I've just serviced a GX4000 that failed after using a C4CPC.
To make it short, the original power supply likely failed, ultimately frying the RAM.
The C4CPC consume up to 80mA more than a regular cartridge, a GX4000 is consuming about 400mA + 50mA if it has an RF modulator. This slightly exceed the rated current supply of the Amstrad provided power brick.
Therefore I urge you to stop using your Amstrad power supply with the C4CPC.
Instead :
- use any regulated DC 9V to 12V 750mA (positive on center pin, GND on outer pin), powering the 11V entry. The 11V is used to power the 5V regulator and to drive the scart switching pin.
- use the 5V supply input and the DIN rgb output (as if connected to a plus monitor). 5V supply may not work well with GX4000 having a RF modulator when using the SCART plug.
As a general rule, when using the 11V input, using a power supply with a voltage as low a 7.5V will work with the possible exception of the scart switching signal. Using it at lower voltage will minimise the 5V regulator(s) heating.
Failure details :
To fix it, I first replaced the main voltage regulator as it was issuing 7.5V instead of 5V. However, this happened also with the new one.
I then found that the 7805 bypass diode (to protect it when powered from a 5V supply, see attached schematics) failed in a way that feed the 11V on the 5V. So I removed that diode to discover that the RAM chip failed as well.
Once the RAM have been changed, everything worked fine. I've also replaced the diode with a new one.
Now, what happened ?
I suspect the power brick to have failed, or at least had a transient that made the diode fail, which in turn fried the RAM, which roughly protected the remaining part of the GX4000. The GX4000 jumped to 1A with the dead RAM.