Hello from Greece

[rmbrowngr]

Although I'm saying "Hello from Greece", I'm British from East Anglia, and have been living and working in Greece from almost 25 years.

I still have my first computer, the ZX81, and last time I plugged it in it still worked, although it had a very dark screen. I since learned this is a "back porch" issue with the ULA. I got my ZX81 for my birthday back in 1982 (if memory serves me well). I learned BASIC and played some simple games. I never bought a 16K RAM pack and I remember typing in a 1K pinball game, in assembly, from a magazine. It was long and painfully.

After a year or so, I move on to an Acorn Electron, and gave the ZX81 to one of my brothers. He eventually returned it and it sat in a cupboard at my parents home for many years.

When my father pasted away four years ago, I remembered that the ZX81 was in a cupboard, searched for it, and brought it back to Greece. I then demonstrated to my second son, who was interested in computers. I then put it aside again because of work, family etc., but now I want to get back to it and give some upgrades and fix the back porch issue. And BTW, it is boxed, but the outer cover has split.

My current list of "to do" items are:

• Fix the back porch

• Change the RF to composite

• Internal upgrade of the memory

• And may be replace the keyboard. I remember the Enter key had suffered from game play.

My wish\purchase list:

• The wonder ZXpand. Like gold dust to get hold of I understand.

• New soldering iron and kit, to be able to do the above. My current one is from the 80's, takes ten years to warm up, has large a wobbly tip

• New multi meter. Again, my current one is from the 80's.

I do have a question about the power supply. Should I get a replacement? I've heard the original power is not that great.

[mrtinb]

Welcome to this great forum.

I still use the old PSU without any problems with Wilf's ZXBKBv3 external keyboard, ZXpand and UDG4ZXpand.

I bought the great and cheap TS100 soldering iron from AliExpress, and I recommend the BC-2 tip for these tasks. It gets to 400°C fast, and has a display that shows the temperature. You can even adjust the temparature to your liking. Great value for the money.

https://www.aliexpress.com/item/1005001365820291.html

[1024MAK]

Hello and welcome to our forum Richard!



I hope I got your name correct. I’m assuming you are the same rmbrowngr from StarDot forums?

I hope you enjoy this forum

My current list of "to do" items are:

• Fix the back porch

• Change the RF to composite

• Internal upgrade of the memory

• And may be replace the keyboard. I remember the Enter key had suffered from game play.

If you need any help with these, have a look at the hardware forum area. And you can also ask for help.

My wish\purchase list:

• The wonder ZXpand. Like gold dust to get hold of I understand.

• New soldering iron and kit, to be able to do the above. My current one is from the 80's, takes ten years to warm up, has large a wobbly tip

• New multi meter. Again, my current one is from the 80's.

Unfortunately the designer and manufacturer of the ZXpand is not likely to produce any more anytime soon. So that only leaves the secondhand/preowned market. And as with any device produced in limited numbers for a hobby market, they don’t come up for sale very often .

There is a wide choice of irons and multimeters. If you buy an iron that was made in China, do check the earthing of the case and the bit. It’s preferable for the bit to be earthed to prevent damage to semiconductors from static electricity or from leakage currents from the mains.

I prefer to use a chisel tip. The pointy tips that are normally supplied are of limited use.

For a digital multimeter, even the cheap meters are normally accurate enough for hobby use. But the very cheap ones may not have any fuse protection (despite what the text says in the instructions or on the case), or may use glass fuses instead of sand filled ceramic fuses (needed for DC circuits). The test leads and the socket contacts, plus the function switch may also not be very good quality.

So if you can afford it, go for meter that is the equivalent of £20 or more.

I do have a question about the power supply. Should I get a replacement? I've heard the original power is not that great.

The original Sinclair PSU is an unregulated type. They use a conventional design using a safety isolating transformer and a thermal fuse for overload protection. It was available in two different ratings, the (very common) UK700 rated at 700mA (0.7A) and later on, the UK1200 rated at 1200mA (1.2A). Sinclair introduced the UK1200 for use with a ZX81 and the ZX Printer. An unexpanded ZX81 works with either type.

PSUs for the European market are very similar, but have a different model name.

Unregulated PSUs will output a voltage that is higher than the rated voltage if not connected to a load (such as the computer), or if the load is not drawing the rated current of the PSU. The Sinclair PSUs typically have an unloaded output voltage of around 14V to 16V.

This does not matter to a ZX81, as it has a 7805 voltage regulator chip on the board inside the computer (that’s the three terminal chip bolted to the metal heatsink).

Some third party designs of RAM pack do rely on a Sinclair PSU being used, as they take advantage of the unregulated output voltage being about 11V to supply the DRAM chips. It’s the same with the ZX Printer.

The ZX81 itself is not very fussy about the DC input voltage, as long as it is in the range of 8V to 12V (*) DC. So if you are not using an expansion which needs the ‘nominal’ 9V from the PSU to be about 11V, you can use most quality modern PSUs. Although in order to reduce the heat from the 7805’s heatsink, we recommend using a regulated 9V PSU. Occasionally a user may find that a modern PSU causes screen interference.

(*) Note the 7805 will work at higher voltages, but the capacitors connected to this circuit are rated at 16V. And running at above 12V significantly increases the heat from the heatsink attached to the 7805. Hence it’s not recommended.

Alternatively, the 7805 can be replaced with a modern DC/DC converter or switching regulator. These are so efficient that they don’t need a metal heatsink and run cool. They will work with an input voltage of 8V to 16V.

We will certainly try to help with any questions you may have.

Mark

[rmbrowngr]

https://www.aliexpress.com/item/1005001365820291.html

It looks like the same that Adrien Black (of Adrien Blacks Digital Basement) uses. I had thought to get the sames. Thanks.

[rmbrowngr]

Hello and welcome to our forum Richard!
I hope I got your name correct. I’m assuming you are the same rmbrowngr from StarDot forums?

Yes, the one and same. Thanks.

If you need any help with these, have a look at the hardware forum area. And you can also ask for help.

I will do thanks.

Richard