Delta Electronics GPS-350CN-100 need repair

momaka · 05-09-2015, 01:26 PM

Re: Delta Electronics GPS-350CN-100 need repair

Originally posted by goodpsusearch

The only thing that is definitely bad is a B647 PNP transistor, marked with red color in the photos attached.

Yep, that looks like the transistor for the 3.3V rail mag-amp circuit. Need to replace it. Considering the original is described as "low frequency power amplifier", that means you can use just about any PNP transistor. Just match the current rating and type (PNP). I really doubt you need a voltage rating as high as the original. And perhaps avoid transistors with a very low current gain (low hFE). On that note, the hFE doesn't need to match perfectly - just need to get it in the ballpark more or less. The transistors is used for switching here, so the hFE only needs to be large enough to enable the transistor to fully turn ON.
Something like TIP42 might work here (although, be advised that TIP42 is TO-220, so you might have to put it else where and run wires to it). Or B772. Just see what your local shops have, and let us know. It really just needs to be PNP type and TO-92MOD case or larger. I would go for TO-126 like the B772 transistor - it's smaller than TO-220, but larger than TO-92MOD. Or try SOT-223 if you want a ghetto-looking repair

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Originally posted by goodpsusearch

I also attach a photo of the 2 mag amp coils but I can't tell if the one on the left is toasty or not...

https://www.badcaps.net/forum/attach...1&d=1431043164

It does look a bit toasty. Make sure it is not touching the secondary heatsink or the other coil. Perhaps it was shorting on something. Or maybe someone just overloaded the 3.3V rail on this PSU. Who knows. Fix what's broken first and we can go from there. Maybe get two PNP transistors for the mag-amp, just in case

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goodpsusearch · 05-07-2015, 06:04 PM

Re: Delta Electronics GPS-350CN-100 need repair

I checked all the components marked with green color in the following photos and found them ok. I had to unsolder several of them because when soldered on PCB they tricked my multimeter and gave false values.

https://www.badcaps.net/forum/attach...1&d=1431043164
https://www.badcaps.net/forum/attach...1&d=1431043164

The only thing that is definitely bad is a B647 PNP transistor, marked with red color in the photos attached.

I also attach a photo of the 2 mag amp coils but I can't tell if the one on the left is toasty or not...

https://www.badcaps.net/forum/attach...1&d=1431043164

Attached Files

Wester547 · 05-05-2015, 10:32 AM

Re: Delta Electronics GPS-350CN-100 need repair

I find it funny that with accordance to the datasheet, "CapXon GL" (10mm and higher) is supposed to be rated for 6,000 hours @ 105*C endurance... yet it is the one failed capacitor in the unit....

...

Yes, this PSU uses two toroids to derive the +3.3V pins from the +5V pins. Any chance that one of them is shorting to the secondary heatsink (touching it)? Slight discoloration could mean the aforementioned one is bad. Might help to just replace it. One of the other secondary rectifiers or primary rectifiers could still be shorted. In order to test the toroid in question thoroughly, you will need an LC meter.

goodpsusearch · 05-05-2015, 04:29 AM

Re: Delta Electronics GPS-350CN-100 need repair

Checked all caps with esr-micro meter. Every cap appears to be perfectly fine.

Replaced the 2 12V rectifiers with a single KNOWN GOOD 12V rectifier but nothing changed.

This psu has 2 mag-amp coils for 3.3V generation. One of them looks slightly discolored. Could it be the reason it doesn't start? How can I measure the coils?

Wester547 · 05-03-2015, 03:16 PM

Re: Delta Electronics GPS-350CN-100 need repair

Originally posted by kaboom

Don't confuse switching frequency with rise and fall times.

MOSFETS can turn off (or on) slowly as well!

Lack of gate current supply or sinking will do it every time.

BJTs can also switch off too slowly- like in a TV or monitor horiz out, where long off-times would kill the device, and sometimes destroy the power supply (sonys often did this).

Well, it was to my knowledge that BJTs generally have much slower switching speeds than MOSFETs. Regular old BJTs, I mean, not IGBTs. At least that's what the datasheets would have you believe but it's true that they don't tell the whole story. As to switching frequency, I meant the frequency the main transformer was running at. I know that if MOSFETs (and BJTs) aren't properly driven that things can go amuck. And full bridge topology is clearly very capable (1KW+ I believe) along with half-bridge LLC resonant topology so I'm not saying BJTs are useless by any stretch, though it was also to my knowledge that plain old BJTs operate best at switching frequencies below 70KHz, and that their power dissipation was not as good as that of a MOSFET (though I think they might have an advantage as far as their equivalent of ON resistance goes).

And it does look to me that it was meant to be a +12V heavy unit - the label would at least have one believe that with dual +12V rails (10A and 15A) for a combined rating of 17.5A (210W) which dominates the 130W combined rating of the +3.3V and +5V rails. I just think this is a low-end Delta unit, and you can tell the difference between the low and high end units for sure (using -52 material on the +3.3V toroid and -26 material on the +5V/+12V toroid is an odd choice). It's definitely possible that the CapXon capacitor is the culprit (could have failed shorted or open) with respect to the shorted +12V rectifiers (if one, or the other, or both, is shorted).

kaboom · 05-03-2015, 01:39 PM

Re: Delta Electronics GPS-350CN-100 need repair

Originally posted by Wester547

Half-bridge topology will need it as the slow switching speed of the BJTs will require larger bulk storage and a greater transformer with a good turns ratio. As far as I know, Delta's forward PSUs do employ a higher switching frequency for the SMPS transformer (they run at around 100KHz) which means they can get away with a smaller transformer for higher wattage PSUs.

Don't confuse switching frequency with rise and fall times.

MOSFETS can turn off (or on) slowly as well!

Lack of gate current supply or sinking will do it every time.

BJTs can also switch off too slowly- like in a TV or monitor horiz out, where long off-times would kill the device, and sometimes destroy the power supply (sonys often did this).

kaboom · 05-03-2015, 01:35 PM

Re: Delta Electronics GPS-350CN-100 need repair

Originally posted by goodpsusearch

While every rail has a coil and 2 caps (-12V has coil and 1 cap), 12V has no coil and just one filtering cap.

Typical of older designs, where +12 wasn't taken seriously. Or continued for the sake of cheapness.

Originally posted by goodpsusearch

All the output capacitors are Ltec and appear fine except the one used in 12V which is Capxon GL 2200uF 16V d12.5mm and is bad.

Capxon Garbage 'Lytic- no surprise there. I'd replace the ltecs, too, while it's apart; save yourself the grief.

Originally posted by goodpsusearch

I replaced the bad cap, put a fan on it and tested the psu: 5vsb is there, but when you short green with ground, the psu tries to start for fractions of second and shuts down immediately.

Any help? What should I look for?

Is it sqealing when it tries to start?

Check for shorted rectifiers on +12, +5, and +3.3, in that order. If okay, also check small rectifiers for -5 and -12.

Assymetric base drive to the switchers can put net DC into TX primary, in which case base drive ckt needs to be rebuilt. There are two 4.7u 50v lytics that go bad.

It's probably the +12 rectifier, since its cap was open, leading to the output inductor stressting that rectifier, so check that first.

Wester547 · 05-03-2015, 01:04 PM

Re: Delta Electronics GPS-350CN-100 need repair

Delta using run in the mill half-bridge topology and a two-transitor +5VSB circuit in a 2006 PSU....

(I thought Delta was more "forward" thinking than that. No pun intended...).

And only one capacitor and no ferrite coil on +12V?

They could have least used two in parallel.... and of course the sole failed cap in the unit is a CapXon....

No NTC thermistor?

Contrast that to those older Dell 250W Newtons which often had two NTC thermistors on the primary...

That aside, I recommend replacing all the small capacitors on the primary. One of the small capacitors biasing the BJTs (or the critical +5VSB cap) could have gone bad and those smaller LTECs like to go open circuit without showing it. A full recap excepting the primaries might be in order too (though, since they're CapXon, it couldn't hurt to replace them, and there appears to be one more tiny CapXon on the secondary). I'd also check the secondary rectifiers and bridge rectifier for shorts. I do see some of that yellow glue but it doesn't appear to have gone conductive (brown) as yet.

And that transformer is definitely size 39, written right on the transformer. Half-bridge topology will need it as the slow switching speed of the BJTs will require larger bulk storage and a greater transformer with a good turns ratio. As far as I know, Delta's forward PSUs do employ a higher switching frequency for the SMPS transformer (they run at around 100KHz) which means they can get away with a smaller transformer for higher wattage PSUs.