Power Mac G4 MDD "Mirror-Door" won't power up

[Toasty]

Re: Power Mac G4 MDD "Mirror-Door" won't power up

AcBels are fairly easy. A couple of small caps cause the start up failure. Usually most of the output caps are crap/blown. The primary's are fine (UCC's). Look for the threads in here. I did point out the failed start caps in there.

The PSU's interchange, so try the Samsung's in the AcBel unit.

MOSFET's can be very sensitive. The capacitance from your body can be enough to trigger them, although not necessarily 'in-circuit'. Not like the bipolar transistors of old, MOSFETs usually have to be driven 'off' (have their gate charge removed). One of the testing methods (in here too) uses your finger to reset the MOSFET.

Toast

[tj2]

Re: Power Mac G4 MDD "Mirror-Door" won't power up

Thanks, Toasty! For my efforts our lab tech has obtained three more Macs as backups. Two are MDD Macs with the Samsung PSU -- one working and the other with another failed open primary cap in the PSU. The other doesn't work but is a different model and has an AcBel PSU. I'm going to recap the two Samsung PSUs, but I think that I'll give a pass for now on the other Mac. The department is going to owe me for even more capacitors!

I thought about the SMQ, but for some reason the GW grabbed my attention.

I am careful when working with MOSFETs but I wonder how sensitive the switchers and the PFC MOSFETs are to accidental static damage.

[Toasty]

Re: Power Mac G4 MDD "Mirror-Door" won't power up

Good Job! Knew you could do it.

One note: SMQ is a less expensive ($4) than GW. GW has a -slightly- higher ripple rating (160mA), but anything over the HP's 1760mA is excellent.

"originally found that one tested shorted "
-and-
"Later the switchers tested fine"

MOSFET could have been latched in the "on" state.

Toast

[tj2]

Re: Power Mac G4 MDD "Mirror-Door" won't power up

To answer my own question, these Samsung PSUs contain the following capacitors. As the GL caps are not standard for that series, I estimated the ESR (@ 20 C & 100 kHz) and ripple from others of the same dimensions in the series.

1x CapXon HP 390 uF/420 V 35x42
5x CapXon GL 2200 uF/10 V 10x25 57 mΩ 1400 mA
2x CapXon GL 2200 uF/16 V 10x30 35 mΩ 1815 mA
1x CapXon GL 1000 uF/35 V 13x25 36 mΩ 1950 mA
1x CapXon KM 470 uF/35 V 10x20
1x CapXon KM 47 uF/25 V 5x11
1x CapXon GL 470 uF/16 V 8x12.5 92 mΩ 745 mA
2x CapXon KM 56 uF/35 V 6x11
1x CapXon KM 2.2 uF/50 V 5x11
2x CapXon KM 10 uF/50 V 5x11
2x CapXon KM 22 uF/50 V 5x11
2x CapXon KM 100 uF/16 V 6x11

I replaced the 390 uF / 420 V cap by a Nichicon GW 390 uF / 450 V. I replaced the CapXon GL 2200 uF/ 10 V by Panny FC and I replaced the CapXon GL 2200 uF/ 16 V by Samxon GD from the badcaps.net store. I replaced the other CapXon GL series by Nichicon HE. The CapXon KM appear to be general purpose caps, which I replaced by whatever I had on hand, which was a mix of Panny FC & FM and Nichicon HE.

The only problem I could find with the PSU was that the 390 uF CapXon HP had failed open and popped the fuse. Everything else seemed fine, but I did replace the switchers as I had originally found that one tested shorted so I ordered a pair of ST W20NM50. Later the switchers tested fine. The Mac now runs so the experiment now has a working data acquisition system.

[tj2]

Re: Power Mac G4 MDD "Mirror-Door" won't power up

Does anyone have a list of caps in this Samsung power supply? (capacitance, voltage, dimensions, and perhaps original brand/series, or replacement brand/series, or ESR and ripple)

I'm looking at repairing, and probably fully recapping, one of these but I am under some time pressure as we need to get it working by the time the semester starts. The Mac with this power supply hosts a data acquisition board for a laboratory experiment. I'm at least going to order a new fuse, a new primary cap -- the old one is a 390 uF / 420 V CapXon -- as well as new switchers, Q1 & Q2, but I'd like to order new caps for the rest of the PSU at the same time. Fortunately, my department will pay for the parts.

As I haven't had time to check it over thoroughly after pulling it out, I'm not sure exactly what's wrong. The only evidence is a blown fuse. I don't see any burned components or scorch marks on the board. I gather that besides checking the switchers, I should check the bridge rectifier, and perhaps the thermistors. I'm glad to have found on the forum the correct switchers without pulling the heat sink first.

[Toasty]

Re: Power Mac G4 MDD "Mirror-Door" won't power up

Welcome to the forums jex.

Best wishes on schematics. No one here has ever reported finding one. All are proprietary and schematics are not released. Remember, these units are considered "not serviceable" and schematics would be "in-house" only.

If you need help in diagnosis, others here and myself have these units and have repaired them. Indicate your problem(s) and we'll try to help.

Toast

[jex]

Re: Power Mac G4 MDD "Mirror-Door" won't power up

can anyone post a schematic for this p/s...

jex

[Toasty]

Re: Power Mac G4 MDD "Mirror-Door" won't power up

With the unit apart and only plugged into mains, you should have between 170 to 280 volts DC across the mains cap. If you do not, then you need to trace back to the mains for an open circuit or blown component. ?What is your mains power there in India?

Check the small cylindrical, black fuse that is mounted right next to the mains cap. It's marked as on the board F2, a Slo-Blo (time-lag) 2 amp 250v fuse.

If that is bad, suspects are
- IC4, (KA) 1M0680R a PWM controller and switcher in one package. aka: a TOPSwitch, for all intents and purposes.
- circuits connected to T2's secondaries. Including that upright mounted circuit board, in front of which you replaced the little caps.
- a major overload or problem on the computers mainboard that overloaded the other outputs on T2

Toast

Toast

[anticipator]

Re: Power Mac G4 MDD "Mirror-Door" won't power up

Hi, Toasty, Yes there is not even the standby voltages. i checked q1 and q1 and the pins are not shorted. couldn't get the caps which you suggested. I got 'HU3 105 deg C 390uF 450v' as a replacement for the main cap. connecting it didn't made any difference though

[Ed in SoDak]

Re: Power Mac G4 MDD "Mirror-Door" won't power up

Listen to Toasty on this one for sure. That CapXon main filter cap is the root cause of the typical failure mode in this power supply.

Kinda funny, since Mac always seemed to have a superior build-quality. But, CapXon capacitors are universally condenmed as worthless and just about guaranteed to fail.

My first repair is still humming along fine using Nichicon caps. I went for a 450volt main cap and made sure I chose 100C temp ratings for all of the caps.

A friend just gave me his old PS that he had replaced with a repaired one off ebay.

Sure enough the 390 UF cap had opened and one regulator chip was open while it's mate was shorted. That's all I found so far, I suspect just replacing those will repair it.

-Ed

[Toasty]

Re: Power Mac G4 MDD "Mirror-Door" won't power up

Replacements series to use for the mains cap, in order of preference:

390uF @ 420v - 35mm x 40mm - snap-in

UCC: SMQ
Pana: TS-UQ
CDE: 381LX
Pana: TS-HB
CDE: 381LQ
UCC: KMQ

[Toasty]

Re: Power Mac G4 MDD "Mirror-Door" won't power up

>>Now all the pin voltages are zero.<<
Nothing? Nada? No standby voltages?

Report mains cap series. Capxon HP perhaps?

Check fuse now and switchers Q1 & Q2 at the end of heatsink you pulled to replace caps. If either one shows shorted all around, you'll need to pull that heatsink again and replace them BOTH.

Please report findings.

I'll say this again for this thread and others regarding the Samsung PowerMac G4 supplies:

IF the mains cap is a CapXon HP, it -MUST BE REPLACED-. There is a marked history of failures in this series of capacitor (even from a Ukraine electronics site via kc8adu) in which the cap either goes open or shorts then opens. It invariably causes the main switchers Q1 & Q2 to fail (STW20NM50FD) and the primary fuse (8A/250v, Slo-Blo, 5x20) to open (usually violently) as the blackened glass indicates. I recommend a replacement with a ceramic bodied fuse here (Schurter 0001.2513). Another failure can be the destruction of the inrush limiter TH2 (SCK-048).

Toast

[anticipator]

Re: Power Mac G4 MDD "Mirror-Door" won't power up

Thank you Toasty, Cyclones and others. My G4 MDD with Samsung PS has the same problem. There were only +25 Vsb and +5 Vsb. Everything else were zeroed out. I replaced the capacitors hidden under the heat sink following your posts, and after shorting green wire to common, got the fans working. Pin voltages were also proper. When connected it back to my G4 I got the 'jing' sound and it failed immediately. Now all the pin voltages are zero. It is not the fuse either. Any clues would be extremely helpful. Thanks

[cageycruz]

Re: Power Mac G4 MDD "Mirror-Door" won't power up

Thanks Toasty for spot on advice.

I have a Power Mac G4 Mirror door that worked flawlessly for 7 years. Then I moved it and poof, no power. White power button glowed when you pressed it but no fans, no video, nothing.

I Googled and found your tip on the capacitors on the daughter board of the power supply. Tested them and sure enough, both were way off their rated capacitance value. Replaced C129 and C130 with parts from the local electronics shop. Also replaced C135, on the main board, since it was reading 33 uF and supposed to be 56uF. Our shop only had 47uF in stock, so I tried it.

And it all works now. Fans spin, all voltages look right. Can't wait until Monday where I can plug it back in to my computer at work. Looks like I won't have to scrap this G4 and its beautiful Cinema Display.

Thanks again.

[JOHNBOY]

Re: Power Mac G4 MDD "Mirror-Door" won't power up

Good stuff ED but I was more concerned about the quality of caps. I put one together with cheap caps and it didn't start and I put another one together that started but only ran for a few hours. With the better quality caps it has been running for a while with no problems.

[nikon80]

Re: Power Mac G4 MDD "Mirror-Door" won't power up

hola ciclones
existe la forma reparar una fuente de poder mdd g4
gracias carlos
santiago chile

[Ed in SoDak]

Re: Power Mac G4 MDD "Mirror-Door" won't power up

I tried to edit my post to add this, but it had run past the 10-minute editing window.

I made sure I ordered 105 degrees C caps to match the originals and also matched the original voltage and capacitance, without trying to find an "over-rated" part. I could have chosen a higher temperature, voltage or capacitance parts as a sort of safety factor, but the larger size of a beefier cap might be an issue iin this already overly-cramped board.

I did notice while testing the power supply with cover removed, that the heatsink was fairly warm even when the computer had been "shut-down" for quite awhile. I guess you could use a power bar to reduce your electric bill and help lengthen the life of the PS by switching it completely off after shutting down. The trade-off might be you have to replace the PROM battery more often, depending on how long it sits unused.

The original fuse inside this supply was rated at 8 Amps. It's in a physically small package, smaller than about anything I have here. All I had on hand that would cram into the holder was a 6 Amp fuse. It has been working fine, so that may be another way to provide a little additional protection to a power supply wih known "issues." If this 6 Amp fuse blows on me, my plan is to install an outboard fuse in the power supply case that can be changed without removing the supply from the computer and disassembling it. What a pain that process is! You'd think with all the other crap in there, they could at least add an inch or two of wire to the fan connectors and AC supply link! There's ample room for a fuse holder that's accessible without requiring disassembly, but then, to Apple, that invites the unitiated to begin to "fiddle" with it and install their favorite brand of aluminum foil, etc., so I can't say I blame them. But, it's an easy upgrade that would actually help protect the power supply. Easily changed 6 amp fuses are a heck of a lot cheaper than all this other stuff I spent hours sourcing out and soldering in!

-Ed

[Ed in SoDak]

Re: Power Mac G4 MDD "Mirror-Door" won't power up

Hi Johnboy,

I went with Nichicon as I've had good experience with them in other gear that used them from the factory. I ordered everything from Digikey and had to choose one Panasonic for a 1000uf 35v as it wasn't available in Nichicon. That's one of the 13 additional caps I bought as insurance, and I have not installed those yet . It has thus far been working fine with just the 6 caps mentioned above, plus the TH2 and Q1/Q2 pair. Toasty recommended changing out C135, 137 and 141. I threw in C129 and 130 as they are also hidden beneath the heatsink.

I don't have an ESR, but all my tests have not turned up an old cap that I would say has gone "bad," other than the opened main cap, which was way obvious. It didn't provide any sort of capacitance or resistance reading at all, a "dead" giveaway.

Before finding this forum, it took some brain-sleuthing on my part to find Q1 had shorted. Q2 seemed good, but it's always safest to replace these parallel devices in pairs and not trust an old part. TH2 was another obvious, as it was blown in two, but actually still seemed to hold the proper "cold" resistance, which I measured at 6 Ohms. That part number did not produce a single Google hit, so I took my best guess based on advice here, but upped the replacment's cold resistance to 7 Ohms, as that was the nearest inrush limiter I could find at Digikey that was also rated at 10 amps in a size that would fit the crowded space. To me, that one was the real mystery part that the entire repair hinged upon, as I incorrectly assumed it was a "crowbarred" MOV Zener surge protector, and it was totally taking me down the wrong path to correct diagnosis.

I got sidetracked by a current-sensing resistor and a huge choke that at first glance appeared to be a shorted transformer, but in the end we felt the joy of fixing the impossible. And that's what it's all about! I guess I've been dinking around with this since late May, not counting a two-week vacation back east. It was always on my mind, as I tried one little thing or another. Now that it's finally running, the working computer is almost an anticlimax. No challenge there! LOL

The G4 MDD has pulled several 6 to 8 hour sessions since the repair and doesn't seem to run very warm at all here. I'm running it off a UPS, so the incoming AC is stable. The fans are kinda noisy, and it's a big honker that has to sit under the desk where cabling is not very accessible, but I am enjoying the at least 2.5x speed improvement over my old 500 mHz iMac system, which I've used for the past 10 years.

It's just about the newest Mac that can still run my favorite Classic apps, and my cost was just a handful of parts, so I am in total bliss!

-Ed

[JOHNBOY]

Re: Power Mac G4 MDD "Mirror-Door" won't power up

Very nice.

What caps did you use ?

[Ed in SoDak]

Re: Power Mac G4 MDD "Mirror-Door" won't power up

Finally I have some results to share! I'm happy to report the MDD is up and running. I placed an order with Digikey on July 5th and was surprised to see email notification they shipped that same day. Odd, I thought, as it was a postal holiday. Two weeks later, no package, so a couple emails to Digikey and a no-charge replacement order was in my hands yesterday, just three days later. I had the parts in and running last night!

For TH2, I selected a 7 Ohm, 10 Amp replacement, that was the colsest I could find to the 6 Ohms I measured on the old part. I replaced both Q1 and Q2 and the 5 caps hidden under that heat sink: C129, C130, C135, C137 and C141, though they all still tested ok. I had already replaced the main power cap as it was open. Only Q1 was "bad," but I replaced both it and Q2.

This was the "textbook" list of parts for this failure, with the addition of C129 and C130 because you can't get to them once the heatsink is installed. I'd think twice about changing them if I had to do it over, as it was very hard to clear the solder from the holes, which are a tight fit to the lead size. That job alone took an hour for those two caps!

Since they're so cheap, I also ordered replacements for all the other caps in the power supply, but held off installing them. Shotgun too many new parts in at once, you can create problems that weren't there before! But I'm ready if I need them.

This all happened just in time, as my trusty 2001 500 mHz iMac had just failed with a hissing hi-voltage arc in the monitor section. It made a great ozone generator! I got lucky there too. A week ago, a friend gave me a 350 mHz iMac for helping him get his going, so I'm also upgrading that with the parts from my 500mHz.

All in all a good week. I managed to keep my old platform alive and managed a serious upgrade with the now-working MDD. All for a total cost under 40 bucks.

My thanks once again to the board, especially Toasty and Cyclones, for the confirmation of my diagnosis and the necessary tips and info to get the job done!

-Ed