Announcement

Collapse
No announcement yet.

Norwood Micro / Star Logic M19BBK No Power

Collapse
X
Collapse
 
  • Page of 1
  • Filter
  • Time
  • Show
Clear All
new posts
Previous template Next
    #1

    Norwood Micro / Star Logic M19BBK No Power

    My next project involves an older 19" Monitor that I think was originally sold by Compusa, called Norwood Micro model M19BBK. I believe it was also sold under the name Star Logic.

    There is no power when pressing the button. No leds, nothing, completely dead. The ac adapter was swapped - no help.

    I checked a few things I could. All caps are flat and not leaking, so I guess that means they may be good or bad. The fuse (F2) is good and there is 12.33Volts at the fuse. The Diode at F1 (I thought fuses were normally labeled F_ ) meters out on the DMM diode setting and there is voltage, 12.33V on one side and 0 on the other using the board screw hole as ground for the probe. The regulator at U4 has no voltage - so power isn't getting that far. The component at U11 (which is right next to F2 by the power jack) (some sort of regulator?) measures 2.25V, 0, 12.33V (using board screw hole as ground). Theres another component at Q5 that has no voltage on any pin. BTW: I checked all voltages with the inverter board and LCD screen disconnected.

    It looks like the power to this board stops early in the circuit. I'm still very much a beginner at this, but hopefully someone can give me some tips on what to check.

    Pics are attached - let me know if you need any more info or pics.

    Thank you!!
    Attached Files
    Last edited by Rolin; 02-24-2012, 06:35 PM.
    Tags: None
    #2
    Re: Norwood Micro / Star Logic M19BBK No Power

    Originally posted by Rolin View Post
    The fuse (F2) is good and there is 12.33Volts at the fuse.
    Just to confirm, do you get 12.33V on both sides of the fuse?

    The Diode at F1 (I thought fuses were normally labeled F_ ) meters out on the DMM diode setting and there is voltage, 12.33V on one side and 0 on the other using the board screw hole as ground for the probe.
    I have never seen that before. If you check the diode with your diode check function, does it read out of range one way and between 0.4 and 0.7V the other way?

    The component at U11 (which is right next to F2 by the power jack) (some sort of regulator?) measures 2.25V, 0, 12.33V (using board screw hole as ground).
    What is the part number of U11? The part number will tell you whether the output voltage of 2.25 is correct or not.

    Normally, main/logic boards use 5V and then other regulators convert that into 1.8V and 3.3V. With an external power adapter, the preceeding observations may not be applicable.
    --- begin sig file ---

    If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.

    We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

    Please do not post inline and offsite as they slow down the loading of pages.

    --- end sig file ---

    Comment

      #3
      Re: Norwood Micro / Star Logic M19BBK No Power

      Thanks for your help RetiredCaps.

      1) Yes, I have 12.33V on both sides of the fuse- so fuse is good

      2) The diode reads "OL" one way, then .603 the other way. The meter is set to diode testing, and I should mention that I unsoldered 1 lead from the board so it was not in the circuit. I also metered the voltage (don't know if this helps or not, I just did it) - put meter on voltage setting (of course with both legs solder to the board for this), one probe on the screw ground and metered the red probe on both sides of the diode 12.33V one side and 0V the other leg. What did you mean "you haven't seen that before " - what exactly were you referring to?

      3) U11 part number is LM 78L05 442 .

      Looks like it's a Positive Voltage Regulator. I'm new to this, but I believe the data sheet for "05" means it should be 5 volts, whereas my reading is 2.275. Am I understanding this correctly? And if so is this the regulator the problem? Or is something else causing the low reading. Not much in the circuit in this area, so this regulator is highly suspect then ??
      Last edited by Rolin; 02-25-2012, 12:17 AM.

      Comment

        #4
        Re: Norwood Micro / Star Logic M19BBK No Power

        Originally posted by Rolin View Post
        The diode reads "OL" one way, then .603 the other way.
        That is a good reading for a diode.

        What did you mean "you haven't seen that before " - what exactly were you referring to?
        I was referring to the "F" designation being used for fuses, not diodes.

        3) I'm new to this, but I believe the data sheet for "05" means it should be 5 volts, whereas my reading is 2.275.
        From reading a bunch of books, I know enough now that the 78xx is a very popular IC. Same goes for any part with a 1117.

        Yes, the xx denotes the output voltage so a 78L05 should be outputting 5V DC.

        As you can see from the datasheet, the max input is 30V for a 5V output, so 12.33V is within spec.

        So the regulator you have is likely bad unless the caps flanking it are somehow bad, but my first guess would be the regulator itself. A replacement is about 48 cents on digikey.com.

        You are quickly learning about regulators now!
        --- begin sig file ---

        If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.

        We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

        Please do not post inline and offsite as they slow down the loading of pages.

        --- end sig file ---

        Comment

          #5
          Re: Norwood Micro / Star Logic M19BBK No Power

          I am learning! With a little help....!

          Yes, the F for a Diode seems strange.

          I'll place an order for the regulator and see what happens!

          Thanks again, and I'll post an update when I install the new regulator.

          Comment

            #6
            Re: Norwood Micro / Star Logic M19BBK No Power

            Retiredcaps, well once you said the 78XX was as common as the 1777 regulator, I just had to look at my heap of junk. What do you know, I found a 78L05 on an old scrap motherboard. Soldered it in and it worked beautifully.

            As I remember someone gave me this monitor about 5-6 years ago after it failed after only 1 year of service. So this monitor was only used for 1 year which makes it a pretty new - old monitor!

            Thanks again for the help ....

            On to my next project....

            Comment

              #7
              Re: Norwood Micro / Star Logic M19BBK No Power

              Originally posted by Rolin View Post
              As I remember someone gave me this monitor about 5-6 years ago after it failed after only 1 year of service. So this monitor was only used for 1 year which makes it a pretty new - old monitor!
              One reason why the 78L05 may have died in the first place is due to poor quality power coming from the AC adapter. That is, the AC adapter may have bloated caps not doing their job properly.

              A multimeter can measure the quantity of voltage, but not the quality of the voltage. For the latter, you need an oscilliscope.

              C_hegge, who is an active member here, hangs in the Power Supply Design and Troubleshooting forum does a lot of ATX power supply reviews and he uses a scope to check out the quality of the power on the ATX rails at

              http://hardwareinsights.com/wp/categ...upply-reviews/

              Take a look at some of the ripple graphs (sample review)

              http://hardwareinsights.com/wp/2011/...-round-up-2/9/
              Last edited by retiredcaps; 02-25-2012, 07:18 AM.
              --- begin sig file ---

              If you are new to this forum, we can help a lot more if you please post clear focused pictures (max resolution 2000x2000 and 2MB) of your boards using the manage attachments button so they are hosted here. Information and picture clarity compositions should look like this post.

              We respectfully ask that you make some time and effort to read some of the guides available for basic troubleshooting. After you have read through them, then ask clarification questions or report your findings.

              Please do not post inline and offsite as they slow down the loading of pages.

              --- end sig file ---

              Comment

                #8
                Re: Norwood Micro / Star Logic M19BBK No Power

                I was also wondering and concerned why it failed so soon after purchasing new.

                I believe these were fairly cheap monitors from CompUSA at the time - I think they sold around 2004 or 2005 for $300 or so - which at the time wasn't a bad deal. I've read reviews that these did fail. At some point I had another customer come in with a blown AC adapter from another one, so I swapped my good one for their bad one. I eventually opened up the AC adapter and found buldging caps - I replaced them, and that's the adapter I'm using on this monitor. So the caps have already been replaced on this one.

                I suspect this is a very cheap design, so I won't be surprised if the regulator or something else goes again - but hopefully with the new caps in the AC adpater, and the regulator (which is a different brand than the one I replaced) this will last for several years to come.

                I remember checking ripple in circuits over 25 years ago in class! I don't have a oscilliscope - so I guess I'll be working a little blind in some respects. I'll have to check out those links from C_hegge.

                Thanks again retiredcaps...

                Comment

                  #9
                  Re: Norwood Micro / Star Logic M19BBK No Power

                  I've seen this "diode instead of a fuse" thing before in a cheapo LCD monitor with an external PSU brick.

                  The board was labelled for 2 fuses more or less directly after the DC jack (power input).
                  One actually had a fuse, the other had a diode instead. I assume they did this so if someone plugs in a PSU brick with the wrong polarity, it won't end up frying the whole logic board (diode blocks it)
                  Last edited by Scenic; 02-25-2012, 12:17 PM.

                  Comment

                  Previous template Next
                  Working...
                  X