Spectrum polish off

Project Spectrum polish off
Status	finished"finished" is not in the list (Proposed, Initializing, In progress, Completed, Stalled, Abandoned) of allowed values for the "Project Status" property.
Contact	mahjongg
Last Update	2014-05-28

Sinclair Spectrum polish off is a project to restore a donated defective Sinclair spectrum to working order, and to add some additional features:

All Fixes are done, including:

• Replaced blown up 7805 voltage regulator.
  
• Repaired the +12V & -5V generator (replaced two transistors).
  
• Completely replaced foil keyboard by 40 6x6mm buttons, hot glued to the inside and hard wired, the rubber keypad was modified to make place for the buttons.
  
• Built in a 1 transistor preamp to make the cassette input sensitive enough so it accepts signals from a tablet or laptop.
  
• replaced a missing rubber feet
  
• added a composite video output cable
  
• Add a built in joystick port, that works by activating certain keys, by using FET's connected between the keyboard matrix points for the keys, 5,6,7 & 8, and 0 for fire.
  

The latter was also a test case for an identical solution in my ZX14 (ZX81 rebuild). It works, but only when using the right kind of FET's, the first FET's I tried (BS170's) did not work! Probably because of it's largish (200pF) drain-source and gate source capacitances, but using 2N7000 FET's did work. In the ZX14 I will be using 2N7002, which is a 2N7000 in a SOT-23 SMT package instead of the 2N7000's TO-92 PTH package.

A less positive note is that even with the transistor pre-amp the cassette input is still quite finicky and still not very sensitive and needs a lot of signal to work properly.