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Vintage Computers Any vintage computer systems, calculators, video games etc., but with an emphasis on 1980s and earlier equipment.

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Old 24th Mar 2020, 11:50 am   #161
John Earland
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Default Re: Zx81

I tried the '81 this morning and left it running without modifications for just over two hours - unfortunately the same thing happened. The unit rebooted and then the picture was lost. I tried retuning the TV but it was clear that it was the computer. I squirted the freeze spray onto the underside of the PCB where the ULS is situated and immediately the picture returned. I guess this means a new ULA? :-(
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Old 24th Mar 2020, 12:00 pm   #162
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Default Re: Zx81

It does look that way, sorry. You could check other things, for example make sure the +5V supply is 5V when the machine is cold and is still 5V when the machine is running warm and the fault has appeared.

Cooling the ULA may just allow it to run on a bad supply voltage for a little bit longer (stranger things have happened). But at the moment it does look as though you have a thermal fault on your ULA.
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Old 24th Mar 2020, 12:41 pm   #163
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Build the world's first water cooled ZX81!
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Old 24th Mar 2020, 12:46 pm   #164
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Some of the retro parts sellers sell a full length low profile heatsink specifically to go on the ULA which, even when working 100%, normally runs quite hot. But I fear that this ULA may already be beyond redemption.
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Old 24th Mar 2020, 1:09 pm   #165
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I did a look around for replacement ULAs and they're all out of stock. - replica cpld based replacements furnish lots of dead links. I guess it would require more dedicated research than the 10 mins I spent.
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Old 24th Mar 2020, 2:58 pm   #166
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This source

https://retrorevivalshop.co.uk/index...roducts_id=560

...claims to have five of the ones made by the New Zealand guy (who also makes the Vdrives for the Spectrum). Have not used this source myself.
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Old 24th Mar 2020, 5:36 pm   #167
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Oh-thanks for that! I’ll take a look-would love to have this little fella up and running again!
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Old 24th Mar 2020, 6:01 pm   #168
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In the meantime maybe you can get your ZX81 fix by fitting the CCU PCB to the other ZX81, the one with 'dark' video output.
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Old 24th Mar 2020, 6:50 pm   #169
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All this chat about ZX81s has made me get mine out of hibernation as im stuck at home now for the duration .
Might get the old Speccy out too and have a bash at Horace goes skiing !
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Old 24th Mar 2020, 8:08 pm   #170
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Mine has been out a few times as well over the last few weeks - must try again now I have a tzxduino loading some .p files into it!

My Spectrum and the new Next are always on my desk...
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Old 24th Mar 2020, 8:22 pm   #171
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Have any of you seen the new '81 software titles produced by Paul Farrow? His whole website is a treasure trove of interesting ZX things but here he's done a 3D isometric maze puzzle game in the style of Knight Lore / Alien 8 for the ZX81.

http://www.fruitcake.plus.com/Sincla...heElements.htm

Free to download, I believe.
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Old 24th Mar 2020, 8:26 pm   #172
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There was a game called 3D Monster maze for the ZX81 was pretty good considering the constraints of memory.
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Old 24th Mar 2020, 8:31 pm   #173
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Oh, that was virtually the 'Killer App' for the ZX81. I don't think anyone didn't have that game.
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Old 24th Mar 2020, 8:52 pm   #174
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I remember playing that on my friends ZX81. A year or so previously I'd written a 3d maze program for my Commodore PET and I remember being annoyed I hadn't bothered to sell my game as everyone I knew with a Zx81 had 3D Monster Maze
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Old 24th Mar 2020, 9:53 pm   #175
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I never had a zx81-Spectrum was my first and I loved Horace and the Spiders!
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Old 24th Mar 2020, 9:59 pm   #176
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I never had a Spectrum but I was very impressed with it at the time. It's no wonder it spawned the careers of many a computer programmer, you got a lot of computer for not much money. It's a shame Sinclair perused the business market and didn't realise what an opportunity he had in the home computer/games market.
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Old 24th Mar 2020, 11:09 pm   #177
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My recollection is that the ZX81 manual encouraged you to PEEK into the memory and see what was in the various locations. A good way of getting an insight into to what was going on. Data for BASIC programs usually had to be stored in REM statements.
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Old 25th Mar 2020, 8:42 am   #178
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Quote:
Originally Posted by emeritus View Post
My recollection is that the ZX81 manual encouraged you to PEEK into the memory and see what was in the various locations. A good way of getting an insight into to what was going on. Data for BASIC programs usually had to be stored in REM statements.
I never quite got PEEK (still don't to be honest) but as I'm going to be working from home for some time, I might get out my old manuals and start!
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Old 25th Mar 2020, 12:27 pm   #179
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Did anyone have any experience of the Sinclair ROM carts?
They are very collectable nowadays , but they have always eluded me.
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Old 25th Mar 2020, 12:48 pm   #180
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For the ZX81? They were available for Spectrum (for the interface II), but I have never been aware of any made for the ZX81.

For some time now there has been a ZX81 hardware add-on called the ZXpand (see what they did there) which, among other functions, allows ZX81 software in .P format etc to be loaded from flash media. There was, possibly still is, a custom version of the ZX81 keyboard membrane available which has the ZXpand specific keywords / commands on it.

If we want to wax nostalgic about the Spectrum, maybe it's time for a specific thread about that too?
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