exxos's Atari, Amiga & retro forum

stephen_usher wrote: 18 Oct 2024 08:25 Well, seeing as the machine isn't able to get anywhere suggests the lowest bank of RAM, so you only need to look at the lowest 16 chips.

Myself I'd use an oscilloscope to look at the data lines so see if any look "strange". Even without the CPU the Shifter will be trying to do memory access.

rubber_jonnie wrote: 18 Oct 2024 11:11 I'd agree with @stephen_usher and I'd also use a scope to look for stuck address lines.

Of course the RAM issue might be an MMU socket issue, so I'd be tempted to just tweak the socket pins a little to be sure of good contact.

It doesn't need much to tweak the pins so be super careful.

A diag cart is a cheap and useful if you have other ST's to work on since you can pick up useful diag info from the serial port with a PC connected and terminal software.

rubber_jonnie wrote: 18 Oct 2024 11:11 I'd agree with @stephen_usher and I'd also use a scope to look for stuck address lines.

Of course the RAM issue might be an MMU socket issue, so I'd be tempted to just tweak the socket pins a little to be sure of good contact.

It doesn't need much to tweak the pins so be super careful.

A diag cart is a cheap and useful if you have other ST's to work on since you can pick up useful diag info from the serial port with a PC connected and terminal software.

asapreta wrote: 18 Oct 2024 14:29

rubber_jonnie wrote: 18 Oct 2024 11:11 I'd agree with @stephen_usher and I'd also use a scope to look for stuck address lines.

Of course the RAM issue might be an MMU socket issue, so I'd be tempted to just tweak the socket pins a little to be sure of good contact.

It doesn't need much to tweak the pins so be super careful.

A diag cart is a cheap and useful if you have other ST's to work on since you can pick up useful diag info from the serial port with a PC connected and terminal software.

Thanks for all support and tips.
I will put the diagcart in my wishlist.

As you, I am a proud owner of 50-60 retro computers from different companies, like ZX Spectrum, Commodores, Amstrads, Amigas, BBC, Atari 8 and 16 bit, so the wishlist is kinda big...

But I will use the scope to get these stuck address lines, hope I can find them!

Badwolf wrote: 18 Oct 2024 11:31

rubber_jonnie wrote: 18 Oct 2024 11:11 I'd agree with @stephen_usher and I'd also use a scope to look for stuck address lines.

Of course the RAM issue might be an MMU socket issue, so I'd be tempted to just tweak the socket pins a little to be sure of good contact.

It doesn't need much to tweak the pins so be super careful.

A diag cart is a cheap and useful if you have other ST's to work on since you can pick up useful diag info from the serial port with a PC connected and terminal software.

On my STFM, before I sat down and systematically worked on the PLCC socket pins as discussed above, tapping the MMU whilst periodically hitting reboot would show that sometimes it worked and sometimes it didn't. Bit of pressure this way or that might work too.

All you have to do is get it working once with a bit of a tap or pressure here and there to come pretty close to your smoking gun.

Diag cart is must have anyway, though.

BW

stephen_usher wrote: 18 Oct 2024 12:05 Another non-destructive test, which only sometimes works if it's a RAM chip which has failed in a way that it's not stuck low, is to piggy-back a known good RAM chip on top of one of the ones on the motherboard. If you've got multiple 41256 chips then piggybacking multiple chips may (or may not) work to get different behaviour and possibly a working system as a test.

Non-destructive tests are always the first things to try.

Having said that, a black background suggests that the Shifter isn't able to read any RAM, which would point towards the MMU/GLUE and connections to/from that, possibly CAS/RAS lines etc. So, checking those signals both at the GLUE/MMU sockets and on the RAM with an oscilloscope would be a good thing to test.

rubber_jonnie wrote: 18 Oct 2024 14:33

asapreta wrote: 18 Oct 2024 14:29

Thanks for all support and tips.
I will put the diagcart in my wishlist.

As you, I am a proud owner of 50-60 retro computers from different companies, like ZX Spectrum, Commodores, Amstrads, Amigas, BBC, Atari 8 and 16 bit, so the wishlist is kinda big...

But I will use the scope to get these stuck address lines, hope I can find them!

Yes, and my wishlist just isn't getting any smaller, much to the disappointment of my wife!

asapreta wrote: 18 Oct 2024 14:51

rubber_jonnie wrote: 18 Oct 2024 14:33

Yes, and my wishlist just isn't getting any smaller, much to the disappointment of my wife!

Luck you still have a wife!