520STFM: After replacing memory: White screen of death.

Problems with your machine in general.
stephen_usher
Trusted Guru
Trusted Guru
Posts: 854
Joined: Mon Nov 13, 2017 7:19 pm
Location: Oxford, UK.
Contact:

Re: 520STFM: After replacing memory: White screen of death.

Post by stephen_usher » Sat Sep 26, 2020 8:52 pm

I've now checked all lines to the ROMs as well and then decoded the only two memory accesses the CPU makes.

It reads the first two words of the ROM and then stops reading from the ROMs. About a second later the machine crashes and starts again.

It's almost as if the GLUE is stopping the assertion of the ROM lines too early, after only two reads, before the CPU has the address of the start of TOS.
Intro retro computers since before they were retro...
ZX81->Spectrum->Memotech MTX->Sinclair QL->520STM->BBC Micro->TT030->PCs & Sun Workstations.
Added code to the MiNT kernel (still there the last time I checked) + put together MiNTOS.
Collection now with added Macs, Amigas, Suns and Acorns.

stephen_usher
Trusted Guru
Trusted Guru
Posts: 854
Joined: Mon Nov 13, 2017 7:19 pm
Location: Oxford, UK.
Contact:

Re: 520STFM: After replacing memory: White screen of death.

Post by stephen_usher » Sat Sep 26, 2020 9:17 pm

Success! I removed the Blitter socket and the machine sprung to life!
Intro retro computers since before they were retro...
ZX81->Spectrum->Memotech MTX->Sinclair QL->520STM->BBC Micro->TT030->PCs & Sun Workstations.
Added code to the MiNT kernel (still there the last time I checked) + put together MiNTOS.
Collection now with added Macs, Amigas, Suns and Acorns.

User avatar
PhilC
Moderator
Moderator
Posts: 3624
Joined: Fri Mar 23, 2018 8:22 pm

Re: 520STFM: After replacing memory: White screen of death.

Post by PhilC » Sat Sep 26, 2020 9:20 pm

stephen_usher wrote:
Sat Sep 26, 2020 9:17 pm
Success! I removed the Blitter socket and the machine sprung to life!
Well done, now to find out why :D
If it ain't broke, test it to Destruction.

stephen_usher
Trusted Guru
Trusted Guru
Posts: 854
Joined: Mon Nov 13, 2017 7:19 pm
Location: Oxford, UK.
Contact:

Re: 520STFM: After replacing memory: White screen of death.

Post by stephen_usher » Sat Sep 26, 2020 9:22 pm

The data buses are now clean and don't have any noise. I think the empty socket was acting as an antenna picking up RF interference.
Intro retro computers since before they were retro...
ZX81->Spectrum->Memotech MTX->Sinclair QL->520STM->BBC Micro->TT030->PCs & Sun Workstations.
Added code to the MiNT kernel (still there the last time I checked) + put together MiNTOS.
Collection now with added Macs, Amigas, Suns and Acorns.

User avatar
JezC
Trusted Guru
Trusted Guru
Posts: 798
Joined: Mon Aug 28, 2017 11:44 pm

Re: 520STFM: After replacing memory: White screen of death.

Post by JezC » Sat Sep 26, 2020 9:33 pm

Glad to hear that you sorted it out...though all these problems are one of the major driving forces behind the H4/H5 etc.

I've already seen how diagnosing one or two faulty machines can take more time than building the H4... :shock: :roll:

stephen_usher
Trusted Guru
Trusted Guru
Posts: 854
Joined: Mon Nov 13, 2017 7:19 pm
Location: Oxford, UK.
Contact:

Re: 520STFM: After replacing memory: White screen of death.

Post by stephen_usher » Sat Sep 26, 2020 10:10 pm

Actually, RF issues like this would happen on the new board as well. It merely needs the socket leads or internal interconnects to be the right length and you suddenly pick up Radio 2 on the data bus. :lol:
Intro retro computers since before they were retro...
ZX81->Spectrum->Memotech MTX->Sinclair QL->520STM->BBC Micro->TT030->PCs & Sun Workstations.
Added code to the MiNT kernel (still there the last time I checked) + put together MiNTOS.
Collection now with added Macs, Amigas, Suns and Acorns.

tzok
Posts: 222
Joined: Sat Dec 30, 2017 2:27 pm

Re: 520STFM: After replacing memory: White screen of death.

Post by tzok » Sat Sep 26, 2020 10:27 pm

I rather think, there was a short under the socket... was it original "funky" socket, a modified modern one, or a modern one on the adapter board?

User avatar
JezC
Trusted Guru
Trusted Guru
Posts: 798
Joined: Mon Aug 28, 2017 11:44 pm

Re: 520STFM: After replacing memory: White screen of death.

Post by JezC » Sat Sep 26, 2020 10:31 pm

True...but there are lots of inherent noise issues with the older boards as well, so mixing older/aged ICs with the extra noise can easily tip the old boards from (just) working to giving lots of problems/unreliability.

It's pretty impressive how many of these 30+ year old computers work at all - I dread to think how short the lifetime of many of the newer lead-free electronic devices may be!

stephen_usher
Trusted Guru
Trusted Guru
Posts: 854
Joined: Mon Nov 13, 2017 7:19 pm
Location: Oxford, UK.
Contact:

Re: 520STFM: After replacing memory: White screen of death.

Post by stephen_usher » Sat Sep 26, 2020 11:39 pm

Yeah.
Intro retro computers since before they were retro...
ZX81->Spectrum->Memotech MTX->Sinclair QL->520STM->BBC Micro->TT030->PCs & Sun Workstations.
Added code to the MiNT kernel (still there the last time I checked) + put together MiNTOS.
Collection now with added Macs, Amigas, Suns and Acorns.

stephen_usher
Trusted Guru
Trusted Guru
Posts: 854
Joined: Mon Nov 13, 2017 7:19 pm
Location: Oxford, UK.
Contact:

Re: 520STFM: After replacing memory: White screen of death.

Post by stephen_usher » Sat Sep 26, 2020 11:41 pm

tzok wrote:
Sat Sep 26, 2020 10:27 pm
I rather think, there was a short under the socket... was it original "funky" socket, a modified modern one, or a modern one on the adapter board?
No, I put a foam pad underneath (approximately 2mm thick) to make sure that there was no possibility that the underside of the conversion board would get anywhere near the surface.
Intro retro computers since before they were retro...
ZX81->Spectrum->Memotech MTX->Sinclair QL->520STM->BBC Micro->TT030->PCs & Sun Workstations.
Added code to the MiNT kernel (still there the last time I checked) + put together MiNTOS.
Collection now with added Macs, Amigas, Suns and Acorns.

Post Reply

Return to “HARDWARE ISSUES”