Hello from Virginia!

[amigaman07]

Hi Paul.

RE:

My comment on the ULA being very sensitive was aimed at Darren and any reader because his dangerous experiment.

Not having a Dig here everyone, as I am Glad people Post these Comments so other Users do Not Make Mistakes.

I was Very Cautious in my "dangerous experiment", doing the exact Same MOD as this fellow... Michel, and even achieving His Very Same Results! "this worked, the video was very dark and I had to increase the brightness and contrast to almost maximum levels"

I have since Discovered the Minor Differences between the ZX Spectrum and the ZX81 RF Video Outputs, amazing what you can find on GOOGLE these Days, and am now aware of the required Transistor and Resistor in the Circuit.

I have a Spare Working TS 1000 ISS 3 Mainboard, that is Floating about my Computer room, so I will attempt the Transistor and Resistor Composite MOD on this Unit First, before Hacking into my Nice Like New TS 1000!

Darren in OZ

I received another TS1000 but I couldn't get my TV card to tune in to the modulator RF channel. So I thought I would take the board out of the modulator and feed the video signal directly into the TV. Although this worked, the video was very dark and I had to increase the brightness and contrast to almost maximum levels. By analyzing the video signal I saw that the back porch was there but the sync level was way below normal CVBS levels. I thought that I could probably rectify that with a few series diodes, so I took some ordinary 1N4148 diodes, soldered them in series and voila, a beautiful crisp picture! It's a very simple mod that works well for a 210 ULA with back porch but not for ULA that hasn't got this back porch. The diodes also protect the ULA from ESD, so it's a quick simple mod.

Michel

[amigaman07]

Hi all.

Here is another Link for anyone who needs...

http://www.classic-computers.org.nz/blo ... r-zx81.htm

[Papa_Bear]

Can anyone here burn new chips for ZX81's and TS1000's Might be nice to replace the chips with fresh ones.


Also the heat sink for that voltage regular gets really b*tchin' hot isn't there a fix for that as well

[kokkiklhs]

Also the heat sink for that voltage regular gets really b*tchin' hot isn't there a fix for that as well

Why don't you try one of these http://www.ebay.co.uk/itm/282048618934? ... EBIDX%3AIT (I haven't, yet) to replace the 7805? Adjustable, dirt cheap, free worldwide postage and they are supposed to run cool without the need of a heatsink...

[Paul]

Why don't you try one of these http://www.ebay.co.uk/itm/282048618934? ... EBIDX%3AIT (I haven't, yet) to replace the 7805? Adjustable, dirt cheap, free worldwide postage and they are supposed to run cool without the need of a heatsink...

Well there are load of reasons why you shouldn't use these dirt cheap things.
Leaving all political reasons out there are also technical reasons.
1. NEVER use an adjustable power supply when a fixed voltage (or ampere) is needed. If something can go wrong it will.
2. These dirt cheap modules are great for driving dirt cheap equipment. If something goes wrong, so what. My zeddy is precious and shouldn't be harmed. If I want to replace the 7805 then I use something that is known good like TRACO or RECOM voltage converters.

I do have experiences with adjustable power supply. Not exactly these but something quite compareable.
After carefully adjusting the 5V output I was happy I managed this. The first try blew an LED. I then tried out different things:
On every switch on there a was a different output voltage. When I varied the load the voltage also varied. More load - more voltage.
I bought five at he time and only one was near specifications.

Of course you are free to make your own faults if you insist

[kokkiklhs]

Of course you are free to make your own faults if you insist

No, I wont, after I read all these!!
I just made a suggestion, and I was curious to see if someone has made the test so far! Since you give such a bad feedback (and I believe it), I withdraw my suggestion and also my curiosity!

[Moggy]

My weapon of choice...

Should be available in whatever part of the world you live in.

Here for example..

http://uk.rs-online.com/web/b/tracopowe ... onverters/

[Papa_Bear]

The ZX runs at 5v right? why not just... mod it to take USB? since well! USB runs at 5v

[1024MAK]

Welcome on board Papa_Bear !



Please do have a good look around the forum. A lot of the subjects you are interested in may have already been talked about . And there is still plenty going on in the ZX World

The subject of using a switching regulator in place of the 7805 series voltage regulator has come up a number of times before.
Either use a RECOM or a TRACO type. Part numbers in this post.
Have a look at this recent thread where there is some discussion and pictures
And ‪Pictures of my ZX81 fitted with a RECOM 5V Regulator‬

The ZX81/TS1000 itself runs at only +5V, so you could run it off a regulated +5V supply like a USB power supply. Just be sure that the USB power supply is actually a well regulated unit. Some of the cheap USB power supplies are not properly regulated (the output on some varies between +6V and +4V depending on output current). Also if you remove and bypass the 7805 voltage regulator, ensure you use a large label to remind you that it is a +5V input. As using a 9V power supply would kill most, if not all of the chips...

A lot of expansions use the +9V rail, either to feed their own 7805 voltage regulator, or in the case of 16k RAM packs, they use the +9V rail to generate a +12V supply and a -5V supply for the 4116 DRAM chips. So a +5V/USB supply would be of no use if you wish to use these expansions.

Most composite video modifications for the ZX81 / TS1000 use a transistor to buffer the signal. This increases the current to the TV (or monitor) which helps, and provides some protection for the ULA. I recommend one of the video modules that were mentioned earlier (ZX8-CCB or ZXVid). You could also use my test circuit detailed in this post

Mark

[1024MAK]

I've got one NTSC Zx81 and a TS1000 and I'm trying to figure out if it would be possible to mod the system. To run off batteries...

Yes, a ZX81/TS1000 can run off a battery.
Depending on the type of battery you wish to use, this will partly determine the power supply arrangements.
The easiest set-up, is to do the following:-

• Fit a RECOM or TRACO DC-DC converter/regulator in place of the 7805 voltage regulator.
• Replace the NMOS Z80 CPU with a modern CMOS Z80 CPU.
• Replace the NMOS SRAM chip(s) with a modern CMOS 32k byte SRAM (only half will be used, so you get 16k bytes).

These modifications will drastically reduce the power consumption.

• It is possible to go further and replace the ROM with a modern CMOS EPROM or EEPROM.
• If/when a replacement ULA module comes to market, this will use much less power than the Sinclair ULA.

Your ZX81/TS1000 can then run off of either the existing 9V power supply, or from a 9V to 12V battery of any type

Mark