Welcome aboard.

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

I ordered a pair of 590mm belts from http://www.beltingonline.com/ and  they arrived very quickly. The original belts were 588mm so 590mm should be fine. However, they are too small and don’t fit. How can a belt that is 2mm bigger than the original be too small? The answer is in the detail or more specifically … Continue reading DEC PDT-11/150 – Part 7. The disk drive belts.

I am now at the point where the disk controller is passing the RAM test but is hitting another fatal error. The Manual says there is a problem seeking to track 0 and I should replace the defective drive. That’s more than a little harsh and frankly isn’t an option. Take a look inside. When … Continue reading DEC PDT-11/150 – Part 6. Looking at the disk drives.

In the last post I had found a faulty RAM chip on the disk controller board and ordered a replacement from a supplier on ebay. Well, the part arrived Today and one fitting, the error lights on the disk controller went out… For a while. I can confidently say that we are past the RAM … Continue reading DEC PDT-11/150 – Part 5. The new disk controller RAM arrived.

I have been running some tests and learning a lot about this little machine and its ways. It has two layers of self-test. The first is a mandatory Power On Self Test (POST). The second layer is an optional interactive test made available by setting switch 4 on the main DIP switch block and activated … Continue reading DEC PDT-11/150 – Part 4. Self tests and the drive controller

I was preparing to share with you all my efforts driving the ODT with PDP11GUI. I have been using it to assemble Marco-11 assembler code and squirt it across to the PDT’s ODT. The problem is that when I came to fire up the machine to do a bit more and maybe take some screenshots … Continue reading DEC PDT-11/150 – Part 3. Healing hands.

In the last post I described the PDT-11/150 a little bit and the state of play. It was showing signs of life but not talking to me. It turns out the cable wasn’t right. Switch to a new cable, fire up GtkTerm and we’re on the right lines. What we have here is the ODT … Continue reading DEC PDT-11/150 – Part 2.

DEC PDT-11/150

22nd May 2018

This is an unusual one. The PDT-11/150 is one of a series of “smart terminals” based on the PDP-11/03’s LSI-11 chip set and so is basically a little PDP-11 atop a pair of massive 8″ disk drives. It came to me from a friend who presides over a massive collection but is still, like the … Continue reading DEC PDT-11/150

Multicomp revisited.

2nd January 2018

Way back in April 2015 I wrote about building an FPGA computer based on Grant Searles Multicomp. To be honest, it’s not had a lot of use. It has sat, largely unloved, in a cupboard awaiting redisovery. Well. in a roundabout way I have rediscovered it. Back in September last year, I exhibited a few … Continue reading Multicomp revisited.

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

A short step from where you are.