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help identify smd component in DTT set-top box

I am trying to repair a digital terrestrial set top box which had bulging caps, would shut down and had no audio. changed the caps, box works but still no sound. I discovered two small 3 legged smd transistors (at least I assujme thats what they are) burned, presumably due to high voltage and/or poor regulation from the faulty psu. The only reference visible on the components is a '2'. In the same pcb there are others marked '2A', so i'm assuming these two might be the same.

They are on the pcb as Q5 and Q6, and the pcbitself is maerked: HY650

39150 DST VER 1.7 (2004) and it has the Zoran supraTv chip

Now I know these are disposable items, but I don't mind investing a bit of time and effort trying to fix it, as it doesn't owe me anything. I'm all ears as to suitable equivalent parts. TIA

-b.

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b
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:I am trying to repair a digital terrestrial set top box which had :bulging caps, would shut down and had no audio. changed the caps, box :works but still no sound. I discovered two small 3 legged smd :transistors (at least I assujme thats what they are) burned, :presumably due to high voltage and/or poor regulation from the faulty :psu. : The only reference visible on the components is a '2'. In the same :pcb there are others marked '2A', so i'm assuming these two might be :the same. : :They are on the pcb as Q5 and Q6, and the pcbitself is maerked: HY650 :39150 DST VER 1.7 (2004) and it has the Zoran supraTv chip : :Now I know these are disposable items, but I don't mind investing a :bit of time and effort trying to fix it, as it doesn't owe me :anything. I'm all ears as to suitable equivalent parts. :TIA :-b.

Unless you can read the identifying codes on the burned devices you can't find out what the devices are. The only other method is to get a copy of the schematic. Your chances either way are probably zero.

Reply to
Ross Herbert

I assume that this is your equipment and are not trying for a profession repair. If the burned parts are just small signal bipolar transistors, I would remove the parts and use a voltmeter to try to figure out if they are NPN or PNP and identify which leads are C,B, and E. Just replace them with about any generic equalavent. You can even use thru hole parts in a pinch if there is space for them.

David

Reply to
David

On Mon, 15 Jun 2009 16:06:10 -0700 (PDT), b put finger to keyboard and composed:

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2A = 2N3906 / FMMT3906 / MMBT3906 / MMBT3906L / PMBT3906 / SMBT3906 / YTS3906/ MMBT3906W / PXT3906 / SXT3906

I'd check the other 2x numbers in the above reference.

FWIW, here are service manuals for three LG set-top boxes:

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Maybe they will give you a general idea as to how they work.

- Franc Zabkar

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Reply to
Franc Zabkar

Thanks franc. I discovered the two transistors were for muting. Removal restored the sound. that and changing the caps (C365-100uF, C143-2200uF AND ONE OTHER 330uF) and the unit seems to work ok. model in question: Mx-onda TDT MX-STB 5290.

2 of the bad caps were 'CHANG' mentioned here:
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hope this may be of use to others.

-B

Reply to
b

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