Repairing Router Power Circuit

Discussion in 'General Electronics Chat' started by hazim, Apr 10, 2011.

  1. hazim

    Thread Starter Active Member

    Jan 3, 2008
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    Hi all

    I have 6 router and access point (from edimax) devices that want to repair. Their supply voltage is 12V. These devices were damaged when the supply voltage terminals were reversed in mistake.

    I opened them, they have an smps power circuit to feed the circuits, an 8-pin SOP IC is broken (physically) in all the devices. It's the same IC in some of them which is FSP3126 and the others have IC AP34063.. The devices are not identical. These ICs are for DC-DC step-down conversion.

    Now the problem is that these ICs are not available in Lebanon, and I tried to find a replacements for them (uselessly). I'm thinking if there is a single fixed voltage output for the powering circuit, then I could simply make a linear dc-dc converter. But I wonder if this is true since the wall adapter supplies any regulated voltage and current the router needs..

    Any idea? and please what 2A diode I can use to protect these devices? I'm looking for minimum drop voltage possible.

    Regards,
    Hazim
     
  2. SgtWookie

    Expert

    Jul 17, 2007
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    If the 12v supplies were designed to feed a switching supply, a linear regulator won't be efficient enough to deliver the required power, and will dissipate too much heat inside the router/access point enclosures.

    You will need an efficient switching power supply.

    As far as the diode, you might use a 1N5820 through 1N5822 3A Schottky diode, but that will also decrease the overall efficiency of the supply.
     
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  3. hazim

    Thread Starter Active Member

    Jan 3, 2008
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    Thank you for the diodes.. I'm thinking if using two or three 1N5817~1N5819 in parallel may decrease the voltage a little more.

    The routers/access points are fed from 12V DC source yes. They have a multilayer PCB and the power circuit is not separated from the circuit board.. so it's not easy to replace the power circuit with another. The rest of the circuit board and components are mostly not corrupted, that's why I want to fix these devices. What do you advice me to do especially that I don't know what output/outputs the power circuit has..? through them in the garbage?:(
     
  4. SgtWookie

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    Well, you could look at the datasheets for the FSP3126 and the AP34063 (the latter is similar to the OnSemi MC34063)

    A datasheet for the FSP3126 is here: http://www.vivichip.com/datasheet/FSP3126 Datasheet 20070124-1.0.pdf

    A datasheet for the MC34063 is here: http://www.onsemi.com/pub_link/Collateral/MC34063A-D.PDF

    You could figure out what the output voltage is supposed to be by measuring the resistive divider on the board. You will need to isolate the upper resistor from the regulator output and board supply filter caps/voltage rail.

    I don't know what kind of switching regulators that you can obtain in Lebanon, and I won't have the time to research it for you. I tried looking on one of your suppliers' websites before, and it was very time-consuming to find things.
     
  5. SgtWookie

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    Diodes in parallel generally do not work very well unless their Vf's are matched. One diode will have a lower Vf than the others, and will get more current, making it hotter and the Vf drops more, making it hotter - until the diode suddenly burns up. Then the other two diodes have to share the load; one conducts more than the other, and heats up more quickly. Once it burns out, the remaining diode is badly overloaded and burns out very quickly.

    It is your decision. You might learn a good bit about switching power supplies by carefully observing how they were designed, re-constructing the circuit using schematic drawing tools, and then attempting to repair a couple of them. However, it will probably take quite a bit of your time, and you will need to study how the existing switching regulators work, and then try to design an equivalent circuit that is just as efficient.

    I'm sorry, but I simply do not have that much time available to help you with it.
     
  6. R!f@@

    AAC Fanatic!

    Apr 2, 2009
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    post pics, may be I can help
     
  7. hazim

    Thread Starter Active Member

    Jan 3, 2008
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    SgtWookie, I've already seen the datasheets and tried to find an available replacement in Lebanon. To understand the circuit and design another one will take a lot of time and effort and money... and the results are not guaranteed.
    I should repair them for someone and each device repairing should not cost more than 20~25$. So I see it's better to not repair them. I know from the beginning that repairing them will not be that easy but I asked here because you professionals may give me a good idea to go through. I respect you for trying to help me (and others in this forum).
    BTW, I know what you said about paralleling diodes, but I see this is theoretically true but if you used similar diode parts (and better to be from the same manufacturer.. and pack), then what you said will hardly happens. I see 12V car battery chargers uses several 6A diodes in parallel for rectifying.

    R!f@@, sorry for the picture it's not clear... Anyway I don't think a picture will benefit.

    Regards,
    Hazim

    [​IMG]
     
  8. R!f@@

    AAC Fanatic!

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    I think that is a DC to DC converter
     
  9. SgtWookie

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    That was stated in Hazim's first post, 2nd paragraph, where he mentioned that "some of them which is FSP3126 and the others have IC AP34063". The AP34063 is basically the same as OnSemi's MC34063 series.

    As I mentioned before, he'd have to design a DC-DC converter that was at least as efficient as those the routers came with, or the external supplies would probably not be able to keep up - or if lead-acid batteries, would drain them much more quickly.
     
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  10. hazim

    Thread Starter Active Member

    Jan 3, 2008
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    Ok, now I knew that MC34063 is available in Lebanon. One device uses this IC (AP34063/MC34063), 3 devices use FSP3126 which is not available, and there still a device that uses IC MP1583DN, this IC is not available also, but there maybe another manufacturer that name it another name/prefix as the first IC, so I will search for that name and may find the IC.

    MP1583DN datasheet: http://www.bb-electronic.de/mp1583rev1.8.pdf

    Regards,
    Hazim
     
    Last edited: Apr 13, 2011
  11. SgtWookie

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    Since you can get the MC34063, perhaps you can determine what output voltage the other SMPS IC's were generating by the feedback resistors, and then build some custom supplies using the MC34063.
     
  12. hazim

    Thread Starter Active Member

    Jan 3, 2008
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    The Other two ICs have 3A output switch current while that of MC34063 is 1.5A only. Also getting the right inductors needed is not easy in Lebanon..

    I'll try to fix that device which uses MC34063.

    Still thinking if I can get some adjustable step-down smps than can fit my need.
     
  13. SgtWookie

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    Perhaps someone else can help you with that.

    I simply do not have time to research all of the SMPS IC's that have been made in the last few decades that might be suitable, and present them to you in a list form.
     
  14. hazim

    Thread Starter Active Member

    Jan 3, 2008
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    I'll try. I really want to thank you very much not only because you tried to help me in this thread or other threads, but also because you try to help anyone in this great forum which doesn't have a single ad on it... Thank you..
     
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