CST Thor 1 EPROM problem

[bagpuss22]

When it did work, for a short time! I got this boot screen.

[dilwyn]

Could I also ask that the serial number/watermark issues be written up once fully resolved for the Thor information part of my website, please?

Would be good to have the information preserved for the future in case this issue raises its head again for someone else.

[lcww1]

Russ - great pictures! Nice work on the Thor PCB, and I love the screenshot from the Sinclair monitor - it looks as though your Thor has a few extra ROMs on board!

Dilwyn - I’d be delighted to put something together for the Thor section of your site, which is such a fantastic resource and one which has already been of great help to me.

I’ve heard more from Adrian - he’s been extremely helpful, and he has confirmed that the format of his Thor 1 serial EPROM matches those of mine and Russ - there’s the lingering question of whether there’s a checksum in the serial EPROM, and Adrian is thinking of burning a new serial EPROM for his Thor with a different serial number to see whether that affects booting...

I’ve got a new RTC chip and replacement components for the associated RTC circuitry on order - I’ll report on progress once I’ve been able to do some tests...

[dilwyn]

Dilwyn - I’d be delighted to put something together for the Thor section of your site, which is such a fantastic resource and one which has already been of great help to me.

Thanks Liam.

[Witchy]

Evening all,

I feel like I should've joined the forum years ago since I've been on the mailing list forever, still, better late than never!

Liam, you'll like this:

With this new serial number my Thor booted happily into the only demo floppy I have, so the format of the Serial EPROM seems to be:

Code: Select all

0x3FF0: B7  01  EB  01  0B  01  0A  56  08  52  4F  48  54  04
        183 001 235 001 011 001 010 086 008 082 079 072 084 004
        {random number} {-reversed SN-}      R   O   H   T

where the serial is reversed and the first 4 digits are the semi-random number. This does mean that your problem is elsewhere on the Thor unfortunately.

Witchy

[lcww1]

Hello Witchy!
Really glad to see you on this fine forum - and many thanks indeed for your very helpful and informative post- the mystery of the Thor 1 serial/watermark EPROM is solved! Whilst this EPROM rabbit hole hasn't fixed my Thor 1 problem, the investigation has been most rewarding!

I've now replaced a number of the components making up the RTC circuit on my Thor 1 - including the chip sockets for ICs 39 (and IC38, as the sockets of these were corroded), D1 and D2, C5 and C6, and IC39 itself. Alas, none of this has made any difference. The X2 oscillator appears to be ok, and all the PCB tracks in the vicinity check out ok with my multimeter. I've had a quick look on the RTC data bus with a logic analyser, and there's plenty of activity there, but I'll need some time to be able to understand what I'm looking at. Meanwhile, I think I'll try replacing the other easily removable chips, IC36 and IC37, which are involved with the external keyboard, and with the mouse and printer connector respectively. I suppose that it's conceivable that a problem with either of these two chips could prevent the Thor booting.

Along with whatever it is that is causing the boot problem, I think that there is also a problem with the Thor RAM. During testing, I would periodically get RAM errors from Minerva pointing to a RAM expansion fault. Disabling the expansion RAM by grounding pin 9 of IC4 (one of the two PALs on the Thor 1 board), as advised in the Thor TM, has put a stop to such RAM errors.

My thanks again to everyone who has been so generous with their help!

[Dave]

My Thor 16, which seems to boot but doesn't produce video.

Code: Select all

0x3FFF:  04  :004
0x3FFE:  54  :084 - T
0x3FFD:  48  :072 - H
0x3FFC:  4F  :079 - O
0x3FFB:  52  :082 - R
0x3FFA:  10  :016 - might be the model number? 
0x3FF9:  58  :088 - 89/ - year
0x3FF8:  03  :011 - 3/ - batch?
0x3FF7:  01  :001 - 1/ - always 1?
0x3FF6:  2D  :011 - 45 - number in batch?
0x3FF5:  01  :001
0x3FF4:  EB  :235
0x3FF3:  01  :001
0x3FF2:  B7  :183
0x3FF1:  FF  :blank
0x3FF0:  FF  :blank
.
.
.

[Witchy]

Yes! That makes sense about the model number. Mine and Liam's are 8, yours is 16. Excellent

[Jeff$]

Old thread and not sure if you ever solved the serial issue, but from memory the Serial Rom should be put in the first bottom slot (Furthest away from the connector), you have it one slot up going by your photo, so I suspect the Thor security check looks for it in the wrong memory space.

The System Rom, v4.00 in your case (but you could use 4.22 with bug fixes, although reading all the above did they move the serial number position between v4.00 and v4.22, ie 8k and 16k), should be in the next slot above the serial rom (so 5th slot from the connector), this may explain why you could never access most of the Thor Functions.

Thor 8/20/21 Rom Order, Bottom Serial, 5th System Rom, 4th User, 3rd User, 2nd and 1st User only on Thor 8 (not available on Thor 20/21)