old model 464 with garbled screen patterns

[salvogendut]

I got this machine a few weeks ago. It most likely had been stored in a damp place and it showed. Initially it seemed to be working well but the characters in the screen looked a bit off , like they had some 'ghosting' effect. Also some garbage showed up on screen randomly. The power connector also seemed to be not ok and if I touched the machine would glitch and power off and on again, it was wobbly. After I gave I gave it a clean it powered on normally just once more and as I touched the wobbly power plug it powered off and when I powered on again it shows just a garbled screen with some patterns. The patterns seem to change at every power on. Sometimes the border is a different color. Any idea? See pics

[Bryce]

Hi,
     the ghosting and dots are due to the video converter you are using, not a CPC issue. The power socket is obviously very dirty and/or has bad solder joints. Fix the power socket first and then see if you still have problems. If the patterns in the last pics still come after fixing the socket, then one or more RAM IC's failed while you were testing it.

Bryce.

[salvogendut]

Hi,
    the ghosting and dots are due to the video converter you are using, not a CPC issue. The power socket is obviously very dirty and/or has bad solder joints. Fix the power socket first and then see if you still have problems. If the patterns in the last pics still come after fixing the socket, then one or more RAM IC's failed while you were testing it.

Bryce.

Hi,
Thanks for replying. I did manage to desolder and replace the power connector with a new one. The original one was rusted and very dirty. However the situation did not change, I still see the patterns on screen. Would a diagnostic rom help pinpointing the failed chips? I am waiting for one such cartridge to be delivered in the next week. 

[Rabs]

Does this help Garbled Screen Amstrad CPC 464 video failure.?

[McArti0]

40007 you can't use without radiator/cooler

[salvogendut]

Does this help Garbled Screen Amstrad CPC 464 video failure.?

Thanks for the interesting clip. I am planning to study it very closely

[salvogendut]

40007 you can't use without radiator/cooler

I am not. What you see is just the stripped down board after I tried to remove and then re-insert the GA in case there was anything amiss. I noticed this chip gets quite hot and I am not planning to use it long term without its insanely thermal paste smeared heat sink 

[salvogendut]

Would this kind of chip be ok as a replacement? I am trying to order some beforehand

[McArti0]

You could have already broken 40007 without a cooler.

[eto]

You could have already broken 40007 without a cooler.

I never had an issue with running a 40007 without cooler even for a little bit longer. I wouldn't run it for hours without the cooler but I didn't recognize a heat issue when I do a few tests without the cooler applied. 

Would this kind of chip be ok as a replacement? I

yes

[Bryce]

You could have already broken 40007 without a cooler.

Technically correct, but you'd have to run the CPC for quite a while. If the CPC isn't working, I doubt he was running it for more than a few minutes each time.

Bryce.

[salvogendut]

question for the wise ones: how can I debug ram chips without an oscilloscope? If I used an external rom box that is able to boot to a diagnostic program , would that tell me exactly which chips are failed? I have an ULIfAC , can I use that to boot a diagnostic rom? Would that work? I have seen Noel's Retro Lab videos where he is using a Dandanator with a diagnostic program that somehow shows red or green lines on screen corresponding to ram chips

[McArti0]

After Swith On CPC. ROMDIS line to Vcc

O screen You should see narrow stripes.

[salvogendut]

After Swith On CPC. ROMDIS line to Vcc

O screen You should see narrow stripes.

Hey thanks for replying! I am not really familiar with the platform so if you could elaborate a bit what ROMDIS is and what should I do with it, that'd be super helpful!!

[McArti0]

ROMDIS.  Pin22 ROM ic103 cross to +5v like pin28

https://www.cpcwiki.eu/index.php/File:464Schematic_new.png

[eto]

If I used an external rom box that is able to boot to a diagnostic program , would that tell me exactly which chips are failed? I have an ULIfAC , can I use that to boot a diagnostic rom? Would that work? I have seen Noel's Retro Lab videos where he is using a Dandanator with a diagnostic program that somehow shows red or green lines on screen corresponding to ram chips

First of all the good news: Your CPC is almost working. There's just a dead RAM IC (or a few) - and at least it does not have a full short but just does not work. 

As RAM is not working properly your CPC fails during firmware initialisation as soon as it needs RAM. This will prevent you also from running any tools from a normal ROM board as it fails before further ROMs can be initialised. Therefore you need a ROM BOX that can replace the internal firmware. I'm not sure if the ULIFAC can do that - and if it can do that, if it can do it without a working CPC first. Some boards definitely can do that. E.g. Dandanator can do that, M4 also can do that. (Another option could be to replace the internal firmware PROM with an Eprom that contains Amstrad diagnostics - but that requires desoldering the PROM.)

If you have such a board or if you replace the firmware PROM you can use the "lower ROM" version of Amstrad Diagnostics. Amsdiag then runs instead of the firmware and can test your RAM. It also clearly shows which IC is malfunctioning. Check out the documentation on Github for more information. 

Without such a board you might end up with A LOT of manual testing and you might have the chance of causing even more trouble. An accidental short at the wrong pin and another IC could be dead. If you have a desoldering gun and are familiar with replacing ICs the easier solution could be to just remove all RAM ICs put sockets in and replace the RAMs with known working ones.