Looks like I'll be getting a Mega ST4 soon

[exxos]

Well done! Journeys end :)

[rubber_jonnie]

Well done! Journeys end :)

What a journey 😁

[rubber_jonnie]

Well, just when you thought everything was just fine and dandy, the Mega 4 throws something something new at you!!

I was trying to test the V1.1C board in my Mega4 and all was good, but then moved onto the Megabus IDE adaptor. That required pulling the V1.1C, putting in a set of ROMs borrowed from the Mega1, dropping in a CPU and hooking up the Vcc and ACSI pin 10 to the IDE board.

Well after that it was not happy at all. Booting to a white screen at first, so I pulled the ROMS & CPU and dropped in the V1.1Cand it's kind of booting, but now I get a blackscreen with white border, like the RAM is bad.

Ho hum, back to incessant rounds of troubleshooting no doubt!!

I think this machine has the potential to drive me insane, and goes back to the point that just manhandling the board can make it go bad.

I'll test the GLUE and MMU in the H4, see if they are good, then see what else I can find wrong.

[exxos]

I think this machine has the potential to drive me insane, and goes back to the point that just manhandling the board can make it go bad.

Know the feeling :( All these machines are just so fickle its unreal. I think 95% of my time goes on trying to figure out why those machines died for no reason at all. Hopefully a thing of the past now the H4's are here.

[rubber_jonnie]

I think this machine has the potential to drive me insane, and goes back to the point that just manhandling the board can make it go bad.

Know the feeling :( All these machines are just so fickle its unreal. I think 95% of my time goes on trying to figure out why those machines died for no reason at all. Hopefully a thing of the past now the H4's are here.

@exxos God, please do an H4 board for the Mega!!!

[PhilC]

@exxos Isounds like a plan :lol:

[rubber_jonnie]

Well here I am again, dead Mega4, this must be the most frustrating ST I have ever owned. Most have the grace to either let me fix them, or just die. This one is like an extra from the Walking Dead that keeps dying and then reanimating.

Good thing is,the H4 being entirely socketed allows me to easily test chips, and the DMA, Shifter, GLUE and MMU are good. The AY was brand new so no problem there. Pretty sure it isn't the Blitter since it doesn't get that far along.

All the RAM has 5v and a good GND, as do the ROMs, and if I'm honest it looks like a ROM problem again, as I can see /HALT is low,meaning it's active, so either the CPU is getting garbage or nothing and has halted the system, which is what happened last time, or the CPU is getting an externeal /HALT signal. My money is on the former. The ROM set is good though, as it checked out fine in my Mega1.

It's given me a chance to have a go with my logic probe, which is a good quick way to see if there is a signal without dragging out the scope, though that is coming, I'm sure.

What is annoying is that it was working just fine until I started to test stuff in it, and if I put in an IDE adapter and use the ROM on board that, I get a different error, in that there is a black screen with a white border, indicative of a RAM problem, and I can't imagine all the RAM has died.

This board just does not like manhandling.

[Tomswork]

The mega st sounds vexing. I have worked on commodore pet ike that. It still working today and I'm a little less sane. Keep us updated on your ongoing work


Tom

[rubber_jonnie]

The mega st sounds vexing. I have worked on commodore pet ike that. It still working today and I'm a little less sane. Keep us updated on your ongoing work


Tom

Aye, vexing it is @Tomswork

[rubber_jonnie]

Well, back to this old thing again. Seems like it's fully intent on throwing everything at me, kitchen sink included.

Currently, when using on board roms and onboard CPU, I get a white screen. This is what it did previously, and I find the HALT signal is active at the CPU. Either the CPU set HALT or the board did. I'm currently going with the CPU got garbage and halted, which has happened on this board before.

One thing I've discovered about the beta IDE board and the V1.1C boards though, is if you have a ROM problem, it can get you out of a hole, because the CPU and ROM all live together on the IDE board. So I pulled all the ROMS, and plugged an IDE board with CPU into the CPU socket, and lo and behold I get this:

Naughty_Mega.jpg

Which seems to be shouting RAM problem at me. Looking at the schematics, there are a pair of LS244s in the mix as shown here:

LS244.JPG

So I'm wondering if one or both is dodgy. I know MMU and GLUE, plus DMA, MFP and SHIFTER are ok as the H4 has been good enough to test them for me :)

It seems mad that all the memory would die in one go, but I think it's probably worthwhile pulling the LS244s and using the TL866 to check their function. So glad I got the desolder gun, it makes this sort of job nice and easy.

If it's still misbehaving afterwards it's scope time again, and all the previous diags I'll need to go through. Again.