iMac P/S posts then shuts down

[godonr]

I know info about iMac supplies has been posted before but I didn't want to jump NWD's thread. Also noticed several senior members appear to have become very familiar with this bugger lately. I'm hoping someone can point me in the right direction with troubleshooting a supply which comes up for a minute or so then shuts down. While up, all voltages are there. It's an AcBel Apple #661-3350 (614-0296), 180w in a first generation 20". It's had any bulging caps replaced (low ESR) and shows no visible signs of burning coils or diodes. I know it's the supply because the iMac works fine with a known good. Best case scenario, did anyone ever locate a schematic for this guy?

[Toasty]

Re: iMac P/S posts then shuts down

No schematic has been found. Certain areas have been figured out as needed.

All 9 caps in the secondary should be replaced, bulged or not. But, the other 4 small caps are easily replaced, and since you're there... why not? The mains caps are not showing any issues, and it's a personal call as to whether or not to replace them. Again, you're there and it's only another $7 for both of them.

What caps did you use? Brand & Series please.

If it's shutting down:
a) the unit itself is sensing an internal fault and shutting itself down
b) the mobo is sensing a voltage problem and sending a signal back to it to shut down

Toast

[godonr]

Re: iMac P/S posts then shuts down

Replacement caps are Sanyo SE 105degree range.

[Toasty]

Re: iMac P/S posts then shuts down

I do not have a SE series data sheet, but I have seen good reports on them. These are the green w/gold printing, correct?

Where did you get them from? There are fakes of Sanyo on eBay.

The units I have in the shop have been recapped by their owners with Nichicons, UCCs, and some Panasonics. All depends on fitting them in there.

Toast

[godonr]

Re: iMac P/S posts then shuts down

Yes, they're the green and gold and are also in my "known good" supply. The specs are top drawer and from a good source. I'm currently pulling everything off another board to ID the SCRs, regulators, etc. There's 3 transformers on the board with OEM numbers I can't cross. There's actually 11 (15 total) caps above T2. A 120uf/50v hides beneath the heat sink for HS3. I know the caps are ground zero and was hoping you guys discovered something additional to look at next. Any ideas would be great. I have 4 to fix! Thanks

[Toasty]

Re: iMac P/S posts then shuts down

Heh, my bad. The models we've been dealing with are 614-0293 & 614-0294.

All 4 units are same problem? Runs then shuts down?

Pics would be helpful as I can look at your layout and perhaps cross your info to what I have in front of me. There is a diode on them that should be checked. It's a switching diode of 3A or better on the primary side of the heatsink that divides pri/sec.

Have voltages been verified as correct?
How about when connected to unit? (loaded)
Scoped all the voltages for ripple?
All tested on same computer? A mobo problem can be hidden by a good PSU. Maybe the PSU's are picking up on it where the other one isn't?

Toast

[godonr]

Re: iMac P/S posts then shuts down

Right, those are for the 17" I believe. To answer your 4 Q's: voltages have been checked loaded; scoped for ripple (clean); and tested on different units. These guys are known to act like this when the HD's going bad (or just has a problem). Anyway, I've got more to check. I'll get more info together later. Have to checkout now. Appreciate your input. These are really great units with a few unfortunate design flaws (and a bad batch of caps). That's Apple for ya! Thanks for the help. I'm out for now!

[godonr]

Re: iMac P/S posts then shuts down

Apologize for the delay... attached are two jpgs of the 20" iMac p/s. To load the supplies for testing, I jumper 15 (3.3v on/off drops to 0v on power up) and 16 on the 22 pin plug. It carries the same voltages you found on the 17" supply. The problem I'm having with some supplies is after a recap, I'll plug the supply into a known good mobo and the on/off voltage won't drop. Again, I have a known-good power supply which responds correctly with the same setup so I don't think it's the mobo. At this point, I can ID most components (except the SMDs which I don't think I could replace anyway) and would like some advice on where to look next. Thanks

[PCBONEZ]

Re: iMac P/S posts then shuts down

I got some Sanyo I suspected as fake from eBay myself and so I sent some in to Sanyo for validation. Sanyo confirmed they are fake.

One these particular fakes....
The fakes have a Y vent instead of a K vent.
The gold [yellow] color is too dark. [That color looks 'washed out' on real ones.]
The "V" [for volts] is shorter than the letting for the numbers in the voltage rating marking [on legit ones they are same height.]
.

[godonr]

Re: iMac P/S posts then shuts down

Right -- I didn't get these from ebay. They are actually factory and all have K vents. That's why I'm looking for the next likely thing to go after the caps. I now that's a stretch, but...

[i4004]

Re: iMac P/S posts then shuts down

>Again, I have a known-good power supply which responds correctly with the same setup so I don't think it's the mobo.

then you have a gold-mine!
you should scope the working unit(esp. the feedback loop, ie elements connecting secondary to primary) vs. these problematic units.

if it has pwm ics od any cort, concentrate on them..if not, concentrate on transistors...

naturally, if scoping the hot(primary) side be extra carefull...think twice for every move you make...

>except the SMDs which I don't think I could replace anyway

on solder side? any identifiable chips there?

[Toasty]

Re: iMac P/S posts then shuts down

While plugged in to mains 115v (isolation transformer please) but disconnected from mobo and without 15 & 16 jumpered, compare voltages at mobo plug of known good supply to rebuilt unit.

Then, jumper 15 & 16 and compare.

Please report back.

Toast


Attached plug pinout jpeg for reference.

[godonr]

Re: iMac P/S posts then shuts down

>if it has pwm ics od any cort, concentrate on them
Not sure I know what pwm ics od any cort refers to. The solder side has a LM339M, a Z441 and a WT7515. Know what the LM is but have to look up the others. There's also lots of SMD transistors wiht 1P> and 2FL.

[godonr]

Re: iMac P/S posts then shuts down

On a good supply I see 20v @ 22, 5v @ 15 and 5v @ 9 unjumpered;
Jumpered: 22@24v, 21@5v, 20@5v, 19@12v, 18,17,16 gnd; 15@0v; 14@gnd; 13@12v; 12@3.3v, 11@gnd, 10@12v, 9@5v vsb, 8@5v pg, 7@gnd, 6@5v, 5@gnd, 4@5v, 3@gnd, 2@3.3v, 1@3.3v.

[godonr]

Re: iMac P/S posts then shuts down

Toast -- sorry about that, a senior moment... on a bad supply, when it's jumpered 15 goes to 0v but 22 stays @ 20v and 5v @ 9. Whatever switches to jump 22 to 24v also brings in the other voltages and this isn't happening on the problem supplies!

[i4004]

Re: iMac P/S posts then shuts down

if toasty doesn't produce better idea:

>Not sure I know what pwm ics od any cort refers to

should be "of any sort"..typo
pwm ics are its brains, they modulate pulses on the transformer to produce just right amount of power to satisfy the needs of gear it's connected to(in this case mobo)

wt should be something to concentrate on
http://pdf1.alldatasheet.com/datashe...TC/WT7515.html
although it's just a protection unit...but oversensitive protection unit can cause such issues...

see if those faulty psus are latched into protection first...

it seems z441 is main pwm ic but i dunno will we find its datasheet...

[Toasty]

Re: iMac P/S posts then shuts down

Ahh. The +24 volt isn't coming up. 9 is correct and should stay at 5.1v.

Look for a KA78M24 3-legged regulator in a TO-220 case mounted on the heatsink. On the 17's it's marked M6 on the circuit board. Easiest way is to follow the 24v lead back from the connection on the board. Going backwards you should hit a 1000uF @ 35v cap, then this device. The cap is across its output and there is a zener diode on the input leg. It follows back to those 2 diodes D20 & D?? in front of transformer T2. The input to the regulator (per spec sheet) is supposed to be 40v for a 24v output.

See if your getting that voltage at the input when you've jumpered it "on". Again, testing it against the good supply.

Toast

[godonr]

Re: iMac P/S posts then shuts down

Toast --I have a top244y @ m6. If you look at the attachment it's HS2. If it's the 24v regulator it has 6 legs! I have a 17" supply and see what you're talking about. The 20" layout is somewhat different. I need to find what's on each leg of the top244y.
i4004 - those pwms are SMD'd to the solder side of the board and I pretty sure I don't have the skill (or equipment) to desolder them. Any way to verify them in place?

[Toasty]

Re: iMac P/S posts then shuts down

Nope, thats the switcher (TOPSwitch). We'll get there in a bit.

It's the 24v voltage regulator I'm interested in right now. Follow that 24v lead back through the circuit. Unless the 20" doesn't have it, but that would be odd. The 17 & 20 supplies are similar to a point.

Toast

[i4004]

Re: iMac P/S posts then shuts down

>i4004 - those pwms are SMD'd to the solder side of the board and I pretty sure I don't have the skill (or equipment) to desolder them. Any way to verify them in place?

first see where toasty will lead you, and if that doesn't succeed we'll go there.


i didn't mean to desolder them, but to scope particular pins, checking bad psu against good one. in that (minute, you said?) time-span the bad one actually works.

but again, follow toasty's lead...if it fails we'll think about backup plans.