Help fixing a G4 Mac PS - need EE to double check choices

[OrBy]

As the title indicates I have a mirror faced Apple G4 power Mac that has stopped working.
The largest capacitor seems to have vented its electrolyte all over the inside of the PS. (messy and smelly...)

Specs on the bad unit:
CapXon
390uF-420v
HP VENT 105°C
(weird dot)-NEG
And its 43mm tall by 35mm wide

Now it's been 10 or so years since high school electronics but the rest of the PS looks fine so I would like to just replace the capacitor and see if I can get it running again.

Now my questions are - what and where can I find a suitable replacement?
I dug around digikey.com for a bit and came up with the following:
EKMQ451VSN391MA40S
But will that work here?
Should I go with something larger like the EKMQ451VSN471MA40S ?

I would be thankful for any input on this matter.

[davmax]

Re: Help fixing a G4 Mac PS - need EE to double check choices

Go with the larger one ie 470uF it is the right size only 2mm taller. The 390uF comes in two heights one being 50mm tall you do not want to risk getting that version.

Yes both will do the job nicely, height will be the main issue. Some issues are:

1 What made it fail? This may be hard to determine and if you install replacement make sure that it is not getting hot and the circuit is working normally.
2. Absolute cleanup of the exploded material is necessary, it is conductive and will cause problems.
3. Make sure you install with correct polarity.

[starfury1]

Re: Help fixing a G4 Mac PS - need EE to double check choices

well not sure on the PSU construction
(post some pics it might help top side bottom side of psu)

but if it has vented there is most likely some other damage that caused it to vent.
Venting is usually a sign of some other problem.
(I suspect its had more then 420V across it, cant see how thought or possibly huge AC? ripple which could mean a faulty bridge?)
(bridge rectifiers can fail, yet appear ok on a static diode test on an MM)

Its a Mains side issue and I would defiantly check other things such as Mov's bridge rectifier etc.
Since there is only one its a fair bet that this psu might have "Active power factor correction" APFC.

Also that section is LETHAL and has the potential to kill you stone dead!.

So be very very careful and all CAUTIONS & WARNINGS etc apply here
(kill yourself don't blame us, we take no responsibility for your actions)

To be honest, Its really a job for a properly trained technician.
(and this may apply depending on were you live)
Top Cat (forum owner) and a few other here can repair (depending on fault)
if you decided to go that way

This issue is one I would defiantly power up via a series lt bulb
(light bulb trick) standing back when I do and wearing safety glasses.
(EDIT not sure on that with an APFC suppy?)

If you dont know what the above means I'd leave it alone , either get it fixed or buy a new one.

On the cap question,

Normally they tent to be General purpose on that side and a lot of the time 85C but a 105c is better
Again normally same with same 390u 390uf
but (depending) on what feeds it the 470uf would probably be ok
(a little extra wont hurt)
Again not sure on that with an APFC PSU

As I said Ive have no real idea on how the Mains side is done with that psu
I am only guessing.

You might want to wait on someone else to post on this as there are far better people on this forum that know a lot more then me on this subject.

like I said theres a "very high risk" on that side of the circuit a wrong move can bring a world of hurt upon you.

Cheers

You posted in the mean time davmax

[OrBy]

Re: Help fixing a G4 Mac PS - need EE to double check choices

davmax:

Height is a issue as this PS is tight - old the old cap has like 1-2mm clearance at the top

I would love to know what made it fail. It was off when it failed I know that much - it had not been used in a week - and my UPS's show no events and I remember hearing no alarms ether.

Cleanup was performed when I made sure the cap was discharged and de-soldered it.

Polarity was noted before I removed it

starfury1:

I hope not - I have found no one locally to look at it - I was trying to not have it shipped off but if I have to I may as a new one runs $300 US. (I am Canadian so shipping is more of a PITA as well)

If my understanding is correct it is a APFC unit as it can take NA as well as EU mains voltages/freq.

As for the lethality of it - knew that before I even cracked it open that's why the first thing I did was make sure to bleed off the main cap. I have a very clear respect for what these devices are capable of even when they are not connected to power!

Before I took apart the unit I tested it with a KillAWatt meter and found it was drawing 0.07A when plugged in so something was still kicking in it.

Anyway it's late - I will revisit this tomorrow. Thank you for your input guys and have a good night!

for pics please see: http://members.shaw.ca/orby/pics/macps/

[davmax]

Re: Help fixing a G4 Mac PS - need EE to double check choices

Thanks for photos. I had hoped that this would help identify the input rectifier. Unfortunately not. It is highly probable that this rectifier has failed and blown the capacitor so it needs to be found and tested and then replaced if required.

The identification requires some knowledge because these devices come in different packages. It can be found using an ohmmeter (multimeter set to low ohms). Each terminal of the capacitor will be connected to this rectifier. The negative terminal to neg of rectifier similarly the positive of cap to positive of rectifier. So you need to check that both cap terminals lead to the same device. The rectifier will need to be checked for shorts normally there will be a diode connected to every two terminals of the rectifier. No diode = a short. If the test meter has a diode test position select this function. A diode can be identified by placing the meter test leads across each terminal pair in turn. Then do the same with the leads reversed. A diode will give low resistance one way and high resistance the other.

See how you go.

[starfury1]

Re: Help fixing a G4 Mac PS - need EE to double check choices

hey OrBy
yeah its my standard spiel, as there are a lot of total noobs that will have a bash at this and theres nothing wrong with that but it can be potentially deadly so I just try to make that very clear...an MB isn't likely to kill you but a switcher psu has good potential to

just having a look at the photos , Thanks Nice big ones

well looking at them its alien to me no real Idea of how thats put together, but I not a guru on these and this is a mac psu.

marked as Samsung P58 on pcb
it has 4 opto couplers in it
(guessing year is 2002)

I'll see what I can dig up on it
(I have a feeling theres post or comment on that psu somewhere in the forums)

I cant see any other physical damage
(thats not to say something else hasn't died)
and you say it blew while not in use?...Very strange
(although even if off the mains side could still be live)
its on an UPS.....has it been used on that for a long time, just wondering?

Yes unfortunately cost of mac psu aren't cheap and if you can repair it,
it would be the go thats for sure.

Yes Id still like to see if an actual cause of that could be nailed down

I just have no idea how that puppy is put together.
(at this point anyway)

Cheers

Yes Davmax I couldn't see that either?

[davmax]

Re: Help fixing a G4 Mac PS - need EE to double check choices

Thanks for photos. I had hoped that this would help identify the input rectifier. Unfortunately not. It is highly probable that this rectifier has failed and blown the capacitor so it needs to be found and tested and then replaced if required.

The identification requires some knowledge because these devices come in different packages. It can be found using an ohmmeter (multimeter set to low ohms). Each terminal of the capacitor will be connected to this rectifier. The negative terminal to neg of rectifier similarly the positive of cap to positive of rectifier. So you need to check that both cap terminals lead to the same device. The rectifier will need to be checked for shorts normally there will be a diode connected to every two terminals of the rectifier. No diode = a short. If the test meter has a diode test position select this function. A diode can be identified by placing the meter test leads across each terminal pair in turn. Then do the same with the leads reversed. A diode will give low resistance one way and high resistance the other.

See how you go.

Unfortunately as I said earlier the rectifiers come in different forms. I have to date described a single device with four terminals. The basic alternatives are:
1. Four seperate rectifier diodes on the PCB.
2. Two three terminal dual diodes each clamped to a heatsink both connected to form the four diode rectifier required.

So when probing what the cap terminals are connected to, bear in mind these three possibilities.

[starfury1]

Re: Help fixing a G4 Mac PS - need EE to double check choices

seems I was wrong cant find anything here on it (samsung)
or on the net so far for that matter

did find mentions on G4 but this was using the Delta Psu here

which is a more familiar supply

from the pics and I am only guessing,
I assume the mains is feed to the 2 pin connector and this part looks like mains type filtering etc

its possible the bridge rectifier may be mounted on the small finned Heat sink HERE
In fact looking at the bottom pcb tracks it fits with that location HERE
(if I read it right)

There is a chance as davmax has also said it may be stuffed so may be the quick option would be to just replace it.

Since it has by the looks of it a multi pin PCB stuck in the middle of the mains section yep I'd say It uses APFC.

("Power Factor Correction" was forced on manufactures by Gov enviro laws, the idea is to bring the mains Voltage and Current as close to "in phase" as possible, the crude passive form is just a "big inductor" in series with the psu..(if I got it right)...Active is preferred but of course more complex requiring circuitry and a controller IC)


I would also rework the solder joints of any bolted down transistors and transformers

Give the bottom of the pcb a good visual

you I think should check any power trannies or diodes in that area too, just watch out for winding of transformers which could make you think something is short

It looks in ok nick as I said but thats not to say it is...and a failure of that type must have a cause if it spewed it guts all over the place
(its possible it could have failed by its self but I think the other is more likely, I could be wrong thought on this, not the guru)

not really up on APFC type PSU...I am still trying to figure out the old ones

BTW what brand of Cap was it if you know

Anyway HTH and hope you don't mind me reposting parts of your pics

keep us posted

Cheers

Yeah Davmax I was thinking possibly diode type paks too but I think its a 4 pin inline if I got the above right

[OrBy]

Re: Help fixing a G4 Mac PS - need EE to double check choices

I assume the mains is feed to the 2 pin connector and this part looks like mains type filtering etc

Yes!

its possible the bridge rectifier may be mounted on the small finned Heat sink

I would agree as I cannot find more then one or two larger descrete diodes and the other 3 pin parts that are bolted to the other heat sink are all singles and I asume that they would have to be a pair.

There is a chance as davmax has also said it may be stuffed so may be the quick option would be to just replace it.

If I can avoid that I would like to as even trying to get that part out may require the removal of most of the componenets in that area never mind trying to track down the part itself. Assuming that it is the recitifier - can anyone give me an idea as to what values I should be looking for with my meter?

I would also rework the solder joints of any bolted down transistors and transformers

Easly done.

Give the bottom of the pcb a good visual

Doing that as we speak

you I think should check any power trannies or diodes in that area too, just watch out for winding of transformers which could make you think something is short

Noted!

BTW what brand of Cap was it if you know

it was a CapXon and there are about 10 or more crappy CapXon's but they are all on lower voltage side.

Anyway HTH and hope you don't mind me reposting parts of your pics

Post away if it helps!

keep us posted

Yeppers!

Cheers

U2.

[starfury1]

Re: Help fixing a G4 Mac PS - need EE to double check choices

OK well on bridge rectifiers have a look HERE for starters

So if you look at that heat sink and see if it looks like a long one, (it may have a cut on one corner)...see if you can get the numbers off it.
(sometimes its the other way round and you cant)

It does depend on the wattage of the psu and sometimes they cut the values a bit fine.
but me I would use 10A 1000 Volt Vrrm? PIV Bridge Rectifier
(which means Peak Inverse Voltage)

its possibly 6 or 8 amp @ 800V piv but the above would be better device to use

it will probably have "KB XXXX" whatever

You got a multimeter I take it?

testing a bridge is the same as any diode just 4 of them to test
so between the 2 AC inputs it should read open circuit in both directions
(infinite ohms)

between one (then the other) AC input and either + or - it should behave like a diode
open circuit one way near zero
(ohms say 30 odd depending on meter and range)
the other way when you reverse the leads

Depends on the meter and if you use "diode test"or low resistance, continuity to test

As I said, they may appear fine and probably it is
but it can fail under a real voltage, static test like this wont show that
but chances are if it does pass the diode test above it will be ok.

Side point here, thats if you do have to remove it
I cant see what else is in the way there

but for removal I would take the whole thing with the heat sink then remove heat sink and replace it then put it back in with the heat sink on it

Have a look thought this thread too HERE

I have links off it all over the place and there is PeteS "how a SM-PSU works" an interesting read but not quite applicable in your case.

Your psu is the next evaluation by the looks of it...but is still a good grounding in what happens in a switcher
so its worth the read if you don't know much HERE

the basics still hold true

Well again hope this helps

Cheers

Oh if its got crap caps a recap might be an idea while your at it...fix it first thought

[OrBy]

Re: Help fixing a G4 Mac PS - need EE to double check choices

OK well on bridge rectifiers have a look HERE for starters

Cool.

So if you look at that heat sink and see if it looks like a long one, (it may have a cut on one corner)...see if you can get the numbers off it.
(sometimes its the other way round and you cant)

It's longer - I can only get the last two numbers off it "4A" and yes it had a cut in the corner. To get anything else it will have to be removed.

It does depend on the wattage of the psu and sometimes they cut the values a bit fine.

It's a 360watt.

You got a multimeter I take it?

Yuppers!

testing a bridge is the same as any diode just 4 of them to test
so between the 2 AC inputs it should read open circuit in both directions
(infinite ohms)

Assuming the two center pins are the AC in - yes it does read open (OL) in both directions.

between one (then the other) AC input and either + or - it should behave like a diode
open circuit one way near zero
(ohms say 30 odd depending on meter and range)
the other way when you reverse the leads

Using the diode test feature it reads from pin 1 to pin 2 0.461v and reversing it reads OL. This is the same when I test pins 3 and 4 in the same manner. Testing between 1 and 4 I get 1.900v and 0.498v when reversed. I am a bit puzzeled on that reading. Any feedback on thoes numbers?

As I said, they may appear fine and probably it is
but it can fail under a real voltage, static test like this wont show that
but chances are if it does pass the diode test above it will be ok.

Here is to hoping!

Side point here, thats if you do have to remove it
I cant see what else is in the way there

but for removal I would take the whole thing with the heat sink then remove heat sink and replace it then put it back in with the heat sink on it

Noted!

Oh if its got crap caps a recap might be an idea while your at it...fix it first thought

Heh - I was always told one thing at a time!

I do have to say all my high school electronics class time is flooding back to be over the past two days and talking with you guys and it's acutally kinda fun!

I am going to pull the trigger on the EKMQ451VSN391MA40S part from digikey as it is listed as only being 40mm tall and I really don't know if I will be able to get the 45mm tall 470uF one to fit with that case on. But I am going to hold off till we are finished what testing I can do on the rectifier.

[davmax]

Re: Help fixing a G4 Mac PS - need EE to double check choices

Strafury. You have contributed very well. I can leave it to you now.

A couple of thoughts right now.

A rectifier PIV of 800V is heaps, for bridge rectifiers many get away with 400V (not good though).

It has not been stated what the input AC voltage is, however with only one capacitor of 430V it would point to a 230V nominal ie no evidence of two caps as part of a voltage doubler for 115v nom.

[OrBy]

Re: Help fixing a G4 Mac PS - need EE to double check choices

It has not been stated what the input AC voltage is, however with only one capacitor of 430V it would point to a 230V nominal ie no evidence of two caps as part of a voltage doubler for 115v nom.

Up here in Canada I am getting about 121v 59.9Hz from the wall - but it looks like this PS was made to work anywhere and the input data reads that it can take anywhere from 100-120v/200-240v 50/60Hz.

[starfury1]

Re: Help fixing a G4 Mac PS - need EE to double check choices

mostly these days they should work from 90Vac~250vac odd (something like that)

The older ones as described by PeteS (and your talking about davmax) "how it works" post used to have a switch to switch between 110V and 240V (whatever 120V 220V)
These did have 2 caps
(some did "I think!" have an "auto voltage sense switch circuit" to switch between the two mods if memory serves, these probably would have been the last of that breed...I'll stand to be corrected on that but I know some would do full voltage range and I know of one printer psu that worked that way so I am assuming thats how they did it)

As I said not really up on APFC type psu but at 120VAC odd even at peak (from the bridge) your only going to have 120V X 1.414 (squ root 2) which is 170V DC

170V DC across a 450V Cap is a lot of margin for safety
(240VAC would be 340VDC in both cases its a bit less I think)

So why did it go and spew everywhere?

My only thought is a very high ripple AC
Again this happen while it was technically off which even I suppose is more of a mystery

Just on the PIV davmax , yeah agree 600V or 800V is mostly what it would be and yeah...400v piv I think is a bit of a fine margin too

Probably current wise 6A or 8A is more ideal but don't be surprised if its 4A Bridge (seems this can be the case in a lot of cases)
(id again up grade it but thats me)
I suspect yours might be a 4 Amp bridge

I'll get back to you on the bridge as yeah not quite sure
(got to reread what you posted and look at tracks again)

But "if" the two inside pins are AC connections so
(I am assuming 1 is say + DC.... 2, 3 AC ... 4 - DC)
Then if I got it right you should have 2 series diodes in parallel the reading should be open circuit and the equivalent of 2 series diodes.
(1.900V might be right for your meter for 2 diodes but the other doesn't make sense as far as a bridge goes...if I go my facts right and the bridge is centre 2 pin as AC)

Since you are testing in circuit, you may well be triggering another semiconductor junction which would explain it and sometimes you got no choice but to pull it or a lest see if you can de-solder one leg so its not in contact with the PCB (harder an depends on construction)

what Do you have in the way of de-solder gear?

here a pdf on a Bridge rectifier

I have to find some info on how the APFC slots in the the scheme of things...I think some round here posted a block diagram of this
(this is the bit I am really unsure of)

well I'll have to leave it for now

Cheers

[starfury1]

Re: Help fixing a G4 Mac PS - need EE to double check choices

OK just hold the fort here while I get myself unconfused...I am more use to analog meters not digital So stick a hold the comments above I could be wrong

[starfury1]

Re: Help fixing a G4 Mac PS - need EE to double check choices

OK found the issue...I got some 35 Amp Bridge rectifiers (cheap)
seems what its got stamped as AC + DC isn't the case
(now I guess I know why they were cheap, just hope there right specs and its only a case of some idiot stamping them the wrong way round)




NOTE HOW the +DC pin is in a different orientation to the other 3

AC & +DC is reversed on that pin..confusion rains

so yeah the above (post) is correct with the bridge and multimeter

the + - DC should show like 2 diodes in series one direction and open circuit the other
(mine show higher then the sum of 2 numbers wise)
With the package above AC I/P are diagonal to each other ditto DC + -
(I know thats not the package you have was just using it to check what my DMM would show in comparison to yours)

So either something is wrong with it or (more likely)
your turning on another junction somewhere

To be sure remove bridge or if you can isolate either DC + or - from the circuit
Test again (thats a bit of a tall order I know)

CapXon are I believe crap so maybe it did self destruct but there is a risk it didn't and throwing a new cap in could end in the same failure.
So you need to varify as much as you can that northing else is blown etc

(true thought I am more sure with an Analog then digital doing this type of thing)

ok now to see if I can find the other stuff I was looking for

HTH

Cheers

[davmax]

Re: Help fixing a G4 Mac PS - need EE to double check choices

I thought I was going to leave this thread. But if the PSU accepts a universal AC input then the circuitry is very likely to be very different to what we have been discussing. As it apparently has Active Power Factor correction this will mean that a switching pre regulator is used that accepts rectified AC and converts this to a 400V + voltage on the large cap and this a maintained at all input voltages. In this config the main rectifier is not connected to the large cap and therefor no risk of line AC. The rectifier will be connected to a very much smaller cap at the input to the pre-regulator. So why cap failure? Well if the pre-regulator goes wild and the voltage goes too high this would cause a cap disaster and therefore we may be looking for a pre-reg malfunction.

This is getting complex.

[starfury1]

Re: Help fixing a G4 Mac PS - need EE to double check choices

THANK YOU Davmax...
thats what I was going to have to find out, the flow of things

I am suspecting something with the APFC...but Don't know how it all slots together on that side.

As I said it uses 4 opto couplers and the lay out is just alien to me.

I guess if maybe the APFC controller (for starters) can be identified it might give a clue on construction.

Yeah the hope is new cap off ya go

but I am seriously thinking not!

BTW so we are all clear here I think the Bridge Rectifier is OK I think its just
another junction turning on somewhere.

I had a look and as I said before I think this is the "APFC controller PCB"
(there are 2 vertical PCBs) and the one I suspect maybe it is buried between the yellow covered heat sink and the other big one so no way you will be able to look at whats on that without removal.






(See the full pcb photo above if this is a bit unclear location wise)


So maybe the next step, question is
what is most likely to fail on an APFC PSU and kill the Mains type cap? while not in use?



cheers for now

[kc8adu]

Re: Help fixing a G4 Mac PS - need EE to double check choices

a cheap cap is the most likely failure here.
replace and check voltage afterwards.

[OrBy]

Re: Help fixing a G4 Mac PS - need EE to double check choices

Whoa - alot of posts since I have had a chance to check in. It's a busy day at work and still is so not much time to reply. I did get a chance to order the cap from Digikey last night. So I should have it some time next week I hope.