tv smps need help for identifying smd

tv smps need help for identifying smd components

Hello, would like to ask you fir some help. I am working (for some time now) on SMPS from LG plasma TV. I have found
bad smd transistors (or diodes?) and capacitor without any markings on it. Could someone take a look? Any help would be appreciated! ;]

Hi,

Yes, I took a look on your picture.

What exactely is your question?

Klaus

In my photo I marked (with blue squares) two smd transistors (i hope it's a transistor) which are open and smd cap near dridge rectifier which is in question (reads shorted in circuit), they don't have any codes or markings (to identify) on them. So my question is could you suggest me alternative parts for these components to replace. I couldn't locate any schematics of these smps.

Hi,

* impossible to see any part details in your photo.
* I doubt you can verify the function of the devices "in circuit"
* without detailed type / name of the tv, nobody can look for a schematic.

Hopefully the designer of this board sees your thread and can help you.

Klaus

I know everything about TV

LG plasma 42PXRVB ZA and this SMPS is SANKEN PSC10089G M hope that helps.

All parts metiond where pulled out of circuit and tested as it is.

Is it even possible to find commecrial TV's smps scehmatics? It seems that manufacturers keep it in secret.

Hello seldon,
To confirm that the cap in question is actually short circuited, you need to remove and
measure it out of circuit.
Once its out and you find it ok, then the short is elsewhere. But more than likely one
of your semiconductors is the real culprit. Caps rarely go SC. Also, most non-polarized
SMD caps are tan in color, compared to resistors being black. Its a tad hard to see the
cap/resistor in question. You need to provide a more focused picture.
SMD caps won't have any marking on them at all. But the common values on them are
usually 0.1uF or 0.01uF.
You need to measure (with an ohm-meter) across the point where the cap/resistor was
sitting. If there still is a short then you need to trace that track back and isolate anything
associated with the rail that's shorted, but not the ground rail. But use the ground rail
as your reference to measure the shorted rail.
By the way, has the main fuse blown? If so, how violent was it? If its a non-glass type,
then the last question is moot.
If the SMD transistors have a circuit designation of Q or Tr, then they will more than likely
be transistors or FET's. But unless there are actual identifying marks on the transistor bodies,
it would be near impossible to determine their type without a schematic diagram.
As I strain my eyes to see any circuit designations, the transistors in question are marked
with "Q".
Since these transistors are mainly the switching types, you could replace them with standard
SMD transistors, such as: BC846 (NPN) or BC857 (PNP).
Your only problem is in determining what types yours are i.e. NPN and/or PNP's. You need to
also determine the pin-outs of each i.e. B, C and E.
You really need to remove the transistors to determine 100% that they are shorted. But measuring
them in-circuit should be done with an ohm-meter, and not the diode check. If it just reads low ohms
and not a dead short, then more than likely those transistors are serviceable.
Is there any way you can get a more closer picture taken of the solder side of the PCB?
Also would be good to get a picture of the component side as well.
Regards,
Relayer