Altair 8800 replica

3rd May 2023

Acquired an old Altair 8800 replica by Briel Computers.
Looked a bit beaten up, the front panel had some extra 'mystery' holes that looked like they were made with a chisel and some of the lettering had worn away.
I think I have a solution to this.

One of the switches had been replaced, with the wrong type and so was 'wired' into the display board. Will need changing. A few of the switches were dry joint so needed reflowing, the switches are not actually fixed to the front panel and are only supported by the PCB, will look into a solution for this.

There were also a few bodge wires that will need checking.

The wiring to the DIN socket on the back panel left a bit to be desired, this will need rewiring.

The track side of the display board had seen some work, around the switches and the leds with some serious damage, perhaps done with the previously mentioned chisel (heated up!)

And finally (for now) some of the leds had random resistors inserted in series, I suspect that the leds were changed but did not match the originals for luminance.
I am not happy with this type of solution so my plan is to change all of the leds for new ones all from the same source and all checked for the same brightness, I may take the opportunity to swap some of the red ones for other colours, i.e. blue for 'control' and green for 'address'.

5th May 2023

Update on the 3 bodge wires...
The first one was confusing, from U1.pin9 to cable1.pin14 on the main board [B1], however the PCB trace went there anyway so I removed the wire.
This was followed up by a wire on the switch panel from the RESET switch direct to pin 9 of U1 on the main board(again!), and again the PCB trace already went from the RESET switch to cable1.pin14 so this second wire was also redundant and removed.
No idea why any of these were there!

This wire went from U10/pin15 to cable2.pin27, again it looked like the track headed that way anyway but was tested as open circuit.

After removing IC U1 I spotted the problem, my guess was that the person had tried to remove U1 (again with the aforementioned chisel!) and put it under the IC socket instead of the IC and had ripped up the track, and needed to then add the bodge wire.

I did not want to desolder a 40 pin IC socket just to fix one track as the access to it was difficult, so, I reinstalled the wire on the underside of the board rather than solder directly to an IC pin. The little loop back bottom right is so the wire coming out of the via follows the actual track rather than immediately passing over the ground plane.

Finally, I remade the 2 messed up led tracks on the switch panel, adding new vias as the old ones had long gone, along with extra solder resist on some of the nearby tracks. All IC's were removed, cleaned and the sockets treated with DeOxit. The voltage regulators were rebonded with new heatsink compound.

22nd May 2023

OK, so, I was not happy with my repair, I am not a fan of doing bodge wires on the opposite side of the board to the damage as it can make it hard to identify why a bodge wire exists, even though I do document everything in the repair/restoration log, so I removed the wire and replaced it with one that closely followed the damaged track on the topside of the board.

With that done the top and bottom of the main board now look like this...

after the reinstallation of all the LEDs the top and bottom of the front panel board look like this...(note: the LEDs are all the same height now but not XY aligned, will do this when I install the panel)

Next on the list will be the DIN socket wiring on the back panel, needs a bit of a tidy but I am going to relabel the back panel anyway, nothing fancy with this just going to reprint some labels.

I cleaned the panel with wire wool and reinstalled the DIN socket.
<--This is the old panel, and the relabelled version-->

The expansion board required very little work, all chips removed and cleaned, sockets cleaned and treated with DeOxit, the Electrolytics changed for Nichicons and the SD socket cleaned.
Then it was time to reinstall and rewire the DIN socket.

24th May 2023

OK, time to sort out the front panel...
To provide more support to the switches I decided to cut down the old panel so that I could then bolt it right down onto the switches.

I managed to find a firm here in the UK that could print me a new front panel. All I had to do was accurately redraw the panel in some free software called 'Front Panel Designer' by Schaeffer ag. I then sent the design to the panel printer and a few days later the new panel arrived. this fit perfectly over the switches and LEDs

Time to reassemble it all, I noticed that the great man himself had signed the inside of the case so was careful when cleaning this.

Panel and all boards in case, next the great power up...

10th June 2023

A little late posting this but I was distracted by an incoming Amstrad CPC 464 :) (more on this soon). The Altair needed a little more maintenance...
Some of the switch signals weren't getting back to the main board, traced to a dubious IDC connector crimpdown, I just cut the cable then recrimped it.

I made the assumption earlier that because the RAM board looked very clean that it would be fine... it wasn't, the 8515 socket had a bad connection with the IC pin not making contact with the socket, I decided to change the entire socket.

I had been in contact with Vince Briel during this to help with the fault finding, he sent me a amongst other files a new BOOTLOAD.BIN file, this was different to the one I had on the SD card, once I replaced it with the new one it all fired up fine.

So, all finished now, autoboots into CP/M. Downloaded a CP/M book as it would be over 40 years since I last used it!