Peter
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Posts posted by Peter
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I should be able to find a free weekend in February.
Good luck with the baby!
Thanks. It's due any day now.
Peter.
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Any progress?
I'll be visiting a friend at Glenbrook next Sunday, let me know if you
want to be visited too!
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.
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Seasons Greatings!
Hopefully you'll have a roof by Christmas!And, hopefully the New Year will bring a fully working Super-80 !!
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.
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Any progress yet?
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.
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That's good you've fixed the display. Hopefully you can progress with the memory matter as well!
Yes, I'm working on getting to that soon. I'll post the progress as it's made!
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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.
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Hopefully it will help. Let me know when you progress further.
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.
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I forgot to mention that with the program, it doesn't touch the memory between 0-FF otherwise it would overwrite itself.
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.
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You can use your Super-80 to help you identify bad ram.
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.
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If you are seeing spaces (ASCII value of 32) turn into @ (ASCII value of 64), then try changing the DRAM chip that holds bit 5 of the video memory (I think it's U68 if you only have 16k fitted). If you don't have a spare 4116 floating around, just swap the "bit 5" RAM chip with the "bit 0" chip and see if the space characters start changing into ! characters (ASCII 33).
When I first assembled my Super 80, tricky dickies supplied me with a faulty RAM chip, so I found that one out the hard way.
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.
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The El-grafix kit consisted of 1x 2732 eprom, and 1x 74LS165 chip. The circuit diagram was in one of the books I brought over on my visit, the page is titled "Constructing the El Graphix Kit 4 Graphics Kit".
I'm sure I saw it but mistook it for the Dick Smith one.
The missing dot can only be caused by a bad socket on U23 or the 2513. U23 combines the outputs of the 2513 into a stream of dots, which appears on your monitor screen.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.
If you're really sure you've done the memory mod properly, look for bad sockets on the RAM or the chips that address it. Have you tried using 32k or 48k of RAM to see if it changes anything?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.
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Whether you choose the Dick Smith or El Grafix set is up to you,
as is the way you implement it. On my non-working Super-80, I
have both eproms wired up, with a switch to choose which one
I want to use.
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.
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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.
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The keyboard is an unusual design (software-wise). If a key is pressed,
the entire computer freezes until you let it go. You might have a key down
or some lines shorted to each other.
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.
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Welcome to the new member! Good to see another Super-80 fan.
Sounds good, I await your progress reports.Hooray! Some success at last!
I got up at 5am this morning and tinkered some more and managed to get the Super-80 to boot. Alas the keyboard interface needs some work, the cursor disappers when I plug the Z80 PIO in and there's no keyboard response. I think I'll end up replacing the chip socket for the PIO as a standard measure.
I removed several of those crummy IC sockets including Z80 socket, ROM 0, 2513 char gen and some smaller 14 pin sockets. I replaced those with machined pin sockets with the gold plating in the hole. I managed to clean up the video image early on.
What made the difference was I think replacing the socket for U18 which drives the relay, LED and vduenable lines and I discovered here that the chip reset line was not held hi as it needs to be, the track was brocken, I could have done this replacing the socket (I doubt that) but the new socket made no difference until I started checking with the Logic probe. I soldered a jumper wire from pin 1 across to pin 16 and this made some difference. Now the test mode kicked in and the VDU, LED and relay started flashing etc. I added the multiplexing chips and the RAM and eventually got the welcome screen Super-80 V1.2 and the flashing cursor.
Then the memory corruption bug kicked in. Still a few more things to fix.
Cheers,
Peter.
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An enjoyable day, I must say!
Thanks Robert, I'm glad you enjoyed the day. I've started removing the sockets and now have a stable video image. I did find a chip with a missing leg whcich had been causing some problems. Not much time to do anything else this week apart from domestic duties.
The ROM is now being selected by the memory decode circuitry although not as one would expect. I have 1 good monitor ROM without BASIC, that should bring me closer to seeing some results. The original ROM has been damaged. I've bought a larger solder sucker and that should make removing the bad sockets much easier.
I'll report on progress as it's made.
Cheers,
Peter.
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I was wrong about the u28 pin6 connection I should've said pin4 as pin 6 is the output. Anyhow I have a clear picture of @s and ?s alternating on the screen (with the bars from faulty 2513) the poor picture quality was a dodgy socket, wiggling u28 cleared that up. Here's what I get:
1. @s and ?s alternating on the screen.
2. verticle solid bars over the top of each char (faulty 2513)
3. top 3 rows are snakey
4. there's some induced hum scrolling from top to bottom and mysteriosly it's at 50Hz (now what could that be from? need I ask? ) I see it on the scope to.
5. The reset circuit is totally shoddy, the 4.7K pullup isn't doing it's job and there's this 50Hz hum again coming out of the ground signal. I suspect the CPU is in a constant catatonic state as a result.
6. I can't get the VDU to blank, probably related to the hum.
That's as far as I've got so far. Need to socialise some.
I reckon if I can eliminate the mains hum from the ground circuit which is leaking into the reset and video circuit a least the video will be as near to perfect as it can be. And then the CPU may get a chance to clock a few more cycles.
BTW: I have a scanner. things are looking up.
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Most of those signals check out OK on the CRO although there's a lot of noise, very short negative spikes that's fooling the frequency meter and I'd say is responsible for the odd behaviour of the video display.
One really problematic test point is U28 pin6 the manual says it should output bursts of 6mHz at 750kHz. I can't see how this can possibly be correct as one input is constant HI (derived from BusAck#) which comes from the CPU, do you have anything on your diagram? I'm wondering if U28 Pin 6 should be connected to U28 Pin 10 which is a 6MHz input? I can't see how Busack# could ever produce a 6MHz signal if the CPU is runnng at 2MHz.
My super 80 has an interesting mod... instead of 4116's it has 4164 (64k x 1) RAMs. It meant I could get rid of the -5volt supply and only have 8 ram chips, and I get 52k of RAM.That sounds interesting, I've got a bundle of 4164's I've read about a few mods on arcade game PCBs that involve this.
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Yes, that part of the computer has far more chips than it should have had.
I agree, it seems the most complicated part of the system. I've pulled all the chips and started rebuilding. I've found an initial problem with the signals. The output of U30/pin 11 is supposed to be 15 kHz odd, but mine is 32kHz, I've swapped the two chips involved and still get the same value. I'm wondering if the manual is wrong. U30 is a 74LS86 (XOR) (combining 15K and 32K sigs) and U36 is a 74LS92 (div by 12) Can you check yours for me? Up until this point all signals are correct, I'll have a closer look tonight but it's quite suss.
btw, does Garos have a Super 80 as well? He seems to have disappeared...He had one and he's keen on getting another.
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At least I have a few spare TTL chips. One thing that I haven't asked you is if the PC board (out of the box)needed any mods before it worked apart from the link for BASIC in ROM and the suggested improvements.
And, you might be able to compare some waveforms to my computer.That's a good idea. Especially the video circuit, something's not right there.
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Hopefully your monitor and cassette recorder will work, won't know until we try it I guess. But need to get yours to boot up first of course! Any progress?
The Microbee monitor works, strangest thing is though the picture artefacts are very similar to the VHF modulator output (sans noise) there's no door step and the character grid is a little snakey. I think there's some interference somewhere in the video generation ciruit. There's also some sort of scrolling from bottom to top.
At this stage I'm confident that the video circuitry can be debugged and tuned. I can't get the test mode to work at all so I suspect that the CPU circuit isn't quite right. I'll concentrate on that in the short term.
This is my plan of attack.
1. Verify ROM images
2. Verify CPU is functional
3. Check address and databus integrity (using DMM)
4. Check memory decode logic
What I would expect to find is that some logic chips may be defective and or the pins aren't making good contact in the sockets as you suggested earlier. I'm wondering if I should pull all the chips out again and start assembling from scratch following the guide. Before that I'll do steps above.
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The recommended cassette player was one of those flat portable ones from yesteryear. You could have batteries or run it off a power cord.
I know the ones, probably garage sale jobs these days. Do you think the VZ300 job will work then?
Got your email, thanks!No worries. Most Street Directories cover Blue Mountains, I'll email you some directions.
Do you have a working composite b/w monitor with a RCA socket as input? If so I could bring one of my super-80's over for you to look at.I'd love to see a working one. I've got a Micobee amber screen (I think) sitting next to me, could be green. will that do? It's got RCA input.
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There's another suggested mod that I made, it improves the cassette recording. I'll show it to you on my visit.
OK. Sounds good. I've got a few old data cassette devices, a VZ300 and a Small Sony if I can find that. I've got an Atari but no tape bay cover. Of coarse I've never tried these so hopefully they still work.
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OK. I should've checked the grounding of that chip, there seems to be a lot of gunk on the pins too and this could be afftecting the operation. I'll check the schematic as you suggest. I think I've noticed a few discrepancies between board and shematic.
Dick Smith Super 80 computer kit
in Other Emulators [/pc/other]
Posted
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.