Page 5 of 5 FirstFirst 12345
Results 81 to 99 of 99

Thread: SMD id

  1. #81
    Premium Member
    Skepticist's Avatar
    Join Date
    Apr 2009
    Posts
    795
    Thanks
    214
    Thanked 379 Times in 323 Posts
    Rep Power
    269
    Reputation
    6960

    Default

    Does the backlight brightness seem ok with that current?
    Works out to be something like 10W or more of backlighting with the ~80V supply but designing it so close to that threshold was just asking for trouble eventually.
    You could even remove 2 of those resistors with no problems based on the figures recorded (would raise the voltage by 33% but still nowhere near the upper threshold of 630mV) - only if it still occasionally blacks out with 1 removed though

    Oops: 2 x 2 strings in series amounts to about 5W which is still a decent amount of lighting
    Last edited by Skepticist; 24-09-17 at 07:29 PM.

  2. The Following User Says Thank You to Skepticist For This Useful Post:

    loopyloo (25-09-17)



  • #82
    Senior Member

    Join Date
    Feb 2008
    Location
    Mid North Coast NSW . Australia
    Age
    61
    Posts
    1,545
    Thanks
    786
    Thanked 291 Times in 191 Posts
    Rep Power
    243
    Reputation
    3737

    Default

    Quote Originally Posted by Skepticist View Post
    Does the backlight brightness seem ok with that current?
    Works out to be something like 10W or more of backlighting with the ~80V supply but designing it so close to that threshold was just asking for trouble eventually.
    You could even remove 2 of those resistors with no problems based on the figures recorded (would raise the voltage by 33% but still nowhere near the upper threshold of 630mV) - only if it still occasionally blacks out with 1 removed though

    Oops: 2 x 2 strings in series amounts to about 5W which is still a decent amount of lighting
    Yeah it's plenty bright enough and I only run it at 50%.
    I remove one of the resistors and it didn't really make any difference to the readings. Wouldn't be good to remove too many eh? since they will run hotter. What about soldering a 10k across the 2.4k ? that would bring it down to 1935ohms to trick pin10 ?

  • #83
    Premium Member
    Skepticist's Avatar
    Join Date
    Apr 2009
    Posts
    795
    Thanks
    214
    Thanked 379 Times in 323 Posts
    Rep Power
    269
    Reputation
    6960

    Default

    The 2.4k won't make any difference as it's just a sort of disaster defence and kills any inrush to the capacitance of pin 10 but normal current through it will be microamps.
    Did the CRO show the -ve spike voltage shifted up a bit?
    The average you'd read on a voltmeter would depend on the PWM duty cycle
    My numbers show it would be quite safe to take another 4.7ohm resistor out - even if they're only 1/8th watt, 6 of them amounts to 750mW and the voltages measured like ~200mV max represents about 50mW dissipation. That upper trigger point (630mV) amounts to ~500mW dissipation (with 6 resistors) so those resistors would definitely be hot if the current was sustained at those levels for an extended time but it's actually much lower in this case.
    Last edited by Skepticist; 24-09-17 at 08:44 PM.

  • The Following User Says Thank You to Skepticist For This Useful Post:

    loopyloo (25-09-17)

  • #84
    Senior Member

    Join Date
    Feb 2008
    Location
    Mid North Coast NSW . Australia
    Age
    61
    Posts
    1,545
    Thanks
    786
    Thanked 291 Times in 191 Posts
    Rep Power
    243
    Reputation
    3737

    Default

    Quote Originally Posted by Skepticist View Post
    The 2.4k won't make any difference as it's just a sort of disaster defence and kills any inrush to the capacitance of pin 10 but normal current through it will be microamps.
    Did the CRO show the -ve spike voltage shifted up a bit?
    The average you'd read on a voltmeter would depend on the PWM duty cycle
    My numbers show it would be quite safe to take another 4.7ohm resistor out - even if they're only 1/8th watt, 6 of them amounts to 750mW and the voltages measured like ~200mV max represents about 50mW dissipation. That upper trigger point (630mV) amounts to ~500mW dissipation (with 6 resistors) so those resistors would definitely be hot if the current was sustained at those levels for an extended time but it's actually much lower in this case.
    No the (-) spike volts on the cro didn't look any different. Didn't check with multimeter yet but I will.
    I guess I'd better remove another one and check again.
    Last edited by loopyloo; 24-09-17 at 09:03 PM.

  • #85
    Premium Member
    Skepticist's Avatar
    Join Date
    Apr 2009
    Posts
    795
    Thanks
    214
    Thanked 379 Times in 323 Posts
    Rep Power
    269
    Reputation
    6960

    Default

    With 2 resistors removed, the array should measure around 0.78 ohm compared to 8 resistors which measured 0.59 ohm
    If that makes no difference you'll need to trace out the LED drive circuit to work out what's going on there

  • The Following User Says Thank You to Skepticist For This Useful Post:

    loopyloo (25-09-17)

  • #86
    Senior Member

    Join Date
    Feb 2008
    Location
    Mid North Coast NSW . Australia
    Age
    61
    Posts
    1,545
    Thanks
    786
    Thanked 291 Times in 191 Posts
    Rep Power
    243
    Reputation
    3737

    Default

    Seems like my replacement hand held oscilloscope isn't as good as the first one before it failed. It seems to float around a bit.

    I did some measurements then removed a second resistor.
    Multimeter readings all 8-135mV, with 7-158mV, with 6-182mV.
    The oscilloscope pretty much confirms the readings with 8 or 6 resistors, with the lowest spike around 140mV (6 resistors). Over a time the hand held floats down (so I found out) so the reading with 7 resistors would have been wrong.

    So I think it's time to set it up again in the loungeroom, I have a good feeling it's not going to fail with 6 resistors in there.
    Last edited by loopyloo; 25-09-17 at 01:08 PM.

  • The Following User Says Thank You to loopyloo For This Useful Post:

    Skepticist (25-09-17)

  • #87
    Premium Member
    Skepticist's Avatar
    Join Date
    Apr 2009
    Posts
    795
    Thanks
    214
    Thanked 379 Times in 323 Posts
    Rep Power
    269
    Reputation
    6960

    Default

    Clear of the worst case low current trigger point at last
    Fingers crossed it'll be way more reliable now with that ISNS voltage in the sweet zone all the time
    Last edited by Skepticist; 25-09-17 at 01:30 PM.

  • The Following User Says Thank You to Skepticist For This Useful Post:

    loopyloo (25-09-17)

  • #88
    Senior Member

    Join Date
    Feb 2008
    Location
    Mid North Coast NSW . Australia
    Age
    61
    Posts
    1,545
    Thanks
    786
    Thanked 291 Times in 191 Posts
    Rep Power
    243
    Reputation
    3737

    Default

    Yep fingers crossed but I'm pretty confident this time.
    Once again it's been a pleasure working with you ...Thanks.

  • The Following User Says Thank You to loopyloo For This Useful Post:

    Skepticist (25-09-17)

  • #89
    Premium Member
    Skepticist's Avatar
    Join Date
    Apr 2009
    Posts
    795
    Thanks
    214
    Thanked 379 Times in 323 Posts
    Rep Power
    269
    Reputation
    6960

    Default

    NP it's educational all round and fun as well - can't ask for much more

  • The Following User Says Thank You to Skepticist For This Useful Post:

    loopyloo (25-09-17)

  • #90
    Senior Member

    Join Date
    Feb 2008
    Location
    Mid North Coast NSW . Australia
    Age
    61
    Posts
    1,545
    Thanks
    786
    Thanked 291 Times in 191 Posts
    Rep Power
    243
    Reputation
    3737

    Default

    Been back in service since 7pm yesterday.
    No blackouts yet so looking good.

  • The Following User Says Thank You to loopyloo For This Useful Post:

    Skepticist (27-09-17)

  • #91
    Premium Member

    Join Date
    Jan 2008
    Posts
    3,730
    Thanks
    4,591
    Thanked 3,649 Times in 1,504 Posts
    Rep Power
    1008
    Reputation
    38242

    Default

    Oh, the suspense...!!!

    This thread is like ...


  • The Following User Says Thank You to tristen For This Useful Post:

    loopyloo (27-09-17)

  • #92
    Senior Member

    Join Date
    Feb 2008
    Location
    Mid North Coast NSW . Australia
    Age
    61
    Posts
    1,545
    Thanks
    786
    Thanked 291 Times in 191 Posts
    Rep Power
    243
    Reputation
    3737

    Default

    Quote Originally Posted by tristen View Post
    Oh, the suspense...!!!

    This thread is like ...
    Happy to keep you entertained.





  • #93
    Premium Member
    Skepticist's Avatar
    Join Date
    Apr 2009
    Posts
    795
    Thanks
    214
    Thanked 379 Times in 323 Posts
    Rep Power
    269
    Reputation
    6960

    Default

    One of those suspenseful experiences
    You only know it's fixed when it doesn't fail again

  • The Following User Says Thank You to Skepticist For This Useful Post:

    loopyloo (27-09-17)

  • #94
    Senior Member

    Join Date
    Feb 2008
    Location
    Mid North Coast NSW . Australia
    Age
    61
    Posts
    1,545
    Thanks
    786
    Thanked 291 Times in 191 Posts
    Rep Power
    243
    Reputation
    3737

    Default

    WOW ! ... 8 days and going well.
    Consider it fixed.

  • #95
    Premium Member
    Skepticist's Avatar
    Join Date
    Apr 2009
    Posts
    795
    Thanks
    214
    Thanked 379 Times in 323 Posts
    Rep Power
    269
    Reputation
    6960

    Default

    Collective sigh of relief
    If it was going to overheat you'd know by now

  • The Following User Says Thank You to Skepticist For This Useful Post:

    loopyloo (04-10-17)

  • #96
    Senior Member

    Join Date
    Feb 2008
    Location
    Mid North Coast NSW . Australia
    Age
    61
    Posts
    1,545
    Thanks
    786
    Thanked 291 Times in 191 Posts
    Rep Power
    243
    Reputation
    3737

    Default

    NOOOOOOOOOOOOoo !!!



  • #97
    Premium Member
    Skepticist's Avatar
    Join Date
    Apr 2009
    Posts
    795
    Thanks
    214
    Thanked 379 Times in 323 Posts
    Rep Power
    269
    Reputation
    6960

    Default

    Need a little clarification here
    IE have the gremlins been at it again?

  • The Following User Says Thank You to Skepticist For This Useful Post:

    loopyloo (10-10-17)

  • #98
    Senior Member

    Join Date
    Feb 2008
    Location
    Mid North Coast NSW . Australia
    Age
    61
    Posts
    1,545
    Thanks
    786
    Thanked 291 Times in 191 Posts
    Rep Power
    243
    Reputation
    3737

    Default

    Quote Originally Posted by Skepticist View Post
    Need a little clarification here
    IE have the gremlins been at it again?
    Backlights went out again yesterday, just once.
    Gonna have to wait and see how often it occurs.

  • #99
    Premium Member
    Skepticist's Avatar
    Join Date
    Apr 2009
    Posts
    795
    Thanks
    214
    Thanked 379 Times in 323 Posts
    Rep Power
    269
    Reputation
    6960

    Default

    Damn
    Challenges are, well, challenging
    Maybe just one more resistor?
    (If it becomes a regular thing that is)

  • The Following User Says Thank You to Skepticist For This Useful Post:

    loopyloo (10-10-17)

  • Page 5 of 5 FirstFirst 12345

    Bookmarks

    Posting Permissions

    • You may not post new threads
    • You may not post replies
    • You may not post attachments
    • You may not edit your posts
    •