derkom's attempt

[exxos]

Depending on which expansion port I choose, 1.2 - 1.5 Ω, which I would guess is good enough.

Yeah... Check DTACK from the MMU to CPU as well, might also be worth checking other control lines such as, AS,LDS,UDS.

[derkom]

Yeah... Check DTACK from the MMU to CPU as well, might also be worth checking other control lines such as, AS,LDS,UDS.

Checked all of MMU vs expansion, GLUE vs expansion, CPU vs expansion, and MMU vs GLUE. It's all good enough for a multimeter.

[exxos]

Checked all of MMU vs expansion, GLUE vs expansion, CPU vs expansion, and MMU vs GLUE. It's all good enough for a multimeter.

We seem to be running out of things to check :(

What about checking BG,BGACK,BR after reset, they should all be high.

[derkom]

What about checking BG,BGACK,BR after reset, they should all be high.

Logic, logic, and logic.png

They don't seem to be moving at all.

[exxos]

They don't seem to be moving at all.

Thats OK then.... We really need a new ROM to try.. have you tried moving the ROM jumper (think you got it open currently) .

[derkom]

Thats OK then.... We really need a new ROM to try.. have you tried moving the ROM jumper (think you got it open currently) .

Yep, sure have. No noticeable difference in behaviour.

New ROM should be here soonish. I see that it left the UK today. I don't know if the postal strike has created a backlog that might still introduce delays, but at least it's on the way.

However, since @czietz has pointed out that this ROM is indeed looking for the diag cart, it's easy to assume that the ROM is not the problem.

It's quite late here tonight, so I'll stop for the evening, and reflow a bunch of stuff tomorrow and then we'll see where we are.

Without actually knowing what I'm talking about, I don't like the looks of A22 and A23. While I'm watching the repeated bus errors, those two address lines are behaving inconsistently, while everything else seems to follow a pattern. It just strikes me as wrong, and noisy. So maybe reflowing the solder will be the help they need.

[exxos]

Thats the odd things though, its looking for the cart, and still not booting from it anyway. So may be worth checking the ROMx routes on the GLUE to other things like the LS11 and ROM port make sure they are all connected OK.

[derkom]

Thats the odd things though, its looking for the cart, and still not booting from it anyway. So may be worth checking the ROMx routes on the GLUE to other things like the LS11 and ROM port make sure they are all connected OK.

ROMx routes from GLUE to LS11 are fine, and just to simplify things, I pulled the RTC and jumpered the socket to get ROM3 routed straight through to the cartridge port, at which point ROM3 and ROM4 to the cartridge port are fine as well. No change.

I'm confident with LS11's physical connections, but is there any way to test that it is actually functioning? Or does the fact that TOS is apparently loading and looking for the cartridge already mean that LS11 is functioning correctly?

This time I'm really going to bed! :lol:

[PhilC]

LS11 is an AND gate, so you could some how put your LA onto the 3 inputs and 1 output. The output will be engaged when all 3 inputs are enabled.

[czietz]

Suggestion: As soon as you have a known TOS version in there, decode the last few addresses actually read from ROM, i.e., where ROM_CE still gets low. Then one can lookup in a TOS disassembly what the code was actually doing before going wrong.