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S3 Motherboard ?

Discussion in 'TiVo Series3 HDTV DVRs' started by Toshirick, Oct 31, 2013.

  1. Toshirick

    Toshirick New Member

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    Mar 19, 2006
    So Cal
    I have 2 Tivo series 3 (648) that the hard drives failed within a few months of each other and I imaged 2 new drives at different times WD AV-GP 2 TB AV Video Hard Drive WD20EURS and one of the series 3 works great.
    I also replaced the bulging caps on the power supply boards. One of the series 3 tivo was stuck in the powering up screen, new problem. I tried unplugging the fan and the tivo works with no problems, so i bought a new fan and tried it and still stuck in powering up screen and reboots. I checked the voltages and they are good.
    What I did was connected the fan directly to the power supply board 7.5 volts pins bypassing the mother board and everything is working. I have used it for about 2 months and it's been working (No Problems).

    Do you think it's the power supply board or the mother board?

    Thank you Rick
     
  2. unitron

    unitron Active Member

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    Apr 28, 2006
    semi-coastal NC
    Suggest you put a meter on the 2 pin header on the motherboard designed to run the fan and see what you get there.

    As far as I know, the 7.5 is only for the OLED display, and the fan header is fed from the 12 V line, although there's a pulse-width switching circuit in there to vary fan speed.

    If having a load on that header (and therefore a load on the 12 V rail) makes or breaks things, that indicates a fault in the 12V section of the power supply and the most likely cause is a bad cap or 2 or 3.

    I'll be back this evening with a cap list for the 648 of which is on which rail.
     
  3. Toshirick

    Toshirick New Member

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    Mar 19, 2006
    So Cal
    I will check the 12 volt line without the fan connected. If I connect the fan to the motherboard the hard drive does not spin up at all and the tivo goes into the reboot over and over.


    Thanks unitron! I will check the 12v with a meter and report back.

    The fan is connected to the 7.5 volt directly on the power supply board and operates the fan at one speed, but it appears to keep the Tivo in the normal operating temperature so far.



    Thanks again!
     
  4. unitron

    unitron Active Member

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    Apr 28, 2006
    semi-coastal NC
    With the fan disconnected, backprobe the plug that goes into the motherboard to check the +12 V (yellow wire), but check both pins of the fan header separately. One should probably read 0 Volts because it'll be grounded, and the other one should read somewhere between 0 and whatever the yellow wire reads, because it'll be the feed from the yellow wire taken and chopped up, switched on and off really fast, so that the fan sees a shot of full 12 V to overcome mechanical inertia, but the average voltage is lower and the fan goes from powered to coasting a few dozen times a second, or maybe a few hundred.

    Unless the circuit is set up so that one pin is always 12 V and the other one is being connected to and disconnected from ground to do the switching, instead.

    But see what both measure with the meter's negative lead grounded to the metal chassis on the side away from the power supply.

    Regardless of whether the low side or the high side of the fan is switched, it sounds like the extra load on the +12 Volt line draws just enough extra current to make the voltage sag just enough to cause mischief, so I'm suspecting bad caps on the 12 V rail whether they "look" bad or not.

    The 648 supply has 2 caps that I know of on the 12 V output:

    Yellow wire:
    C702 16V 470uF
    C701 25V 2200uF *

    (*since I bought this 648 used, it's not impossible that the 25V cap is a replacement and that it only needs to be 16V rated, so if your C701 is only a 16, don't worry about trying to find a 25--just don't go below 16)

    EDIT TO ADD:

    Got my hands on another 648 and checked the power supply and C701 is definitely a 25V

    END EDIT

    Those are most likely to be the culprits.

    The other caps that might need replacing on "a" 648 board (but not necessarily yours) are:

    7.5V
    Gray wire:
    C603 16V 470uF
    C601 16V 2200uF

    5V
    Red wire:
    C503 10V 3300uF
    C502 10V 3300uF
    C504 10V 3300uF
    C501 10V 3300uF

    3.3V
    Orange wire:
    C403 6.3V 1000uF


    and there are two others that seem to be further back upstream in the switching part--

    C401 6.3V 2200uF
    C402 6.3V 2200uF

    The big cap rated at 200 Volts and 470uF should be just fine, 'cause it doesn't have to work as hard, and the little caps that aren't near the heat sink(s) should be ignorable as well.

    One other thing you could try to see what happens would be to disconnect the hard drive and plug the fan back on the header (after disconnecting it from the 7.5 pin) and see if the TiVo boots up to the welcome screen and just sits there without blinking or rebooting. Just in case there's something from out of left field going on with the fan when it sees a full 12 Volts.
     
  5. Toshirick

    Toshirick New Member

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    Mar 19, 2006
    So Cal
    Unitron,

    Thanks I will order the caps C701 and C702 and then take the the Tivo apart and check the voltages and the other items you recommended and let you know.

    Thanks I really appreciate the direction in which to start and all the help.

    Rick
     
  6. dianebrat

    dianebrat I refuse to accept your reality TCF Club

    10,130
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    Jul 6, 2002
    boston'ish
    It's strongly recommended to review all the caps in teh power supply and replace any/all that might be failing/bulging and any that are the same manufacturer of a failing cap, in general replace them all.

    It's no longer a matter of if the caps in an S3 will go bad, it's a matter of when.
     
  7. unitron

    unitron Active Member

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    Apr 28, 2006
    semi-coastal NC
    What she said.

    A couple or 3 days ago I was also taking note of the caps on an S3 HD supply which I'd already brought back from the dead by replacing two caps about a year ago, and found a third which had started "roundtopping", so you can keep fixing it over and over, or do it once and be done.
     
  8. Toshirick

    Toshirick New Member

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    Mar 19, 2006
    So Cal
    I replaced all the caps including the large one 200 volt 470 uf. The only 3 caps that I have not changed are C220 47uf 50 volts, C227 47uf 25volt and C306 2.2uf 50 volt. I did not order those 3. Tivo did the same thing after changing caps. Switched power supply into the other S3 that I own that is working. The S3 that was working and the power supply that I changed all the caps and did the same thing as the other tivo unplug fan and it works. Exact problem as the other S3. Took the good power supply and put it in the tivo that wasn't working correctly and it works with the fan plugged in.

    Now I know its not the mother board :)

    Checked voltages 12.24 volts, 7.55 volts and 5.22 volts.

    Checked voltage on the Fan pins and it was 12.22. Same voltage if I went to case ground.

    I will order those three caps and change them and give it a try.

    Thanks
     
  9. unitron

    unitron Active Member

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    Apr 28, 2006
    semi-coastal NC

    Let me see if I followed that.

    Two more or less identical TiVos, but on one (TiVo A) having the fan plugged onto the fan header on the motherboard causes problems.

    Recapped power supply A on TiVo A.

    Problem remains.

    Putting power supply B in TiVo A fixes TiVo A, but putting power supply A into TiVo B moves the fan problem to TiVo B?

    Fans were NOT swapped between TiVos?
     
  10. Toshirick

    Toshirick New Member

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    Mar 19, 2006
    So Cal
    unitron,

    Yes exactly! I swapped fans also. Same problem.

    Rick
     
  11. unitron

    unitron Active Member

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    So the fan problem follows the power supply, regardless of which fan is in the equation?
     
  12. Toshirick

    Toshirick New Member

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    Mar 19, 2006
    So Cal
    Yes. I feel better knowing it's not the motherboard.
     
  13. unitron

    unitron Active Member

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    semi-coastal NC
    What are you reading on the orange wire on those power supplies when they're connected to a motherboard and hard drive and fan and plugged in?

    Check both.

    The fan is not a huge current draw, so if hooking it up is the tipping point, there's still something wrong with that one power supply.
     
  14. Toshirick

    Toshirick New Member

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    Mar 19, 2006
    So Cal
    Unitron,

    I will check and let you know.

    Thanks-Rick
     
  15. Toshirick

    Toshirick New Member

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    Mar 19, 2006
    So Cal
    Unitron

    I checked all the voltages with the fan plugged in.

    12.48 volts

    3.29 volts

    5.05 volts

    7.59 volts

    I have not checked the voltages on the good power supply.

    Thanks Rick
     
  16. unitron

    unitron Active Member

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    Apr 28, 2006
    semi-coastal NC
    Those readings are within spec, so I'm stumped.

    The symptom, add fan to power supply's total electrical load, get failure, implies that the fan is the straw that breaks the camel's back.

    Can you come up with a SATA data cable to temporarily replace the one that's part of the combo cable and power the hard drive from an external source?

    Apply power to the hard drive, then, with the fan not connected, power up the TiVo, let it boot all the way, then plug the fan onto the motherboard, and see what happens.
     
  17. Toshirick

    Toshirick New Member

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    Mar 19, 2006
    So Cal
    Unitron,

    I have a series 2 fan laying around so I connected it and the tivo worked. Wrong size fan, so I ordered a correct size new fan from weeknees and tried it and it work :D. I dont understand because I used the fan from the other S3 tivo and it did not work. Both tivos have fans that i purchased from amazon.

    I wanted to say thank you for all your help.

    Rick
     
  18. unitron

    unitron Active Member

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    Okay, armed with all of that information, I've come up with the only possible diagnosis of your problem.


    You have gremlins.
     
  19. Toshirick

    Toshirick New Member

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    Mar 19, 2006
    So Cal
    Nicely said. It makes no sense.

    Thanks again!
     
  20. unitron

    unitron Active Member

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    Your symptoms or my post?
     

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