From time to time the slide servo relay does not switch. Till now I was not able to figure out the reason. By using the original circuit with the darlington amplifier of 7523 and 7516 the relay does not react in any way. A fun fact is that the delivered 12V are not converted into 5V (G & G1) but rather converted to 6V by a 7506 which is not part of the documentation. This little fellow has to burn the other 6V into pure heat without any cooling.
But when the tape deck CPU gets powered with 6V maybe the high level of its outputs are also 6V. The Arduino board has to transfer its input voltage to 5V since the ATmega CPU can only handle 5.5V. Therefore I assume the changed voltage of PB4 does not deliver the right value to enable the darlington transistors to switch the relay. In that case the resistors 3545 and 3922 needs to be recalculated. The last time I have done such calculations were 25 years ago and I need to learn it again. However, I did not want to wait for such a long time and decided to go by “feelings” and changed the 3545 to 1M and 3922 to 20Ohms. Anyway the relay switched by using this values but not all the time. Maybe the free wheeling diode 1N4001 I used in my replacement circuit is not good enough to handle the inductive capacities of the relay – but right now I do not have any other diodes on stock.
Another reason can be the cables and experimental boards I was using because it seems that from time to time the board loses contacts especially in short switching times like 40ms. I need to improve this circuit.
