After fixing a VIC-20 for a friend the other week, and seeing how nice/easy they are to work on, I thought I’d take a peek on eBay and get some ‘spares or repairs’ computers from my childhood, before the end of the weekend, I’d grabbed:
1. Commodore 128D - advertised as good condition, but was tripping their RCD, had been repaired by a little known YouTuber previously, looked OK in photos, not many left and probably the one I remember well as I was in my teens when we had one.
2. BBC Micro Model B - just said the PSU was making noises and might need recapping, but stated as VVGood condition.
3. C64 Bread bin, advertised as good condition and shows rolling rf output.
Two of them turned up today, C128D and the Beeb..
BBC Model B - I was amazed how clean it was, 9.5/10 and very uniform slightly yellow, but about the exact colour I remember at Junior school being let loose on one. On getting the PSU (Wong) out, everything looked OK, no obvious cap issues at all and after 30 mins of checking everything I could in-circuit, I fired up the PSU unloaded and it was spot on, so checked the main board and no shorts, all looked OK, so reassembled, turned on, and ‘beep’, looks to be powering up, and instantly noticed a noisy speaker.. checked YouTube and seems an easy fix, and I am now wondering if the seller mistook that for noise coming from the PSU!.. I’ll hook it up to a monitor tomorrow, and will order a recap kit anyway, but might have struck gold on this one!
Doesn’t look so yellow in real, camera WB seems to be struggling.
Commodore C128D - total opposite to the Beeb, 5/10 condition, slight damage to case tabs, corners, yellowing (patchy), and very dirty with a dose of corrosion and heavy oxidisation of metalwork..
(The rf module can is 100% rusty)
This is a project and is worth saving as they are medium rare and should be salvageable, it shares the main board with the regular c128, so worse case I could always swap that out, but will try to save.
The PSU was a surprise:
The ‘youtuber’ fitted a Meanwell PSU and 9V AC transformer, however, a catalogue of ‘oversights’:
1. They’d cut up some plastic cabinet corner brackets and epoxied them to the base, then half screwed in some self tappers, but 3 of them had broken away from the epoxy and the PSU was flapping around inside.
2. Being on plastic brackets, they used some ground braid and soldered two ground wires to the PSU PCBA, screwing the ground braid to the base. Unfortunately, the moment the PSU became loose, it pivoted over the ground braid (exposed copper) and shorted out quite a bit on the PSU.
3. Inexcusably they’d used some inappropriately thin wire for incoming mains to the PSU and ac transformer, certainly not rated for 13A.. I guess the rationale was that the PSU should only draw 60W max, and even less for the 9V AC, except guess what fuse was in the (poorly fitted) plug on the supplied IEC? Yup.. 13A.. had the short been on the incoming side, that would have certainly got quite toasty.
On getting the PSU out the housing, with it no longer shorted, it checked out OK, enough to power in unloaded, but doing so revealed it was dead, no DC at all.. so did some digging, the non resettable radial fuse on the incoming neutral was blown…
The plan is to:
- Get a new meanwell PSU, as this one has been shorted badly, and is not easy to work on and might get something with better protection.
- 3D print a proper holder for the PSU and put in a top mounted grounding solution to the chassis.
- I will keep the small 9V AC transformer, that’s intact, but will put a fuse inline on the primary so if anyone does put a 13A fused IEC lead, it’ll be protected!
- strip all boards, clean, clean and clean some more… then do some electrical checks and go from there.
[edit] - The PSU is a mean we’ll RPD-75A which is actually not bad, medically approved with 2 MOPP of isolation and overspecced at 75W , so applaud the choice.., so might see if it’s just that radial fuse (can bodge a link across to try it), but cant Find a schematic so fault finding is a bit limited for me.. I can take a stab at the main rail generation paths, but their is a lot if protection circuitry that I’m not familiar with.
Ive got basic electrical/electronics knowledge (degree) and years of ‘proper’ software engineering, but there is a reason I needed up doing software and not hardware.. my brain can’t handle ‘analogue’.
youtu.be
All tested working and pulled from consoles I did Mods on 
