Given that some fans will just attack each other even if they are not playing, it could be any time. I am going for day 2 (15th June) - just have a feeling...

Happy Birthday Jan - have a good one

This makes more sense now on the switch side of things. The switch enable will trigger that lower of the 3 comparator's (there are 4 in the 339 package), and that in turn will switch Q6 on, allowing the SW pin to rise towards +12V, it would normally be dragged to 0.6V by the bias resistor to -12V a...

Loving the old 'bench ammeter'

all the best with the clean up. Hope you are able to salvage the majority of the material.

This makes more sense now on the switch side of things. The switch enable will trigger that lower of the 3 comparator's (there are 4 in the 339 package), and that in turn will switch Q6 on, allowing the SW pin to rise towards +12V, it would normally be dragged to 0.6V by the bias resistor to -12V an...

Thanks Martyn - I couldn't see that for looking last night !!

A decoder would have been my guess too.

Does anyone have a circuit diagram for the CST RAM expander, or failing that if someone has one or a picture of one with which has the ROM components populated - this is the part of the board that plugs into the QL itself, - there are 4 28 pin sockets that appear to be wired up as ROM's with CS fed ...

Actually - rethinking the switched transistor - if the switch is in the NC position, the transistor will be biased off, so the voltage at the SW pin is free to rise (depending on the circuitry on the board in the monitor), but as the switch is pressed, the transistor will be briefly biased on, befor...

C1, R1 and CR1 are all connected to the base of the first transistor, C1 and R1 provide frequency sensitive feedback for the 2 transistor amplifier stage. In the Green circled area, it's missing a blob to join these connections. Regarding the last area of the circuit, logic tells me the emitter shou...