Is is worth recapping the power supply?

[CompactManiac]

Hi - I've a Macintosh LC and a Performa 475 which I know share some common components.

There was no sign of life when I switched the LC on so I thought it might be an issue with the power supply.
The Performa 475 is working fine so I opened both up and moved the good power supply from the 475 to the LC.
The failing power supply was made by TDK and the working one was by Astec.


The LC is now working which is great so I was wondering wouldit be best to seek out a brand new power supply for the LC or get the old one recapped?

This is the current failing power supply:

 

[robin-fo]

I recently recapped a TDK unit using the Console5 kit. The big capacitor didn‘t (quite) fit (I kept the original which was still ok) but the rest was quite enjoyable.. I prefer to recap as long as the PSU is not beyond repair because finding and fitting a replacement in a safe way is much more complicated in my opinion. And it keeps the computer more original.

 

[robin-fo]

You really need to recap your LC logic board, there is already substantial corrosion visible. The sooner you do it, the easier it is.

I recapped my LC just a few days ago and it had less corrosion, but there was already some trace damage preventing keyboard and mouse from working. Luckily, I found the broken trace quickly, which is seldom the case.

 

[Phipli]

Yeah, that needs an urgent logic board recap and clean I'm sorry to say. If it's working now, it won't be within a few months, especially after being powered up with the caps leaking. See around the sound circuit at the back left especially?

The electrolyte is drawn to power traces by the flowing electricity and starts corroding them faster when you power it up.

It's not a hard machine to do. First priority is to get the caps off and clean the board. The safest method, especially if you don't have lots of practice, is what we call "the twist method". The inside of the caps is like clay, so if you get some needle nose pliers and rotate the capacitors they just come off, leaving the two feet. It sounds horrible, but it causes so much less damage than overheating a pad. I've lost like, one (already damaged) pad in ten machines this way, Vs it being much harder with two irons, heated tweezers or hot air (all of which I've previously tried). Once all the tin can capacitors (other types are ok as they are), bathe it in a tray of IPA (not the beer) to get the electrolyte off the board, occasionally brushing it gently. Then dry it out - I put mine in the oven at about 60°, but you could use a hair dryer or something.

At this point, the board is "saved" and won't be getting worse, so you can take your time getting around to the actual recap.

 

[robin-fo]

+1 for the twist method! Feels horrible, but never pulled a pad off this way!

 

[Phipli]

(To be clear, we're not animals, but because of the corrosion the pads come off more easily than a new board, so the normal amount of heat you'd use for desoldering a component is sometimes enough to break a pad. Many of us have realised that mechanical removal is more reliable because it doesn't soften the resin in the PCB and the legs on the caps are only weakly held on)

 

[cheesestraws]

not the beer

spoilsport

 

[Phipli]

spoilsport

I'm not banning the use of the beer, just suggesting it might be better to imbibe than to submerge a logic board in

More of a dark beer person myself though.

 

[robin-fo]

I sometimes also had the feeling the heat from desoldering strongly accelerates a chemical reaction during which the capacitor juice dissolves the PCB and therefore weakens the bonding of the copper to the PCB.

 

[Phipli]

I sometimes also had the feeling the heat from desoldering strongly accelerates a chemical reaction during which the capacitor juice dissolves the PCB and therefore weakens the bonding of the copper to the PCB.

I saw the figures for the overall percentage weakening of the PCB from heat and even at soldering temperatures (remembering they're higher with modern lead free solders too) it is a significant proportion of the total strength. Like, major fractions. Hang about a little too long or a little too hot and most of the adhesion between the pad and the board are gone. Combined with corrosion and it is even worse. Those pads almost leap off the board

Sadly someone keeps deleting the bookmarks saved in my brain, so I have no idea where I saw it.