Spectrum Computing

Hello all first post and newbie here.

I have over the last few months fallen back into the 8-bit era and rather than go with my childhood machine the C64, I jumped ship to the Speccy and am loving it!

However I have one issue that has sprung up and that is that the two Comcon interfaces I have acquired both fail to function when connected to my 128k Toastrack and work as expected on the 48k. I had been under the impression that a Comcon was just plug and play but have struggled to find anything out on the net to the contary until now that is. I found a Crash article yesterday stating that Frel Ltd carried out a mod to existing Comcon interfaces for the sum of £4.00. So now I am trying to find out what this mod was? Is it jumper wires or something more exotic? If you own one and it functions on your 128k please could you post a picture of the internals front and back so I could see the changes they implemented. I'd like to get one of these compatible as there are some keyboard only titles I'd love to map to a joypad.

Thank you in advance.

What’s your Toast Rack’s logic board version number? If it’s Version 2 or 2-1, then the only difference from the 48K’s edge connector is that the CLK signal is not present. There weren’t many peripherals that required it, though.

Does the computer lock up or does it just not acknowledge any input for the interface?

Thanks for the reply. I was under the impression that it was the Spanish issues 128k models that had the issue with the CLK signal not being present on the edge connector?

My board is a version 6U and no lock up from the CPU just the mapped keyboard letters aren't replicated by the joystick inputs when testing in basic or trying in a game.

Here's the only snippet of information about said mod I can find from Crash April 1986.

Frel have cornered the market for mechanical interfaces: their Comcon interface costs a whacking E19.95, but it is fairly durable and has a through port so you can use the sound boosting features of the Turbo Ace at the same time. The only snag is that the Comcon won't work with the Quickshot 2 rapid fire option. Frel are at 1 Hockeys Mill, Temeside, Ludlow SY8 1PD. The standard Comcon won't work with the 128K machine (Frel will upgrade it for a fee of f4.00). but a new version which is compatible with both machines is on the way.

NeoStuey wrote: ↑Wed Feb 07, 2018 10:54 pm Thanks for the reply. I was under the impression that it was the Spanish issues 128k models that had the issue with the CLK signal not being present on the edge connector?

Aye, that’s correct.

NeoStuey wrote: ↑Wed Feb 07, 2018 10:54 pmMy board is a version 6U and no lock up from the CPU just the mapped keyboard letters aren't replicated by the joystick inputs when testing in basic or trying in a game.

NeoStuey wrote: ↑Wed Feb 07, 2018 10:54 pmThe standard Comcon won't work with the 128K machine.

Hmm. This is curious. Have you taken the interface apart? See if anything is connected to pin 13 on the lower side. (The pins are numbered right to left; the right side being the one with the keying slot/notch.) The signal on pin 13 is the only (meaningful) connection that is not present on 128K machines, compared to the original 48K Spectrum. It is, however, present on the +2, so if you have access to one, you could hook the Comcon to it and see if it works.

Thanks gain.

No there doesn't appear to e a trace from that pin on the lower side of the interface. I'll post some pictures a bit later to show what it has on it.

I see. Well, that’s a little baffling, I must say. Can’t think of anything else off the top of my head.

Okay here come the images of the two interfaces.

If nothing else seems wrong, it could be a difference in the power rail, and/or too long cables (signal drops with length).

I also have 2 or 3 Comcon Interfaces, but I have never tried them in a 128K.

hmmm, it is puzzling but in that snippet from Crash they do specifically mention a mod being offered by the manufacturer.

RMartins any chance of popping open a Comcon, just four screws and no glue to worry about perhaps we could compare PCBs and any additional features?

Same for anyone else especially anyone else who has first hand experience of using one a 128k, as I really would like to get to the bottom of this, thanks.

Yup. It’s pin 13 on the lower side, all right. (The key slot is technically pin 5, so you must have miscounted.)

Looks like it’s connected to pin 12 of the third IC from the left. I can’t quite make out what it is, but it looks like it’s a 74LS02, which is a quad NOR gate. Pin 12 is one of the inputs of NOR gate 4.

I’m not sure why they chose to use lower pin 13 on the edge connector. This is a combined IORQ and A0 signal. It enables the use of even numbered ports.

If my assessment is correct, you could probably reroute that connection to upper pin 17 on the edge connector via a 470 Ohm series resistor.

Thanks Ast A. Moore.

ahh! That's my bad and you are right I didn't count the key slot as a pin so as you say I miscounted.

I don't have the necessary components to hand to try that out and would also be interested to see if this was the fix Frel Ltd implemented their mod.

NeoStuey wrote: ↑Thu Feb 08, 2018 8:00 pm I don't have the necessary components to hand to try that out

Any resistor around that value will do: 390, 470, 500, 510 Ohm. For the purposes of testing, you don’t even need to desolder the lead from lower pin 13. Simply wiggle a resistor between it and upper pin 17 (making sure you don’t short anything). Hook the interface up to the Toast Rack and see if it works. If it does, you can think of a more permanent solution, in which case you’ll need to lift pin 13 entirely and leave it unconnected.

Again, I make no promises.

Ast A. Moore wrote: ↑Thu Feb 08, 2018 8:51 pm

NeoStuey wrote: ↑Thu Feb 08, 2018 8:00 pm I don't have the necessary components to hand to try that out

Any resistor around that value will do: 390, 470, 500, 510 Ohm. For the purposes of testing, you don’t even need to desolder the lead from lower pin 13. Simply wiggle a resistor between it and upper pin 17 (making sure you don’t short anything). Hook the interface up to the Toast Rack and see if it works. If it does, you can think of a more permanent solution, in which case you’ll need to lift pin 13 entirely and leave it unconnected.

Again, I make no promises.

THANK YOU!

As I didn't have any resistors but couldn't resist trying I ran a small piece of insulated wire from pin 13 underside to pin 17 topside and plugged it all in (with more than just my fingers crossed). And now I can confirm the Comcon inputs were detected as key presses as desired and I know I know how to overcome the hurdle I had I will return to mod it permanently once I have the necessary components to hand. At Least now I know I can play Escape from the planet of the Robot Monsters with a joypad now and older titles like Stop the Express.

Thanks again for the input and your time helping me with this.

NeoStuey wrote: ↑Fri Feb 09, 2018 9:08 pm As I didn't have any resistors but couldn't resist trying . . .

I see what you did there.

NeoStuey wrote: ↑Fri Feb 09, 2018 9:08 pmThanks again for the input and your time helping me with this.

Hey, no problem. I’m glad my hunch was too far off the mark.

NeoStuey wrote: ↑Thu Feb 08, 2018 7:04 pm ...
RMartins any chance of popping open a Comcon, just four screws and no glue to worry about perhaps we could compare PCBs and any additional features?
...

Eventually, I could, but currently all 3 I own are in the storage room, and not that easy to access, since my last scavenging ...

NeoStuey wrote: ↑Wed Feb 07, 2018 10:54 pm Here's the only snippet of information about said mod I can find from Crash April 1986.

Frel have cornered the market for mechanical interfaces: their Comcon interface costs a whacking E19.95, but it is fairly durable and has a through port so you can use the sound boosting features of the Turbo Ace at the same time. The only snag is that the Comcon won't work with the Quickshot 2 rapid fire option. Frel are at 1 Hockeys Mill, Temeside, Ludlow SY8 1PD. The standard Comcon won't work with the 128K machine (Frel will upgrade it for a fee of f4.00). but a new version which is compatible with both machines is on the way.

Just for completeness: Yes, this is on Page 108: https://archive.org/details/crash-magaz ... ew=theater