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Remove Q14. No effect.
Replace 7406 with a new one. No effect.
This requires a bit more thinking 8-/.Then the cluestick hit me. I cut R64, because I saw that the LM324 tacho amplifier always output a low value. Duh, should have seen that immediately. This signal is motor speed control, and cutting it made the signal a bit higher but not enough. But if that amplifier would start to output 5V this should definitely increase the signal, a lot- and it should get to that level because the motor is idle, i.e. at start the voltage of that comparator should be high, and it should decrease as soon as the motor gets up to speed. Clearly that part does not work!
To test I disconnected R64 from the LM324 side, and put a constant 5V on it. That shows this:
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Yellow: P10 of E8, blue: base of Q13. This made the motor run like mad 
, I switched off as soon as I heard the sound which explains the odd end of the signal.
Now we know that the tacho part is not working, it is always-low while it should be high initially. Redoing an earlier image that already showed a problem by putting probes on all ports of the LM324 (pin 5, 6, 7):
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It seems very clear that the chip is dead here; pin 6 
is higher than 2V, Pin 5 
is around 1.9V.. This should cause the output to swing to +5V. Replacing the LM324.
With the resistor still cut this shows a lot more promise:
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The output swings high immediately, as it show considering the inputs Let’s try with R64 connected..
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That fixed it The image shows the motor being controlled, and indeed the motor runs up and down with every “read block” command 🎆 . The test program now shows another error though:
| Code Block |
|---|
End packet received: [success], unit 0
Read tape 1 block 40 for 8192 bytes
ERROR: Unexpected end packet: [seekError], unit 1 |
Can easily be because the tape ran off its wheel