Power supply schematics

Discussion in 'Electronics Resources' started by elguasio, Nov 23, 2008.

  1. elguasio

    Thread Starter New Member

    Nov 23, 2008
    My computer doesn't turn on (Dell XPS Generation 4).

    I have found the power on button have no power, since this power supply (Newton Power Ltd. NPS-460BB D) is switched by this only button I traced back to the power supply section that gives power to the power on button.

    Apparently the transformer that feeds the power on button circuitry is not good (transformer: MP-130B DET 0436 (06) 0336A DT-E16-099T).

    With this info I can try replacing the transformer, but I still would like to see the schematics to make sure before doing any soldering on the PCB.

    The question is: where may I get the schematics for the Newton Power NPS-460BB D power supply?

    Thanks for any suggestions.
  2. studiot

    AAC Fanatic!

    Nov 9, 2007
    Even if you are an experienced electronics engineer I would advise you not to mess with a suspect laptop supply.

    Set against the cost of a new XPS if you damage it, the cost of a new supply is peanuts.

    What is the model number of your XPS? It will start with M and be on the label on the underside.

    Have you tested the power supply? What voltage is it rated for?
    You can get cheap replacements quite readily.
  3. elguasio

    Thread Starter New Member

    Nov 23, 2008
    This is a tower not a laptop.

    Dell Dimension XPS Generation 4
    The model #WHL
    The service tag is CMMXG61.

    The power supply is rated for 460 watts 110 VAC.

    Yours is good advice, that is the reason why is always a good idea to double check the output voltages of all leads coming out from the power supply after the repairs had been done. They have to be exactly as the manufacturer specifications.

    Upon checking the numbers on the transformer I couldn't find the required part. I checked on Mouser.com and Digi-key.com Do you have another parts supplier?

    Thanks for your help.
  4. studiot

    AAC Fanatic!

    Nov 9, 2007
    Mains fed computers don't use transformers, at least in the conventional power sense. They are SMPS (switched mode power supplies)

    The power supplies are sealed units within the box will not work unless the correct loads are present at the appropriate sockets on the connector.

    These loads are usually provided by the motherboard.

    Further there is data interchange between the power supply and the motherboard during bootup.
    This is to prevent incorrect voltages appearing on the logic chips, messing things up.

    The sequence is the front panel push button provide a momentary closed contact. this activates the run up sequence in the power supply.
    During this run up no external voltages appear, except one small independent 5volts supply.
    This powers certain sensing circuitry on the motherboard, not to do with memory or processor.
    When all the voltages have stabilised at their correct levels the power supply asserts the Power Good line and applies the voltages to the outputs.
    This signal causes the motherboard to initiate its own startup (the boot sequence).

    The economics of repairing these is even more heavily weighted towards replacement, they can usually be had for less than the cost of an hour's tech time.
    I carry a plug in tester and simply replace (not open) if faulty.

    What more do you need to know?
  5. elguasio

    Thread Starter New Member

    Nov 23, 2008
    Studiot you really make your point.

    My case is just that I'm retard! HAHA

    Yes I will buy the power supply!

    But as I said I'm retard an old retard that just want to see if he can still fix something.


    Yes this particular power supply doesn't have any voltage on the start up button. The particular transformer I talk about is the one responsible for suppling such voltage. It is on the main PCB of the power supply.

    I saw this particular power supply problem as a challenge, and you see it as another repair job.

    Yes, your approach is the correct one: replace instead of repair.

    Yes I will buy the darn power supply!

    But I still want to repair it! HAHAHA

    Thanks for your patience Studiot! HAHAHA
  6. studiot

    AAC Fanatic!

    Nov 9, 2007
    There's nothing wrong with wanting to root around inside the power supply for experience, if you have the technical background.

    Many of the psus I see that die in service get passed on to groups of retired hobbyists who strip them for the many usable components that remain.

    If you want to do this I'm sure many here will help, but we need some details to go on.

    How much do you know about switched mode power supplies?
    It is less likely that the transformer has failed compared to other components.
    Don't forget you will see no voltages around the transformer unless these are functioning correctly.
    Be aware that the unit probably contains power schotty rectifiers that look like old fashioned power transistors, but with two legs not three. These often fail.
    Look also for signs of burnt or blown components such as capacitors and resistors.
  7. JohnMWWarks

    New Member

    Dec 29, 2008
    This is highly incorrect as I have 20 years of experience before you go blowing yourself up lets get a few things straight about switched mode power supplies.

    1. There is not data excahnge at all between the power unit and the
    motherboard. A simple thyristor/triac latching on circuit is used, as you
    not really want 25 amps on the back of the power switch. You simply
    apply a couple of volts to the GATE of a thyristor or triac to make
    it conduct. It will continue to conduct across the ANODE/CATHODE
    (Thyristor) or MT1/MT2 (Triac) until you remove the GATE voltage.
    No logical data involved at all.

    2 Switching power supplies do use transformers they are generally
    smaller and operate at higher frequencies. In a swiched mode power
    unit all you are really doing is rectifying the mains input and then
    chopping it with an oscillator and applying it as a pulsed DC to to the
    transformer. That way the transformers run more efficiently and do
    not to be as large, for a given amount of current.

    Thgey are fixable some have fuses in, it is unlikely the transformer will blow but if a replacement fuse still blows then you need to replace the rectifier bridge - simple as that

    cheers John
  8. studiot

    AAC Fanatic!

    Nov 9, 2007
    Welcome to the forum, John W.

    I think you do yourself (and others) a disservice.

    Firstly, most emphatically, none of my advice should lead to someone blowing anyone or anything up.

    Quite the reverse in fact.

    Secondly, there are power units on the market that contain no transformers whatsoever. I would not recommend these for safety reasons. Circuitry has been discussed in these forums recently.

    Thirdly, I gave a broad brush treatment of the subject of SMPS. I also offered more detail if requested.

    Fourthly, the sequence of control signals that pass between the psu and the motherboard are as I described. They are most definitely at logic voltage levels, wave shapes and timings or the system will not activate. All 'logic levels' are achieved by electronic circuitry (including thyristors) when translated into hardware. So what?

    Computer smps usually incorporate a supervisory chip ( there are not many different models available) which performs this logic.

    Finally, if anyone going to repair a computer smps should be aware that the components have higher ratings than normally found. This applies to temperature, surge capability, Schotty rectifiers etc.
    Replacement with normal components will soon lead to the explosion you were worried about in the first place.
    Unfortunately these higher spec components are difficult for individuals to source.
  9. weekly

    New Member

    Feb 27, 2009
    These days,my Newton Power NPS-460BB was broken,no power.I found this page.Finally,I managed to fix it.It worked again.I am from Mainland of China.
  10. studiot

    AAC Fanatic!

    Nov 9, 2007
    This week I had in a Dell Dimension C521 in for service.

    The owner was adament that the power supply was blown and he wanted the psu replaced.

    "How do you know it is the psu?" I asked. He said that the machine wouldn't turn on and he had been told by a computer 'expert' it was the power supply.

    "Funny" I said, unplugging the psu from the motherboard and checking with my psu tester, "everthing reads normal here. This psu works perfectly"

    The vents from the processor cooling cowling were completely blocked with fluff.

    "How do you like your microprocessor?
    Lightly toasted?
    Well cooked?
    Burnt right through?"

    Welcome, Weekly.

    We would be interested to hear how you fixed your psu.
  11. gregdevid


    Feb 4, 2009
    Hi friend,

    In this critical situation u find all the systems hardware and other system parts. And be sure to check the wire with cabling.
  12. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
    Here is a useful Flowchart (literally) for working with "No Power On".

    First, is the 110/220 switch on the back all the way to the correct position? I've had some fun by moving it to the exact middle, you need to mess with it a very small amount at a time, so that both contacts are open. The fact it is stiff and hard to move keeps it there. Make sure nobody pulled that prank on your system. ;)

    Second, Voltmeter on system, NOT INSIDE POWER SUPPLY, between the black (ground) and grey (power good) wires on the wide white ATX connector. Also check between black and purple (Standby Power). If the power supply fan spins, check the other voltages at the ATX connector as well, Red = 5V, Yellow = 12V, Orange = 3.3V.

    If you have voltages on some lines and not others, you need to get a "real" power supply tester. They put a selectable heavy load on the supply, and have both LED's for Good/Not Good, and sometimes an LCD display as well that gives more information. You don't want to leave it running at max power longer than is needed for the test, though. the little fan can't keep up with 300-700W Dissipated. A basic tester is around $25 US, and is sufficient to load down a 250W (and higher, just not full load) with simple LEDs. I don't remember what my selectable load one cost, but it was major overkill, and it wasn't me paying for it.

    If it is determined the power supply is bad after the above info (including flowchart), then replace the PSU. Repairing a PSU sounds like a fun idea, and can be easy if something simple is broken, but is often an exercise in futility, not to mention dangerous to possibly lethal if you do not have the equipment and knowledge to work with them! The equipment is expensive, and the knowledge is gained by apprenticeship and hands on, only being shocked will remind many people. Thus, never work on Line powered items alone, or where nobody can hear you scream.
  13. studiot

    AAC Fanatic!

    Nov 9, 2007
    Although if you have a good 'engineering vocabulary' it may be best to work where no one can hear you!