Binary Dinosaurs

I have a 75160 GPIB transceiver chip arriving hopefully tomorrow. In the meanwhile I thought ‘might as well remove the current one for testing, it might be ok!’ One swift-ish removal later… Bugger. Didn’t need that pin anyway* (*lies) Mouse pee is bad stuff, kids. Just say no.

Eep. And double eep. With the new 75160 fitted (despite how it was sent to me) I fired up the Agilent monster logic analyser and stepped through the boot process. When I left it it was in a loop seeking on the floppy drive, giving up, doing stuff then repeat. Might it actually be booting?

I have a 75160 GPIB transceiver chip arriving hopefully tomorrow. In the meanwhile I thought ‘might as well remove the current one for testing, it might be ok!’ One swift-ish removal later… Bugger. Didn’t need that pin anyway* (*lies) Mouse pee is bad stuff, kids. Just say no.

For those of you who haven’t been following the #positronJapes I got this machine in 2021, it had been rescued from a shed. Unfortunately it had been home to rodents, damp and lawks knows what else for decades and had clearly been stored on its left hand side. This is the GPIB section as was.

#positronJapes The morass grows as a 6th pod enters the fray so I can see what status the GPIB is returning to the CPU.

(It DID work with the Positron 900 'datapulse exchequer', and actually did a seek with the 9000 controlling it 2 weeks ago. Nothing since)

#positronJapes The morass grows as a 6th pod enters the fray so I can see what status the GPIB is returning to the CPU.

...and what it's showing is a constant /SRQ assertion, or Service Request. Unfortunately the OS9 code can't deal with this and just loops. Does anyone know anything about seemingly the only Positron floppy controller to exist in the world? 😆 /n

#positronJapes The morass grows as a 6th pod enters the fray so I can see what status the GPIB is returning to the CPU.

New toy! This is a 1981-ish Fluke 9010A troubleshooter that I’ve borrowed; since it has a 6809/6809E pod you might be able to guess what the next machine on the bench is. Yep, the Positron 9000 that I’ve had for years but still not managed to fix because this is the only one left*

(*I know there’s another one, it sold the year before I got this one and seemingly disappeared. Hopefully the owner is working on it and is going to burst forth with a working machine going ‘tadaaaa’ any day soon)

@snuggsy187.bsky.social @0xc0de.bsky.social Managed my own bit of Stag on the way back from Orkney yesterday, but since it was over 500 miles to drive AND I needed a pee this was the only pic I could take. Since the weather was splendid the place was rammed.

Got an odd one today. A 74LS08 AND gate connected to a 74LS92 decade counter. Gate 3 of the AND outputs to pin 14 of the counter. One of the inputs to gate 3 is a clock signal, the other is low. Therefore the output MUST be a clock. But it isn't. I've swapped both chips to no avail. Trace time!

I’ve had a dead Executel 3910 in for repair for months, attacking it on and off. It’s the reason I bought my monster Agilent 16702A logic analyser and learned how to use it. I fixed the initial issue and the Executel worked, then it didn’t. This was a crash I’d not seen before. 1/7

Weirdness keeps happening. The machine works but the video doesn’t init - it beeps correctly and the tape seeks. With the Agilent I can see that the code is working the same way the demo machine does, so this is hardware. I continue annotating the EPROM dumps using my Executed source code. 6/7

I’ve had a dead Executel 3910 in for repair for months, attacking it on and off. It’s the reason I bought my monster Agilent 16702A logic analyser and learned how to use it. I fixed the initial issue and the Executel worked, then it didn’t. This was a crash I’d not seen before. 1/7

The demo machine uses non-interlaced RGB while all the other production machines use interlaced. This makes no sense to the Viewdata people I know. Testing with Tandata Prestel terminals that also use MR9735 and non-interlaced RGB show that all the dead chips work fine in non-interlaced mode. 4/7

I’ve had a dead Executel 3910 in for repair for months, attacking it on and off. It’s the reason I bought my monster Agilent 16702A logic analyser and learned how to use it. I fixed the initial issue and the Executel worked, then it didn’t. This was a crash I’d not seen before. 1/7

The issue was video, the Executel uses the Plessey MR9735 as a video chip, it’s from the TELEVIEW viewdata chipset from Prestel days. One big fault with Executels is the video loses the sync signal at the MR9735 and I’ve never discovered why. 2/7

Good fun at the @computinghistory.org.uk meet up today. I took some of last year’s RetroFest exhibits to show - Sinclair QL with Schön keyboard and my CST Thor - along with something I’ve never seen at any retro event, the Mancomp replacement keyboard for the ZX Spectrum. Should do a feature on it.

Here’s a thing I’ve had for yonks, and it was in the warehouse at $DAYJOB for even yonkser before that as it was bought new for a customer who never needed it. It’s an ASUS P5GD2 Premium ‘wireless’ edition, even has a dinky little aerial, aw. But look at the caps! They’ve never been powered…

Digital audio out, SP/DIF, FireWire 400, gigabit Ethernet and 4 USB2. It even has, get this, a Floppy drive header that supports 360k 5.25” drives!