exxos's Atari, Amiga & retro forum

The DIP switch for the keyboard arrived today and I've managed to solder it in whilst cooking dinner.

I'm now just awaiting the replacement case screws now and the Beeb will be effectively finished.

Spending Friday evening in A&E was on my to-do list tonight. (Slight reaction to some food.)

Down in Cornwall at my Dad’s place… I’ve been into to loft to get down one of the last few computing items I still have down here, a Zenith green screen monitor.

It looked really manky as it had been in the loft for about 30 years and in Cornwall that means lots of mold.

It took quite a bit of cleaning to get that off, then it was time to switch it on.

When first turned on the screen bloomed bright and shimmered. I thought the worst and it’d need a lot of recapping. However, it settled down after about 30 seconds. It seemed OK until I tapped it and the display started wobbling from side to side every second or so, another tap and the frequency changed, another tap and it was back to normal. I thought that it must be a dry joint. Opened up the back and couldn’t see anything. Put it back together and it worked fine.

The display has got better with a bit of a warming up. Probably the caps getting back into the swing of things after 30 years.

stephen_usher wrote: 31 Oct 2021 20:15 Down in Cornwall at my Dad’s place… I’ve been into to loft to get down one of the last few computing items I still have down here, a Zenith green screen monitor.

It looked really manky as it had been in the loft for about 30 years and in Cornwall that means lots of mold.

It took quite a bit of cleaning to get that off, then it was time to switch it on.

When first turned on the screen bloomed bright and shimmered. I thought the worst and it’d need a lot of recapping. However, it settled down after about 30 seconds. It seemed OK until I tapped it and the display started wobbling from side to side every second or so, another tap and the frequency changed, another tap and it was back to normal. I thought that it must be a dry joint. Opened up the back and couldn’t see anything. Put it back together and it worked fine.

The display has got better with a bit of a warming up. Probably the caps getting back into the swing of things after 30 years.

Any pots that might need a spot of Electrolube?

All the controls (other than the variable inductor on the back) are fine.

stephen_usher wrote: 01 Nov 2021 07:58 All the controls (other than the variable inductor on the back) are fine.

Splendid :)

After I've got it home I may recap the board just in case but I don't have all the tools I need here.

Well, I didn’t do anything to the monitor when I got home after all as I got distracted by model railways and DCC.

For the last couple of evenings I’ve been trying to get the DCC++EX system working. This uses an Arduino Mega plus motor control board to generate the power/data wave form for the DCC train control protocol.

Anyway, I had the oscilloscope connected to the track without a loco so as to test things safely, or so I thought. Anyway, the control chip on the motor board just constantly overheated whenever the track power was switched on and I couldn’t work out why. The waveform on the oscilloscope showed horrid overshoots and a DC offset I’d not seen from a proper DCC controller too. I thought that it must be a duff motor board.

To test this I connected the ground lead on the probe to ground on the board and the probe lead to one of the outputs and there was a nice square wave now and the chip didn’t get hot. Similarly for the other output. I connected the probe back with the leads on the two outputs and suddenly the chip started heating up. Oh!

Obviously the capacitance of the probe and oscilloscope was throwing things massively out of kilter. The act of observing really did change the experiment in this case.

Anyway, without the oscilloscope connected it does actually control trains!

I finally got around to testing my Apricot F Series RAM board in the F2 this evening, as I had it open to image the ROMs.

Swapped the jumper, plugged it in and switched on… Works! :D

Tomorrow I’ll make up a floppy adapter board and controller clock halving board and see if I can get the F2 working with normal floppies. I have a suspicion that I don’t need the ATTiny85 to seek the floppies as the newer floppies don’t seek themselves and the ROM is seeking them manually.

Floppy adapter and controller daughter board built, tested and boxed up. I can post it tomorrow.

The F2 ROM most definitely seeks the drives itself, so no need for the ATTiny85 on this board, just some bridge wires in the socket.