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What do you do when a computer does not start anymore? No OS, not even a BIOS or any sign that there is any ROM at all? No way left to load any diagnostic tool?
Quickly think up a small program that accesses the memory area of the disappeared ROM and displays the bytes it finds there on the 7 segment LED display, enter it with the hey keypad and then look what's going on on the bus with the oscar, I mean oscilloscope.
The program displayed a constant 'FF', meaning that there is no memory at that address. The value comes from 8 pullup resistors that set the data lines to a defined value when no memory is selected. The ROM is gone, as if it was not there at all.
Chip select ... perfect signal, as if the computer was brand new and not almost 40 years old.
Address lines? All fine. Data lines? Lots of activity, as it should be. Memory read signal...
Tipping at the board with the test probe must have changed something. The ROM is back! The test program now displays the contents of the ROM and calling the ROM works fine again.
In a few months the old computer will be 40 years old and losing that ROM would have been terrible. Of course I could build some replacement, but the original ROM itself is irreplacable. It's so old that I could not even find the pinout or a datasheet of it, much less get one or locate a suitable device to program it. Any new replacement would have ruined the original state of the old computer. Fortunately it looks like it was just a case of aging bus connectors.
I have lived with several Zen masters - all of them were cats.
His last invention was an evil Lasagna. It didn't kill anyone, and it actually tasted pretty good.
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Whip over the PCB with a soldering iron looking for dry joints. Do remember that your current iron and solder will be lead free, and a 40YO PCB will not - so you will need a replacement tip, a lower temperature, and probably leaded solder.
Bad command or file name. Bad, bad command! Sit! Stay! Staaaay...
AntiTwitter: @DalekDave is now a follower!
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This was the very first board I ever assembled, so you bet the solder is not unleaded. 
I doubt there are 1000 of this old computer in working condition left on the entire planet and I'm glad I'm not the only one to keep them alive[^].
I have lived with several Zen masters - all of them were cats.
His last invention was an evil Lasagna. It didn't kill anyone, and it actually tasted pretty good.
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An Elf! you have a live Elf!
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They are not as dead as you may think. People still build new ones, often just to learn. Some parts have become hard to get, but the processor has still been in production.
Just look at this gallery[^] and see for yourself in how many sizes and shapes an Elf may come.
I have lived with several Zen masters - all of them were cats.
His last invention was an evil Lasagna. It didn't kill anyone, and it actually tasted pretty good.
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My stepfather has one which I learned (Tiny) BASIC programming on. He built a 60mA current loop interface which we use to drive a KSR-33 teletype.
AFAIK the ELF-II is still functional  .
Software Zen: delete this;
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My poor parents would have died if I had dragged in a huge noisy teletype.
The Elf must at least have had two expansion cards. The same one fixed with the ROM and also the serial and parallel I/O, plus cassette interface. The second one most probably was a 4k static RAM board, which was the minimum you needed to run Tiny BASIC.
If you used the teletype as a terminal, you did not have the pleasure of seeing Tiny BASIC in its full glory on the Elf's graphics chip at 64x32 pixel(!) resolution. Each character was about an inch high on the screen and there was only enough romm for six lines of 16 characters. A 300 baud terminal slow, but with 16 lines of 64 characters you could at least read something.
And don't tell me you never played some games on the Elf, low resolution or not.
I have lived with several Zen masters - all of them were cats.
His last invention was an evil Lasagna. It didn't kill anyone, and it actually tasted pretty good.
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I seem to remember there being a 4K RAM board, and John would have used the I/O board as part of interfacing to the teletype. We had it hooked to a car battery on a trickle charger to keep the 1.5K Tiny Basic interpreter loaded. Fat-fingering that in on the hex keypad was quite a job.
I remember playing Star Trek on the teletype a lot. The worst program we ever wrote on it was a mortgage amortization calculator my stepdad wrote. For every month it calculated the remaining principal, interest, and so on. It ran overnight printing out the entire table  .
I wonder if that KSR-33 contributed to their divorce a few years later...
Software Zen: delete this;
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Want th have an (emulated) Elf?
Look at the screenshots at the bottom of the page![^] Do you see Tiny BASIC?
There is no screenshot, but the emulator should also have an image of one of my first running programs for the Elf II.
I have lived with several Zen masters - all of them were cats.
His last invention was an evil Lasagna. It didn't kill anyone, and it actually tasted pretty good.
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and flux, don't forget the flux..
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What about the flux capacitor?
veni bibi saltavi
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Use it as a decoupler for the plasma relays.
Bad command or file name. Bad, bad command! Sit! Stay! Staaaay...
AntiTwitter: @DalekDave is now a follower!
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I would say it is time to get a new board and solder anything anew... The components (like the ROM) may be in good order, but an old, trembling connection may fry all...
And in any case - do a copy of the ROM content... It may come handy if the ROM dies despite all your effort...
"The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge". Stephen Hawking, 1942- 2018
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Kornfeld Eliyahu Peter wrote: do a copy of the ROM content
In those days they actually were so nice and printed a hex dump of the ROM on the back of the schematic. Still, the first thing I did was to save the content of the ROM onto a cassette tape - using the code in the ROM. When I find the time, I will sample a WAV file from the tape and import the code to my PC. Then I can make a disassembly and extract some code which I am going to need.
First I get my new Elf running, then the old Elf gets an overhaul. 40 year old bus connectors obviously tend to be a little loose.
I have lived with several Zen masters - all of them were cats.
His last invention was an evil Lasagna. It didn't kill anyone, and it actually tasted pretty good.
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Yes, we already know you are a wizard, now you are just showing off. 
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Slacker007 wrote: know you are a wizard
You mean this is not the wizards' guild here?
Nobody here reads books which no normal people can understand?
Nobody here then does stuff which normal people don't understand?
Then no computers do things which normal people don't understand?
Nobody here then comments the results in a way that normal people will not understand?
Nobody here who those normal people don't expect miracles of every day?
Slacker007 wrote: now you are just showing off
Nah. Showing off is just for those normal people. Here I hope to find someone who understands what I'm writing about.
I have lived with several Zen masters - all of them were cats.
His last invention was an evil Lasagna. It didn't kill anyone, and it actually tasted pretty good.
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Yes we do - but now your doing stuff that we non-normal people don't understand.
There is a limit you know!. (or at least there ought to be).
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Look at a computer magazine from 1980[^] and see for yourself how much wizardry has changed since then. Let me assure you that this used to be fairly common knowledge.
I had this issue back when it was new and read that article about those new shiny 16 bit processors.
I have lived with several Zen masters - all of them were cats.
His last invention was an evil Lasagna. It didn't kill anyone, and it actually tasted pretty good.
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I remember in the days of the Commodore PET, when chips weren't soldered onto the motherboard but were mounted in whatever-you-call-it thingies that it made it easy to replace the chips, every 6 months or so, when something stopped working, I'd lift up the lid and make sure all the chips were fully seated, and connectors given a wiggle, and presto, the problem would be solved for another 6 months or so of thermal cycling. 
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Marc Clifton wrote: whatever-you-call-it thingies
Sockets, perhaps?
I have lived with several Zen masters - all of them were cats.
His last invention was an evil Lasagna. It didn't kill anyone, and it actually tasted pretty good.
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CodeWraith wrote: the original ROM itself is irreplacable. It's so old that I could not even find the pinout or a datasheet of it, much less get one or locate a suitable device to program it
Heck, if it's that old, I might even have one in a box somewhere around here, along with the data sheet. What's the part number?
Will Rogers never met me.
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74S471[^]
All the usual suspects claim to have a datasheet, but once they have lured you to their pages, they admit that they don't have it.
Edit: Found a datasheet[^]
I have lived with several Zen masters - all of them were cats.
His last invention was an evil Lasagna. It didn't kill anyone, and it actually tasted pretty good.
modified 15-May-18 5:47am.
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Sorted?
Bad command or file name. Bad, bad command! Sit! Stay! Staaaay...
AntiTwitter: @DalekDave is now a follower!
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A E L N R Y
Software rusts. Simon Stephenson, ca 1994. So does this signature. me, 2012
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