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  Defective Saitek RISC2500
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   Author  Topic: Defective Saitek RISC2500  (Read 7300 times)
Kostea
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Re:Defective Saitek RISC2500
« on: January 5, 2013, 12:13PM »
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Hi Mychess,


I totally agree with what you said.

The GAL chips are replacing many individual chips, making the circuit board simpler and smaller in size.

RISC2500 has 2 GAL chips, I have a bad one and a good one.

For example, for the good GAL chip which I decoded, it would be needed 3 chips (with AND and OR logic gates) just to accomplish the function of one output, and this GAL has 8 outputs. I'm not saying that this GAL replaces 24 chips, it's between 10-15 chips in my estimation.
All in all, the 2 GAL chips replaced about 20 individual chips, this basically made the circuit board half the size it would have been.

Good catch with the copy protection!!!

Fortunately, TASC Holland did not protect the GAL chips, I was able to fully read one chip, decoded and validated its programming, it's 100 percent correct.
I was also able to retrieve about 10 percent from one of the bad chips, and that data is also correct.
However, if they were protected, I would have known right away, the device programmer would give an error message when attempting to read the chips.
Also after looking at the JEDEC files, the bit G1 is not present, that is what would copy-protect the GALs.

The use of a digital/logic analyzer is a great idea.
For this particular case, the logic analyzer needs to have at least 17 leads/inputs.
The GAL chip has 20 pins. We substract the + (Vcc) and the - (GND), and that leaves 18 pins. I noticed that the Output Enable pin is connected to a fixed voltage, and that leaves 17 pins with variable/changing inputs/outputs.
I can find a good and cheap 16-lead logic analyzer, but that's not enough, the next option is a 32-lead one, which is expensive.
Anyway, in order to properly troubleshoot some of the old chess computers, sometimes is needed at least 24 leads, 16 for the address bus and 8 for the data bus.
I have never been in a situation to need that, and I have plans B and C if the need ever arises, I mean there are ways around that.
But let's say that I have to troubleshoot a TASC R30, who might have the bigger GAL20V8 instead of GAL16V8, and then a 32-lead logic analyzer comes in handy.

If I had a working RISC2500, with the GAL soldered, I would not risk pulling it out.
I would have used the logic analyzer to create a truth table with the various input to ouput combinations.
Then I would have minimized/simplified the logic equations by using the Veitch-Karnaugh method, and then create a JEDEC fuse map to load into the bad GAL.


By the way, if TASC Holland would have used PALs instead of GALs, this chess computer would have lasted forever.
I prefer PAL more than GAL, as much as I prefer PROM instead of EPROM. I don't like eraseable stuff.

I'm still debating it, I might replace the GALs with PALs, making the RISC2500 immortal.


Seeing that no one has that GAL data file so far, I completed some steps of the plan B.


I got 10 percent of data I read from the bad GAL, it's better than nothing.
I have drawn the schematic for the circuit around that GAL chip, now I know what is the function of the chip, and which pins are the inputs and which are the outputs.
Half of the GAL pins can be programmed as either input or output, and to know what type they are, is one the most crucial things in this situation.
Then I will try to come up with a correct configuration, which will be time consuming.

I don't know the memory map of RISC2500, so this part will be trial and error.
An ARM2 CPU, when it starts/resets it runs from the memory location 0 (zero), so the EPROM should be located there. However, this CPU is tricky, and after start from EPROM, it can change the memory map on the fly, it might not be the case but I have to take that into account.

I might have to take a look at the software in the EPROM, and do some reverse engineering.

I planned to do that anyway. Just wanted to see if the Montreux really has a 380,000 moves opening book.
Each individual move encoding takes one byte for the "from" field and one byte for the "to" field.
So physically it can't have 380,000 moves. It needs 380,000 x 2 = 760,000 bytes = 742 kb to encode that, the EPROM is a 256kb which is only about 60 percent utilized, the rest is blank/empty.
Only by counting the same moves multiple times, for the several variations of a certain opening, that number can be achieved.
I might have to run a script that will list all possible variations.

By the way, the Montreux has the AEGON 1994 opening book, but the RISC2500 does not have it.
For the most part, the chess engine is the same in the RISC2500 and Montreux, but I prefer to attack the bigger Montreux, once I have that one decoded, I will also have the RISC2500.

Sorry for the long post, if you ever can't fall asleep, keep a copy of this post by the bedside.


Regards,
Kostea
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mychess
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Re:Defective Saitek RISC2500
« Reply #1 on: January 5, 2013, 01:35AM »
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Hello,

Use pal/gal in a electronic circuit has two usages:
- Simplify the circuit
- Prevent copying of circuit: pal/gal generate output signals according to logical formulas of the input signals .
I fear that in the case of electronic chess games, two goals are sought.
For that, the circuit pal/gal can be protected from reading their internal code.
In this case only the use of a digital analyzer can find the formulas.

Best regards,
Mychess.
« Last Edit: January 5, 2013, 01:44AM by mychess » Report to moderator Logged
Alain Zanchetta
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Re:Defective Saitek RISC2500
« Reply #2 on: January 3, 2013, 10:18AM »
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Hi Kostea,

thanks for the details, this is really interesting (I learnt a lot : I must admit that I know nothing about hardware) !
I had once got access to a few ROMs which I should still have somewhere but if I understand correctly, it is unlikely that GAL files would have been there too. I am not at home now but I'll check anyway this week-end.

Good luck,
Best regards,
Alain
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Kostea
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Re:Defective Saitek RISC2500
« Reply #3 on: January 3, 2013, 12:37AM »
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Hi Alain,


Thanks for replying and for the very good advice!


My thinking was that since I have posted here before, I'd try here first.

I realize that I have very little activity here, and haven't really contributed to the forum as much as I wished or could.

However the other option was to join a new forum and on my very first post to ask for help.


Well, after all it's a small world and is possible that some from the German forum are members of this forum or at least visit here every now and then.



I have a few things I'd like to add to my original post.


- just to eliminate some confusion, the EPROM chips are not the same as the GAL chips.
The EPROM contains the chess engine, while a GAL chip contains a bunch of logic gates and flip flops and ways to interconnect them in the desired configuration.

- per their datasheet, the GAL chips are rated to hold their data for 20 years.

- in the near future, it's possible that more and more RISC2500 will break down when their GAL chips lose their data. Then it will be the Montreux's turn.
TASC Chessmachine has one GAL chip, another potential victim.
This could also apply to TASC R30 if they use GAL chips.

- it's not a good idea to desolder the GAL chips in order to copy their data.
No matter what your skill level is, this is like playing Russian roulette.
These GAL chips are now on their last leg, and a little misapplied heat here and there, a little electrostatic discharge, and you're the owner of a newly broken chess computer.

- the best chance to copy the data is by the owners of a Montreux or a RISC2500 (the ones which have a circuit board like the one from the Montreux), their GAL chips are installed in sockets, and easy to extract while carefully avoiding bent pins and static electricity.
Unfortunately my 2 RISC2500 are the early production run, the CPU is installed on the same side with all the other integrated circuits and the GAL chips are soldered, while the newer RISC2500s and the Montreux have the CPU "under" the circuit board and the GAL chips are in sockets.


I want to make it very clear, I'm only asking if someone already has the data file.
I did not ask anyone to open up their chess computer and copy the data file just because I need it.
Please do not break your chess computer!


Thanks,
Kostea
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Alain Zanchetta
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Re:Defective Saitek RISC2500
« Reply #4 on: January 2, 2013, 09:36PM »
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Hi Kostea,

that's really a pity that the other Risc is defective too !

you should try to post the question on shachcomputer.info forum : not only are there more people than here but they seem to have skills in electronics that we do not have.

Best regards,
Alain
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Kostea
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Defective Saitek RISC2500
« Reply #5 on: December 29, 2012, 09:16PM »
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Hi,

I have 2 RISC2500 chess computers, one was working, the other was defective.
Today I had some spare time, and planned to do something that I put off for a very long time.
I was trying to fix the defective RISC2500, and I found out that one of the GAL16V8 chips was not working properly.

Thinking that I could copy the GAL data from the other one, I powered on the working RISC2500, but that one it's also broken, happened sometime within the last 3-4 months since last time I used it.
What I found was that this one has the same chip GAL16V8 defective.
What a freaky coincidence!

I was wondering if anyone has the .JED (JEDEC) file for the data that is programmed into these GAL16V8 chips, and would be willing to send it to me.
I have a programmer which can write the file into the GAL chip, and I also have a few brand new GALs.

The old chips are not bad, and can be reprogrammed and reused, it's their data that has been erased over time.
One chip was totally erased, the other had maybe 10 percent of data left.

There are 2 GAL16V8 chips in the RISC2500, the Mephisto Montreux has them as well.

The chip that's erased is the one close to the power transistor, it's on the left side of CPU if you hold the chess computer orientated with the EPROM on the right side.
The chip is numbered U14, however that inscription is on the circuit board right under the chip, and is not visible unless the chip is removed.


Thanks,
Kostea
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