I still can't get the Torch motherboard to boot. While I was poking around the motherboard and looking over the schematics, I saw that the service processor for the board - a 6303R which is a variation of the Motorola 6803, itself a later variation of the original Motorola 6800 - had a couple of pins connected directly to the keyboard connector. These were Tx and Rx. Hmmm. I wonder...
I dragged the keyboard out of the box that it's been sat in for the last year or so and plugged it in to the keyboard port. Curiously, this uses a version of the UK telephone socket as a connector. Odd but functional.
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| Probin', probin', probin'. Keep probin', probin' probin'. |
With the Torch switched on and pumping out its sad 'Beep Beeeep Beeeep Beeeep' to indicate a processor timeout, I started to probe the keyboard pins using my oscilloscope. I was very pleased to see that pressing a key on the keyboard generated a signal. It also generated a signal when I lifted of the key. Nice. This means that the keys are working. After spending ten minutes carefully running over every key I am pretty confident that every key on the Torch keyboard is working fine.
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| Press... |
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| ...and release. |
It's not a mechanical keyboard but the build quality is excellent and it feels like it would be much better to type on than some of its contemporaries (looking at you Amiga A500 Mitsumi and Samsung keyboards). Not a patch on the IBM Model M but not bad.
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| Yep. It's a keyboard. |
So, what now? Well, after taking a break from this machine I've come back to it and started to go back over everything I looked at previously. So far:
1) The board is drawing a lot of current. Nearly 5amps! Some chips get quite warm but nothing gets burning hot. I've checked all of the ceramic and tantalum capacitors and, while some were out of spec (and so replaced), none were shorted. It's possible I suppose that there is some damage that I haven't found on the traces.
2) Touching one of the connections on the power lead causes the computer to turn off - or at least the screen goes black. Without working drives or any other indicators it's difficult to know what else might be happening. I'm assuming that the offending cable must be coupled to pin 4 of the service processor that, with the original power supply, would be held low for a couple of seconds to shutdown the machine.
3) With nothing connected at switch on, there is a tiny quiet 'beep' with a pale blue screen. After about 30 seconds the fault beeps start - short, long, long, long - which repeat until the unit is switched off. Previously I had lines running down the screen followed by garbage filling about the top 1/4 of the screen. This is, apparently, the 6303R loading a program called 'SIMON' which then copies another program (called ERMA) into video RAM which should then be run by the main processor to start loading the hard disk OS. But this is the point where my machine apparently stops.
4) I have tested the 68010 in an Amiga A500 and it works fine. I also bought a second DMA controller from eBay which made no difference. The main concern on the three main processor type chips is the MMU. It's a Motorola 68451 MMU and is, to put it bluntly, rarer than rocking horse shit. If it's the MMU that's stopping the boot process then I'm slightly screwed. Partly because I don't have a spare to check if the original is faulty but mostly because I don't have a spare to replace it if the original is actually faulty.
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| DMA Controller - It controls...er...DMA. |
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| The three stooges. CPU to the right, MMU in the middle and DMA controller to the left. |
With all that in mind, I have started to look at the Caretaker ROM. There are, apparently, a couple of versions out there. Mine has 1.3 but there is a version 1.2. I might try to get hold of that and find a spare EPROM to write it to. Couldn't hurt..
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| Caretaker ROM with 6303R just up and to the left. |
Other than that, I am really out of ideas. While the schematics I re-drew are useful, they aren't really giving me too many clues as to how the machine actually works. The technical manual has some useful snippets but, sadly, isn't actually that technical.
On the plus side, that tiny Sony monitor with the Trinitron tube is still running like a trooper and I'm fairly certain I could make up a cable for my Amiga to run on it. I haven't dared plug in the bigger monitor yet though.. Maybe tomorrow.
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