dilwyn wrote: ↑Thu Feb 15, 2024 4:36 pm
I wonder if the labelling on the "8049" implies it could be one of the replacement 8049 chips, such as the Schön one? They were intended as anti- keybounce replacements for some keyboards. Had side effect of affecting serial comms in some ways.
Very interesting. Where could I get more information about this possible replacement?
The battery area was under the heatsink and near the modulator - but I've never seen a board fitted with it. I did make this mod myself on and old QL, but it involves some tweaking with the reset signal during power up - if I did it again I'd use one of the power management chips that locks out the chip select, and a 3 pin reset device to give a cleaner reset signal that's power dependent as well as switch operated.
Pr0f wrote: ↑Fri Feb 16, 2024 7:32 am
The battery area was under the heatsink and near the modulator - but I've never seen a board fitted with it. I did make this mod myself on and old QL, but it involves some tweaking with the reset signal during power up - if I did it again I'd use one of the power management chips that locks out the chip select, and a 3 pin reset device to give a cleaner reset signal that's power dependent as well as switch operated.
This is very interesting. Do you have photos of it? Do you document it or do you have more information?
No photo's I'm afraid - but if you look at the issue 5 board - there is a wire link or zero ohm resistor that connects pin 40 to VCC - it's marked on the PCB as a diode - and that's the first clue - this is the VCC for battery - which should be a wired or'd pair of diodes - one that from VCC to pin 40 and one from the NiCD battery via a diode to pin 40 - whichever has the higher voltage feeds the ZX8302 chip with voltage. I used a constant current circuit made from an LED, transistor and a pair of resistors to provide trickle charge to the NiCd battery.
The issue with the reset circuit is the need to stop the QL trying to do anything with the ZX8302 whilst VCC becomes stable - since we already have a circuit around the reset pin with diode / resistor capacitor - we can highjack this signal to drive a pnp transistor or FET to hold the PCEN high until the reset in has stabilised - thus no access possible until reset has gone high.
The ZX3802 clock seemed to work quite well at 3.6v from the NiCD.
Much of what you wrote is a mystery to me, but I do not lose sight of this valuable information, because in the QL community in Spain they are working on this issue, and I think it can be useful. I really appreciate you taking the time to write it up in detail. I really enjoy these resources.
How cool is that! Check out the mdv drives in the front panel. Someone really went to town with that one. I wonder what that display/drive unit started life as, some other luggable computer or entirely home made?
I'm always fascinated by QLs with 5.25" drives too, as the use of 5.25" drives was very brief and almost everyone seems to have moved very quickly to 3.5" drives (or skipped 5.25" completely). I have never found evidence of any original software being supplied on 5.25" disks, but of course they would have been just as useful to store your own data on as their smaller brethren.
Edit: just noticed the modified keyboard made of 2 QL tops with added F5 - F10 keys and a number pad! Whoever made that must have spent an awful lot of time on it and was very creative.
https://QXL.WIN
Collector of QL related computers, accessories and QL games/software.
Ask me about felt pads - I can cut them to size and they have proved excellent for mdv data recovery.
