15 October 2017

RetroChallenge 2017/10: Part 5

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NEC PC-8401s' Capacitors & NiCd Sorted

Since discovering the leaky capacitors in the PC-8401s LCD module (last post, Part 4), I've replaced the problem components and the screen is now working without further issues. So, while had the main case opened I also decided to replace all the other potentially problem components and give the unit a good service.

I replaced all the capacitors with like for like values. The one exception being a 1200uf 25v, which is now a 1200uf 35v variety. The extra voltage level is not an issue, though the replacement capacitor is twice the length of the one it replaced, luckily there was space to lay it on it side.

The other remaining problem component was the 30 year old NiCd battery, which amazingly hadn't vomited it's guts all over the motherboard. The NiCd battery inside the PC-8401s is there to keep the DRAM and system clock ticking over should there be no main battery or indeed mains power. (No compact flash for 1985 user convenience).

1 Frand Super-Capacitor Battery Replacement

I decided to replace the battery with a 1 frand 5.5v super capacitor. I've previously made similar modifications to my Tandy M100 and M102 machines to good results, with RAM storage remaining intact for over a month before (until I got board waiting) I reapplied mains power. Similarly to the previous m100 modification, I bent the pins of the capacitor over horizontally before attaching wires which are the soldered on to the PCB. The capacitor itself is attached to the circuit board with double sided tape, keeping very firmly in place.

So next time it's back to doing something else arguably useful with a 30 year old computer.

See RetroChallenge IntroPart 1Part_2Part 3Part 4, Part 5Part 6Part 7Part 8
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