Peter

Hi All, Good to see more talk about the Super-80. I'll get back to mine soon. I'm not sure I'd donate mine to use as a pattern for the artwork although I would be in reproducing and aquiring another! Cheers, Peter.

Thanks. It's due any day now. Peter.

Robert, Sorry I checked too late. A visit would've been good although I'm spread thin these days. My wife is due to have the next baby end of next week, I'll probably be home for the whole of Feb and will have time to get back to the Super-80. I would've liked to show you the behavior I'm seeing with the memory corruption. Peter.

Seasons Greatings! We're getting there, slowly. I've spent a few hours since Christmas resocketting to no avail. I feel I've solved most of the socket troubles and the memory corruption problem may be unrelated. It appears that the RAS and CAS signals become unstable and the corruption starts at the lower RAM addresses and moves up eventually messing up the video page and you start to see the results on screen. Sometimes the system reboots by it self or goes into test mode automatically as the RAM locations get changed. I'll have to step out and get some more IC sockets as I seem to have run out. Peter.

None yet, My house is missing a roof and I've had to spend all my spare time mucking around doing work on the house. I've observed that the memory corruption problem is also temperature sensitive, cold days it takes a while to show up but on hot days it's there almost instantly. Hopefully I'll get a chance this weekend and over christmas to spend some time on it.

Yes, I'm working on getting to that soon. I'll post the progress as it's made!

It is an odd problem. I suspect that 50Hz hum may have snuck back in, without looking at the CRO trace I remember that the 50Hz hum often took a while to manifest. I'd have a nice clen signal and then after a minute or two it would appear and that's similar to this random character problem. I may have removed the hum from the video generation circuit but isolated it to some other part of the system. I installed a new 74HC165 chip in place of the TTL LS165 (which are hard to find) and the video dislay is now perfect so the original chip had a bad input causing the last dot or column of dots on each char to not display. I figured that an HC165 would work in this situation considering that it was being driven by a CMOS EPROM. I haven't put the 2513 back in yet but it may not work correctly if I do. When I get around to doing the EL-Graphics mod the HC165 would be Ok there.

I managed to replace RAM bank 0 with new sockets. It took me about an hour and a half to prise off the housings and desolder the pins from all 8 sockets. The problem still persists even after I replaced the RAM sockets. One other symptom is this, initially the CAS line on bank 0 is logic hi and after 20 seconds or so it starts to oscillate with what appears to be a short lo pulse and that's when the characters start to change at random. The other CAS lines on bank 1 and bank 2 remain logic hi while this is going on. This eliminates the RAM sockets, next I'll replace all the sockets for the chips involved in memory address decoding and multiplexing. I'll trace the CAS line signals further upstream when I get a spare moment.

Yes, although that range does get modified, when I set the video page to 00 I can see bytes changing, actually it appears as though single columns of characters are modified at the same time. That might tell me something.

I've just tried out those methods you suggest and there does seem to be a problem. Initially the odd memory location has the wrong value (not 0 or 1). Above 8000h the memory looks really bad, nothing consistant. I typed in the program and executed it then rebooted and examined pages starting from 0000h and there appears to be lots of inconsistancies there too. Anyway I'll replace the entire row of sockets at bank 0. and do some more testing. The memory corruption is more evident in the first 16K of RAM. The next 16 are more stable and I can type in commands etc. without the thing becoming unusable. Still it won't boot with switches set to 48KRam.

Hi Shred, I will try that, I have new 4116s in bank 0 but that's not to say none are faulty. My Super 80 has very bad sockets that I've been gradualy replacing. I think I may have found the problem, U75 74LS139 is in a bad socket, the pins are giving suspicious signals, weak and sometimes non existant depending on how much pressure I exert on the pins. After pushing it a little I've had several minutes of stable behavious, no random characters while pushing down on it. Once I release pressure it takes several minutes for random characters to slowly appear. I'll resocket the chip over the next couple of days. Next problem: I found a dry join on the CAS signal line resistor, no conntinuity to RAM bank1, I fixed that so now I have 32K RAM. I've filled bank 2 but suspect it's got some bad chips (old ones) as the Super 80 won't boot with the switches set to 48K RAM. I'll get to that one eventually. I've also cobbled up an EPROM version of the 2513 Char Gen ROM. I'm still missing the last dot on every char line with this in place of the new 2513 so I am confident that the 2513 is good and I haven't damaged it. This leads me to believe that the 74LS165 (U23) could be the problem. Peter.

I'm sure I saw it but mistook it for the Dick Smith one. I've resocketed both and still have a missing dot. I'm not too worried about it yet but I'll put the CRO on it soon to see what's happening with the signals. I'm seeing random characters appear all over the place. A large portion turn into @s I don't think I'd have any video display if the mod was done incorrectly. I've even resocket U76 and U50, no improvement. I've probably missed something. Those solder fumes can't be good for me! I've got brand new 4116s in there but you may be right the sockets could be the problem.I'll put another row in and see what that does.

I'd rather the EL-Graphics upgrade, just need to see a schematic for that and since I've replaced the sockets with machined pin versions the durability is much greater. I'll create a DIP header to plug into the 2513's socket as I have the hardware to do that it shouldn't be a problem. I haven't had any success with the memory curruption mod. I've made the changes but the problem still exists. I've tripple checked and can't see anything wrong with the changes. I'm also getting a problem with the characters, the rightmost pixel of each char is missing. Sometimes they appear but then dissapper so the 2513 is OK, there's a signal emminating from all the 2513 output pins. It could be a socket issue again.

I'll try and fix the random characters tonight, Overall it seems quite stable, power off - power on cycles give the same result i.e. no need to tweek any chips to get it to run so I'm quite pleased. So there were two broken tracks that I found, 1 from pin 1 to pin 16 on U18 and the other from pin 24 to pin 21 on U26, that was the main problem with failure to boot. About the lower case kit. I thought that I copied the EL-Graphics details from your technical docs? What I have in front of me is the Delux Character Generator from Dick Smith. Is this the same thing as the EL-Graphics upgrade? The Dick Smith one has lots of chips and it looks like it piggy backs some existing chip sockets on the Super 80 board (painfull). I though the EL version had an eprom and a 74LS266 chip? Looks like I need to get the details of the EL version. I'm expecting a new set of EPROMS containing 8R5 version this week. Fortunately the V1.2 Monitor ROM that I had burn't into the EPROM was a good one.

OK I'll check that out. Just trying psych myself up to do the memory corruption bug. Those crummy IC sockets are tricky to get off. In the end I resorted to brute force, side cutters, front cutters and a bit of leverage lifts the plastic carrier off leaving the pins till attached to the PCB and then these are desoldered individually followed by a cleanup with the desoldering tool to get the holes clear. How strange, I was just looking at the S80 keyboard as I'm writing this,lo and behold there was a key lower than the rest, I hopped up, gave it a wiggle, plugged in the PIO and I now have a working keyboard! I'm very greatfull for your assistance. Now I'll do the mod to clear up the garbage characters (more now with the PIO plugged in. Cheers, Peter.