Macintosh Quadraa 630 dead power supply

[Wilykat]

Apple part 614-0037. I got this recently very cheap and it doesn't power up at all. The motherboard was checked with a known good power supply, it worked so this one needs a recap.


Top cover with the label. There's rust but it seems to be on the outside only, no rust inside or on the PCB


The board after I took it out of the case. The 110v mains unplugged from this board, unlike Antec which soldered the AC wires into the PCB.

I did Google for info but I ran into a problem: all the info I could find on recapping similar power supply, those were Antec brand with different capacitors. Mine is Dyna Corp but uses the same Apple part number. Google didn't turn up anything useful other than air filter. I guess I got a rare variant?

With no existing guide I figured I should document some stuff while I worked on this.

After I desoldered all the caps (except for 2, one on COB the vertical board with chips near DC out rails, and one honkin' big cap near AC input) and there's residue that looked like 3 or 4 caps had leaked by the DC out rails


Caps list, rating, and size

Primary and secondary is obvious. DC out is the cluster of caps next to red/yellow/black wires for DC out to computer. COB is the one vertical board near the DC out wires.

If I could remember where, I can do ESR testing on some. My cheap ESR tester is unreliable with caps over 1000uF

[PeteS in CA]

Re: Macintosh Quadraa 630 dead power supply

Judging by all those nice Thomson CSF box film capacitors, that P/S must be on the order of 35 years old. So those output caps are probably all bad. Cap technology has probably progressed to the point that using parts newer than UCC LXZ series or Nichicon PW series risks having stability problems. If still available, I'd even suggest UCC LXV series or Nichicon PS series. When dealing with compensated control loops, there is such a things as output capacitors that are too good.

[Wilykat]

Re: Macintosh Quadraa 630 dead power supply

Macintosh Quadra 630 came out 1994 so under 30 years. Either Dyna Corp used old stock or those caps were still used in mid 90s.

Should I replace those or leave it? And what about the big one? It seems to be glued on but it seems to be only on AC mains, likely after bridge rectifier so it probably operated at 120Hz to smooth out the mains AC wave.

[PeteS in CA]

Re: Macintosh Quadraa 630 dead power supply

Mea Matha Goofa. The big input 'lytic is from Rubycon, a good vendor, and those are not stressed to the same degree as the output capacitors.

I didn't notice it yesterday, but that Dyna Comp P/S is flyback topology, which is really stressful on output capacitors. It's recognizable by the seeming lack of an output inductor (ignoring the little ferrite rod inductors). The "transformer" is actually a coupled inductor in which the primary winding functions as the output inductor. It may not be visible, but there should be a thin spacer creating a gap in the "transformer" core. Perchance is that 8-pin IC on the primary side a UC3842?

[linuxguru]

Re: Macintosh Quadraa 630 dead power supply

NCC LXFs were known to leak electrolyte out of the bottom bung and fail. LXZ, LXV, KZE or KY should be durable replacements. In a pinch, KMG and KMH should work.