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Mains Switch replacement

Started by gertk, September 20, 2011, 08:14:13 PM

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Just a sneak preview of my mains switch mod. These are the old and the new switch and the modification needed on the switch. I will have to openup one of my G7400s to make some pictures of how it is mounted.
The first pictures shows the old and new switch side by side. The new one can handle 128 Amps inrush current and can safely switch off with 4 Amps flowing through, more than enough for the current required for the Videopac.
>>G7000 G7200(P+S) G7400 N60 JET27 VG5000 ZX80 ZX81 ORIC-1 COMX35 Aquarius<<


8 bits of fun


Here a picture of the end result
>>G7000 G7200(P+S) G7400 N60 JET27 VG5000 ZX80 ZX81 ORIC-1 COMX35 Aquarius<<


Just a small addition to mounting this switch:

Disclaimer: if you have no experience with electrics and soldering I would advice you to let someone do this which is qualified or capable!

You will need:

  • a power switch like the one on the photos
  • a small soldering iron (15 to 40 Watts will do, or even better: a temperature controlled soldering iron)
  • soldering tin
  • some small cutters
  • a small sharp knife (scalpel or a small 'break off' kind of hobby knife)
  • a midsize Philips type screwdriver
  • some workspace

Unplug the G7400 and leave it alone for some minutes. Some G7400 power supplies keep the smoothing capacitors of the mains part alive for several minutes which will give you a nasty shock when you touch the back of the powersupply board.

Find a padded surface to lay the G7400 upside down if you want to prevent scratches on the top.

Remove the bottom of the G7400.

You will find two circuit boards: the large main board and the smaller powersupply board.
The powersupply board is held in place with two 'philips' screws with a fairly large head with a white plastic (insulating) washer underneath. Remove these screws and lay them aside.

The powersupply is fixed to the mainboard with three wires (red, brown and black) which can not be detached. Find some piece of cardboard or thick plastic (a CD or thin DVD box will do fine too) and lay that on the mainboard. Now carefully turn over the powersupply board without straining the wires and lay it on the piece of cardboard or plastic on the back of the mainboard.

You will have now a clear view of the mains switch.
Unscrew the two 'philips' screws of the switch.

You will find that you can not lift the switch as the big red/orange button is still attached. Take a firm hold of the switch and pull it vertically and the button will fall off on the other side.

When you have removed the original switch there are two small plastic 'pins' sticking out of the mounting place next to the holes where the screws were, these will get in the way with the new switch. You can carefully remove them with a sharp knife or some small cutters.

Now take the two screws with the large diameter heads which were used to mount the power supply from the white plastic washers.  We are going to use these to mount the new switch. Put the screws which held the old switch into the washers and put them aside, you will need them to mount the powersupply later on.

Modify the mounting plate of the switch as seen on the photos above, the material can be cut with some small cutters.

Desolder the cables from the old switch. You might need to strip and resolder the ends before soldering them to the new switch.
On the picture of the end result you can see that the two cables (brown and blue) are soldered to the bottom lugs of the switch and the thinner black and brown cable is soldered to the top lugs (viewed from the mounting position). Stick the end of each cable about halfway through the lugs and bend the end back (like a hook). Solder the cable to the lugs making sure the solder attaches to both the cable end and the lug.

When placing the new switch you will find that it now can move left and right a bit, don't worry: once the two screws with the large heads are in place it will sit tight. Turn in the two screws but do not tighten them so the switch is still able to move left and right.

Take the button from under the G7400, be careful not to strain the powersupply wires as you will need to lift the whole G7400, you can also slide the G7400 to the edge of the table and catch the button.

The next part is to make the button more evenly leveled with the top when the G7400 is switched off:

Take the old switch and carefull cut the top square section at the first rib of the stem/pin where the button was on.
The small piece you have cut off will function as a filler for the button. Push this part into the square hole in the button as far as it will go.

Now carefully press the button onto the switch while holding the switch, this is a bit fiddly. It should snap on and the switch is now probably in the 'on' position. Try pressing the button, it should click nicely and move without sticking to the sides of the case. You can adjust the switch for best results. If the switch moves correctly, tighten the two screws and try again pressing the button. It should move without problems and sound like a true mains-switch should  :) If you notice any stickiness, loosen the two screws and adjust the switch slightly to the left or right meanwhile pressing the button.

Turn over the power supply to its original position and mount it with the prepared screws with washers. The washers are strong enough to take the weight of the powersupply even with the screws with smaller heads.

Mount the back on the G7400 and turn it over. Try the switch again and if you are satisfied connect the G7400 to your screen and mains outlet and it should be working OK.

>>G7000 G7200(P+S) G7400 N60 JET27 VG5000 ZX80 ZX81 ORIC-1 COMX35 Aquarius<<