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Old 03-18-2023, 10:33 AM   #1
ohren
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Default Original Xbox 1.0 PSU: Foxlink FTPS-0002 Rev. B. 12 V low, 5 V high transformer?

Hello!

I'm looking at an original Xbox PSU: Foxlink ftps-0002 rev. B. The 12 V output is too low, and the 5 V output is too (?) high. Unfortunately I don't have an oscilloscope but only a DMM for diagnosis.

Measured voltages with no load:

After rectifier diodes
12V: 6.17 V
5V: 5.67 V

Secondary transformer pins AC measurement (really don't know if this says anything)
12V: 2-2.5 V
5V: 1.04 V


I also have another (working) Xbox psu from Delta. The same measures there, in order, being: 10.79, 5.36, 8.9-11.9, 6.3-6.9 V (depends a bit on probe polarity apparently due to DC component?)

Also, measuring AC on transformer input pins just confuses me greatly and I imagine a DMM is the wrong tool. The sick PSU measures ~10 V (really?) The healthy PSU measures ~150 V. Again, I'm not sure it says anything to measure presumably square wave pwm at hundreds of kHz with a DMM, and also seems to depend on probe polarity as well as the specific voltage setting on DMM. I guess I don't have the theory or technique down for AC measurements.

Observations and details

* I'm not aware of any service manual or schematics for this PSU
* I don't really have any easy load to measure with (Xbox will not stay on)
* 5.67 V for 5V rail is out of spec assuming a 10% tolerance. Assuming a 5% tolerance would put the Delta out of spec too.
* Bulk cap stable at 315 V
* Switching transistor seems fine
* 12 V cap healthy (1014 uF 0,06 ohm ESR) according to cheap component tester and my eyes
* All twin rectifier diodes healthy (symmetric 150-200 mV drops which I understand is ok for Schottky). All their joints were resoldered for good measure.
* 5/12 V rails share transformer T1 while 3.3V uses T2, so I assume a single feedback for each transformer (two optocouplers and two switching transistors in total)
* 3.3V output stable
* I assume 5 V being too high is because 12 V is too low (?) Both 5 and 12 V go to the control board so I'm assuming both levels are taken into account for feedback
* 5 and 12 V rails are separated by 36 ohms in accordance with heatsunk resistor of corresponding color code
* I can't really get at the vertical PWM control board (tl3845) during operation, and only half of the board otherwise. It's wedged between the bulk cap and primary heat sink. I did figure out what's connected to it although I fail to deduce the transformer topology from it, since I'm not that experienced with different types of smps designs.
* I can get at the vertical control board only with difficulty. It's covered by all the output cables.
* I hear a buzzing from the transformer which doesn't sound entirely healthy (see attached audio)
* Earlier, when the sound changed momentarily the output voltage jumped up momentarily, a volt or so. It stopped doing that.
* Measuring one pair of the three T1 pins on the primary side (in 750 V AC mode) changes the sound it becomes quieter
* Percussive maintenance doesn't produce an effect
* I suspect maybe some mechanical trigger to the problem: it appeared after I took the PSU out to inspect and resolder the (previously repaired by me) AC input jack. This was in response to stepping on the plugged in end of the power cord and hearing a crunching sound. Since there was no visible damage on the board I attributed the crunch to 15 year old hot glue coming loose when the AC input jack bent downwards. Still, some mechanical stress is put on the board when pulled out of the Xbox and my inspection was probably the cause.


I strongly suspect the transformer. How do I go about confirming that?

Am I jumping to conclusions before checking everything properly? Did I miss something obvious?

What should my next step be in troubleshooting?
Attached Images
File Type: jpg BF756F8F-901A-4A6E-8CB7-05C3266EA3B2.jpg (365.7 KB, 9 views)
File Type: jpg F1A82E3F-B151-4B7D-A9A5-D3255E7D1899.jpg (225.1 KB, 11 views)
Attached Files
File Type: zip Xbox PSU.zip (105.9 KB, 1 views)
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Old 03-18-2023, 01:19 PM   #2
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Default Re: Original Xbox 1.0 PSU: Foxlink FTPS-0002 Rev. B. 12 V low, 5 V high transform

You need to test the PSU with a higher minimum load on the 5V rail. I would say 1 Amp minimum on the 5V rail.

Use a 12V car light bulb rated for 20 Watts or more or an MR12 12V halogen bulb rated at 20, 35, or 50 Watt. Connect this bulb to the 5V rail. The 12V rail should measure much closer to normal now.

Quote:
Originally Posted by ohren View Post
Unfortunately I don't have an oscilloscope but only a DMM for diagnosis.

...
Secondary transformer pins AC measurement (really don't know if this says anything)
12V: 2-2.5 V
5V: 1.04 V
Most regular DMMs won't show proper AC voltage at the output of an SMPS transformer. So it's a test you can skip doing in the future.



Quote:
Originally Posted by ohren View Post
Also, measuring AC on transformer input pins just confuses me greatly and I imagine a DMM is the wrong tool.
Yes, DMM is NOT something you should use on the high-voltage side of an SMPS's transformer. Again, the high switching frequencies combined with high voltages will show meaningless results at best. At worst, some meters can even get damaged. So that's another test to skip in the future. The only way to measure switched AC on the primary side is with an oscilloscope AND ONLY if you have an isolation transformer (otherwise, you'll likely blow your scope or the PSU fuse.)

Quote:
Originally Posted by ohren View Post
* Switching transistor seems fine
Well, if it wasn't, you wouldn't get any output from the PSU.

Quote:
Originally Posted by ohren View Post
* 5/12 V rails share transformer T1 while 3.3V uses T2, so I assume a single feedback for each transformer (two optocouplers and two switching transistors in total)
The smaller transformer is for the 3.3V Standby supply.

Once the Xbox sends a PS-ON signal to the PSU, the main PS turns on, which generated the 5V, 12V, and 3.3V rails. 3.3V rail appears to be generated from the 5V rail through a mag-amp circuit - pretty much the same thing as a group-regulated ATX PC PSU.

Quote:
Originally Posted by ohren View Post
* I assume 5 V being too high is because 12 V is too low (?) Both 5 and 12 V go to the control board so I'm assuming both levels are taken into account for feedback
Yes.
And note the current (and power ratings) of each rail.
5V: 13.2 Amps (66 Watts)
12: 1.4 Amps (16.8 Watts)

The original Xbox uses a variant of the Pentium 3 CPU. CPUs of that era drew their power from the 5V rail instead of the 12V rail, much like the early AMD Athlon CPUs and Pentium II's. So it's expected that even with the Xbox running idle, there would still be at least 5-10 Watts of load on the 5V rail (i.e. 1-2 Amps). If you're testing the PSU without an Xbox motherboard and without any load, then it shouldn't be a surprise that the 5V rail runs high and the 12V rail runs low. Of course, this may not happen with every Xbox PSU. Depending on who made the PSU and how it was designed, the 5V and 12V rails could read close to spec without a load. But some PSU designed won't... and it appears that this is one that may not be. So to verify, put a load on the 5V rail and see if the PSU voltages appear more normal. Again, try to put at least 1 to 2 Amps of load on the 5V rail. The 12V rail should be OK without a load, but if you want to connect something like a low-power PC fan, that should be OK.
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Old 03-19-2023, 03:47 AM   #3
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Default Re: Original Xbox 1.0 PSU: Foxlink FTPS-0002 Rev. B. 12 V low, 5 V high transform

FWIW, the recent modchipped 1.6 I got had a 733/128 marking on the CPU - I'm much inclined to believe it's a Celeron Coppermine - a standard P3 at the same speed is shown to have 256KB of cache.
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Old 03-19-2023, 04:15 AM   #4
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Default Re: Original Xbox 1.0 PSU: Foxlink FTPS-0002 Rev. B. 12 V low, 5 V high transform

You can read about it here: https://en.wikipedia.org/wiki/List_o...-128"_(180_nm)

Quote:
A custom Coppermine-based Pentium III version was developed for Microsoft's Xbox game console. The only significant change was that the chip lost half of its L2 cache, dropping it down to 128 KB. Unlike the Celeron Coppermine-128 variant with the same size L2 cache, but reduced 4-way L2 cache associativity, Xbox's Coppermine core kept all of its 8-way L2 cache associativity from the Pentium III. This means that the Xbox CPU's L2 cache is more efficient than Celeron's. The Xbox CPU was manufactured onto the same Micro-PGA2 packaging as notebook chips, but in a BGA (ball grid array) format.
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Old 03-19-2023, 06:38 PM   #5
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Default Re: Original Xbox 1.0 PSU: Foxlink FTPS-0002 Rev. B. 12 V low, 5 V high transform

Quote:
Originally Posted by momaka View Post
You need to test the PSU with a higher minimum load on the 5V rail. I would say 1 Amp minimum on the 5V rail.

Use a 12V car light bulb rated for 20 Watts or more or an MR12 12V halogen bulb rated at 20, 35, or 50 Watt. Connect this bulb to the 5V rail. The 12V rail should measure much closer to normal now.


Most regular DMMs won't show proper AC voltage at the output of an SMPS transformer. So it's a test you can skip doing in the future.




Yes, DMM is NOT something you should use on the high-voltage side of an SMPS's transformer. Again, the high switching frequencies combined with high voltages will show meaningless results at best. At worst, some meters can even get damaged. So that's another test to skip in the future. The only way to measure switched AC on the primary side is with an oscilloscope AND ONLY if you have an isolation transformer (otherwise, you'll likely blow your scope or the PSU fuse.)


Well, if it wasn't, you wouldn't get any output from the PSU.


The smaller transformer is for the 3.3V Standby supply.

Once the Xbox sends a PS-ON signal to the PSU, the main PS turns on, which generated the 5V, 12V, and 3.3V rails. 3.3V rail appears to be generated from the 5V rail through a mag-amp circuit - pretty much the same thing as a group-regulated ATX PC PSU.


Yes.
And note the current (and power ratings) of each rail.
5V: 13.2 Amps (66 Watts)
12: 1.4 Amps (16.8 Watts)

The original Xbox uses a variant of the Pentium 3 CPU. CPUs of that era drew their power from the 5V rail instead of the 12V rail, much like the early AMD Athlon CPUs and Pentium II's. So it's expected that even with the Xbox running idle, there would still be at least 5-10 Watts of load on the 5V rail (i.e. 1-2 Amps). If you're testing the PSU without an Xbox motherboard and without any load, then it shouldn't be a surprise that the 5V rail runs high and the 12V rail runs low. Of course, this may not happen with every Xbox PSU. Depending on who made the PSU and how it was designed, the 5V and 12V rails could read close to spec without a load. But some PSU designed won't... and it appears that this is one that may not be. So to verify, put a load on the 5V rail and see if the PSU voltages appear more normal. Again, try to put at least 1 to 2 Amps of load on the 5V rail. The 12V rail should be OK without a load, but if you want to connect something like a low-power PC fan, that should be OK.
Couldn't have asked for a better answer. I was hoping you'd reply based on your replies in https://www.badcaps.net/forum/showthread.php?t=95744.

Turns out you're absolutely right, and I didn't need to find a lightbulb; I tried it again in the box again and it just worked. What am I even doing here... It was repeatedly shutting down when powering it up before. If I fixed it it might have been bad joints on the rectifier diodes who were sharing a heatsink, since they were the only ones looking matte. The only problem after that was some arcing between the diode pins, but they seem to have dug their own isolation slot by now.

Thanks for pointing out what tests I don't need to bother with in the future — it's something I always want to know! Sometimes I only get advice on what to do next without learning how they figured it out. And I will rewatch that EEVBlog episode on blowing up my scope if I ever get one. As far as I remember I can always use mains earth as a reference without isolation, but that's it. (Would the negative lead of the bulk cap not work?)

Quote:
The smaller transformer is for the 3.3V Standby supply.

Once the Xbox sends a PS-ON signal to the PSU, the main PS turns on, which generated the 5V, 12V, and 3.3V rails. 3.3V rail appears to be generated from the 5V rail through a mag-amp circuit - pretty much the same thing as a group-regulated ATX PC PSU.
I always do this kind of mistake. A transformer just for standby power sounds a bit much to me so I assumed it did something more, considering 3v3 was spot-on unlike the other rails. Now I have to go back and look, and look up mag-amp circuits.

If I understand you right you're saying that the 12 V rail is actually low because the 5 V rail is high (not vice-versa), since the assumption that 5 V has a constant load is broken combined with the fact that they share the same feedback signal.

This will no doubt all come in handy on my subsequent repairs. In fact, the day after starting this thread I came across another Xbox (and other treasure), so I went from one working box to three just now. A bit ridiculous — I don't even have that many good controllers! I should start a thread about repairing broken plastic screw posts.

Last edited by ohren; 03-19-2023 at 06:46 PM..
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Old Yesterday, 01:53 PM   #6
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Default Re: Original Xbox 1.0 PSU: Foxlink FTPS-0002 Rev. B. 12 V low, 5 V high transform

Quote:
Originally Posted by ohren View Post
As far as I remember I can always use mains earth as a reference without isolation, but that's it. (Would the negative lead of the bulk cap not work?)
That's the exact way to do it if you want to blow up your oscilloscope!
You can confirm this very very easily:
Measure from the negative of the bulk cap to chassis ground WITH A MULTIMETER
If the value shows anything else than 0.00VAC AND 0.00VDC then it is not a ground and if you connect your oscilloscope ground lead = mains earth ground cable then you will have sparks flying!

If instead you float your scope the scope will not explode when you connect it, but you will die when you touch the exposed metal on the BNC connectors, or switches, or whatever else is metal on the scope.

Please see this thread in addition to the EEVBlog video on how not to blow up your oscilloscope:
https://www.badcaps.net/forum/showthread.php?t=96508
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Old Yesterday, 05:53 PM   #7
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Default Re: Original Xbox 1.0 PSU: Foxlink FTPS-0002 Rev. B. 12 V low, 5 V high transform

I must've remembered incorrectly

I think I read through that thread a while ago. Good compilation, thanks! Been careful around those heat sinks since then.

Come to think of it the negative lead, even discounting the cap's charge, is only at mains earth potential 50% of the time... I'm really not touching AC often enough. I foresee an explosion.
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