Amstrad GX4000 - What Could Have Been? (A Janstrad Special)
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05-01-2024 8:24pm#1
Often the butt of jokes given its weak library, lack of exclusives, and comparatively low power at time of launch...the Amstrad GX4000 is certainly up against it. What can be said about it, has most likely been said already - but could it have been a better machine? Well, yes. In this thread I'll be doing some timely maintenance on the GX4000 (new caps and a new voltage regulator), then I'll be doubling the RAM from 64K to 128K (ok for stock games this isn't necessary, but it does open up more modern homebrew titles and a few of the 128K-needed CPC games), and then to finish off, I'll pair it up with a C4CPC Cart that'll allow me to play the MANY unofficial GX4000 ports.
Granted, after all that, it'll still be a GX4000, but at least it'll be able to play a much bigger library than it was originally granted. Let's crack on!
^^ A nicely boxed example, not mint by any stretch, but not bad at all. Pretty sure these dropped even lower than £50 blips at some stage too when they were being cleared out.
^^ Oops, I may have invalidated any guarantee from Amstrad by doing what I'm about to do....
^^ An interesting side note, Burnin' Rubber sounds like it might be the most intense, exciting, and thrilling game possibly ever created??
^^ Ok, getting to the console itself...it's actually a very nice looking machine. Very slick design, definitely a 90's UFO vibe off of it, but I like it!
^^ Original scart lead (which has started to react with the polystyrene, and has gotten a little stiff over the years.) The original power supply also, and because it's not recommended to use the original power supply if using a C4CPC, then I'll need something new/modern to take over.
^^ Brand new power supply and scart cable.
^^ A quick power on test to make sure it all works before I do any work on it. Not sure if Burnin' Rubber lives up to the blurb above...
^^ x2 screws and a few clips on the underside of the shell, and we're in. There's a good few caps to get through. I'm doing the caps as a preventative measure more than anything else. There's no signs of leakage etc, but at this age, I'm a happy member of the 'preventative maintenance' camp.
^^ There didn't seem to be a cap kit for the GX4000 listed in any of the usual places, so I had to compile my own from CPC Ireland Farnell.
^^ An interesting factory bodge on both controller ports, how very Amstrad.
^^ Oops, on one of the larger caps, the eyelet came away. Thankfully, there's an obvious trace right beside it, so the repair is easy.
^^ Copper of the trace exposed, and a small piece of resistor leg soldered into place (thus reconnecting the trace, and the new capacitor.)
^^ Fully recapped. Quite a few of the new caps are smaller than the original ones, which is absolutely fine here.
^^ Fallen Amstrad heroes!
^^ The original voltage regulator has served its time too, and ready for retirement. I'm replacing it with a 78S05, which is ever so slightly more efficient. It won't fail any time soon either, so this GX4000 should be good to go for another few decades!
^^ Some new thermal compound applied, and then all soldered up.
^^ Time for a quick power on test, to make sure everything is as it should be!
^^ Excellent, maintenance done and ready to move forward now!
^^ The wonderful C4CPC in place, let's take it for a test run.
^^ A game never made for the GX4000. Let's see how it goes...
^^ Cool, works perfect.
^^ Now, time to see if a 128k Demo works with the standard 64k...
^^ As expected. Let's remedy that...
^^ To do the mod, we need the x2 additional ram chips, and a resistor.
^^ The x2 existing RAM chips shown here at the top of the pcb. There's no space on the pcb for more RAM, as the console was only designed to have 64k.
^^ To fit the RAM, we need to piggy back the new RAM atop the existing chips. Pin 16 of both new chips has been lifted, as we need to provide a separate signal to those pins.
^^ New RAM soldered to old chips. It's not my finest work, but it should be fine.
^^ Pin 16 of both new RAM chips connected together with some enamel wire. All that's left left now is to provide these two lifted pins with a signal from the CPU.
^^ This is the only tricky bit, pin 91 is the one we need here. It's been tinned here.
^^ Enamel wire now connected to Pin 91 of the CPU, and linked to both lifted pins of the new ram chips.
^^ To actually enable the new RAM chips, we need to enable them via the memory controller. This is done by bridging pin 8 to pin 11 via 10k Ohm resistor. We're all set...
^^ Running the RAM tester via the C4CPC, we can see the GX4000 is now detecting 8 banks of ram (0-7), instead of normally 4. It's looking good...
^^ Sweet, the 128k demos now work perfectly!
^^ Now everything on the C4CPC cart works perfectly.
^^ That's it. There's several hundred (maybe more?) CPC ports available to play, all of the original GX4000 games, and the few CPC Plus games also, now available to play on the GX4000. It's RAM has been doubled, it's got some minty new caps, and a lovely C4CPC to play with. Great Success!
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Comments
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I wasn't very happy with the soldering of the the ram upgrade, so decided to revisit it there today and fix it.
^^ I changed it to a standard piece of wire to link the two new ram chips, and redid the enamel wire onto the CPU. It was a while since I'd done any intricate soldering, and on the day, forgot to use flux. It was ok, but with flux, I've a much nicer join onto the cpu leg.
^^ I really wasn't on my game the day I did this! Luckily in opening it back up today, I noticed this silliness and fixed it. Thankfully it didn't cause any issues. For anyone not into soldering/repairs, the capacitor shown above is soldered in backwards and the negative side of the cap (denoted with the stripe) is soldered into the positive position (denoted by the plus sign)! Derp!
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