Thor blank screen on boot...

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Dave
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Thor blank screen on boot...

Postby Dave » Tue Feb 19, 2013 5:54 pm

I recently bought a CST Thor of unknown spec/history. It powers up, the hard drive spins up, but it makes no sound and gives no display. Does it give the same video output as a BBQL?

I have the manual for it so I shall dive in, but the manual is 4cm thick, so it may take a while to find the relevant information ;) Any quick pointers on common Thor faults and problems would be.... GREAT!


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dilwyn
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Re: Thor blank screen on boot...

Postby dilwyn » Tue Feb 19, 2013 6:45 pm

Dave wrote:I recently bought a CST Thor of unknown spec/history. It powers up, the hard drive spins up, but it makes no sound and gives no display. Does it give the same video output as a BBQL?

I have the manual for it so I shall dive in, but the manual is 4cm thick, so it may take a while to find the relevant information ;) Any quick pointers on common Thor faults and problems would be.... GREAT!

Never owned one, but there are various documents, tech and service manuals supplied by various people on my website at http://www.dilwyn.me.uk/docs/thor/index.html in case those are any use :geek:


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tofro
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Re: Thor blank screen on boot...

Postby tofro » Tue Feb 19, 2013 7:56 pm

Dave,
except the Thor 16 - Which was entirely new Hardware incorporating a "real" 68k, the Thors were based on standard QL boards with a piggy-packed 68020 instead of the 68008. So all the typical QL flaws apply and all QL spares should work. They did, however, have ROMs of their own.

The 16, however, is different, but if I remember right, it was standard Motorola HW, even down to the peripherals, drawn from the 68k Hardware Manuals. So I wouldn't expect any custom chips or other difficulties in obtaining replacement.

As far as I know, there were much more Thor 20/25 as Thor 16 - The 16 came pretty late.

Regards,
Tobias


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Re: Thor blank screen on boot...

Postby Dave » Tue Feb 19, 2013 11:22 pm

The mainboard says it is a CST Thor 16, and NOTHING inside the case is at all familiar QL hardware. Here's a photo, attached.

I checked the PSU and all voltages look normal, within expected ranges (5.2v, 11.78v, -12.03v). There are at least half a dozen PAL chips, and one Varta battery that is almost certainly dead.

Looks like there will be much manual reading in my future.
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IMG_0534.jpg
CST Thor


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tofro
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Re: Thor blank screen on boot...

Postby tofro » Wed Feb 20, 2013 7:36 am

Dave,

so it's a Thor 16, quite a rare beast then. I guess you won't find much of hardware documentation for it. But it's definitely worth keeping.

Lacking more information and circuit diagrams, I would start checking and replacing parts that are obviously broken or tend to break with age.

One definite thing would be the battery - The old Varta block batteries tended to break and leak even after two years and it could well be the battery has done a bit of "unintended PCB etching" under its body over time. Unfortunately, what leaks out from there is conductive acid! Remove it and clean the PCB under and around it. It could well be the problem.

Have you got a scope? If yes, check for CPU clock and video circuitry. Especially look for capacitors that also tend to break (dry out and lose capacitance) with age.

Regards,
Tobias


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Re: Thor blank screen on boot...

Postby Dave » Wed Feb 20, 2013 4:31 pm

After a little checking, I can add the following:

250 UK Thor XVIs were built, then production was moved to Denmark, with slight hardware revisions. Then, CST failed. This is a Denmark Thor. It has a Rodime SCSI HD, 2MB of RAM, and every interface everyone ever dreamed about in 1998. It retains a QL-style expansion port.

Later this week, I will disassemble it, clean every socket, re-test the PSU, check the capacitances of all the capacitors, remove/replace the Varta battery, check the EPROM images, then re-assemble and re-test.

There will be a photo essay of it here.


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Re: Thor blank screen on boot...

Postby Dave » Wed Feb 20, 2013 5:10 pm

Well, I had some free time, and so I used it informatively.

I'll attach the photos, and draw conclusions in the next post.
Attachments
IMG_0540.jpg
IMG_0539.jpg
IMG_0538.jpg
IMG_0537.jpg
IMG_0535.jpg


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Re: Thor blank screen on boot...

Postby Dave » Wed Feb 20, 2013 5:19 pm

IMG_0542.jpg

IMG_0541.jpg


As you can see, the battery leaked, and there's a blue corrosion and crystalline growth on the 74LS03 next to the battery. I will clean this first to see the state of the components, and desolder the 74LS03...

More in a little while...


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Re: Thor blank screen on boot...

Postby Dave » Wed Feb 20, 2013 6:05 pm

Pin 10 of the 7403 (IC27) was corroded through. This means corrosion could go inside the plastic encapsulation, so the IC needs to be replaced. The acid also ate some of the through hole plating

Also, the 100uF cap (CE1) adjacent is toast. The 1kOhm resistor (R29) is good.

I have 100uF caps in hand, but no spare 74XX03...


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Re: Thor blank screen on boot...

Postby Dave » Thu Feb 21, 2013 4:41 pm

I ordered 50 74LS03 ICs for only $2 more than ordering one. They should be here by the weekend.

I read the technical manual, and the board expects a NiCad pack of 3.6V in that space, which discharges over a two week period, and is charged whenever power is on. I can make a suitable pack from three 1.2v LiIon cells and a single chip charge controller. Most LiIon cells these days for retail use contain charge controllers within the AA battery package, anyway. I will post photos when I make it. If anyone would like additional batteries made, speak up now!



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