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Powertran Cortex Issues

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plagued

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Joined
Jun 30, 2024
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Hi all, I'm just in the process of restoring a Cortex that's been sat in a garage for 20+ years with a mouse living in it. I thought I was on a winning streak until I've hit a hit of a dead end.
@davidloudfoot from what I've experienced the basic light should be flashing. If it's solid on it's not booted.
There's not a lot needed to get it to boot, and it'll boot with quite a few of the chips removed from the other circuits. All logic, ram and roms tested fine for me and my boot failures were caused by bad sockets on the IC9 and IC10 buffer chips. I also had a failure on the LM339 on IC 20 that was holding the CPU in reset.
I'd start by removing all the chips and cleaning the pins and sockets with contact cleaner. When it boots you should see read activity on all three of the roms (pin 2) for about the first second and then nothing (as it's copied the roms into ram and doesn't need them anymore)
I got it all up and running, but then watched as it slowly start to glitch out and crash. I had so many issues related to the sockets that I took it upon myself to "relive the fun of building it for the first time!!!" and without losing the will to live (only lost about 90% of it) desoldered and replaced almost all of the sockets (ran out of sockets and I'm waiting on more for the serial/floppy circuit)
I now have it back up and running ... but no video :(
I have tested (about 5 times) all the video memory, traced all the lines, swapped out the CPU and the 9929 and data logged the data and address busses, and can't work out where the issue lies. I'm getting a white screen sometimes with black bars down it, it's like the graphics chip is getting no data, but I can see it on the lines when you press a key. I know the system is booting as you can output to the serial port rather than the screen.
But I've been reading over all the schematics and tech notes and have the board on the test bench, so if I can help at all with the CPU and memory circuits I will happily ... just don't turn to me if the video circuit's not working :p
cortex.jpg
 
Superb info, I too have been thinking about swapping all the IC sockets as I much prefer the round pin sockets with gold plating rather than the somewhat cheap sockets originally fitted. I have had to do one already as when pulling the chip the socket came up rather than release the chip.

Yes all my chip legs do seem to be somewhat grubby and oxidised but so far all those I have pulled have gone into the logic tester and passed. ( I am awaiting the new Backbit V2 tester which should be here next week) Backbit will let me test the TMS chips, that said I have already swapped the CPU and 4500 for known working spares and still not managed to get it to boot.

I have checked the ROMs and they do have content ( I was worried that over time the EPROM might have self wiped ) - I have 2 sets - the original 1.1 versions and a revised set of 2764's that I have put the code into to allow the WD2797 Floppy controller to be fitted.

I will drop some pictures on here later and I also am working on some marked up versions of the circuit schematics with pin numbers marked ( if any one would find these useful )

My plan at the moment is in stages...

1) get the board running just as it is in native order
2) fit all the Ebus components inc the 9911 and the 74ls612 ( yes I have the gold dust DMA chip)
3) fit Replacement EPROMS on a daughter board to allow me to use my existing 2764 that allows the floppy 2.0 to work ) ( I have a old CDOS 2.0 disk which I hope and prey still works )
4) fit the WD2797 floppy board and get floppy's working
5) fit the Maplin V9988 hi res kit board on a riser board above the ( then to be empty video chip socket )
6) fit static ram chips to replace the 64k and also use the memory mapper to expand memory

Going to be fun !
 
There is a copy of the manual with pin numbers marked here but you do need to be a bit careful as I've found a couple of cases where the wrong pin number is noted, like on the 9929 where reset is shown as 36 rather than 34. It's also a newer revision of the schematics than the originals (in the ETI mag) with some corrections.
Also on the subject of schematic changes ... not related to booting issues, but I thought I'd throw it in here while I remember (as I thought I'd discovered an issue with my board while I was trying to trouble shoot)- The original schematic shows the CPU hold going to IC 12 which I'm pretty sure is a typo rather than a board revision as it correctly shows IC12 as an inverter in the parts list, the updated one shows IC 2 which is the flipflop that it's connected to, but ... the schematic shows S and R going to +5v. I thought this was my issue until I checked and there's no traces at all to pins 10 and 13 ....
 
Oopse, my display issue was my own fault. Shorted A0 and A1 on one of the 8118 IC's ... no ideas how I missed it as I've been beeping out the sockets and tracing the address lines ... but oh well, back up and running.
Regarding the boot light sequence - (this is the motherboard marking not the case)
Holding reset and I have TIME lit and nothing else
Release reset and I get -
TIME and IAQ for about 1s (while it reads the eproms)
Then IDLE permanently lit and TIME flashing about once per second when booted
you can see flickers of activity on IAQ

My next issue is I can't seem to get the floppies working. I can write to them with a greaseweazle so I think the drives are good, but trying to format on the cortex and I just get a flash of activity on the drive light and an immediate failure, no matter the combination of heads/density etc. This is the last section of the board to replace the sockets on, so I'll leave diagnosing this until that's out of the way.
 
There's a little bit of fault-finding information - including the sequence of lights on the front panel - in the Powertran II Manual that may be useful (see page 47 of http://www.stuartconner.me.uk/powertran_cortex/downloads/Powertran_Cortex_II_Manual.pdf).

The F18A replacement for the VDP gives a VGA output and bypasses (doesn't use) the on-board VDP RAM. I've tested this on my own Cortex and it works well. It's a bit difficult to get hold at the moment but small batches are occasionally manufactured. See https://www.arcadeshopper.com/wp/store/#!/F18A-VDP-replacement/c/116455519. There another drop-in replacement for the VDP being developed that uses a Raspberry Pi Pico that may be of interest - see https://forums.atariage.com/topic/3...18a-drop-in-replacement-powered-by-a-pi-pico/.
 
AHH thanks for that. The Pico vdp looks interesting. I've got a load of picos, level shifters, buffers etc kicking about, I may give that a go. I tried most of the video fixes to try and get the pal signal stable, but it's just crap :)
 
ok, the repair has stalled on the floppies.....
This cortex has two Canon MDD110, which seems to be the much less popular single sided version of the MDD210.
If I use the PC serial app to upload the SAFORMAT app, no matter what I select I get a flash of activity on the floppy and it immediately quits out with an unable to format error. There's no seek or head movement on either floppy drive. I've tried a number of different disks. I've also connected up the drives to a greaseweazle and that seems to be able to write to the drive fine.
If you type "boot" the drive does head to track 1 and bounces about there trying to boot ... but as I don't have any actual disks I have no idea if it would actually boot, and I don't know what profile I'd need with the greaseweazle to write one (I've tried a couple of different configurations and they write but don't boot)
Interestingly the "size" jumper was set, which the instructions say is for 8" drives, but I've desoldered this and it makes no difference.
Any advice is welcomed as I don't know if I have a config issue, or a hardware issue with the cortex or the floppies. I do have some other spare drives and a gotek which I've had no luck with, but again I don't know how either the drives or the jumpers on the cortex should be setup...
 
plagued said:
ok, the repair has stalled on the floppies.....
This cortex has two Canon MDD110, which seems to be the much less popular single sided version of the MDD210.
If I use the PC serial app to upload the SAFORMAT app, no matter what I select I get a flash of activity on the floppy and it immediately quits out with an unable to format error. There's no seek or head movement on either floppy drive. I've tried a number of different disks. I've also connected up the drives to a greaseweazle and that seems to be able to write to the drive fine.
If you type "boot" the drive does head to track 1 and bounces about there trying to boot ... but as I don't have any actual disks I have no idea if it would actually boot, and I don't know what profile I'd need with the greaseweazle to write one (I've tried a couple of different configurations and they write but don't boot)
Interestingly the "size" jumper was set, which the instructions say is for 8" drives, but I've desoldered this and it makes no difference.
Any advice is welcomed as I don't know if I have a config issue, or a hardware issue with the cortex or the floppies. I do have some other spare drives and a gotek which I've had no luck with, but again I don't know how either the drives or the jumpers on the cortex should be setup...
Click to expand...
So does greaseweazle 'exercise' the drives so you know the heads move and it can detect track 0 etc.?
Have you got the drives correctly terminated when connected to the Cortex?
Do you have a simple logic probe so you can check what the interface signals are doing?
Where physically are you? I might be able to mail you a boot disk if my Cortex still works and I can remember how to create one.
 
Stuart said:
So does greaseweazle 'exercise' the drives so you know the heads move and it can detect track 0 etc.?
Have you got the drives correctly terminated when connected to the Cortex?
Do you have a simple logic probe so you can check what the interface signals are doing?
Where physically are you? I might be able to mail you a boot disk if my Cortex still works and I can remember how to create one.
Click to expand...
yes, I can get the drives to move with the greaseweazle and in theory read and write to the drives, but I'm not confident on the config for the disk images/drives.
I have the drives configured as they were (which I'm assuming it was working originally), and a quick check of dipswitch settings and termination and it looks ok, the only thing that doesn't make sense to me is why the "size" jumper the manual says is for 8" drives is set...
I've also tried a GOTEK with the flashfloppy firmware, and making a config like:
[CORTEX]
mode = mfm
rpm = 300
rate = 500
cyls = 80
heads = 2
secs = 16
bps = 256
interleave = 1
skew = 0

I can get it to accept some of the disk images I have.... but I get the same boot issue where I can see it seeking the first few tracks (physically on the floppy drive, and via the screen on the gotek) but no boot..... but I have no idea if the cortex will work with a gotek, or again if my config is correct.
I've used a scope as per the trouble shooting guide and can see an approximately 2u signal on pin 5 of IC70 and pin 26 of IC76 and I can also see a low signal on pin 5 of IC76 to suggest it's seeing track0 ... but that's as far as I got with the "probing"
I'm in Bromsgrove UK, so quite a way from you, but in the same country :p
 
plagued said:
yes, I can get the drives to move with the greaseweazle and in theory read and write to the drives, but I'm not confident on the config for the disk images/drives.
I have the drives configured as they were (which I'm assuming it was working originally), and a quick check of dipswitch settings and termination and it looks ok, the only thing that doesn't make sense to me is why the "size" jumper the manual says is for 8" drives is set...
I've also tried a GOTEK with the flashfloppy firmware, and making a config like:
[CORTEX]
mode = mfm
rpm = 300
rate = 500
cyls = 80
heads = 2
secs = 16
bps = 256
interleave = 1
skew = 0

I can get it to accept some of the disk images I have.... but I get the same boot issue where I can see it seeking the first few tracks (physically on the floppy drive, and via the screen on the gotek) but no boot..... but I have no idea if the cortex will work with a gotek, or again if my config is correct.
I've used a scope as per the trouble shooting guide and can see an approximately 2u signal on pin 5 of IC70 and pin 26 of IC76 and I can also see a low signal on pin 5 of IC76 to suggest it's seeing track0 ... but that's as far as I got with the "probing"
I'm in Bromsgrove UK, so quite a way from you, but in the same country :p
Click to expand...
What floppy controller IC do you have? The original TMS9909?
With the GOTEK mode set to MFM, you have the DENSITY jumper fitted?
Any better if you change the bps setting from 256 to 250?
 
Stuart said:
What floppy controller IC do you have? The original TMS9909?
With the GOTEK mode set to MFM, you have the DENSITY jumper fitted?
Any better if you change the bps setting from 256 to 250?
Click to expand...
yes it's the TMX9909
The Density jumper is hard wired on.
If you change to 250bps the Gotek errors on the disk image. I've messed around with most of the basic options like rate at 250 as well.
It would be good to get a known good Gotec/flashfloppy config working..... assuming you can
 
It's not totally clear, but it looks like the DENSITY jumper needs to be *removed* for DD (which gives a logic 1 input to IC63). So if the DENSITY jumper is hard wired on, that gives you SD - might want to try adjusting your GOTEK config accordingly. The SIZE jumper should be fitted for 5.25", which I think is what you found. The table of jumper settings in the documentation (Table 1 in Part 2) is wrong in the original documentation, but corrected in the Cortex II doc (copied below). A '0' is jumper fitted to pull the signal down to ground. A '1' is jumper not fitted so signal pulled high through a resistor.
1725150129228.png

Just been trying out my two ex-BBC Micro dual floppy drives with my two Cortex boards, and none of them work - on doing a BOOT the drive 0 starts spinning but is not seeking to track 0 as far as I can see. And the heads are dirty and scraping the magnetic coating off the disks. ;-(
 
I gave removing the size jumper a go, but it's made no difference. If you try and run SAFORMAT no matter what you select the minute you try and format, the drives spin up, but the program has already displayed
Unable to format track
formatting aborted
The drives spin and lock but only for a second then unlock (physical disk lock) but no head movement.
If you BOOT then you get the head movement but it just bounces back and forward looking for the first track to boot .... so the boot process at least looks like it's working, but I have no boot disks. My gut feel though is there's an underlying issue with the cortex. It's just annoying as I don't know if the cortex has an issue or both the floppy and gotek have issues, or the all have as I've not seen any of them actually working in this setup.
 
I'm getting a slightly different issue; I can get through the SAFORMAT process, the disk head moves across 80 tracks and looks/sounds like it's formatting, etc and the program ends. Then I run the DISKIMG program, all looks well, but when I try to run install the image "Recovery Utils 80SSSD.dsk" I get an immediate "Disk Write Error". Anyone had any experience at this point please?
 
You're getting further than me. There is a section in the guide for writing the floppy that states you need to change the density setting to read the disk. Is there any possibility you also need to change to write it?
I followed the trouble shooting steps in the main document regarding the 2us on pin 5 of IC70. I even installed a pot to see if changing the interval made any difference to my issue, which it didn't.
You don't happen to have a gotek kicking about do you? would be good to know if you could get the format step working with one, even if the write didn't work.
 
I haven't made any positive progress but I have ruled things out. I have changed drives, disks, cables, the 5 volt power rail down by 0.2v as it was a little high, the version of PC CommsUtil 1v0 and 1v3, and the associated files. I haven't been able to swap the FDC TMX9909 but as the rest of the disk system seems to be working I'm guessing its okay.
As for the Density and Size jumpers, both mine are in, as per Stuarts posting above. I believe the jumpers are only read at power up and Reset. They can be over-written by software, but I don't know if the PC CommsUtil program does over-write them.
I haven't started checking the disk system electronics for signals yet but it's getting close, so you're ahead of me on that score. I don't have a Gotek I'm afraid - (I had to look that up as I've never heard of it). I see that it uses USB Memory. Memory retention for USB's isn't as good as that for floppies? So we'll have the same problem in 40 years time. LOL!!!!! Seriously though it might the the way to go. I wonder if anyone nearby has one I could try?
 
What country are you in. If you're in the UK I could post one over to try. They're only about £15 from china then you update the firmware to flashfloppy which is fairly simple to do.
You can also fit a better screen for about £1 if you want one and even put a little buzzer in to make fake floppy noses.
My issue is you make a, or use an existing, config to set them up for the device they're going in, but I'm just guessing at the config values and as I have no idea if the config is wrong or my Cortex is faulty (or some other issue) it makes diagnosing the problem somewhat difficult.
I was going to try and reach out to the guy that wrote the emulator to see if he could help with a gotek config, as he should know a hell of a lot more about the cortex disk format than me.
 
I'm in the UK, Devon, just up the road from Stuart. I've been researching the Goteks since you brought them to my attention. I'm sure you've done more than me but I found this site https://github.com/keirf/flashfloppy/wiki/Gotek-Models that has a lot of information, including a list of Gotek models to avoid. What model are you using/trying to get working? This site looks good too https://github.com/keirf/FlashFloppy/wiki/Hardware-Mods. I'm sure I've seen a list of disk parameters recently, but I can't find them at the moment. I'll have a dig.
 
I found some disk drive timing details in the Manual for the drives I'm trying to use; Cumana (Shugart 465) 5.25" floppy drives. They might be useful for correcting the config?
 

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  • Shugart 455 & 465 Floppy Disk Manual.pdf
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I've got a few gotek drives, the one I'm testing with is the middle one AT32F415 which while it has some restrictions due to the ram, what were trying is so basic I can't imagine it would be an issue. Essentially I'm trying to make a config to boot the pre made drive images, so simple read operations. I could try with an older one, I'd just have to pull it out of something else. It's just another element in the "something doesn't work, but I don't know which something" pot :)
I'll take a skim through that shugart manual
 
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