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.

On Mon, 15 Jun 2009 16:06:10 -0700 (PDT), b wrote:

: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,
resumably due to high voltage and/or poor regulation from the faulty
su.
: The only reference visible on the components is a '2'. In the same
cb 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.

"Ross Herbert" wrote in message
...
On Mon, 15 Jun 2009 16:06:10 -0700 (PDT), b
wrote:

: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,
resumably due to high voltage and/or poor regulation
from the faulty
su.
: The only reference visible on the components is a '2'.
In the same
cb 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.

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

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

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

http://www.elektronikjk.republika.pl/s1.html

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:

http://www.jordansmanuals.com/Defaul...Model=LST6100P

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

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

On 17 jun, 09:28, Franc Zabkar wrote:
On Mon, 15 Jun 2009 16:06:10 -0700 (PDT), b
put finger to keyboard and composed:

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

http://www.elektronikjk.republika.pl/s1.html

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:

http://www.jordansmanuals.com/Defaul...duct=Set-Top-B...

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

- Franc Zabkar
--
Please remove one 'i' from my address when replying by email.

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 hehttp://www.badcaps.net/
forum/showthread.php?t=388&page=5&pp=20
hope this may be of use to others.
-B