Faulty RAM *RESOLVED*

[Marcel_X]

Hi everyone,

I am working on my third (and last) QL. The first two are working, but I saved this one for last. It is the most crusty one of them all... It has been stored with the keyboard removed, so a lot of dust has piled up. I did clean it, but it didn't boot properly other than a bunch of garbage on the screen. Removed the ROM and put a Minerva one inside.
Minerva is supposed do a better RAM check, but sometimes there is still only garbage on the screen. And sometimes it gives the address of the faulty RAM.
But these addresses are different every time!

Here are some pictures. I only have 4 spare 4864 chips lying around. Is there a ROM image of decent RAM test software that I could plug in the back so I can figure out which ones to replace?

Any help is appreciated!

Marcel

[Pr0f]

The Minverva ram test is pretty good - those numbers it generates are the data written and read back - and more tellingly - the bottom one is the RAM address it failed at - with those numbers in the low 20000's that means the first block of RAM (lower bank) which *may* be defective. I say *may* - because anything causing a bit on the bus to be pulled high or low could cause an error that looks like memory error. Also - you have a regular pattern in the display in the bottom picture - which hints at something like either a failed chip or a bad bit on the bus.

It's worth carefully removing socketed chips, clearning contacts and the socket if possible and reseating them - see if that might resolve the error.

[Derek_Stewart]

Hi,

You could use the ramfail_bas program on the Minerva Utilities disk, which will identify the ram chip in question.

Look at Nightfall Crew where the QL ram failure is analysed:https://www.nightfallcrew.com/?s=minerva+ram+fail

and there is an online Ram Fail script which may help:
https://www.nightfallcrew.com/minervaram/index.php

[tofro]

I would argue with the relatively "ordered" picture we see (no hint of random DRAM bits in the video memory at all, which hints to "no RAM at all" rather than a single RAM chip defect) you have a problem with the bus transceivers (LS257, LS245) or the ZX8301. The first faulty address Minerva sees is also the first RAM address. CPU obviously seems to be working. Apparently, DRAM contents doesn't reach the 8301 properly.

I have, however, yet to see a "partially working" 8301 (i.e. "normally", when the 8301 is faulty, you get no picture at all).

[Marcel_X]

Hi Gents,

Thanks for all the hints and tips! And what do you know... I reseated the 8301 and 68008 and it is working now!
Pfew, I was already getting nervous. Especially because the values were completely different each time.
Or worse, nothing at all except garbage and the buzzer that wouldn't stop.

Again, thanks!

Marcel

[tofro]

Oh, yes, it helps a lot when the CPU and the ULA are actually connected to the computer!

[Marcel_X]

Oh, yes, it helps a lot when the CPU and the ULA are actually connected to the computer!

Well they were in their sockets. But being in a moist attic for more than 35 years doesn't help.
Especially the notorious red socket for the 68008... That one starts to crumble when I look at it.
And the main 15 MHz crystal has quite a bit of green rust on it.
I already have a new membrane for this one. And I managed to get a replacement CAPS LOCK key from eBay.
Mine was broken. And this QL has a superHermes. I think it is the light version.

Anyway, another QL is alive!

[Pr0f]

superhermes are a rare find!

That will give you some options with the keyboard, but sadly not PS/2 directly.

[XorA]

superhermes are a rare find!

That will give you some options with the keyboard, but sadly not PS/2 directly.

Not that rare, I'm sick of them!

It's only a converter cable for old ps/2 keyboards though.

[Derek_Stewart]

Hi,

I used to use a PS/2 keyboard on a Superhermes, an AT Keyboard to PS/2 keyboard is required. These can be bought commercially or made.

This was also used on the Q60 AT Keyboard to PS/2 keyboard.