Spectrum polish off: Difference between revisions

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


Fixes done until now:<br />
All Fixes are done, including:<br />


* Replaced blown up 7805 voltage regulator.<br />
* Replaced blown up 7805 voltage regulator.<br />
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* 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.<br />
* 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.<br />
* Built in a 1 transistor preamp to make the cassette input sensitive enough so it accepts signals from a tablet or laptop.<br />
* Built in a 1 transistor preamp to make the cassette input sensitive enough so it accepts signals from a tablet or laptop.<br />
*replaced a missing rubber feet<br/>
* replaced a missing rubber feet<br/>
*added a composite video output cable<br/>
* added a composite video output cable<br/>
* 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.</br>
The latter was also a test case for  similar solution in my ZX14 (ZX81 rebuild). It works, 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.
 
<br/>
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.


[[File:Spectrum with real keys and joystick interface.JPG|900px|Spectrum keyboard with real keys and joystick interface]]
[[File:Spectrum with real keys and joystick interface.JPG|900px|Spectrum keyboard with real keys and joystick interface]]
TODO:<br />
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.

Revision as of 23:10, 28 May 2014

Project Spectrum polish off
Status In progress
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 similar solution in my ZX14 (ZX81 rebuild). It works, 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.

Spectrum keyboard with real keys and joystick interface