Faulty Amstrad, what could it be?

[chicknchock]

HI Everyone, i was wondering if anyone can help assist me with this issue?

here is a video of what happens when cpc is switched on


amstradfailinh - YouTube

any advice or info on what this is so i can get it sorted would be appreciated,
and i was so eager to play rebelstar!!!


((Sorry if this has been posted three times ive been having issues with pc at work...)0

[MacDeath]

The main issue is that you have a monocolour green monitor.... you'll never get a good coloured picture out of it.




sorry, had to do the joke.
have you tested on another monitor anyway ?

BTW it seems it gets stuck on rebooting... may be issue with ROM or firmware, or on/off circuit (bad unstable contact) at first glance.

[ralferoo]

I can't think what'd be causing it to reset like that - maybe something has fallen inside and is shorting something...

But the good news is that most of the things that fail seem to be working OK - the CPU, ROM, RAM and CRTC all seem to be largely working.

Another ideas is that perhaps the monitor idea isn't too farfetched - it could even be a dodgy power supply in the monitor...

[Grimmsqueaker]

That could be as simple as the on / off switch on the right hand side, possibly a dirty connection making it reset

[chicknchock]

Hi guys I managed to try the cpc on another monitor and same prob...

I tried the green monitor on a working cpc and it worked fine, so certainly a prob with the Computer and not the monitor...

I do like green, it reminds me of pipboy 2000 off fallout 3 lol!

Do these things have removable rom chips like an Amiga, maybe I could swap them around, maybe loose connection inside? I will get screw driver out tonight and have a look!

[chicknchock]

That could be as simple as the on / off switch on the right hand side, possibly a dirty connection making it reset

Thanks for suggestion I will try that

[Bryce]

Somethings causing a reset, probably due to a voltage drop. It could be the power switch (on the CPC) being very dirty, or it could be a chip (which is most likely getting hot too). Try bridging the switch on the PCB first and see if that helps.

Bryce.

[chicknchock]

Thank you Bryce... I got another cpc now...

I unscrewed them both and split in two...
Tried fully working cpc top half with faulty bottom half and still a prob, so it's certainly the board or a chip...

I took two chips off working cpc half and swapped and its still resetting.. So it's either another non removable chip on the board or maybe the power / display port or a faulty resistor...

This is turning into a head ache lol...

FYI I have tried the assumed faulty top half with working board half and that config works...

There isn't much to these things!!

[Bryce]

My guess is that you either have a dodgy RAM or dodgy CRTC.

Bryce.

[chicknchock]

Crtc? Sorry I don't know what that is.

[robcfg]

It is the chip labeled '6845', and it's part of the video signals generation.

[ralferoo]

It looks fine from the video ... certainly, the horizontal registers are visibly set correctly and the lack of vertical hold could be explained by the constant resetting.

That's why I think the CPC is mostly fine - you wouldn't be seeing any text at all if the lower ROM and CPU were faulty. The RAM is obviously well enough to be able to boot that far and hold a recognisable copyright message, but there might be another bank that's intermittently faulty that later causes it to crash.

It always seems to crash when accessing the upper ROM (i.e. basic), so if could be something as simple as a short from the high ROM address line to GND.

Thinking about it, I'm a bit suspicious about the gate array as the border is bright on some of those images, and it should be dark blue just like the background. It's true that when the gate array is first powered up, the border can be anything, but its colour would have been changed by the time the copyright message is displayed and then remain that colour through a reboot. The gate array also drives the top bit of the ROM address too.

Oh, and if you're trying to diagnose a problem, you'll probably want the schematics... Grab them from here: Service Manuals - CPCWiki

[Bryce]

He said he tried "the two socketed chips" from a known working CPC, which means he's tried a different CPU and Gate Array, so they must be ok.

Bryce.

[chicknchock]

Thanks for the in depth help guys, i'm wondering if it could be something as simple as a dry solder joint somewhere on this board....but could that cause strange behaviour shown in the video?
other then that i'm wondering if it could be indeed a ram issue....

it would kind of make sense....

I dont fancy finding out though which chip it could be, i gave up removing surface mounts a long time ago and my hands are older then they were, i think i would burn the board to bits, its looking fragile!!

Something which is odd, is that I have tried to wiggle the Video cable, and also applied a little bit of force to push it in further then it should go (i have been very carful) and i seem to be getting to different stages of boot before it crashes... without force i get a rolling screen.... but with slight force it stops and just locks....

i dont know if this is just me messing with the cable and causing issues with the signal or if this is having significance with the boot process...

interestingly i havn't had it boot hang any further then the words SOFTWARE LIMITED.

its all very strange and i thank you all again for your input...

i may have to invest in a soldering iron!

[chicknchock]

He said he tried "the two socketed chips" from a known working CPC, which means he's tried a different CPU and Gate Array, so they must be ok.

Bryce.

Indeed yes i have tried replacing both chips from a working cpc and this didnt help.

sorry my other  message was awful with grammer and punctuation (i'm hiding my online activity at work and it gets tricky  )

[Bryce]

Thanks for the in depth help guys, i'm wondering if it could be something as simple as a dry solder joint somewhere on this board....but could that cause strange behaviour shown in the video?
other then that i'm wondering if it could be indeed a ram issue....

it would kind of make sense....

I dont fancy finding out though which chip it could be, i gave up removing surface mounts a long time ago and my hands are older then they were, i think i would burn the board to bits, its looking fragile!!

Something which is odd, is that I have tried to wiggle the Video cable, and also applied a little bit of force to push it in further then it should go (i have been very carful) and i seem to be getting to different stages of boot before it crashes... without force i get a rolling screen.... but with slight force it stops and just locks....

i dont know if this is just me messing with the cable and causing issues with the signal or if this is having significance with the boot process...

interestingly i havn't had it boot hang any further then the words SOFTWARE LIMITED.

its all very strange and i thank you all again for your input...

i may have to invest in a soldering iron!

It could be many things:

1 - An IC that shorts to ground when activate.
2 - A dodgy capacitor
3 - A Video signal shorting to GND

The cable waggling results are suspect, can you try the CPC on a different monitor?

Bryce.

[Gryzor]

You didn't say if you tried cleaning/bypassing the power switch?

[chicknchock]

You didn't say if you tried cleaning/bypassing the power switch?

I tested a working top half of 464 (keyboard&psu) with the assumed faulty board and was still having the same problem so that was ruled out, thank you thou.

i've ordered a soldering iron e.t.c. and hoping to have it all soon so i can start messing about, im not letting this beat me lol

[Bryce]

Don't "mess about" if you're not sure what you are doing. I spend a lot of time trying to save the resulting mess of such experiments.

Bryce.


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