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Hi All

Just purchased a ? Non Working CPC464.
It has a Tiny MotherBoard.

The Video display looks like this :-

Amstrad CPC464 16-Nov-2017 Board Info
Board 40010
      MC0044A
      Z70374
Chips
UM 6845R
40010
40009
Zilog Z0840004PSC

"" Update""
The Del Key Beeps.
If I go to start the tape This shows on screen as characters.
if i do "CLS" that works
so most of it is working except the Video is Unwell.

Thanks     Ray

Hi All


Swapped the 40010 with known working one.
Swapped the Z80     with known working one
The Fault still persists ?
It looks like 2 Pages of the same thing horizontally offset ??

Ray

Hi All


6845 Is having a Lobotomy at the moment and a clip (40 Pins).
Stay tuned
Ray

My bet is that one of the MUX's between the CRTC and the RAM has failed / stuck.

Bryce.

@bryce


Ok Thanks I will have a look,
I am part way through replacing the 6845 at the moment.
I will have a look at the Mux area after that.
Thanks


Ray

Quote from: Bryce on 08:33, 16 November 17
My bet is that one of the MUX's between the CRTC and the RAM has failed / stuck.
Bryce.

Yep that is the area that is faulty


I have called this part of the fix Gotcha Part 1


Gotcha Part 1
6845 Pin 10 to Pin 3 IC 9 Trace Open on Motherboard
Now The display has only 1 image not 2
Nearly there

Ray

Hi All


We are up to Gotcha Part 2


I have now 2 lines on the IC 109 74LS153  Pins 12 and 4, BOTH these Lines are HI, ( I have Replaced the IC 109)
these only come from IC 108  8645 (Replaced)  Pins 17 (M213)  and 16 (MA12)


I have checked these lines to +5 Volt line ( With the Power Off) and they are NOT directly connected to +5 Volts.


I am Verrrrry Stumped.


What do these OUTPUT lines do and how are they activated (6845) .


? ?  Replace the ROM  ? ?


Thanks     Ray

Quote from: Audronic on 03:07, 17 November 17
I have now 2 lines on the IC 109 74LS153  Pins 12 and 4, BOTH these Lines are HI, ( I have Replaced the IC 109)
these only come from IC 108  8645 (Replaced)  Pins 17 (M213)  and 16 (MA12)

Pin 16 and 17 are muxed with A14 and A15. It's expected that they are high all time. Screen is located in 0xC000 to 0xFFFF.

Quote from: Audronic on 03:07, 17 November 17
? ?  Replace the ROM  ? ?

Could so a checksum and compare to a working CPC?

@Gerald


Thanks for the Ramtest ROM.
Finally i got it to work (hard to put in slot 7) Used TFM's old ROManager 64, and it worked in the NEW D-Rom (TotO Thanks)
This machine is a wonderfull challenge, I think its time to Snip out the 40009 ROM (No Socket Damn)
Photo included


Ray

Hi All


FIXED
Two Tracks (Traces) OPEN under the sockets of the 4 Mux Chips 74LS153's U109, U104, U113, U105.
The Tracks looked a little Black in colour.

Bryce You were Correct Thanks for that.
Gerald Thanks for your help.

Ray