Broken LASER 200 8-bit computer from 1982 - A Challenging Repair! - Can it be fixed?
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- čas přidán 12. 09. 2024
- I got this old and non-working Laser 200 with garbled video output. Can I fix it ?
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This seemingly easy repair of the little 8-bit computer from 1982 became a little more complicated and time consuming than I first thought.
The Laser 200 computer was also sold under the names VTech Laser 200, Salora Fellow, Texet TX-8000, and Dick Smith VZ 200.
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Fantastic fault finding effort. Most people would have used the motherboard as a Frisbee long before lol. Great video thanks for sharing 😁
Thanks for watching!
Great job! I was so happy for you when it finally booted properly. You have great patience - a lot of people would have given up on it.
Thank you!
Nice work!!! Many rabbit holes but you did it!
Thank you! Cheers!
Great work! Somewhere in the future someone will have to work on that machine again and they praise you for putting in all those sockets!
Well done Tommy, that was a tricky one 👍
Thanks 👍
Great job, Tommy! Perseverance paid off! Those precision sockets (with round holes), when properly made, are the best, but they are _not_ made for multiple insertions. When an IC is inserted, its pins cut into the round hole, creating a tight groove with perfect fit and perfect contact. But if multiple different ICs are inserted, or even the same IC inserted multiple times, into the same precision socket, each insertion creates a different groove, and quickly the grooves merge and become so large no contact is made anymore. For test boards, which require multiple insertions, traditional double-wipe sockets are much better! The clicking sound from that ROM is almost certainly sparking from a loose bond wire, which connects the die to the pins. In boards like this, which are easy to desolder and have only a few chips, it can be faster to simply remove all ICs, test them individually, and socket the entire board. You solve the problem faster and at the end you are even better off, as a fully socketed board will make things easier and safer for the rest of the computer's life. Careful diagnostic before desoldering is only a thing for more delicate boards and boards with lots of ICs, or if you have a CZcams channel focused on your diagnostic skills; then you do it for the show. 🙂 By the way, although I understand your nostalgia for this machine (I have similar nostalgia for the ZX81), this computer takes the cake for the _worst_ built of the 80s, even in a decade known for very poor quality products! This thing is so incredibly poorly made it's amazing it became a product at all!
Thanks :) About the socket, I was not aware that the round hole sockets was not made for multiple insertions. But it became more and more loose.Yes, I agree about the machine being poor quality.
I like your perseverance! That's a great quality!
Thank you!
Great video, looks like the Laser 200 could have been made by the same Hongkong company who made the Lambda 8300.
Thx:)
glad you not give up, rewarding when you win and fix it.
Yes, for sure :)
That was satisfying! Good thing you had the working machine to test with.
Yes it was!
There are some logic chips that have a different pinout (and sometimes functionality) in a different technology. For example: 7400 and 71H01 (pinout), 7486 and 74L86 (two gates have a different pinout), 7454, 74H54 and 74LS54 (4x 2-input vs. 3x 2-input and 1x 3-input vs. 2x 2-inout, 2x 3-input). Lots of testers do only support the "LS" or "standard" version.
OK, thanks :)
Persistence pays off! As you mentioned, it's actually very nice to have most of the chips socketed anyway, so I consider the time it took to do that as an investment in future troubleshooting.
Yes, sure :)
Hurray! I'm glad you got it working. 🙂 I recently had to replace a failed ROM in my Dick Smith VZ200, and I learned an interesting thing from a fellow owner: You don't need an adapter to use a 27C64, and you can -- in fact -- replace both mask ROM's with a SINGLE 27C128 + a couple diodes if you like! The trick is to properly change the jumper wires (which includes that weird bare wire that looks like a repaired trace). I used a pair of 27C64's on mine, burned with the latest v. 2.1+ version of the VZ ROM (originally for the VZ300, but totally compatible with the 200). (I kept the working 2364 with half of the original ROM, of course, but since I had to burn one, I figured I may as well burn a pair of matching, latest-version EPROM's.)
I really, really wish that VTech had labeled the chip sockets and jumper holes, as the total lack of labels meant that, even with the knowledge that it was an easy thing to change the jumper settings from 2364 --> 27C64, I still had to spend quite a bit of time "beeping out" the proper jumper holes (includes some previously unused ones which had come from the factory filled-in) to wire to which. In the end, the jumper settings for 27C64 turned out to be SIMPLER than the jumper settings required for using the factory-provided 2364 ROM's! 😲
I will also confess that, when confronted with that rat's nest of jumper wires, I, too, initially replaced the 74LS245 (which switches the bus from "system RAM" to "video RAM"), only to later discover that the real problem was a failed mask ROM.
You're right, I used to fix it just by replacing the EROM, leaving only one new one and using 2-3 diodes, because in most machines the ROM is broken.
When it was finished and opened, I was very happy.
@@KiKi-gw9ciNice!
BTW 245N can be replaced with 645N direct modern replacement.
Well done! You didn't give up and showed a lot more patience than I would have had and it payed out in the end! Congrats!
Thanks!
I've heard chips make sound before. I got a broken Konami Scramble (bootleg) arcade machine that didn't work. One of the i8255 made a weird sound that repeated every time the watchdog triggered. I thought maybe the chip was bad so I replaced it with a different manufacturer. That one also made the sound. So I tried a third one and that also made the exact same sound. They didn't make any sound when I fixed the machine (an LS74 for the interrupt generation was bad)
Strange thing!
Absolutely brilliant work Tommy!!. By far the best and most informative video information on Laser/VZ-200 repair out there. I have a VZ-200 (as they were known here in Australia) with very similar issues and will be following your guide to see if I am having the same problems :) Outstanding stuff!!
Glad it helped
Many 8-bit computers around that time had that combination of Z80 CPU + 6847 video controller, which is an odd couple, since the 6847 works better with Motorola CPUs. Other similar beast is the NEC PC 6001. In Brazil there was the CCE MC-1000, which nobody knows the parentage and is one of the Great Unsolved Mysteries of the Brazilian retrocomputing scene. The most accepted theory is that it's a clone of the Rabbit RX83 from Hong Kong.
Thanks for the info :)
I enjoy your videos alot.
I thought you picked U9 instead of U6 also when burning ;)
Thanks! U9 is the component number in the PCB. But it was a xxxx-06 labeled chip. The other was xxxx-07
That is awesome.
Murphy's Law in action!