Zx81 - Page 9 - UK Vintage Radio Repair and Restoration Discussion Forum

John Earland · 24th Mar 2020, 12:50 pm

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? :-(

SiriusHardware · 24th Mar 2020, 1:00 pm

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.

Slothie · 24th Mar 2020, 1:41 pm

Build the world's first water cooled ZX81!

SiriusHardware · 24th Mar 2020, 1:46 pm

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.

Slothie · 24th Mar 2020, 2:09 pm

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.

SiriusHardware · 24th Mar 2020, 3:58 pm

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.

John Earland · 24th Mar 2020, 6:36 pm

Oh-thanks for that! I’ll take a look-would love to have this little fella up and running again!

SiriusHardware · 24th Mar 2020, 7:01 pm

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.

electronicskip · 24th Mar 2020, 7:50 pm

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 !

Timbucus · 24th Mar 2020, 9:08 pm

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...

SiriusHardware · 24th Mar 2020, 9:22 pm

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.

electronicskip · 24th Mar 2020, 9:26 pm

There was a game called 3D Monster maze for the ZX81 was pretty good considering the constraints of memory.

SiriusHardware · 24th Mar 2020, 9:31 pm

Oh, that was virtually the 'Killer App' for the ZX81. I don't think anyone didn't have that game.

Slothie · 24th Mar 2020, 9:52 pm

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

John Earland · 24th Mar 2020, 10:53 pm

I never had a zx81-Spectrum was my first and I loved Horace and the Spiders!

Slothie · 24th Mar 2020, 10:59 pm

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.

emeritus · 25th Mar 2020, 12:09 am

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.

John Earland · 25th Mar 2020, 9:42 am

Quote:

Originally Posted by emeritus

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!

electronicskip · 25th Mar 2020, 1:27 pm

Did anyone have any experience of the Sinclair ROM carts?
They are very collectable nowadays , but they have always eluded me.

SiriusHardware · 25th Mar 2020, 1:48 pm

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?

24th Mar 2020, 12:50 pm	#161
John Earland Hexode Join Date: May 2013 Location: Middlesbrough, North Yorkshire, UK. Posts: 442	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? :-(

24th Mar 2020, 1:00 pm	#162
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,085	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.

24th Mar 2020, 1:41 pm	#163
Slothie Octode Join Date: Apr 2018 Location: Newbury, Berkshire, UK. Posts: 1,287	Re: Zx81 Build the world's first water cooled ZX81!

24th Mar 2020, 1:46 pm	#164
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,085	Re: Zx81 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.

24th Mar 2020, 2:09 pm	#165
Slothie Octode Join Date: Apr 2018 Location: Newbury, Berkshire, UK. Posts: 1,287	Re: Zx81 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.

24th Mar 2020, 3:58 pm	#166
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,085	Re: Zx81 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.

24th Mar 2020, 6:36 pm	#167
John Earland Hexode Join Date: May 2013 Location: Middlesbrough, North Yorkshire, UK. Posts: 442	Re: Zx81 Oh-thanks for that! I’ll take a look-would love to have this little fella up and running again!

24th Mar 2020, 7:01 pm	#168
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,085	Re: Zx81 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.

24th Mar 2020, 7:50 pm	#169
electronicskip Nonode Join Date: Oct 2010 Location: Gloucester, Glos. UK. Posts: 2,122	Re: Zx81 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 ! __________________ Oh I've had that for years dear!!

24th Mar 2020, 9:08 pm	#170
Timbucus Octode Join Date: Mar 2019 Location: Barry, Vale of Glamorgan, Wales, UK. Posts: 1,348	Re: Zx81 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...

24th Mar 2020, 9:22 pm	#171
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,085	Re: Zx81 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.

24th Mar 2020, 9:26 pm	#172
electronicskip Nonode Join Date: Oct 2010 Location: Gloucester, Glos. UK. Posts: 2,122	Re: Zx81 There was a game called 3D Monster maze for the ZX81 was pretty good considering the constraints of memory. __________________ Oh I've had that for years dear!!

24th Mar 2020, 9:31 pm	#173
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,085	Re: Zx81 Oh, that was virtually the 'Killer App' for the ZX81. I don't think anyone didn't have that game.

24th Mar 2020, 9:52 pm	#174
Slothie Octode Join Date: Apr 2018 Location: Newbury, Berkshire, UK. Posts: 1,287	Re: Zx81 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

24th Mar 2020, 10:53 pm	#175
John Earland Hexode Join Date: May 2013 Location: Middlesbrough, North Yorkshire, UK. Posts: 442	Re: Zx81 I never had a zx81-Spectrum was my first and I loved Horace and the Spiders!

24th Mar 2020, 10:59 pm	#176
Slothie Octode Join Date: Apr 2018 Location: Newbury, Berkshire, UK. Posts: 1,287	Re: Zx81 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.

25th Mar 2020, 12:09 am	#177
emeritus Dekatron Join Date: Jan 2012 Location: Brentwood, Essex, UK. Posts: 5,208	Re: Zx81 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.

25th Mar 2020, 1:27 pm	#179
electronicskip Nonode Join Date: Oct 2010 Location: Gloucester, Glos. UK. Posts: 2,122	Re: Zx81 Did anyone have any experience of the Sinclair ROM carts? They are very collectable nowadays , but they have always eluded me. __________________ Oh I've had that for years dear!!

25th Mar 2020, 1:48 pm	#180
SiriusHardware Dekatron Join Date: Aug 2011 Location: Newcastle, Tyne and Wear, UK. Posts: 11,085	Re: Zx81 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?