Weird CPC664 Fault

[Audronic]

Hi all 

I am Having problems with a CPC664 Motherboard repair.
I was wondering if you may have struck this before.
Can you Help

This is using Geralds WIP Tester

Thanks Keep safe 

Ray

03 9 397 7695 In Williamstown Victoria

[Audronic]

A small update.

Boot up screen is Unwell
The top line should say "AWA" not Isp ?

Any thoughts ?

Thanks

Kep safe

Ray

[GUNHED]

A bug in the firmeware ROM?

[eto]

Maybe a malfunctioning CRTC or broken traces from CRTC to the multiplexers. 

How did you start Geralds RAM test? From ROM? Can you also try LLopis' Amstrad Diagnostics?

[Audronic]

A bug in the firmeware ROM?

Hi Gunhed

Ok Thanks

I have changed the 40015 rom and this has helped
About an Hour later only a Blank screen Grrrrrrr

I am about to change the Gate Array and see what happens.

Thanks

keep Safe

Ray

[Audronic]

Maybe a malfunctioning CRTC or broken traces from CRTC to the multiplexers.

How did you start Geralds RAM test? From ROM? Can you also try LLopis' Amstrad Diagnostics?

Hi Eto

I Have a lower rom board with Geralds and Noels Diags - Switchable..

Thanks I will buzz out the lines from the CRTC  to the Mux's

Keep Safe

Ray

[Brocky]

i think one of the lines on the mux's has failed...
i dont think a buzz out will help... better off lookin at the lines on a scope if ya have one...the physical connection could be fine but one of the chips is outputting bad signal on a line

im not sure about geralds diag... but on noels, if you get a memory error you should be able to track down which ram chip thats 'failing' is connected to which mux chip
(i know ya can with geralds too but.. i not sure what numbers correspond to which ram chip)

[Audronic]

i think one of the lines on the mux's has failed...
i dont think a buzz out will help... better off lookin at the lines on a scope if ya have one...the physical connection could be fine but one of the chips is outputting bad signal on a line

im not sure about geralds diag... but on noels, if you get a memory error you should be able to track down which ram chip thats 'failing' is connected to which mux chip
(i know ya can with geralds too but.. i not sure what numbers correspond to which ram chip)

HI Brocky

Ok I am half way thru testing the continuity, I will keep going to Pin 40 from the CPU to all pins connected to where ever.
Yes I have a scope will do that next.

Ok Noels Diag gives Me 1 Beep (HI) goes thru the Memory test, screen changes to Blue and 3 LOW Beeps and that's it ??

Thanks

Keep Safe

Ray

[Audronic]

Hi Brocky

Have tested all the pins from the Z80 to what it is connected to all Test OK

I will look at the Mux chips with the scope

Thanks

Here is a copy of the Test points for a CPC664
From the Z80 to wherever.

Keep Safe

Ray

[eto]

I have changed the 40015 rom and this has helped
About an Hour later only a Blank screen Grrrrrrr

Did it fully work after changing the ROM? 

Is it blank grey screen with black border now or just a black screen?

[Brocky]

noels diag seems to be passing which is a little odd.. should show a screen with green and red bars if the ram is bad....

&7C  = 0111 1100
&78  = 0111 1000

...could bits 3 be bad? maybe bit 1 and 2 aswell? could still be linked to mux or even crtc... im speculating!! i cant find any info on gerard... the version here shows a different tester...
check the lines with scope around the lower bits ram and muxs and .. n see if theres anything you can see

theres a good bit on it at 8:40 mark in noels vid...

[GUNHED]

A bug in the firmeware ROM?

Hi Gunhed

Ok Thanks

I have changed the 40015 rom and this has helped
About an Hour later only a Blank screen Grrrrrrr

I am about to change the Gate Array and see what happens.

Thanks

keep Safe

Ray

Oh. Good you got one step forward. But I'm sorry to hear about the black screen. Could be some kind of interruption of power or a signal due to heat, but the chances for that are not the best.

Really HOPE it will all work out for you and your nice CPC664. 

[Bryce]

Hi Audronic,
      if you haven't tried a different CPU, then do that first. Then check the timing of the reset circuit. Then check for cracks / dry joints on the address lines around the CPU area.

Bryce.

[Brocky]

edit: oops sorry .. i didnt mean to post!

but yeah dont listen to me! ... bryce knows what hes doing!

[Bryce]

edit: oops sorry .. i didnt mean to post!

but yeah dont listen to me! ... bryce knows what hes doing!

Don't underrate your own suggestions, even the most experienced experts forget or miss the simplest things sometimes. Every opinion should be heard.

Bryce.