RF Video Distortion

[balford]

Oops, what have I started

Replacing the CPU will cool the overall system down even more as the CMOS parts will run almost cold compared to the original NMOS CPU.

And you're right, the switch mode regulator is much more efficient and generates almost no heat, removing the need for a heatsink.

Here's my Issue 3 board with all the above mods, plus an internal 16k mod for good measure (you won't need this with a ZXpand):



B

[sirmorris]

Does the new regulator allow the board to fit in the case? It looks a little tall.

[balford]

Nope, fits fine, it's only 10mm or so high

B

[sirmorris]

Sweet. I see a Farnell order coming on..

[1024MAK]

The disadvantage with fitting a switch mode regulator and a 10 MHz Z80 CPU is that you will need to update you own ears to cope with the higher frequency ultrasonic sound output from the Zeddy...

Of course, the above statement could just be complete fiction
It is the clock circuit (oscillator) in the ULA and the 6.5 MHz ceramic filter which sets the speed of operation. The 6.5 MHz clock is divided by two resulting in a 3.25 MHz signal. It is this signal that controls the speed of the Z80 CPU. A 10 MHz part is rated to operate up to and including 10 MHz. So when clocked at 3.25 MHz, it will err, operate at 3.25 MHz...

I hope that clears the fog a little

Oh and just to clear a little more, the switching regulator needs no heatsink as it is much, much more efficient than a conventional series pass voltage regulator like the 7805.

Oh and welcome to our Zeddy forum

Mark

[RetroMike]

Sweet. I see a Farnell order coming on..

Me too

Thanks for the info too Mark, I think that using up less power is a good thing, and should extend the life of my board, as well as saving some money in the long term, and with the price of electrickery these days, it won't be long before it breaks even

[Prime]

Which switched mode reg did you use? Would be interested to try this in one of my 80/81 Machines.

Cheers,

Phill.

[balford]

Hi Phill,

I used this exact part: http://ie.farnell.com/jsp/search/produc ... KU=1861095

However the one I linked to on page 2 of the thread is an equivalent part and is a good bit cheaper I've used these to good effect on both my '81 and an Issue 4A Speccy board.

B

[RetroMike]

Well, I went and bought a pair of regulators (one for the Zed, one for Speccy), plus a z80, and will see how I do with the install. I've got a new keyboard membrane from Rich at RWAP now and have installed that, as well as the membrane and faceplate I bought for my Speccy, but there's a break in the power cable on that, so I've ordered a new plug and soldered in a new socket onto the board this avo in preparation. Still waiting for validation over on "World of Spectrum" before I can ask any questions over there

Once I close up the case of Zed2, it'll be quite a nice modern machine by comparison, and the case is actually in better nick than Zed1, which is a bit scuffed in the middle. Hope Charlie is enjoying playing with it

Is there any way to repair the raised text on the Zed's case? I'm a plastic modeller too, and was thinking of lashing some red enamel paint onto the worn edges of the ZX81 legend to see whether that improved it any. If there are any better techniques out there, I'm all ears

[balford]

Well on the Speccy, just make sure it's a 2.1mm dc plug (2.5mm won't make reliable contact), and ensure that the tip is wired for negative / outside positive. Don't plug it into the Speccy until you've verified this!

Also, I'm not a huge fan of using the existing power supplies due to age etc. What I've done is to buy a 9v 2A supply off eBay, replace the plug so it's wired correctly for the Speccy, and then make up a lead with a 2.1mm socket at one end, and a 3.5mm mono plug at the other. Using this, I can use the same supply on both ZX81 and Speccy machines, just needing to add the little adapter when using the '81.

As for the raised lettering, I'm lead to believe that all you need is some suitable paint, a fine brush and a steady hand. Since I'm unfortunately devoid of the third item, let us know how you get on

B