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HP L1905 19" TFT monitor repaired

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    #1

    HP L1905 19" TFT monitor repaired

    Hi,

    I repaired an HP L1950.

    Symptom:
    - CCFL briefly on for a moment, the shuts down
    - Sometimes when repeatedly pressing on/off I could get the ccfl's
    to come on, albeit at rather low light output. No shutdown then at all.

    I had a spare trash picked HP 1940 with working electronics.
    So I Connected the panel to it: The ccfl's came on fine & showed excellent brightness.
    So panel was Ok.

    Checked the two output transistors in the inverter. Q808, Q809 They seemed fine.
    No bad caps. (well....they were cheap, Hp dissapointed me a bit, by using 'Elite' caps) Checked them for ESR, all good, except one in the standby circuit.
    Replaced those.

    Stiil symptoms kept the same...

    Then I checked the BEL-5A fuse. FP801
    (maybe I should have done that in the first place )
    It was 17 ohms...

    Hmm. It's a low value but it should have been around 0,5ohms.
    Replaced the fuse: monitor works fine for now

    Could it be by the fuse just beeing around 17 ohms, that still allowed
    the inverter circuit to work sometimes?
    You would think if there had been a severe short it would be at a much higher value?

    We'll see if the fuse blows again. but so far so good.
    I resoldered the HV transformers just in case. (was thinking of the infamous Benq LCD)

    Just for reference, In case someone repairs a similar monitor:

    Main SMPS & Inverter board part number: E162032 Vol 3
    Bad cap was C707 in standby part of the smps.
    Trade name: HP L1950
    Inverter fuse: FP801

    Greetings,
    Steven
    Last edited by steven.va; 03-16-2013, 02:55 AM. Reason: Title shows wrong model number. Would a moderator be so kind to replace 1905 with 1950? thanks!
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    #2
    Re: HP L1905 19" TFT monitor repaired

    Originally posted by steven.va View Post
    Could it be by the fuse just beeing around 17 ohms, that still allowed
    the inverter circuit to work sometimes?
    Yes. When the fuse isn't completely open, current will flow. It will act like a 17 ohm resistor.

    As you noted a good fuse should measure less than 1.0 ohms.
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      #3
      Re: HP L1905 19" TFT monitor repaired

      Originally posted by retiredcaps View Post
      Yes. When the fuse isn't completely open, current will flow. It will act like a 17 ohm resistor.

      As you noted a good fuse should measure less than 1.0 ohms.

      Thx!
      Monitor continues to work fine so far.

      Comment

        #4
        Re: HP L1905 19" TFT monitor repaired

        Thanks for your previous work and detail above Steven.

        I found a similar model number monitor, HP L1950g, but the power board number was identical, out in the rain yesterday. I thought at least I might be able to re-use the cool horiz/vert swivel mount that came with it.

        Left it in a boiler room overnight and powered it up this morning.

        Slightly different symptoms, with this one I found that the backlight wasn't coming on at all, but under good light I could see the monitors menu, then the desktop when a VGA cable was connected.

        Opened it up to find the same Elite caps, none looked bulged or leaking, and did a search to see if anyone had worked on this monitor/power board before and found this thread.

        Tested FP801 and found it open.

        Made a temporary bridge with a paper staple, and the monitor backlight comes on now, looks like a nice monitor.

        Why would the fuse go bad? Is there something else that we should be checking, or do these types of fuse deteriorate over time/use?

        Also, it might help future searches if the title was changed to relect the actual model number of the OP's monitor, L1950, not L1905.
        Last edited by tmcw; 11-23-2017, 07:49 AM.

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