exxos's Atari, Amiga & retro forum

Maybe it was sub-standard solder too.

stephen_usher wrote: 02 Apr 2022 12:41 Maybe it was sub-standard solder too.

I wouldn't be surprised if the solder was sub-standard, I just really don't get how all of them got that bad, it's just like somebody was bashing the keyboard for hours and hours to make nearly every joint crack.

This afternoon I've done a couple of jobs.

PIA removed and socketed:


It came out nice and easily with no problems.

Socket in:


And keyboard de-soldered and re-soldered:


Sadly the keyboard still doesn't work, which means that the only thing it can really be is the 6821 PIA, so off for a hunt for one of those now.

Well, pair of 6821 PIAs on order, just in case the other PIA is dead too!!

Fingers crossed it'll revive the keyboard.

I guess that you could desolder the other chip and swap them in the same way that you can the 6522(?)s in the BBC Micro as a test?

If the fault moves then you know it's the chip. If it doesn't then either both are dead (less likely) or it's something else.

Actually, looking at the schematic IC24 could stop the keyboard working if it's gone up the creek and feeding stuff back up. It's a 244 and connected to an external port, the parallel port, which could get zapped by static. I'd remove that first.

Also, swapping the 6821s should be a good test as if the keyboard one is faulty then swapping it over would allow the keyboard to work but sound and the tape interface would stop working.

stephen_usher wrote: 02 Apr 2022 21:03 Actually, looking at the schematic IC24 could stop the keyboard working if it's gone up the creek and feeding stuff back up. It's a 244 and connected to an external port, the parallel port, which could get zapped by static. I'd remove that first.

Also, swapping the 6821s should be a good test as if the keyboard one is faulty then swapping it over would allow the keyboard to work but sound and the tape interface would stop working.

I had considered swapping the 6821's but can't find a second socket, so it's out until I can find one. Pretty sure I have some, just need to find it, though the 2nd 6821 does look like I could remove it without too much of an effect on the rest of the machine.

I have 2 spares on the way in case both are dead!!

I have also considered the 244 as a problem too, so will probably pull that tomorrow and see if it helps. The 244 is just a buffer for the printer port, but given the amount of sharing with the keyboard lines it could drag it down if dead, and I do have spares and a socket.

@stephen_usher I pulled both the 74LS244 (Made no difference) and the 2nd 6821.

Swapping the PIAs I can now use the keyboard:


Though the original keyboard PIA is clearly marginal as it 'sort of' works, with occasional flashes and garbage on screen, which I'm told is normal because of the way it's hooked up.

I half expected it as the machine boots with garbage on screen with the 2nd PIA removed, though you can see the cursor blinking in amongst the mess.

So, it's a solid diagnosis: PIA that looks after the keyboard is faulty or at least marginal, so once the replacements arrive it should be ready to go. In the meantime, I think the key switches could do with a little Electrolube too.

:)

Excellent! Progress. :-)

stephen_usher wrote: 03 Apr 2022 16:16 Excellent! Progress. :-)

Yeah, pretty happy with it now I know the right parts are on the way.

I have to say it has really awful solder throughout, seems very like lead free and takes a lot of heat to melt.

All done now though, and quite pleased it has a composite out too, though the green screen is somewhat vomit inducing!

Looking at 64k upgrades too.

Once you upgrade to 64K (ROMs also?) and have a nice blue flashing cursor, you will then be typing everytime the command to get into 32k mode to play games :)

I don't know if it is still being made, but there was a floppy disk emulator. Same guy who did Amstrad 464 one.

(It's been a few years, but I think I always had to drop into 32k mode to play anything. Might have been due to the Dragon 64's initial boot ROM being different? Can't really remember).