GX4000 digital joystick port repair

[beaker]

Hi, I have a problem with the digital joystick port 1 on my GX4000. I bought it off ebay last month and the port had a few pins missing and wouldn't work at all so I thought I'd have a go at repairing it myself and try and learn a bit of soldering.
I bought 2x 9 pin D-Sub from ebay that connects to the PCB as the original one did. Desoldered the old one and carefully bent the resistors(?) to one side and soldered one of the new ones in putting the resistors back into place. Now I can move left and right and both fire buttons work but the up button refuses to work so it's a bit better than before. I tried this with 2 controllers that seems to work fine with Burnin' Rubber on port 2 and 2 games, Burnin' Rubber and Switchblade. I tried adding a bit more solder incase it was a bad connection but this didn't work. As far as I can see the soldering I did was only around the pin I was trying to solder so there should be no contact between pins. I desoldered that port and tried the second D-Sub, this time cleaning that part of the board with some rubbing alchohol. Again, I had the same problem.
As I'ved tried 2 D-subs I am assuming they are both working and there is contact being made between the pin and PCB.
Anyone have any idea what I can try or if I've messed up somewhere?

[Gryzor]

Hello Beaker, and welcome to our forum

I don't really get how "a few pins" could be "missing"... how on earth could that happen? Anyhow, assuming your soldering is ok, have you tried following the routes on the motherboard to see if these are ok?

[MacDeath]

Aren't some pin naturally not connected ?

As the PLUS/GX range already include the "Y cable" ?


According to the page on the wiki, on PLUS' the fire3 is not connected per exemple...



I also heard the GX4000 to be prone to break on the joyports...

Perhaps you simply got some broken pins.




As you can see, with a Joystick splitter, the pin 9 is no connected.

Also I posted there some extract from the Service Manual, the one with the full schematics...
As you can see not every pins are actually connected.

But IMO this is quite a Shame Amstrad made not extra effort on those ports...
I mean A good Joystick with 3 buttons or Autofire or even a mundane Mouse  ready to connect is great...

But I guess having no Voltage inside the Joypads is perhaps better for security concerns, as you may spill your Soda or beer on those.

[Bryce]

If both joysticks have the same issue, then the problem isn't at the port end. Rather the part of the circuit that is common to both joysticks has a problem. The inputs of the joystick are joined together by two diodes (D120 and D124 for the up signal) and then go to the AY-3-8912 (Sound generator chip). First check if the entire keyboard works. If it does, then the AY itself is fine, if it doesn't you've got a faulty AY. If the AY is fine, then it's just the connection from the diodes to the AY that's broken/cracked/melted/eaten by your hampster. Check with a multimeter, whether there is a connection between the anode of D120 or D124 to pin 14 of the AY. They should be connected, if not, that's where the problem is.

@MacDeath: Pin 5 and 9 of the Sub-D aren't used/connected, but the physical pin should still be present.

Bryce.

[beaker]

 Hi, thanks for the great replies. Finally got some time to have another go at it. When I used the multimeter between D120 and pin 14 of the AY and it made a connection and I was able to use the controller properly. Couldn't see anything obvious on the PCB as to why there was a break in connection so I ended up soldering a wire on the base of the board between the 2 and now I have a fully functioning GX4000
Not sure if that was the right thing so do but ignorance is bliss
Think I may see if there are any evening classes on electronics to get a better understanding.

[Bryce]

No, that was exactly the right thing to do, trace breaks aren't always visible. The main thing is your CPC works again. It was most likely a dry joint at the AY end, unless the GX4000 got some physical abuse, it's rare that a track would crack or break.

Bryce.