Author Topic: Circuit repair (Read 5434 times)

lesr389 · « **on:** November 08, 2015, 12:01:00 am »

I am trying to fix this board. I believe these are fuses that need to be replaced. How can i find out what these are or where i can buy new ones?

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tec5c · « **Reply #1 on:** November 08, 2015, 12:16:22 am »

As discussed in your other thread, they are not fuses, they are diodes.

Testing these as you would test a fuse would show an open circuit (leading you to think they are faulty fuses)

Ian.M · « **Reply #2 on:** November 08, 2015, 12:19:14 am »

If the reference number marked by silkscreen on the PCB next to them starts with 'D', that would confirm they are diodes. Its rare to have anything other than a diode or occasionally a small capacitor in a clear glass MELF style cylindrical package.

lesr389 · « **Reply #3 on:** November 08, 2015, 03:13:12 am »

Yeah d11 d12 and d13. How can i find a schematic or find out what kind of diodes the are ie. Voltage

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lesr389 · « **Reply #4 on:** November 08, 2015, 03:14:13 am »

Oh i see...i havent checked for cont.

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tec5c · « **Reply #5 on:** November 08, 2015, 03:22:29 am »

In your other thread you said you thought they were fuses and that they were faulty. How did you come to the conclusion that the circle components are the cause of the fault?

Edit: Seeing as you have made two threads for the same topic I suggest you only reply to this thread as it is in the repair forum.

Do you own a digital multimeter? This would be how you test the diodes to know if they're faulty or not.

What is the brand/model of the TV?

Ian.M · « **Reply #6 on:** November 08, 2015, 04:05:41 am »

From the other topic:

Quote from: lesr389 on November 08, 2015, 12:06:07 am

I am trying to repair a TV. The hdmi ports stopped working one at a time. There are 3 ports. What i think are fuses apear to be bad. Can anyone confirm this and maybe tell me where i can buy new ones?

All the diodes look visually OK with no blackening or cracking so I don't know where you got the idea that one of them is 'burnt'. Careful testing with a DMM would at least tell you if they are shorted, which would be the most likely failure mode.

All the HDMI lines look like they go to U6, the TMDS351 3-to-1 HDMI Switch chip, and the symptoms would match it having failed, probably due to ESD damage, but possibly due to a faulty external device that applied out-of-spec signal levels to the HDMI port it was plugged into.

lesr389 · « **Reply #7 on:** November 08, 2015, 04:10:49 am »

A friend of mine gave me the TV. I didnt think devices would deliver damaging signals (high voltage) so i should probably tell him what ever he was using couldve caused it

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lesr389 · « **Reply #8 on:** November 08, 2015, 04:12:00 am »

Yes i have a pretty good fluke. Im not 100% on testing diodes

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lesr389 · « **Reply #9 on:** November 08, 2015, 04:12:38 am »

The tv is an apex ld4088

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Ian.M · « **Reply #10 on:** November 08, 2015, 04:22:30 am »

Its also possible its just corrupted service settings. If the part of the NV memory that tells the system controller's firmware what options are present on your model has the wrong data, the syscon may not know how to switch to the correct input. As connector J13 isn't present on the PCB, and it taps into all the HDMI3_IN lines to its fairly likely that there is another model variant that has different options - maybe a different input board on J13.

lesr389 · « **Reply #11 on:** November 08, 2015, 04:34:11 am »

Would that make the ports go out one at a time? And how can i test it

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crispy_tofu · « **Reply #12 on:** November 08, 2015, 04:45:05 am »

Quote from: lesr389 on November 08, 2015, 04:12:00 am

Yes i have a pretty good fluke. Im not 100% on testing diodes

To test those diodes, switch the multimeter to diode mode ( >| )and put the red probe on the side of the diode furthest to the black stripe. Then put the black probe on the side closest to the stripe. The reading should show less than 1V.

lesr389 · « **Reply #13 on:** November 08, 2015, 04:47:19 am »

Quote from: crispy_tofu on November 08, 2015, 04:45:05 am

Quote from: lesr389 on November 08, 2015, 04:12:00 am
Yes i have a pretty good fluke. Im not 100% on testing diodes
To test those diodes, switch the multimeter to diode mode ( ?| )and put the red probe on the side of the diode furthest to the black stripe. Then put the black probe on the side closest to the stripe. The reading should show less than 1V.

But i dont have to remove it like i would with a cap right?

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lesr389 · « **Reply #14 on:** November 08, 2015, 04:48:36 am »

And if the chip was bad how could i check it

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Ian.M · « **Reply #15 on:** November 08, 2015, 04:55:55 am »

Corrupted service settings could kill one port at a time, but it would be just as likely to kill them all or kill something else like the tuner. You cant fix that sort of thing without the service manual. If you are lucky, that + the original remote is all that's needed, but on some makes/models you need a specific test jig or a PC interface cable and special service software.

U6 is only a $6 USD chip, so if you cant find a free copy of the service manual, getting someone experienced at SMD rework to change it would probably be a worthwhile gamble.

lesr389 · « **Reply #16 on:** November 08, 2015, 07:54:25 am »

How can i know for sure its the chip?

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tec5c · « **Reply #17 on:** November 08, 2015, 09:18:49 am »

Do you own or have access to an oscilloscope?

lesr389 · « **Reply #18 on:** November 09, 2015, 05:58:24 pm »

I might be able to use one at work

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Author Topic: Circuit repair (Read 5434 times)

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