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These are the random jottings of Andy Collins, a Fifty-something bloke who still thinks a blog or website is a good idea.

Here you will find small nuggets of information about Hovercraft, retro-computing and other stuff that amuses me or appeals to my sense of wonder.

Recent posts

So another Retrochallenge comes to a close. What did I do lately? Well, in the last 24 hours I have tested all of the 74 series chips, with the exception of the 74LS163 (my tester won’t touch them). All were fine, no problems at all. I swapped the 74LS 163s around to see if the … Continue reading RetroChallenge 2017/10 – Last day

Well progress has been slow but thanks to some helpful and knowledgeable people (here), progress has been made. So what do I know now that I didn’t know before? Well, I burned a ROM that just tried to access an imaginary I/O port. When I ran that and watched the _IOREQ_ line, I saw it … Continue reading RetroChallenge 2017/10 – Slow progress

So here we are, two thirds of the way through the month and the Nascom-1 is looking just as it did when I started 🙂 But now, take a look at this picture… This is the Nascom with a ROM in it that fills the screen with NULLs. I’ve just pressed reset. Now look at … Continue reading RetroChallenge 2017/10 – More clues but what do they mean?

Oh now this is getting a bit disappointing. It was a bit too much to think the tri-state buffers had failed and changing them one by one made no difference. Hmm. I think that the screen memory is OK because the noise on the screen shows each of the bits both set and cleared so … Continue reading RetroChallenge 2017/10 – Mid challenge – all the red herrings.

So here’s a thing. I recently met up with an old acquaintance who I hadn’t seen in years and as we’re both retro-computing fans we were talking about old machines. I have just received an email from an old acquaintance of mine who is a dedicated retro-computing fan and has spotted my plight in these … Continue reading RetroChallenge 2017/10 – Purely by coincidence

Having checked the clocks and finding things look well, it’s time to see if the ROMs are OK. The Nascom uses 2708 EPROMs. These are 1k by 8 bits and must have been one of the first EPROMs available. The problem with them is that they need three different voltage rails and most modern EPROM … Continue reading RetroChallenge 2017/10 – More things it’s not

In my last post I was suspecting the clocks. Now I’m not so sure there is a problem with the clocks. Having traced them through everything looks fine. I’m not sure what I was doing wrong but the symptoms haven’t changed but I’m seeing bus activity now and also the _CS_ on the main 2708 … Continue reading RetroChallenge 2017/10 – Still looking for clues

Yesterday I checked the voltages with my DMV and everything looked OK. Today I checked with the ‘scope just to check for ripple and they all look pretty clean to me. Clocks I also saw that there was a running clock but overnight I became increasing worried that it wasn’t a very good clock. Here’s … Continue reading RetroChallenge 2017/10 – and the beat goes on

So, it starts. In my last post I said that I intended to fix my newly acquired but already much loved Nascom-1. Up until now I hadn’t even powered it on but the time has come. Tada! So that’s it, random nonsense. The reset button makes the screen flicker but the nonsense doesn’t change. The … Continue reading RetroChallenge 2017/10 – Let’s see what we’re up against

It’s that time again and this time around I shall be trying to get my Nascom-1 running. I’m not going to even power it on until Tomorrow and the start of the festivities but the previous owner told me that it was working and stopped dead about half an hour after being powered up. Follow … Continue reading RetroChallenge 2017/10 – Throwing my hat into the ring.

A short step from where you are.