SMD RAM fo...

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 a...

exxos wrote: ↑Mon Jul 19, 2021 9:46 am 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.

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 b...

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-...

czietz wrote: ↑Fri Jul 09, 2021 10:50 amI 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.

As the TT was never sold without FPU, the TOS 3 developers did not bother checking for the FPU before using it. Okay, nice to know... This one seems to be sorted out by plugging in the new FPU. TOS 3 .06 doesn't. Proof: My TT with Atari TOS 3.06 booted to the Desktop without any drives whatsoever: ...

Okay, interesting thing... I got a working FPU (68882) from a friend, I've plugged it in the socket and suddenly the TT starts to boot - I can see the Atari logo, memory test.... Then it waits for a long time and ends with 2 bombs, but I'm still missing the DCU (UA01) on motherboard and no floppy or...