CPC 464 doesn’t boot, shows blocks on screen

[hatman72]

Hi everyone, I'm hoping that someone can suggest what might be wrong with this early 464 with a 40007 Gate Array. 

When I start it always ends up at this screen with alternating blocks of 128 characters in light blue and purple. There is no beep if I press delete. There seems to be lots of activity on the board and no chips seem to be getting excessively warm. The problem is that since only the CPU and GA are socketed I don't want to start desoldering chips at random as I do not have a desoldering gun. 

The computer came to me this way and has been stored in a loft. I have no idea whether it was working when it was put there. 

[Bryce]

Hi Hatman72,
      that's not a classic RAM failure. I'd suggest you start by cleaning the pins and reseating all socketed chips and see if it helps.
What's your level of electronics knowledge and do you own any test equipment?

Bryce.

[hatman72]

Hi Hatman72,
      that's not a classic RAM failure. I'd suggest you start by cleaning the pins and reseating all socketed chips and see if it helps.
What's your level of electronics knowledge and do you own any test equipment?

Bryce.

Thanks Bryce. I've had both socketed chips (GA and CPU) out. I know the CPU is ok but my other (working) Amstrad has a 40010 GA so I can't easily test that. 

I own a multimeter and a cheap oscilloscope (which allowed me to check there's activity on all the RAM chips, but I'd consider my electronics knowledge to be fairly basic.

[salvogendut]

Hi, I am no expert but had recently a similar problem. What really helped me to debug the 464 was the cartridge you see in the pic. I got it off Ebay

[hatman72]

Hi, I am no expert but had recently a similar problem. What really helped me to debug the 464 was the cartridge you see in the pic. I got it off Ebay

I have an M4 card, so installed the diagnostics ROM on that. Unfortunately it doesn't boot from that either   

[Rabs]

Maybe this video may help

.

In this video there is a similar screen pattern, sometimes, but also the usual grey screen black border RAM problem display.

You cannot view this attachment.

In this GadgetUK finds that IC112 74LS32 Quad OR is faulty. Not quite sure how the floating output he finds relates to the issue as pin 11 selects the printer latch but pin 8 does select the data latch (by the way I made pin 8 float on my test board and I get the usual grey screen RAM problem symptoms).

No idea if this is the same as your problem but saw it and thought I would share.

[salvogendut]

Hi, I am no expert but had recently a similar problem. What really helped me to debug the 464 was the cartridge you see in the pic. I got it off Ebay

I have an M4 card, so installed the diagnostics ROM on that. Unfortunately it doesn't boot from that either 

I do not own an M4 but I do own a ULIfAC and tried using it to debug this and that did not help for me. Maybe it has to do with the fact that whatever booted the ULIfAC tried to access RAM (even when I used a CONFIG.TXT with just the diagnostic ROM) where this one cartridge does not

[hatman72]

Maybe this video may help

.

In this video there is a similar screen pattern, sometimes, but also the usual grey screen black border RAM problem display.

You cannot view this attachment.

In this GadgetUK finds that IC112 74LS32 Quad OR is faulty. Not quite sure how the floating output he finds relates to the issue as pin 11 selects the printer latch but pin 8 does select the data latch (by the way I made pin 8 float on my test board and I get the usual grey screen RAM problem symptoms).

No idea if this is the same as your problem but saw it and thought I would share.

That does look very similar, and I have seen mine produce the pattern in different colours occasionally, especially if the cassette deck is plugged in. It does look like a sensible thing to check. 

[Rabs]

That does look very similar, and I have seen mine produce the pattern in different colours occasionally, especially if the cassette deck is plugged in. It does look like a sensible thing to check.

Either way I would follow the advice by @Bryce.