Saturday, April 23, 2011

Compaq C500 - LED's Flash Rapidly, and never posts or starts


Unit arrives with following symptoms:
Flashing LED's on the power panel, and the power LED on the front edge flashes continuously. [See video]


When I connected the DC source with the battery inserted, I thought the charge light would come on as it should regularly. Since it didn't and flashed at the same rate as the other LED's this told me what area to check. When checking the MOSFETs PQ5, PQ49, and PQ4 all of them were of the same type [FDS4435] but PQ49 had a short in both directions with meter set to DIODE mode.  This indicates the FET is shorted. So that was the first thing to replace and test again. 


When I replaced the PQ49 FET and plugged in the charger (with battery inserted) the charge light came on, as it normally should.  Upon powering the unit, it posted normally on external monitor. 


Since it was a power in/charge circuit I assumed everything else was fine and reassembled the unit.  All items work. USB/Wifi and other peripherals.  So the unit was tested with OS loaded and everything fine there, and allowed the battery to fully charge. 



40 comments:

  1. hi mayo:i have one acer extensa problem is that display comming on external monitor but not comming on LCD of laptop.i have checked the lcd and also its cable on another laptop but it is ok the problem is there on motherboard.i have also checked the connector of lcd on motherboard it is also ok.so can u give any suggesation.thanks

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  2. What model ACER Extensa? Can you send

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  3. What model ACER Extensa? Can you send

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  4. is that GPU problem,will i reflow it.because one tech said that if display comming on external monitor it is because the external monitpr have seperate GPU.but i not agree with this.i think there is only one GPU on motherboard which works for both external and internal displays.what you say?

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  5. There is only one GPU. It may have a switch built in to direct output to LCD or External. They often use ALT-F4 to switch modes.

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  6. Mr mayo i know about switch but here i am asking about that in which area of motherboard will i check for fault for not comming display on laptop's LCD.i have checked every thing working fine.i am asking about chip level

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  7. You may want to check on the GPU or the graphics controller (if Intel).

    It may be needing a warm reflow, (not high temperature). Other than that, visually check the connector on the motherboard for the LCD, and also see if the back of the LCD is connected. Those are the only problem areas that may cause that problem. I try to avoid diagnosing problems, unless there is a know fault with a particular model.

    Good Luck

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  8. ya problem was in LCD connector.thanks for help

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  9. Hi, thanks for making this blog. I had this exact problem and fixed it using your excellent info. The laptop worked for a couple of days but will now not post.

    The symptoms have changed slightly - the charge light will go on with the battery and ac plugged in but when you power on the power light gives out two long flashes.

    Any ideas what may be causing this?

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  10. Hey Mayo, how can I get access to the C500 video?

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  11. i have a problem with my compaq c500 as there no power going to the inverter after the cable got cut into when hinge broke need help to locating what supply power on motherboard?

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  12. Yamada: That is impossible to tell. It could have shorted all the way back to the GPU. Or the GPU could have been the original problem.

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  13. Mr. Mayo,
    I have the same flashing LED problem. How did you test the MOSFETs? You went with SI4435 instead of FDS4435BZ are they better?

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  14. unknown: I don't quibble over specs. Many of them are virtually the same anyway. I use what is readily available. Some HP units will use Mitzuki Electronics parts. (ex: ME4468) and I change them with what I have if they are blown. I try to remember which ones are important and function, not which manufacturer is better. But I do feel the MExxxx are inferior to Fairchild's 'Power Trench' because they do not have Zener or Schotzky diodes in them for better switching and protection. But that is a preference, not a rule.

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  15. hey hi mayo this is mohammed shaikh,
    i have a Compaq presario c500, its power led keeps blinking n no display on the screen as well as on external monitor. please guide me which area to check as feel its a north bridge problem but i am not sure.

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  16. I'm not sure of every problem on every machine. I only post on what I find.

    When the unit exhibits no power, I check all the mosfets in the Power In circuit first. If that does not find the problem, I check the unit with a battery. If it powers on with battery, I check parts (Caps/Mosfets) in the Power circuit. It is usually a failed part in that area.

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  17. Excellent advice on the Presario C500 mosfet chip. I sourced the chips from a Chinese supplier on e-Bay and the instructions for disassembling on bukisa.com. My tip? - I tried a 15w soldering iron with a very fine bit, but it didn't transfer enough heat quickly enough. A 25w iron with a more standard bit did the trick, both for removing the faulty chip and soldering the new one in.

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  18. A 15w iron is for SMT parts really small diodes/resistors and such, and not for MOSFETs, some MOSFETs have a large heat dissipation surface on the bottom and will never get enough heat to be removed. For those I use a 45w iron.

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  19. I learned that lesson the hard way last night. My little WallyWorld iron just couldn't cut it. I will be upgrading.

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  20. hi Mayo I got an Acer Aspire 5516 aft heat up it freez then sleep/hibernate and restart some time any solution please

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  21. Adrian: That is to protect the computer from KILLING THE cpu/gpu by overheating. A cap that stores a charge keeps it off unit the cap discharges.

    If you don't solve the problem one of these times it may never come on. Clean the unit (blowing out the lint/dust) then clean heatsink and apply new thermal compound.

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  22. Thank you for this posting. Great information. Help me fix my Compaq laptop. Happy to donate to the "cause". Keep up the great work...

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  23. Hi. Useful info, and I would love to try this as I have these exact symptoms. Hoever on eBay I can find 3 variants of this chip - the SI4435DDY-T1-GE3, the SI4435DY and the SI4435DYPBF
    Which one do I need. My motherboard has the FDS4435 too.
    Would appreciate a response and will gladly donate if this helps me :)

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    Replies
    1. Check Newark Electronics for parts, not Ebay. Too much clutter, not enough info.
      www.newark.com

      Delete
  24. WMR Computers
    They are essentially the same, except the Fairchild (FDS4435) uses a zener diode in the mosfet. I guess this is to reduce the bounce when the power is applied.
    ?Here is the links for comparison.
    http://www.fairchildsemi.com/ds/FD/FDS4435BZ_F085.pdf
    and
    http://www.vishay.com/docs/72123/72123.pdf

    Any donations are greatly appreciated by all. Seems sometimes small, but it does go toward posting and knowing that details are appreciated.

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  25. Hi were you testing the FDS4435 on the board was it ok to test them this way?
    am getting readings on all pins on PQ49 and PQ4 but PQ 5 the last set of 2 pins is open not sure am testing them right?

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  26. Sorry just seen your how to test page i think my FDS4435A are drain to source and PQ49 is given me short circuit ie meter is showing 001 while the other 2 are around 541 and 580

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  27. Sorry how probe the mosfet? unmounted? you can upload a video. my laptop compaq presario c700 no charging any batery(tested new batery). only show conected and not charging on windows. i see from chile.

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  28. Thank you. I saved a friends Compaq C500 from the rubbish tip because of your blog. I have given you full credit here http://www.badcaps.net/forum/forumdisplay.php?s=26fd43d59781d9229da8ce5d91de4743&f=23. Thanks again.

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  29. Hi I have a HP Compag Presario C500 whit the same problem, I replace Mosfet PQ4, PQ5 and PQ49 whit mosfet SIA04407. Now the battery get charge wen i touch the power botton the light comes on, after a few secons it start to flash and stay that way. The unit dos not turn on.
    My Email is jorgeduard@hotmail.com or jchandler@pancanal.com

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  30. SIA04407 is not the same chip. I cannot find specs on that chip number.

    The chip in the pictures are SI4435BDY or SI4435DDY [30v P-Channel -11a]. If looking from exact replacement. Try Vishay.com Digikey.com or Newark.com, or Fairchildsemi.com (they have a cross reference table).

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  31. Dear mayo, I'm going to replace this defective mosfet with an AO4435 instead of FDS4435BZ, but some specifics are slightly different, do you think am I wrong doing so? Thanks for reply.

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    Replies
    1. I wouldn't recommend it. The Fairchild was there for a reason, and the AO has a higher current rating. I think it was -13a and the FDS was only -8a, Though it could handle it, you never know if the parts on the other side could handle the extra current. Especially if it was a short condition. As well as the Fairchild having a zener for additional protection. So the switch is not just turning on/off, it also limits the amount of current.

      So - Not recommended as a substitute.

      Delete
    2. Thanks for answering so fast, so I need to find FDS, could I have any suggestions where to buy those ones? In your previous post you said to stay away from e-bay (maybe because too many transistors are counterfeit?) Any trustable retailer in European Union? Thanks a lot in advance, regards

      Delete
  32. Dear mayo, I'm going to replace this defective mosfet with an AO4435 instead of FDS4435BZ, but some specifics are slightly different, do you think am I wrong doing so? Thanks for reply.

    ReplyDelete
  33. Dear mayo, I'm going to replace this defective mosfet with an AO4435 instead of FDS4435BZ, but some specifics are slightly different, do you think am I wrong doing so? Thanks for reply.

    ReplyDelete
  34. Hi, thanks for your valuable forum, I replaced the defective PQ49 and it was a very hard job for me, moreover I am a little worried because a bit of solder has dripped on the yellow dot to the left of the mosfet. Could i have damaged anything? What's the function of that yellow circle? Sorry for the stupid question, but i'm a beginner and very eager to know about. Thanks everybody, have a nice day.

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    Replies
    1. What yellow dot? The solder pad is a test point for meter probes.

      If you mean the solder pad that is directly left of the IC, it should be no problem. But you can use solder wick to remove excess solder. As stated previously this site is intended for techs. Especially if you don't have any experience with soldering. It is a delicate job, that cannot be learned or taught online. So be careful, that's all I can say to novices.

      Delete
  35. Looking at your picture, it's the yellow dot located 1 cm below the digit "2" of PR27, just touched by the rectangle in which PQ 49 is enclosed. I know this is a for techs site but I decided to have a try rather than throw the MB away. So is that a test point? Thanks again...

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I cannot repair laptops for you via the internet, I can only answer questions related to posts. This is because I have not had experience on every motherboard that is out there. Bear with me.

If you do need it repaired. Contact me for quote (US/CDN Only)

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