*** M E M O R U M ***

Hi.

Just picked up my first MTX 512. I think the case has been over zealously cleaned, so there are no serial number labels or anything that identifies the specific unit. Inside, it is a 4000-04 motherboard. So far, so good.

The system boots, but rather than seeing a "Ready" prompt, I'm consistently getting "Rd'dx". Although the keys all work, most commands I enter elicit an error response. One command that does work is PANEL. Here I can see that the ROM contents are inconsistent with the expected values from the dumps I've seen (rough guess is about 75% of the bytes match). I'm guessing BASIC commands are not being recognised because the wordlist (at address 253B) is also corrupted. Is this likely to be a ROM fault or could it be voltage related? Has anyone seen anything similar? I'd appreciate any suggestions on next investigation steps.

-Brian.

Hi Brian,

It’s a VRAM issue

Regards
Dave

Hints here

http://www.primrosebank.net/computers/ ... repair.htm
http://www.primrosebank.net/computers/ ... _fault.htm

Four minutes to reply - gotta be a record, yes?

Or are you just sitting there Dave, refreshing the "New Posts" page?

gunrock wrote: ↑30 Mar 2025 21:21 Four minutes to reply - gotta be a record, yes?

Or are you just sitting there Dave, refreshing the "New Posts" page?

I really do need to get a life don’t I ?

Thank you for the very quick response. I assume that you are referring to one or more of the 4116 chips failing, which is also a common curse on the Spectrum. As mentioned, I'm completely new to the MTX, so I'm therefore intrigued to understand why a VRAM issue might also cause basic BASIC commands to trigger a "Mistake" such as a PRINT "ABC" statement. Could this be a secondary issue or just a misunderstanding on my part?

BrianF wrote: ↑31 Mar 2025 08:50 Thank you for the very quick response. I assume that you are referring to one or more of the 4116 chips failing, which is also a common curse on the Spectrum. As mentioned, I'm completely new to the MTX, so I'm therefore intrigued to understand why a VRAM issue might also cause basic BASIC commands to trigger a "Mistake" such as a PRINT "ABC" statement. Could this be a secondary issue or just a misunderstanding on my part?

Yes

Follow the link at the bottom of the page of the second link that I sent previously

Fix the VRAM issue first, then we can assess any other issues

Thanks. Will follow through on the linked instructions and come back here after completion.

BrianF wrote: ↑31 Mar 2025 08:50 Thank you for the very quick response. I assume that you are referring to one or more of the 4116 chips failing, which is also a common curse on the Spectrum. As mentioned, I'm completely new to the MTX, so I'm therefore intrigued to understand why a VRAM issue might also cause basic BASIC commands to trigger a "Mistake" such as a PRINT "ABC" statement. Could this be a secondary issue or just a misunderstanding on my part?

The simplest way to think of it, is that the text input buffer is in VRAM.

So the corrupt line of text that you see on screen is what ultimately gets fed to the basic interpretter.

gunrock wrote: ↑30 Mar 2025 21:21 Four minutes to reply - gotta be a record, yes?

Or are you just sitting there Dave, refreshing the "New Posts" page?

You do know you can subscribe to a topic or a sub-forum. Then you can get an email to alert you to any new posts...

BrianF wrote: ↑31 Mar 2025 08:50 Thank you for the very quick response. I assume that you are referring to one or more of the 4116 chips failing, which is also a common curse on the Spectrum.

4116 or equivalent DRAM chips failing are a common problem in most systems that use them...

BrianF wrote: ↑31 Mar 2025 08:50 As mentioned, I'm completely new to the MTX, so I'm therefore intrigued to understand why a VRAM issue might also cause basic BASIC commands to trigger a "Mistake" such as a PRINT "ABC" statement. Could this be a secondary issue or just a misunderstanding on my part?

Because the BASIC editor uses the video RAM by reading the characters in the video RAM.

Failures of mask ROM chips are uncommon.

While I was writing this, Martin has jumped in...

Mark

Martin A wrote: ↑31 Mar 2025 19:57

BrianF wrote: ↑31 Mar 2025 08:50 Thank you for the very quick response. I assume that you are referring to one or more of the 4116 chips failing, which is also a common curse on the Spectrum. As mentioned, I'm completely new to the MTX, so I'm therefore intrigued to understand why a VRAM issue might also cause basic BASIC commands to trigger a "Mistake" such as a PRINT "ABC" statement. Could this be a secondary issue or just a misunderstanding on my part?

The simplest way to think of it, is that the text input buffer is in VRAM.

So the corrupt line of text that you see on screen is what ultimately gets fed to the basic interpretter.

Thank you (and Mark) - this is the piece of the puzzle I was missing! I'm feeling a little more positive about the condition of the machine now.