464+ -> 6128+ upgrade... what have I done wrong this time???

[Chinnery]

I've been working on upgrading my 464+ to 6128+ spec, but, as usual, have stumbled at the first hurdle.
I've added the resistor required, the caps and the memory chips, but when I start up the CPC I get either a black screen (using a game cart), or a green screen with random hieroglyphs on. If I remove the extra 64k of ram, everything works as it should... What have I managed to mess up this time?
The memory chips I've tried are labelled NEC D41486C-10. Are these too quick or incompatible. I have 5 of them, and tried them all in different combinations, but don't really have a way of testing to see if they're good. I have gone "off road" by moving the two wires to C21 and C23 to under the PCB, but a continuity test/ohms reading suggests that I've not cocked that bit up.


h e l p!!! 

[gerald]

I've been working on upgrading my 464+ to 6128+ spec, but, as usual, have stumbled at the first hurdle.
I've added the resistor required, the caps and the memory chips, but when I start up the CPC I get either a black screen (using a game cart), or a green screen with random hieroglyphs on. If I remove the extra 64k of ram, everything works as it should... What have I managed to mess up this time?
The memory chips I've tried are labelled NEC D41486C-10. Are these too quick or incompatible. I have 5 of them, and tried them all in different combinations, but don't really have a way of testing to see if they're good. I have gone "off road" by moving the two wires to C21 and C23 to under the PCB, but a continuity test/ohms reading suggests that I've not cocked that bit up.


h e l p!!! 

I would suspect the memory device.
Adding the 2nd bank even without the resistors should not prevent the cpc from working. Most of the resistors are only used to configure the ASIC and enable the 2nd bank, except R155 that route the second bank CAS from ASIC to DRAM.
If you have your additional RAM on socket, just test each additional ram individually in each socket.
If only one of the device is dead, it should prevent the CPC to start whatever the socket is.
If one socket has a problem (like CAS flying in the breeze), a device mounted on it will prevent the CPC to start.
If both device are dead, then there is no option

[Chinnery]

... except R155 that route the second bank CAS from ASIC to DRAM....

Ah, thank you. This was the clue I needed. It seems in my effort to get R155 as flat as possible to the PCB, I had managed to damage it, so it was no longer connected internally... either that or it was originally broken.  (much more likely me breaking it!)
I have replaced that resistor and everything is now working great!
Again, thanks