Hi All,
I feel I should mention something else I found after replacing the RAM (a few days later).
I was thinking about things a little more, and remembering a post by Gerald regarding the original GX power supply and a GX he fixed...
http://www.cpcwiki.eu/forum/amstrad-cpc-hardware/%28please-read%29-gx4000-with-original-power-brick-and-c4cpc/I think I may have been lucky with my fix in that I use a 5v power supply and run it off the CTM monitor.
If I had used a larger supply (9v) in the other socket, I may have blown the RAM again (or worse).
After re-reading the above post, I tested the protective diode that Gerald mentioned... D183 on the board (near the voltage regulator with the heatsink).
It appears mine is testing as shorted, therefore it would be doing nothing (no protection).
Running on 5v only is fine, as all the circuitry is 5v anyway, but beyond that I might have been in trouble.
Just thought I would mention this to anyone looking at fixing a 'dead RAM' GX400, as my assumption with these is that somewhere along the line, someone has used either a faulty GX power supply or simply a wrong voltage supply (or in the wrong socket). And I'm also going to assume that if the RAM is fried in this situation, there is a good possibility the Diode is also taken out.
I would say it is well worth testing the diode as part of the RAM swap.
If the fuse (RAM) does not blow quick enough, the fix may not be so bASIC
Cheers,
Shane