Garbled screen

Started by Curlypaul, 04:28, 19 January 22

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Curlypaul

I came to test my new 512kb ram board and find my CPC464 has developed a fault, showing a garbled screen.


It changes, but mainly it's blue and yellow vertical rectangles or light green columns, and very occasionally, a crazy vsync. The prevelance of blue and yellow suggests some sort of initialisation is happening?


Nothing is hot, ram and crtc show occasionally flushes if warmth, gate array is warm after a minute. It's an early one with a heat sink.


In order to eliminate the ram. I tried the expansion anyway, but still the same result. It's a Revaldinho, am I right in thinking when it's working, the ram on the motherboard isn't used? I tried all compatible jumper settings.


I hope it's not the gate array :(



Bryce

Hi Paul,
the first thing to check is the voltage, is the 464 board getting 5V or has a dodgy PSU, dirty connections or a dodgy power switch dropped the voltage to less than 4.75V?
Also, try reseating the socketed IC's in the 464.

Bryce.

Curlypaul

Thanks Bryce, I will check the voltage level tonight. Overlooked that as the psu is new. I reseated and cleaned the legs on all but the Gate Array, didn't want to get covered in paste, but I'll give that a shot tonight :)

Bryce

New PSU... always a suspect. What's its (claimed) ratings?

Bryce.

Skunkfish

Hi Paul,
I'm a bit worried that might be the GX4000 PSU that was purchased off me? Hopefully not as that's 9V and 1.6A!
Thanks,
James.
An expanding array of hardware available at www.cpcstore.co.uk (and issue 3 of CPC Fanzine!)

Curlypaul

Quote from: Bryce on 12:43, 19 January 22
New PSU... always a suspect. What's its (claimed) ratings?

Bryce.


5v 2amps. It's the one from the cpcstore, I think. It's not brand brand new, I've had a good few hours out of it.


Quote from: Skunkfish on 15:55, 19 January 22Hi Paul, I'm a bit worried that might be the GX4000 PSU that was purchased off me? Hopefully not as that's 9V and 1.6A! Thanks, James.



If you are the guy behind cpcstore, then yes my order had a gx4000 psu in there, but I've not plugged that into the CPC :)

Skunkfish

#6
Phew, I did have a moment of panic there!

I am the guy running CPCstore, but I don't think the PSU is from me.

The ones I'm selling are the TT Electronics SW3088-C2, rated 5V @3A.

From testing, they normally supply just under 5.1V, with a slight drop-off to around 5.05V after 2.5A.

Spec sheet is attached.
An expanding array of hardware available at www.cpcstore.co.uk (and issue 3 of CPC Fanzine!)

Curlypaul

I don't think it is actually is it. I will double check what it's doing tonight.


With the ram card though, in a 464 is the original ram not used?

Skunkfish

If you set the DIP switches to Full Shadow mode (Switches 1 & 2 to ON), then the external RAM is used in place of the internal for most purposes...


An expanding array of hardware available at www.cpcstore.co.uk (and issue 3 of CPC Fanzine!)

Curlypaul

Thanks dude.


Finally got a minute to take a look, this gate array appears to have just 3v on both vcc1 and 2.


There's 5 from the PSU with no load, and 4.75 at the Z80, and a clock signal. There are a few spurious looking solder joints that I need to attend to on the plate caps on the ram chips, and I guess check the transistors around the gate array? I've learned something about the fault anyway

Curlypaul

ok so I took the gate array out as it there was thermal paste all over the place and gave it all a good clean. Still seem to have 5v everywhere apart from accross the gate array. With the gate array removed the socket does have 5v across the pins, not sure if this is a red herring or not.


Would be useful if I had another machine to test with

Joseman

Quote from: Curlypaul on 15:43, 30 January 22
ok so I took the gate array out as it there was thermal paste all over the place and gave it all a good clean. Still seem to have 5v everywhere apart from accross the gate array. With the gate array removed the socket does have 5v across the pins, not sure if this is a red herring or not.


Would be useful if I had another machine to test with
Hi
Maybe test what are the ohms between the gate array ground and the other pins outside the board?

Curlypaul

Quote from: Joseman on 18:37, 30 January 22
Hi
Maybe test what are the ohms between the gate array ground and the other pins outside the board?


You mean maybe the resistors on the 5v in?


Just snagged an aparently working motherboard, probably overpaid, but I wanted to be sure it had the 40007 the same as mine. Mine doesn't have the thick white factory bodge wires, but I'm assuming that's not an issue so long as the chip part numbers match.

Joseman

Quote from: Curlypaul on 20:12, 30 January 22

You mean maybe the resistors on the 5v in?


Just snagged an aparently working motherboard, probably overpaid, but I wanted to be sure it had the 40007 the same as mine. Mine doesn't have the thick white factory bodge wires, but I'm assuming that's not an issue so long as the chip part numbers match.
no, i was thinking that if you check the pin ground on the gate array itself with all other pins of the gate array, well it have to show some results... now that you have 2 GA you can check it the two gate array bring the same results on all this values. I have little knowledge but maybe is a step.

Curlypaul

#14
Quote from: Joseman on 20:17, 30 January 22
no, i was thinking that if you check the pin ground on the gate array itself with all other pins of the gate array, well it have to show some results... now that you have 2 GA you can check it the two gate array bring the same results on all this values. I have little knowledge but maybe is a step.


Yeah I have had a look at some of the other pins, there is a clock but I don't have the equipment to see how fast.

I seem to have a unlisted variant, it's a Rev 1 but it doesn't have those white wires, which apparently have resistors in them, I've got just got resistors on the pcb. Don't seem to be be able to attach pictures here, but I'll submit to the wiki if the completeness is appreciated. The gate array a plain 40007, no revision numbers so I'm guessing this is one of the first of the production line.


Nworc

Quote from: Curlypaul
I came to test my new 512kb ram board and find my CPC464 has developed a fault, showing a garbled screen.
It changes, but mainly it's blue and yellow vertical rectangles or light green columns, and very occasionally, a crazy vsync. The prevelance of blue and yellow suggests some sort of initialisation is happening?

Hey, sound's like you made a new demo, but in hardware, not in software. :)

Would you mind to take a picture of the monitor showing this bug and adding it here? Maybe if one could see the effect, we might have an idea where this effect comes from.

Curlypaul

I will later, the spare board turned up today and starts up at least. I'm hoping it's not the gate array and I can get myself two working boards, but I'll document it here and try and get a decent pic for the wiki.


Audronic

This is what the screen looks like.

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If it Ain't Broke PLEASE Don't Fix it.
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As I Live " Down Under " I Take my Gravity Tablets and Wear my Magnetic Boots to Keep me from Falling off.

Curlypaul

Thanks, was getting frustrated with it, dunno why it wrapped it all in links

Nworc

#20
Cool, nice picture!

To me the picture looks like the display of uninitialized RAM. I saw something similar as I played around with the CPU hardware wise. Maybe the CPU is not working, maybe the RAM is not powered.

Curlypaul

Quote from: Nworc on 00:02, 03 February 22
Cool, nice picture!

To me the picture looks like the display of uninitialized RAM. I saw something similar as I played around with the CPU hardware wise. Maybe the CPU is not working, maybe the RAM is not powered.


You weren't wrong when you said I'd created a demo, imagine it zooming in and out and some scrolling.


Thankfully these rev 1s are socketted, it appears I have two dead ram chips. I could have just took a punt on the xheapest thing to replace  :picard:  but I got new tools and a full spare motherboard.


Need to look at options on connecting a modern keyboard, if there are any?

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