18-01-2013, 03:54 PM
This one was found in a box of bric a brac at an auction by Dennis and was passed over to me to see if it was worth getting fully working again. Along with the computer was a full set of leads, PSU and a nice bundle of games. The outside case was pristine, almost as if it had only been taken out of the box in 1984 when these models were launched. There was one small scratch on the underside of the case and a collapsed spacebar, something that was the norm on this particular model as the spacebar would get a hammering on "shoot em up" games. This particular model had the "enhanced" keyboard, to be honest I'm more traditional and prefer the dead flesh variety.
Powering up was ok with the customary "K" symbol on the screen but a number of the keyboard buttons would not work correctly. Taking the case apart found the smaller 5 conenction ribbon lead adrift. Re-fitting did not restore operation as a piece of ribbon had broken off inside the socket. No amount of picking out with a pin would get the fragment out plus the contacts in the socket were shot anyway. The whole keyboard membrane had seen better days so it was onto T' Internet to source a replacement unit.
Inside, this is a Spectrum 4b motherboard, unlike earlier models the heatsink has been re-arranged to run along the back of the board rather than top to bottom as on the earlier revisions. A quick check inside showed the board to be in tip top condition with no signs of items plugged into the expansion strip being pulled out while the computer was powered. A classic sign is no operation, a hole burned in the 7805 regulator and the associated circuitry looking unhappy and distressed. So far lady luck was running my way.
Getting a membrane unit was the easy part, getting the socket to plug the membrane flylead into was much more difficult as parts are obsolete. If you need to obtain the 5 and 8 pin sockets they are Molex part No's 22-02-3053 and 22-02-3083. The old socket was carefully desoldered using a sucker gun and a 1mm bit on a 25w iron, just the right amount of oooph for the job. After cleaning out the holes the new socket was fitted, check the orientation, and the motherboard re-fitted to the lower case.
The membrane pad is held in the upper lid, which also contains the keyboard. From the bottom up the assembly is keyboard, rubber keyboard push pads, membrane pad, fibre panel and finally metal backing plate, all held in with 5mm deep screws. Another fouling point is that the membrane pad flyleads are held under a pair of clamps and this can damage the unit, so not too tight when assembling. Finally the floppy spacebar issue. The spring of the bar relies on the spring of the rubber keyboard push pads underneath (or one in this case) and the pads under this particular bar were just about played out. A pair of C64 keyboard springs underneath the bar restored normal operation.
Final re-assembly, a couple of new internal anti rub foam pads in strategic locations, power on and a nice "K" symbol along with a working keyboard. A very nice working example of a bygone age computer.
Powering up was ok with the customary "K" symbol on the screen but a number of the keyboard buttons would not work correctly. Taking the case apart found the smaller 5 conenction ribbon lead adrift. Re-fitting did not restore operation as a piece of ribbon had broken off inside the socket. No amount of picking out with a pin would get the fragment out plus the contacts in the socket were shot anyway. The whole keyboard membrane had seen better days so it was onto T' Internet to source a replacement unit.
Inside, this is a Spectrum 4b motherboard, unlike earlier models the heatsink has been re-arranged to run along the back of the board rather than top to bottom as on the earlier revisions. A quick check inside showed the board to be in tip top condition with no signs of items plugged into the expansion strip being pulled out while the computer was powered. A classic sign is no operation, a hole burned in the 7805 regulator and the associated circuitry looking unhappy and distressed. So far lady luck was running my way.
Getting a membrane unit was the easy part, getting the socket to plug the membrane flylead into was much more difficult as parts are obsolete. If you need to obtain the 5 and 8 pin sockets they are Molex part No's 22-02-3053 and 22-02-3083. The old socket was carefully desoldered using a sucker gun and a 1mm bit on a 25w iron, just the right amount of oooph for the job. After cleaning out the holes the new socket was fitted, check the orientation, and the motherboard re-fitted to the lower case.
The membrane pad is held in the upper lid, which also contains the keyboard. From the bottom up the assembly is keyboard, rubber keyboard push pads, membrane pad, fibre panel and finally metal backing plate, all held in with 5mm deep screws. Another fouling point is that the membrane pad flyleads are held under a pair of clamps and this can damage the unit, so not too tight when assembling. Finally the floppy spacebar issue. The spring of the bar relies on the spring of the rubber keyboard push pads underneath (or one in this case) and the pads under this particular bar were just about played out. A pair of C64 keyboard springs underneath the bar restored normal operation.
Final re-assembly, a couple of new internal anti rub foam pads in strategic locations, power on and a nice "K" symbol along with a working keyboard. A very nice working example of a bygone age computer.
