Thread: Sinclair ZX81
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Old 7th Aug 2017, 2:59 pm   #62
SiriusHardware
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Join Date: Aug 2011
Location: Newcastle, Tyne and Wear, UK.
Posts: 11,485
Default Re: Sinclair ZX81

The only drawback with ZXpand is that it (as far as I am aware) connects through the self same edge connector as the original RAM pack did, so is potentially prone to the same 'bump' problems. Nothing beats an internally fitted RAM upgrade for stability.

Audio loading of software is all part of the, er, charm, especially if you are loading from a digital source which outputs the same signal at the same consistent level every single time so it is virtually guaranteed to always work first time.

For those who do go for a ZXpand there is also a version of the remanufactured replacement keyboard which has the alternative key legends printed on it for ZXpand specific commands. They've even got that covered.

The ZX series always did have a good selection of third party hardware to go at, see also those items produced by a gentleman called Paul Farrow who produces beautifully designed and documented add-on hardware for ZX computers - mainly for his speciality, the Spectrum, but also for the '81 as well.

For Ken and his ULA, I bought a late version ('2C210') ULA - the one in which the video 'back porch' problem is fixed - quite recently from an online supplier who had found a large quantity of them somewhere. He is currently offline while recovering from a serious illness, but hopes to be back up and running some time around mid or late August (2017, for anyone reading this in two years' time). So if you still think you need a ULA in a few weeks' time, have another look around then.

I do think you should do a few more checks on clocks, supply voltages, and other signals such as _RESET before buying a ULA - pity you don't have anyone nearby who can loan you a working ULA to try.

This nicely redrawn ZX81 circuit diagram may assist with fault finding.

http://www.mainbyte.com/ts1000/good_schematic_hi.jpg
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