Reading tapes from other KIM-1

KIM kenner 6 1978 Hans Otten Dutch, translation to English Hans Otten 2021

Reading tapes recorded on another KIM-1 or bought like Tiny basic, Microsoft KB-9, Miccrochess and Micro Ade was not that easy. Many many errors, especially the hypertape format.

Reading and writing of my own tapes, after having configured the PLL following the guide in the User manual, and keeping the cassette recorder clean, now is flawless. With the motor control (see Micro Ade manual appendix) it is a pleasure!

I read and tried all advices, like adjusting the azimuth of the recorder head, cleaning etc. Maybe the variations in tape speed between recorder and my player and the resulting frequency shift was a problem?
What really helped was looking with an oscilloscope at the output of the PLL (pin 7 of the LM311) we can see clearly the problem:

No real problems with noise or dropouts, just deviations between different recordings, so the PLL does not operate correctly. Bought tapes showed the pictures Wrong 1 and Wrong 2. And that leads to reading problems, the software makes the wrong decisions on ‘0’s or ‘1’s.

The following procedure was developed to read the bought tape, store it and save the program on my own tapes:

  1. Start reading the problem tape, 1873G
  2. Connect a simple voltmeter to pin 7 of the LM311 or Expansion connector-X
  3. Now change the PLL variable resistor to a reading of 2.7V. A scope would show ‘Correct’
  4. Start the read again
  5. Save the program
  6. Repeat with your own recording or the user Manual PLL set procedure

This helped me to read the problem tapes. Only for Microsoft Basic I had to play with the output volume, large variations in the recorded signal. But it worked in the end and now I have my own recordings on tape, several stored and working copies. One can never have enough backups!