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Just waiting for you to iron the bugs out of the assembly instructions Jim. ;-) Good to hear you're getting some space to carry on playing.

Stuart.
 
Thanks Stuart,
I just bought one as a spare incase it's differnet to the ones that other Jim kindly sent me for testing.
Sheds are built, i just need it to stop raining so i can fully waterproof, insulate and line them !!

Jim
 
Welcome Steve,

The perceived wisdom seems to be to test the power supply before (re-)connecting it to the main board.

What was the spec of your Cortex? Disk drives?

Stuart.
 
Is there any source for Cortex PCBs? I did own one and was made throw it out - something to do with marriage. I would really like to build one again.
 
A few of them turned up on eBay within the last year or so that were actually new old stock Cortex II boards. Other than finding a deal like that, your only options now would be to find an assembled one for sale (they do turn up now and then) or to take the time to do a new board layout (a bit expensive to do the boards though, as there isn't a huge base of Cortex owners out there). Patience is the real key--I had to hunt for several years before I found one, but they've started to turn up a lot more often since I started this thread a few years ago.
 
Finally got my recently built Cortex kit back onto the bench in the new workshop.
Still got one of the 2 old problems, it sees keypresses from the keyboard but not the correct ones.
Without shift, ctrl etc pressed most keys generate a space on the display.
With control pressed most keys generate graphics characters.
The graphics key and shift don't seem to alter what the keys do.
The signals leaving the keyboard seem correct but i will be sure tonight when i get the USB logic analyser hooked up to it.
Then it's going to be looking at the input port chips on the motherboard, i've already swapped the chip out but that hasn't helped.
Though, when i was working on it before swapping the chip input out (74LS251) did cure the problem for a short period of time.

At the moment the seeming overheating of the cpu problem seems to have gone, but did i swap the CPU out when i was working on it back in last November, i can't remember :-(

Jim
 
Confirmed that the keyboard is outputing the correct data, next task is to find out why it's not being read and displayed correctly by the system.

Quite often during the incorrect keyboard reading (most of which come up as spaces) the system jumps from Basic into a monitor program.
How is one supposed to access the monitor normally ?

Thanks,

Jim
 
Thanks Stuart, that has confirmed what i thought, the system shouldn't be jumping straight to the Monitor from a keyboard press.
Shortly afterwards the system started locking up again, and not restarting with reset or power cycle until powered off for a few mins.
I managed to find the spare cpu that other Jim kindly send me ages ago and fitted that, that got rid of the lockups and unexpectedly got rid of most of the keyboard problems.
The only problem left with the keyboard is that sometimes the case of the letters was wrong and the number keys did control characters, this turned out to be corroded pins on the keyboard control chip.
The original that came with the keyboad was dead, not oscilating. The replacement from Ebay was s/h and had corrosion on the tops of some of the legs, i thought they were ok on the lower section but it seems not. A good scrub with the fibreglass pen and all is working correctly in the keyboard dept.
Next bit to look at is the video out, i'm currently feeding the TV out into a Wintv card in a PC and the picture is pretty awful, very unstable with lots of noise on the picture.

Jim
 
I'm glad the chip came in useful, Jim! Let me know if there are any others that give you sourcing problems during the build--I might have some. I also found a bunch of newer keyswitches with caps that may work as substitutes for some of the original ones. I bought some but I haven't tried them for fit yet--but they do come with a two-part cap, so they are pretty much usable for any regular keytop position that doesn't need to lock.
 
BillEaves said:
PS. I should also have all the Cortex User Group newsletters still around somewhere.
Click to expand...

If you can scan in and upload issues 1, 5, 8 and issue 22 onwards (if they exist) then it would complete the current set that is available.
I'm especially interested in issue 8 as i believe it has details on the various 74LS2001 replacement circuits.

Many thanks,

Jim
 
Many thanks Jim. I'll test out the TMX9909 chips you sent me once i have the system stable without the FDC chips fitted.
I'll also do a resistance and diode test comparison between your chips and the TMS9909 i got from China before i try the Chinese one in the board.
It's not uncommon for Chinese chips to be something totally different remarked.

At the moment the intermittent keyboard reading problem has come back, it worked perfectly for about 2 hours the other day then started displaying spaces instead of characters.
Pressure on certain areas of the main board around the input port chips made it read the correct keys while the pressure was applied, so i guess i've got a dodgy IC socket there somewhere. They were all brand new so it's a bit of a pain.

I tried it on a normal TV (LCD) instead of the Wintv card in the PC and the picture quality was much better, even more so once i turned off the PC.
Probably normal for this age of computer on a TV output but it does have the problem mentioned in the newsletters of being too far to the left.

Jim
 
Will be interesting to hear the results of the TMS9909 from China. If you were going to remark a chip, wouldn't you choose to do something a bit more common? I wouldn't have thought that the world-wide market for this particular chip extends very far from just this forum ...?

Stuart.
 
Who knows how they decide what to fake.
We had several 100 MAX479 quad opamps at work that were actually remarked 7404 type hex invertors, i even connected one up and it worked as one.
Also 78L05 and PCF8577 chips that were just empty packages with no silicon inside.
These were from mainstream UK suppliers, not direct from China.

Jim
 
Latest update.
Another session with the Logic analyser revealed that there were 2 problems with the keyboard input, one was that D0 was always high, the other that D2 was stuck at about 2v with a very poor signal.
D0 turned out to be the ribbon cable not crimped quite well enough in the IDC connector, probably why the problem had been intermittent, should have checked the cable ages ago !
D2 was a faulty 74LS157 on the keyboard.
An unlikly occurance happened when i went to look for a replacement 74LS157, i took down all my tubes of chips and in doing so a 40 pin chip dropped on the floor, i picked it up and looked at the part number, it was only another 2376 keyboard controller.
I had no idea i even had one, i bought a replacement for the dead original off ebay but haven't been happy with the rusty pins.
So i've fitted the newly found one (which works) and kept the rusty one as a spare.
Touch wood, the keyboard problems are finally banished.
Now to get on and test the tape and serial ports and then fit the floppy drive interface chips.

Jim
 
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