32-bit acorn hardware • Re: RISCPC Power Supply Refurbish - 4 Kits Available

I've just repaired my 0197,010 Issue 4 after it packed up this evening (I guess the Econet LAN Party finished it off!). Capacitor list and some repair notes included!

First a couple of warnings:

• Watch out for the polarity marks on the PCB, they can be quite deceptive. The black dot on the silkscreen is actually the positive end of the capacitor!
• The caps and inductors (and oddly IC1) are stuck down with hotmelt glue. To remove it, put a bit of isopropyl on it and wait a few minutes. Pull carefully with a suitable tool (pliers, forceps) and it should pull cleanly away. If any is left, apply more isopropyl and repeat.
• I'm pretty sure C13 is the startup capacitor, so if the PSU won't power on and you're desperate, try replacing that one first. But if you're doing that, replace all the small (physical size) ones because they won't be far behind.
• DC-side regulation is, as usual, an LM431 (IC4). There are two optocouplers, IC2 and IC3. These are Sharp PC123 type. I have no idea why they used two, as there's only one TL431-type feedback element.
• Q5 and Q6 are Unisonic 8050 type, Q4 is an 8550. You might recognise these from my previous repair of an R260 power supply. Hitron seem to like them. Maybe they got a lifetime supply for cheap...
• Just about all the small Chemicon capacitors I removed measured high ESR and lower than specified capacitance. A few were bulged. The 3300uF Nichicon filter caps both measured good. As always these devices stress the capacitors a bit, so if you can, replace them all.
• This model of PSU runs fine off-load for short testing. With no load, you'll find the 5V-out is about 5.1V and the 12V is a volt or so low. If you want accurate(ish) readings, hook up a sacrificial hard drive.
• Offboard connections: P1 is mains power in. P2 goes to the choke in the top lid. The fan goes to the little Molex connector near the DC-out. The 230/115V switch goes to the "115V" pins between the two big input filter caps.

Capacitor list for the 0197,010 Issue 4, made by Hitron.

Part designation - Original part -> Replacement part I used

C13 - 47uF 50V (Chemicon KME) -> Panasonic FR = EEUFR1J470B (note increased voltage = 63V)
C26 - 22uF 50V (Nichicon MH) -> Panasonic FC = EEUFC1J220
C27 - 1uF 50V (Chemicon KME) -> Chemicon KMG = EKMG101ELL1R0ME11D
C24 - 33uF 25V (Chemicon KME) -> Panasonic FC = EEUFC1E470 (note increased capacitance = 47uF)
C36 - 100uF 50V (Chemicon KME) -> Panasonic FC = EEUFC1H101 -- this one is slightly too large in diameter and sits slightly proud of the board, on top of the diode next to it.
C30, C23 - 10V 3300uF Rubycon YXB -> Panasonic FR = EEUFR1A332B
C35 - 470uF 35V Chemicon KME -> Panasonic FR = EEUFR1E471Y

Big filters (didn't replace these as I didn't have spares on hand) -
C28, C33 - 16V 2200uF Chemicon KME
C34 - 35V 1000uF Chemicon KME

Main AC filters (these almost never fail so I left them in place) -
C9, C10 - 200V 330uF Chemicon KMH

Statistics: Posted by philpem — Mon May 20, 2024 11:59 pm

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