Faulty RAM or 8301

[Derek_Stewart]

Hi,

You say that Minerva is reporting an external ram fault, is that on the Minerva front screen?

If the QL is getting to the ram text, the 8301, 8302, CPU ard working

If the 8301 is not work there will be no video ouput.

If the 8049 is not working the red Minerva logo usually is displayed without anything else.

Internal onboard ram is tested by Minerva and if ram test fails a location number is displayed.

The ramfail_bas program or Nightfallcrew web page will show the location of the bad chip.

If the ram failure is on external expansion, I would remove the expansion and get the QL in 128K basic setup working, then look, at the ram expansion.

I have some QL spares if required.

[Chris_68]

Hi,

You say that Minerva is reporting an external ram fault, is that on the Minerva front screen?

If the QL is getting to the ram text, the 8301, 8302, CPU ard working

If the 8301 is not work there will be no video ouput.

If the 8049 is not working the red Minerva logo usually is displayed without anything else.

Internal onboard ram is tested by Minerva and if ram test fails a location number is displayed.

The ramfail_bas program or Nightfallcrew web page will show the location of the bad chip.

If the ram failure is on external expansion, I would remove the expansion and get the QL in 128K basic setup working, then look, at the ram expansion.

I have some QL spares if required.

Thanks, yes it was on the front screen. I now trying to find what's wrong without memory expansion, most likely something happened when I replaced CPU socket and faffed around measuring.
I had some progress so now I have something on my monitor ( see attachment). So my fingers crossed I haven't fried my 8301 they are rare as hens teeth, don't know if I have a problem with CPU/RAM/ROM though...

Cant figure out how to attach a MP4/MOV so will be a screenshot.

[Pr0f]

I'm assuming the black lines are just related to how the photograph was taken and that you have a solid "tweed" pattern on the screen - does it change at all - or just statically displayed?

[Chris_68]

Hi

It’s not static, the black stripes moves from top to bottom.
I’m away today but can try to zip a short movie. But the good thing is (I guess) that the 8301 seems to work to some point at least. Yesterday it was blue static but no cursor.

Can’t get everything
/Chris

[Chris_68]

Hi,

QL_Screen.mp4.zip

(683.96 KiB) Downloaded 58 times

Attached is a video of the output to monitor, If reboot it is all black. (QL_Screen)
Checked more or less all pins on the CPU, see jpg and all connections as supposed.

Two questions, anyone who have an example of input and output signal from LS245 and LS257? I can attach an image from oscilloscope for comparison.
CLK signal is it supposed to be a sinusoidal instead of a square wave?

Thanks for all help this far.

[Pr0f]

The crystal xtal pins will have a sinusoidal wave form, the cpu clock should be more a squarewave - but be careful of your scope settings and probe settings - as these can affect how the scope will see the signal.

Your video shows the tweed pattern ok - so this means the ZX8301 is reading the dynamic RAM - but - the sync is not working - could be the lead / the monitor or the QL

[Chris_68]

Hi,

Excuse me for being slow in responding, Haven't had any real progress, I will receive LS257 I ordered the other day, let's hope that will help.
And yes Prof you were right, there was a loose cable in the connector, I realised later that night. But when I was about to update in this post you had already suggested that

Can I boot and measure the signal coming from pin 37 on 8301(ROWL) without any LS257 soldered in?

/Chris

[Chris_68]

Hello,

Just an update, everything is now working again or at least afaik.
So if someone finds this link and having similar problems then replace 74LS245 and 74LS257 as suggested by others. After I changed those 3 ICs and reflowed all solder joints directly related to CPU/8301 it was back to life.

Thank you for your help and feedback.
/Chris

[Maskenlos]

Good to hear that you fixed this issue.

Stephan