Xbox has low 12v, cause?

[jayjr1105]

Re: Xbox has low 12v, cause?

Here are pictures of the psu.

Is that a 110v unit or 220? I have several 110v power supply's but never once saw that model. I think it's trash tbh.

[Justin1091]

Re: Xbox has low 12v, cause?

It's a third party Chinese PSU, I found a reference to it here https://www.reddit.com/r/originalxbo...m_source=share

It's 220, bought when the original one died in 2004. If only I'd known back then..
Shame of the cap replacement, but oh well at least I had some practice soldering again.

[jayjr1105]

Re: Xbox has low 12v, cause?

It's a third party Chinese PSU, I found a reference to it here https://www.reddit.com/r/originalxbo...m_source=share

It's 220, bought when the original one died in 2004. If only I'd known back then..
Shame of the cap replacement, but oh well at least I had some practice soldering again.

At least in the north american models, the xbox power supply's are rather stout. I repaired a dozen XBOX consoles and the only thing wrong with any of them was cracked solder on the input jack.

[momaka]

Re: Xbox has low 12v, cause?

Well guys, the result is disappointing. Zero change, still exactly at 10.80V.
3.3V is still high as well.

I'm starting to think this psu is crap. Any more ideas?

Yeah, to be 100% honest, the PSU does look like a crap design. But before we conclude that completely, could we also see some pictures of the under(solder)side so we could try tracing the PSU circuit?

I suspect the 3.3V rail may not have any regulation and could just be provided straight out of a tap on the main transformer... which would explain the terrible cross-regulation. Furthermore, I don't see a coupled (toroid) inductor on the output, so this tells me this PSU uses flyback / discontinuous design, and those do rather poorly with cross-regulation.

My only hope is that the TO-220 component by the orange wire is some kind of a regulator for the 3.3V rail. On that note, since I'm not 100% familiar with these old Xbox PSUs... are the wire colors indicating the voltage rail like on PC ATX PSUs? (i.e. yellow = 12V, red = 5V, orange = 3.3V, and purple = 5VSB??) If so, that could help me trace what's going on with this PSU (and with the solder-side pictures, of course.) But I suspect it may be a crap design to begin with. Let's see, though.

At least in the north american models, the xbox power supply's are rather stout.

The EU versions should be exactly the same as the US. As O/P noted, though, this is a cheap "replacement" PSU... hence the really no-name brands inside (seriously, I've never heard of "STO" cap brand before - good thing it's on the primary and without APFC, because then those caps won't see much stress and should last.)

It's 220, bought when the original one died in 2004. If only I'd known back then..

You can probably get a US / North American version and convert it to 220/230/240 easily... if it isn't already a universal input.

[Justin1091]

Re: Xbox has low 12v, cause?

Yeah, to be 100% honest, the PSU does look like a crap design. But before we conclude that completely, could we also see some pictures of the under(solder)side so we could try tracing the PSU circuit?

Hi, sure: pictures are attached.

My only hope is that the TO-220 component by the orange wire is some kind of a regulator for the 3.3V rail. On that note, since I'm not 100% familiar with these old Xbox PSUs... are the wire colors indicating the voltage rail like on PC ATX PSUs? (i.e. yellow = 12V, red = 5V, orange = 3.3V, and purple = 5VSB??) If so, that could help me trace what's going on with this PSU (and with the solder-side pictures, of course.) But I suspect it may be a crap design to begin with. Let's see, though.

Yes, same as with PC PSUs. I think you can even use a PC psu, but the pins need to be switched as a Xbox uses different pinout.
I'm looking for a broken Xbox right now to swap out the psu, perhaps I can extract the new capacitors from this supposedly thrash psu and use them there. Still, I'm very interested in if this psu is in fact bad, the reason for it being bad and how to spot bad psu's like these! Heck, maybe it output the bad voltages all these years without me ever noticing?

[stj]

Re: Xbox has low 12v, cause?

looking at the pics,
resolder the transformers and check that the parts on the heatsink arent electrically connected to it - one of the thermal pads looks questionable

[momaka]

Re: Xbox has low 12v, cause?

OK, so looking at the pictures and analyzing the PSU, I noticed a few things.

But before I mention anything else, first please look at the attached image in my post.

I put a red square box around a trace that looks broken. Please check that and let me know what you find.

As for the rest of the colored dots... these indicate to what rectifier the wires connect to. On that note, check the solder joints on the TO-220 rectifier (attached to the heatsink) for the 5V rail (i.e. the one close to the red dot in the lower right corner of the picture.) I think I see some crack rings... though that might be just the picture too, of course.

Also measured the atx connector:
Orange: 3.85
Purple: 3.62
Green: 3.55
Grey: 3.85
Yellow: 10.80
Red: 5.00

OK, I know these voltages were taken before the PSU recap and you said they didn't change after the recap. But something crossed my mind: did you also recap the motherboard when you looked at the voltages the 2nd time? If not, do that and then check them again. Just want to make sure the bad caps on the motherboard are not somehow getting the PSU stuck in some kind of a boot-cycle.

Next... I notice the pinout you posted says that the purple wire should be the 3.3V standby supply... but from what I traced on the PSU, this might actually be the *brown* wire (and indeed I can almost make out on the PCB that it says "3VSB" above the brown wire.) Please double-check me on this - i.e. check what voltage you get on the brown wire and post it here.

If the brown wire is indeed 3VSB, then I wonder what the purpose of the purple wire is. Can you read what it says on the PCB for me for the purple wire? I can't quite see it on the pictures.

Also, I know this is unlikely to be the case, but... check your multimeter batteries, just in case. Low batteries tend to make meters read higher voltages... which in this case doesn't make much sense for the 12V rail, as it's reading lower, but does make sense for the 3.3V rail and 3.3VSB. So just want to make sure this is not anther factor (probably isn't, but still worth mentioning. )

Lastly, can you post another picture of the black square component next to the output wires? I really can't figure out what it is and what it does.

Still, I'm very interested in if this psu is in fact bad, the reason for it being bad and how to spot bad psu's like these! Heck, maybe it output the bad voltages all these years without me ever noticing?

It's quite possible that the PSU has always been outputting crazy voltages like this. Indeed the pictures confirmed my suspicion that the 3.3V rail has no secondary regulation whatsoever. And to make it worse, the PSU is flyback converter... so that means no coupled output toroid to alleviate some of the cross-regulation issues (well, since the design is flyback, the main transformer sort-of acts like a coupled inductor... but it's not great at it, since in general, flyback designs are not known for good voltage stability on a multi-rail design.) So in short, this is absolutely piss-poor design!!! That 100% explains the crap regulation. Moreover, I can't tell if the 3.3V and 12V rails even play any part in the feedback for the voltage regulation or not, given how centered the voltage is around the 5V rail (well, they probably do, but perhaps not given enough "weight".)

It gets even worse, though. Notice there is no monitoring chip or comparators on the secondary side at all. All I see is a bunch of TO-92 transistors and maybe a few TL431 shunts. This tells me this PSU also likely lacks a lot of protections. It probably has basic short-circuit protection for the 3.3V, 5V, and 12V rail... but that's likely it.

Another thing I notice is that there are only TWO optocouplers. Normally, there should be 3 for designs like this: one for the standby supply (the one with the small transformer) and two for the "main" supply. With the latter two, one is used for feedback / voltage regulation, and the other simply to turn On and Off the main PS on the primary side. I'm not exactly sure how they accomplished this design here with just TWO optocouplers total. My guess would be that the one used for the feedback / voltage regulation of the main PS is also used to signal when the main PS should turn On/Off... which IMO is another big No-No for this PSU.

So how to tell if a 3rd party PSU is going to be bad... well, IDK exactly - at least not without opening it. But my general expectation is that most all "replacement" 3rd party PSUs are crap, so just avoid them altogether, if possible.

perhaps I can extract the new capacitors from this supposedly thrash psu and use them there.

Yes, if the values match.

[Justin1091]

Re: Xbox has low 12v, cause?

looking at the pics,
resolder the transformers and check that the parts on the heatsink arent electrically connected to it - one of the thermal pads looks questionable

Only the middle pin of those components screwed to the heatsink are NOT connected to it.
At the power cord section heatsink, only one pin is connected to the heatsink. I measured using the pins on the bottom side of the psu.

OK, so looking at the pictures and analyzing the PSU, I noticed a few things.

But before I mention anything else, first please look at the attached image in my post.

I put a red square box around a trace that looks broken. Please check that and let me know what you find.

Good eye, but it was some flux from the solder wire.

As for the rest of the colored dots... these indicate to what rectifier the wires connect to. On that note, check the solder joints on the TO-220 rectifier (attached to the heatsink) for the 5V rail (i.e. the one close to the red dot in the lower right corner of the picture.) I think I see some crack rings... though that might be just the picture too, of course.

True, was in the picture only. I don't see cracks.

OK, I know these voltages were taken before the PSU recap and you said they didn't change after the recap. But something crossed my mind: did you also recap the motherboard when you looked at the voltages the 2nd time? If not, do that and then check them again. Just want to make sure the bad caps on the motherboard are not somehow getting the PSU stuck in some kind of a boot-cycle.

I checked them again, did notice something odd but maybe it's normal?
Yellow: 10.73v
Red (x3):5.00v
Orange:3.85V
Purple: 3.63V
Green 3.56V
Grey: this was strange. As soon as I touch it the console switches off (and can be turned on again using the power button). It does connect to 5VSW on the PSU so probably all I did was simulate a power off?

Next... I notice the pinout you posted says that the purple wire should be the 3.3V standby supply... but from what I traced on the PSU, this might actually be the *brown* wire (and indeed I can almost make out on the PCB that it says "3VSB" above the brown wire.) Please double-check me on this - i.e. check what voltage you get on the brown wire and post it here.

If the brown wire is indeed 3VSB, then I wonder what the purpose of the purple wire is. Can you read what it says on the PCB for me for the purple wire? I can't quite see it on the pictures.

My posting of the diagram has messed things up a bit. I was confused by the orange and brown colors. Let me try to explain, I have a 1.4 Xbox, in which there is no brown used. All I have is:

Black
Yellow
3x red
Orange
Purple
Green
Grey

This PSU has an adapter (just a plastic wire block) in order to also work in later (1.6) Xbox models, which do use the brown wire.

I did not measure brown as it does not go into the motherbord ATX socket.
To be clear: brown (unused by my xbox) written on PSU PCB:5VSB
Orange written PSU PCB: 3.3V and I get a reading of 3.85V
Purple written on PSU PCB: 3.3VSB and I get a reading of 3.63V

Also, I know this is unlikely to be the case, but... check your multimeter batteries, just in case.

I will do this as soon as I get a spare battery.

Lastly, can you post another picture of the black square component next to the output wires? I really can't figure out what it is and what it does.

Is attached to this post.

[Justin1091]

Re: Xbox has low 12v, cause?

'Broken' Xbox arrived. Swapped the PSU, which is way heavier and all is fine (11.90v).

It even powers on differently, instead of instantly powering on with a click (as if something is pushed) it now powers on after a delay of 1 second and no noise. Shutting down also takes a bit longer. Even the m/b and gpu temperatures went down from ~50 to ~34 in idle.

I will take all capacitors from the chinese psu and throw it away. Shame to see they're still being sold online.

Now to find a new psu for the 'broken' Xbox (it's dvd drive can't read anymore, but I'll try to fix it).

While a different outcome than I initially hoped, I'm glad it works now and many thanks to all of you!

[stj]

Re: Xbox has low 12v, cause?

next to reflash the bios and fit a terrabyte harddrive and all the games.

[momaka]

Re: Xbox has low 12v, cause?

'Broken' Xbox arrived. Swapped the PSU, which is way heavier and all is fine (11.90v).

It even powers on differently, instead of instantly powering on with a click (as if something is pushed) it now powers on after a delay of 1 second and no noise.

The clicking noise on that crappy PSU is probably the relay that you showed in your last picture... which I just can't decipher why they even have that in there. It's almost as if they designed some kind of a "universal" Xbox PSU, and this was some workaround to get it to work with all versions?

In any case, I'm guessing we are done with it... and probably for a good cause!

I will take all capacitors from the chinese psu and throw it away. Shame to see they're still being sold online.

Well, if you haven't already, there may be a few other parts you can scavenge from it... that is, if you do work on electronics (if not, then probably not worth bothering.) IC1 and IC2 on the primary might be some kind of current-mode PMW controllers like UC384x family or similar, and those usually come in handy once in a while with PSU repairs. The MOSFET on the primary side and the rectifiers on the secondary side are also quite useful parts to keep around, along with the snubber network components (high-power resistor and 1-2 kV cap) and EMI/RFI filter choke + X2 & Y2 caps. And AC receptacle plug!

While a different outcome than I initially hoped, I'm glad it works now and many thanks to all of you!

Yes, unfortunately the Chinese design of the cheap PSU wasn't much we could work with. :\

next to reflash the bios and fit a terrabyte harddrive and all the games.

Are there actually that many games for Xbox that you can fill a 1TB HDD? I imagine 250-500 GB would be sufficient... but then again, I've always kept my distance from consoles (apart for repairing them for a repair shop for a while), so I don't really know.

[stj]

Re: Xbox has low 12v, cause?

there's a pretty large number