Search found 283 matches

by Pr0f
Wed Jun 13, 2018 8:56 am
Forum: The Off-Topic Section
Topic: World Cup 2018 Including Patio Chair Sweepstakes
Replies: 32
Views: 862

Re: World Cup 2018 Including Patio Chair Sweepstakes

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... ;)
by Pr0f
Wed Jun 13, 2018 8:54 am
Forum: The Off-Topic Section
Topic: Happy Birthday!
Replies: 148
Views: 51909

Re: Happy Birthday!

Happy Birthday Jan - have a good one :D
by Pr0f
Fri Jun 08, 2018 11:12 am
Forum: The Off-Topic Section
Topic: Need electronic expert advice for a project
Replies: 13
Views: 405

Re: Need electronic expert advice for a project

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...
by Pr0f
Fri Jun 08, 2018 11:09 am
Forum: General QL Chat
Topic: Hello? Anyone here?
Replies: 8
Views: 438

Re: Hello? Anyone here?

Loving the old 'bench ammeter' :-)
by Pr0f
Thu Jun 07, 2018 10:52 pm
Forum: The Off-Topic Section
Topic: Fire
Replies: 18
Views: 484

Re: Fire

all the best with the clean up. Hope you are able to salvage the majority of the material.
by Pr0f
Thu Jun 07, 2018 10:28 pm
Forum: The Off-Topic Section
Topic: Need electronic expert advice for a project
Replies: 13
Views: 405

Re: Need electronic expert advice for a project

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...
by Pr0f
Thu Jun 07, 2018 11:31 am
Forum: Hardware
Topic: CST RAM expander
Replies: 2
Views: 177

Re: CST RAM expander

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

A decoder would have been my guess too.

:D
by Pr0f
Thu Jun 07, 2018 9:17 am
Forum: Hardware
Topic: CST RAM expander
Replies: 2
Views: 177

CST RAM expander

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 ...
by Pr0f
Wed Jun 06, 2018 11:53 pm
Forum: The Off-Topic Section
Topic: Need electronic expert advice for a project
Replies: 13
Views: 405

Re: Need electronic expert advice for a project

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...
by Pr0f
Wed Jun 06, 2018 11:46 pm
Forum: The Off-Topic Section
Topic: Need electronic expert advice for a project
Replies: 13
Views: 405

Re: Need electronic expert advice for a project

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...

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