Nexxen wrote on 2025-06-01, 11:01:Over the years, and the help of some you, I developed a sequence of check before powering up "unknown state" boards/circuits. […]
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Over the years, and the help of some you, I developed a sequence of check before powering up "unknown state" boards/circuits.
I bought a PCChips 741LMRT board as is "untested / unknown working order" for close to nothing.
1. shorts or suspicious low resistance
2. visual inspection
3. power on free of cards, cpu
4. power on
5. power on with cpu and diag card
6. add stuff
-----
The board came with a Celeron 500.
Board was ok until power on with cpu: the -- -- was on 😀
I tried to swap the cpu, add ram + buzzer: board would issue a cycle of BIOS codes starting from 00 to 9F (the last possible value, maybe this one is wrong)
Suspects: cpu voltage, BIOS with bit rot.
And copious amounts of dirt. Cleaned thoroughly.
Replaced the BIOS with one from another board, C1 appeared. Reflashed old BIOS rom and tested again, POST.
C-500 wasn't working. Tested on another board: POST.
Why??? 🤣
After letting the 741 warm it'll POST with the C-500, caps need a replacement session.
I tested 2 BIOS roms, AMI and Award. Can't tell which is better.
Nice, I was initially confused as to whether the board was working but that's a quick repair 😀 So the board won't start from cold with the Celeron 500 fitted, how bad are those capacitors?
I bought another broken laptop! This one was an Olivetti Echos P120E which I have its cheaper relative the P100E and I'm quite fond of it - this one was shown as broken in the listing and has a completely destroyed hinge plastic on one side:
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Quite a while back I bought an Acer laptop with a similarly busted hinge and 3d scanned it and made a big faff of it with too much complexity for a small plastic part: Re: What retro activity did you get up to today?
This time since it's a basic shape of a cylinder with some screw mounts and other minor features, this time I made a design in fusion 360 using calipers and a radius measuring tool:
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The new part is printed in clear PETG, the original screw threads were liberated from the broken plastic and melted into this new replacement. This could only really work with the right hinge which doesn't have too much cabling in it - the 3d print has much more material in the empty space where there's room to give it some strength, it's got to accomodate the backlight cable so there's a cable trench modeled in. Overall I'd say this design took a couple of hours to design and an hour to print.
Something to note about this 3d print is that it's printed left-to-right so that the layer lines are in the rotation axis of the hinge, this is so that layer separation can't be a cause of plastic failure. If it was printed in the other orientation i.e. from the bottom to the top then potentially the layers of plastic around the screws could become a weakspot, but because it was printed vertically with supports, the stress and forces from the hinge are spread across all the layers.
The print is also set up to use enough perimeters that there is no infill in this part, it's almost completely solid and is much stronger because of that.
Then cheap epoxy was spread over the contact area of the two parts and they were squeezed together, somehow this white epoxy cures very quickly and gets very hot. But it works well and works better than the clear epoxy I was using before.
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Now it's sanded back a bit, sadly the epoxy cured too quickly to be able to smooth the area properly but it's super strong. With a little sanding and some fresh paint on top it looks pretty good:
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Once I could actually use the laptop, I then discovered that the mainboard seems to be broken - it can start up but like my other olivetti is just showing a blinking cursor and never does anything after. I think the DS12885S RTC chip is faulty since it's got power and the data signals are good, but it's not running the 32.768khz clock crystal. Now to get a replacement for that to see if this can be got up and running after I spent all this time fixing the hinges
(the other hinge was also just about to break but this was fixed with epoxy reinforcement on the inside and melted-in staples on the outside).