iMac G4 17" 1GHz Power Supply Repair

Hi there! I have an old iMac G4 that we've had as an ornament at work for many years, I just brought it home and noticed it was dead, completely lifeless.

At first I replaced the PRAM battery without effect, then I've tried troubleshooting the PSU which does not seem to output anything (but 220V reaches the board)

Visually it looks ok, the board is the PSCF161101A.

I've desoldered all the caps and I intend to replace them but I've been seeing various mentions of an IC failing on these boards and I want to have a running start in case new caps doesn't do it.

TechKnight has a Youtube clip where he fixes a similar board by replacing something called TDA4863 I think

On the PSCF161101A there is a vertical green PCB that has an 8-legged chip labelled "393" and "253A", I've also seen references to these failing but very unsure.

So what I'm looking for is likely / plausible error sources. I'm not very good with electronics but I can solder somewhat decently and troubleshoot with a little handholding =)
 
For the record, if anyone else happens to stumble across this post, the PSU only needed a recap. The despite the existing ones looking alright and testing ok in my cheap-o tester they were obviously not fine. System is working perfectly fine once again!

... also if you dismantle these things please take note of where the screws go, I put the long ones in the wrong place and gave my machine some unnecessary cosmetic damage but sure beats the scrap pile.
 
For the record, if anyone else happens to stumble across this post, the PSU only needed a recap. The despite the existing ones looking alright and testing ok in my cheap-o tester they were obviously not fine. System is working perfectly fine once again!

... also if you dismantle these things please take note of where the screws go, I put the long ones in the wrong place and gave my machine some unnecessary cosmetic damage but sure beats the scrap pile.
Thanks for mentioning the screws. I’m usually good about noting that, on my take-apart notes, but your comment kept me on the lookout for them. I was also going to recap the PSU in one I just acquired - did you happen to save the capacitor list?

Is there a fuse located above the power inlet (just to check)?
I noticed the black cable (of the two going back to the monitor – and not the inverter cable) was at least slightly crushed while joining the two halves at some point in the past. I think that it just tore up the sheathing, but it could be more damaged, so I’ll have to check further.
 
At this point I don't remember unfortunately. I tend to swap my brain to /dev/null at regular intervals, don't remember a fuse:D

I did note down the capacitors but PLEASE NOTE that there are several revisions of these PSUs and I'm in 230V-land. So it might, or might not, be relevant at all. And I take no responsibility for these values to be correct, I strictly noted down the ones I removed and I recommend you do the same. Note down name, orientation and values. Orientation is likely clearly marked on the PCB but better safe than sorry.

---8<---
C2 68uF 450V
C3 100uF 35V
C201 68uF 450V
C206 680uF 16V
C204 1500uF 25F
C205 1500uF 25V
C301 22uF 50V
C215 1uF 50V
C219 100uF 25V
C216 10uF 50V
C212 10uF 50V
---8<---

I replaced them all with the best equivalents I could find and it worked great afterwards.

Fingers crossed that cable is alright!
 
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