Newton Power NPS-400AB Powers on for 2-3seconds then powers off

[dicky96]

Hi Guys
I have this Newton Power NPS-400AB ATX PSU here. It powers up, runs for a few seconds then shuts down. If you power it off at the mains then back on it repeats the same actions

It's a bit of a beast, it has two PCBs. As best I can tell one PCB has the PFC and 5V STB circuitry, the other has the main switching transformer and secondary output inductors and capacitors. It looks like the voltage comparators and PWM controller are on a vertical PCB on the low voltage side.

There is a 10 way connector between the main supply low voltage side and what I think is the 5V STB secondary side on the other PCB but I can't imagine why this connector needs so many wires if that is what it is. Actually some pins are connected together so there are 7 individual wires on this connector.

All the electrolytic capacitors look OK, visually

Does any one have a schematic for this or some experience of these PSU and can advise what may be the problem.

Thanks

[dicky96]

Re: Newton Power NPS-400AB Powers on for 2-3seconds then powers off

Sorry I forgot the pics

[PeteS in CA]

Re: Newton Power NPS-400AB Powers on for 2-3seconds then powers off

Check to see if 5VSB drops out when the outputs shut down. If it does the problem is in the standby regulator circuit, which also supplies primary and secondary Vcc for the various ICs.

If the 5VSB is OK, carefully check the voltage across the big 390uF, 450V capacitor. If the PFC is working it should be around 390V. If it's significantly lower than that the PFC is not operating.

If the PFC is OK, find out why the main inverter is getting shut down.

That P/S is over 13 years old. While Newton Power (a division of Delta Products) is a good company, the electrolytic capacitors are getting old. The small value ones around the PWM and the standby regulator especially tend to go bad.

[dicky96]

Re: Newton Power NPS-400AB Powers on for 2-3seconds then powers off

OK I got back to looking at this

The 5VSB is working continually and stable

The PFC is working and stable, I have 378 Volts

I had a good look at this PSU and the odd thing is, I can't work out where the PWM controller for the main supply is.

There is a vertical PCB which has some chips (on the low voltage side) and I can see a small transformer where you would expect to see the drive to the switching transistors.

But I had a look on the vertical PCB (I desoldered it) and I can only see some LM339, some chips marked ST logo and 324 (op amps?) some other 8 pin op amps and a 24C02 EEPROM! Then there is a wide 16 pin chip I can't identify, marked 7K25 1002DS I thought this may be a microcontroller as it is near the EEPROM but if it is, I don't see a crystal, which seems odd

There is a funny 8 pin connector coming out of the PSU marked P8 and this has 6 wires on it. One of these wires (the blue one) goes to a point near the vertical 'controller' PCB and is marked VCC_EEPROM. Why would an ATX PSU have an eeprom, and what is this P8 connector for? What would it connect to?

I turns out I have another identical PSU which powers on but has 5V low, it is 4.1V. I also noticed this one would not power on with a load (two old IDE HDDs)

So I opened that one up and thought I could eliminate the problem on the first one to either the PFC + 5V STB board, the main PSU board, or the vertical controller board, by swapping the boards

First I connected the PFC/5V STB board to 'working' one, it powered on and off again same as the the first one - great I thought, the problem is on the PFC/5VSTB board, but when I connected the 'working' PFC/5V STB board that now also powers on and straight back off again

Any suggestions -I can't seem to get a handle on where the problem is.

I'll upload a video on my YT channel showing the various things I tried with this one - right now I have two identical PSU that power on and straight off again. I hoped I may end up with one good one out of two, seeing as they originally had different faults

[PeteS in CA]

Re: Newton Power NPS-400AB Powers on for 2-3seconds then powers off

Having worked for Newton Power's corporate parent, Delta Products, 1998-2001, I am 99% sure that the "1002DS" is a combination PFC controller and PWM controller, and "7K25" is the date code. If it is, it is an ASIC and I do not know whether it is available other than to Delta service people (my time at Delta was 4 jobs ago).

[dicky96]

Re: Newton Power NPS-400AB Powers on for 2-3seconds then powers off

Thanks for the info Pete

This PSU has a separate PFC controller for sure

The video is here
https://www.youtube.com/watch?v=UEoBpppEBh8

[dicky96]

Re: Newton Power NPS-400AB Powers on for 2-3seconds then powers off

I pulled all the capacitors, they check good for value and ESR

I removed the three opto isolators on the PFC board, and checked them - they don't read the same as each other, one in particular is not turning the transistor fully on for the same LED current as the other two

I know the PFC runs OK, but one of the opto isolators I notice is (correctly) oriented the opposite way round - so sending some signal too the low voltage side, not from it.

I'm guessing possibly this is a Power OK signal from the PFC to the SMPS controller and would be a good reason for it to shut down if the opto isolator isn't working properly. I used to see this type of failure a lot in the early 90s when I worked for a company specializing in industrial electronics repair, where opto isolators would go kinda 'lazy'.

I've ordered some as they are cheap. I also have a second PSU of the same model behaving in the same way now, though originally that one would stay powered up but with 5V low.

https://www.youtube.com/watch?v=DMp0twZjgNM

Have others here seen opto isolotors fail in this way? Any other suggestion on diagnosing this one?

Cheers

[stj]

Re: Newton Power NPS-400AB Powers on for 2-3seconds then powers off

i have seen bad opto's
if they get overdriven (philips - i'm calling you out) then the led slowly loses output.