exxos's Atari, Amiga & retro forum

Might be worth trying Diagrom now as it could simply be a ram fault etc

You have got the bodge wire done under the CPU I assume ?

exxos wrote: 15 Feb 2020 14:49 You have got the bodge wire done under the CPU I assume ?

I presume you mean for DTACK? I've done all the fixes here: https://www.exxosforum.co.uk/forum/viewt ... 335#p28958 bar the DMA resistor swapout, but I'm not getting that far.

It looks awfully similar to the Mega4 TBH, which is in some respects easier to troubleshoot, and in others the H4 is easier.

What I can say is that when I plug in the diag cart, the ROM LED does not illuminate during boot like on a working machine, and if I select EMUTOS on the diag cart, the LED for that does not illuminate either.

On a working machine the red ROM LED lights and boots to diags, and with EMUTOS selected both LEDs light and the blue one for EMUTOS flickers as it seems to be accessed.

It seems to me that the ROM is inacessible and can't be read, so the CPU is sitting there, probably in a halted state, but I need to check those pins to see what they're doing.

No idea what LEDs your referring to... But if you remove the H4 CPU You can do what I suggested with your mega..

exxos wrote: 15 Feb 2020 17:00 No idea what LEDs your referring to... But if you remove the H4 CPU You can do what I suggested with your mega..

On the diag cart I have it has 2 LEDs. A red one that indicates the selected ROM is being accessed, and a blue one that flickers like a drive busy light when the EMUTOS image is enabled. They are quite useful.

And yes, I'm going to try what you suggested on both the H4 and Mega. I know the Mega has a good CPU now, and that the ROMS are good too, and it also seems the CPU is driving /HALT low, not the mainboard. I've posted on the other thread about the Mega.

The H4 is behaving vary similarly though.

rubber_jonnie wrote: 15 Feb 2020 17:20 On the diag cart I have it has 2 LEDs. A red one that indicates the selected ROM is being accessed, and a blue one that flickers like a drive busy light when the EMUTOS image is enabled. They are quite useful.

It that something you added ? I was going to add them on my carts, but the LED being driven from the ROM lines just prevented the cart from booting. I didn't want to add a buffer just for that, so didn't bother.

exxos wrote: 15 Feb 2020 17:21

rubber_jonnie wrote: 15 Feb 2020 17:20 On the diag cart I have it has 2 LEDs. A red one that indicates the selected ROM is being accessed, and a blue one that flickers like a drive busy light when the EMUTOS image is enabled. They are quite useful.

It that something you added ? I was going to add them on my carts, but the LED being driven from the ROM lines just prevented the cart from booting. I didn't want to add a buffer just for that, so didn't bother.

@exxos No, at the time you didn't have your carts available, so I got one elsewhere, and it came already fitted with them. They are a useful diag tool.

Ok meanies, you know who you are,I have a plan.Well sort of.

But I'm not telling you, because you're all mean.

:sigh:

And just because.....

:girldance:

They don't mean it really.
:awwww:

We're all rooting for you to fix the H4!

JezC wrote: 05 Mar 2020 16:35 They don't mean it really.
:awwww:

We're all rooting for you to fix the H4!

@JezC At least somebody is trying to be nice :)

Still no plan telling though. At least not until it's all gone sideways and I need to regroup.