General Stuff(tm)

[PhilC]

Can't fault you for that Stephen. My collection is anything but traditional but does have its moments.

[rubber_jonnie]

Anyway, so, the list of faults was:

1. Dead TR4 transistor (+12V & -5V DC-DC circuit)
2. Dead TR3 clock amplification transistor.
3. Dead ULA
4. One dead 4116 RAM chip
5. Mostly dead ROM
6. Dead modulator. (How can you kill a flippin' modulator?!)

I've ordered a complete new case from Retro ReNew, which should arrive next week, and the ULA replacement board should arrive on Tuesday. Once that's done another Speccy will be ready to face the World again.

Wow that's quite the parts list, I know exactly how you feel.

This has got me in mind to get my spare Spectrum board running, it just needs a ULA as it came without one and a couple of upper RAM ICs that I stole for something else. And a case, keyboard etc...

I'll be looking to see how your case turns out.

And who the heck can manage to kill a modulator!!!

[stephen_usher]

Given the stuff I've previously got from Retro ReNew the case should look indistinguishable from the original.

Changed the composite mod from the capacitor to the transistor version and it's not as muddy on the Samsung telly. Still not great, but not muddy.

[stephen_usher]

Yay! More brokenness in the "spare" ULA.

This time it's the pin which reads the first column of the keyboard matrix. It should be an input but it's outputting ~2.3V and the 10K pull-up isn't raising it very high. There's also bleed-through of the other keyboard columns pulling it down, and it gets worse as the ULA warms up.

I found this out when trying to run the diag ROM keyboard test with a spare (and not very good) Spectrum+ keyboard membrane.

[stephen_usher]

The replacement Spectrum ULA unit arrived today.

Fitted it as dinner was cooking... Working well... Then I tried the DivMMC Future... CRASH.

Tried different CPUs and some worked better than others.

Without the SD card inserted the machine booted into normal BASIC. Click in the SD card and very colourful things on the screen.

Tried the diag ROM and that showed corruption as soon as the SD was pushed in.

Given this I started looking again at the EPROM decoding diodes. Found some smaller diodes with a lower voltage drop, removed the ones I'd previously installed and replaced them with the small ones and... it works. Obviously the voltage drop was causing issues, maybe timing.

The case should be arriving on Thursday now, so I can get a full machine by then.

Another thing which arrived today is a 7" HDMI screen I'm going to use with the Pi400. I'm looking to use the Pi400 as a VoIP telephone exchange with a virtual modem to be used with the copper to VoIP rack mount box and a 4G router, which will probably arrive tomorrow.

I've therefore brought the Pi400 down and tried to plug it all in... to find that I've lost the high power USB-C power supply! How could I do that?!!! *sigh*

I'm sure it will turn up... after I need it.

[stephen_usher]

Phew! Found it eventually.

New 7" screen works well. Not bad for ~£35. Just have to design and print a case for it now.

[stephen_usher]

So, the final part of the random Spectrum repair arrived today, the case.

So, to recap, this week's replacements have been the ULA.

IMG_3913.jpeg (331.71 KiB) Viewed 173 times

And the ROM decode diodes.

IMG_3914.jpeg (335.83 KiB) Viewed 173 times

Followed by a thorough soak test with the naked PCB and a lashed up Spectrum+ keyboard mat.

IMG_3915.jpeg (288.9 KiB) Viewed 173 times

The Retro Renew case uses the original moulds so everything fits fine. The only missing thing is the red printing on the back for the ports. But it mostly looks the part.

IMG_3917.jpeg (270.59 KiB) Viewed 173 times

[stephen_usher]

I haz t-shirt for Cyber Legends (and Retro Computer Festival)!

IMG_3919.JPG (299.17 KiB) Viewed 112 times

All artwork done on a QL using ArtICE, mostly in 1988 but updated recently.

[stephen_usher]

Further preparation for the shows...

Here's the heart of my comms set-up, a Raspberry Pi400 with 4G router and a nice little 7" display.

IMG_3921.jpeg (385.96 KiB) Viewed 95 times

This will be connected to a Mediatrix copper phone line to VoIP unit to allow me to connect modems to it.

The Raspberry Pi400 will be running the Asterisk virtual PBX with softmodems which can then connect to Internet located Viewdata sites.

I need to design and build a case for the display.

[stephen_usher]

A week after I fixed the ZX Spectrum the diag cartridge kit arrives.

Something new to solder.


In other news, I printed a case for the Raspberry Pi display, though I had to modify it with a Dremel slightly.

IMG_2399.JPG (263.04 KiB) Viewed 37 times

The only issue with this was that the black filament had become damp and hence brittle and as the filament was withdrawn from the hot end of the printer it snapped inside the hot end. This meant an unexpected (and first) dismantling of the Bambu Lab X1 Carbon head and replacing the hot end with a spare.