🇬🇧 Amstrad CPC664: Part 2 (Troubleshooting Starts) [TCE

Unfortunately this fellow doesn't work at the moment - no video output. The CPC664 originally came with the 40008 gate array, later replaced by the pin-compatible 40010. The orignal 40007 in the CPC464 isn't pin compatible.
I can see that there is a 4MHz clock into the Zilog Z80 but not much else activity. There has been some repair work done on this machine - I can see that three of the DRAM chips have been replaced (now socketed) and I don't believe the 40010 is original to the machine.
Let's see.
vRetro's 40007 & 40010 replacements:
www.vretrodesign.com/collecti...
Open source replacements:
github.com/codedchip/AMSGateA...
Interesting read about the Gate Array:
www.grimware.org/doku.php/doc...

[@australiancomputermuseum]

Thanks for the shout out! Even if it's not running on the day, it'll be good to have a 664 on display to complete the set!

[@Brfff]

I'm planning on heading on down around 5am-ish ... I'll bring down the HP Series 80 stuff as well!

[@MrWaalkman]

@16:24 Pin 13 on that TC74HCU04P looks knackered.

[@jason-birch]

If the Z80 is getting a clock, the only thing that would stop it outputing DRAM refresh on A0-A7 would be BUSACK low, as this would mean the Z80 frees the buses for external use. So A0-A7 should be active if BUSACK is high. And the gate array won't do anything until the BIOS tells it to.

[@Brfff]

Yep, good 4MHz signal at 05:44 ... didn't check the lower address lines I think, will check.

[@WacKEDmaN]

BUSACK and BUSRQ isnt used on the CPC...they broken out to the expansion port.. but i cant see them anywhere else on the schematic... (BUSRQ and NMI are both pulled high) the GA owns the bus... its controls it all.. reads MREQ, M1, RD, IORQ, generates Clocks, INT, ROMEN, RAMRD, READY, MWE, CAS, RAS, and toggles the 74LS244 enabled pin to read or write to the data bus..aswell as generating video signals...

[@MrWaalkman]

What about the MC6845P? Nice seeing a clock signal without any extra baggage. :)

[@WacKEDmaN]

just a heads up....40007 and 40010 pinouts are different! ..you might want to grab the correct pinout for probing!! :P id start with the diag expansion will bypass the rom and ram... will let you know if the z80 and GA are good no screen at all suggests CRTC isnt sending H/Vsync to GA...GA is bad, or Z80 is bad... once you can get something on screen you can test ram/multiplexers/buffers... the clock into the z80 should be 4mhz (pin 6 on the z80)... you seem to be probing the clock for the sound which is only 1mhz... NPHI is the Z80 clock on the 40010 (pin 19 on the GA).... NCPU (pin 14) is the 1mhz sound and memory clock

[@Brfff]

Yep - I should've been a bit clearer in the editing but I'm using the 40010 pinout when checking signals from 05:05 onwards ... "let's try that again" ... good 4MHZ clock (05:44)