Teac lcd2681fhdr, no stby

[attainteddragon]

SOME HISTORY ON THIS ONE (rather boring, skip to the entertaining part)

i got this one from another repairer that told me that he changed out ds3 (shottky diode on the secondary side). he applied power and said that it instantly took the diode out again. i found that the diode is ok and assume that he must of been having a late night and was probably delirious from tiredness. the only thing is that he replaced it with a matching spec of diode.

MY FINDINGS

there is no power on the secondary side of the p/s and have the unit on the bench.
this p/s is starting to look worse for wear as between both of us, we have removed a large chunk of this p/s trying to find the problem.

i have not been able to find a schematic.

p/n- LK-P1260412A made by leke
pcb no- CQC09001033440

i have 322v on the main filter cap (so pfc is there, just not boosted yet)
the 322v shows up on the 2 right hand pins on the transformer (as you look at it from the bottom), and the direct associated components.
i only have mvs on the start up cap (has been esr and capacitance tested)

i am unsure how the stby is derived from primary to secondary on this board. teach on this one. i'm used to a separate stby transformer.

i started looking at the stby ic (u102)
struggled to make out much of the info on it, so no data sheet.
but it looks like

top line (missing text)TBAAA
second line 753
third line mya

readings from this ic

pin
1- 58mv
2- 96mv
3- 0
4- 0
5- 0.08mv
6- 0.05mv
7- nc
8- 303v

i have been staring at this chip thinking that there must be a signalling voltage, but without a datasheet, i personally would just be guessing.


i'm sure someone will point out something that i should know.


thanks for reading my novel, hope i don't end up releasing a part 2.

[Andrew F. Ali]

Re: Teac lcd2681fhdr, no stby

This is an always ON PSU, so I don't think you would see a StdBy 5V, per say.

[attainteddragon]

Re: Teac lcd2681fhdr, no stby

if it is meant to be always on, it still has the issue with, well, not being on.

i have been searching through my spares to try and find a similar board to compare with,
as i know there a few variations of this board. but no luck yet.

i will also have to see if i can find a schematic from one of the other variants.

[R_J]

Re: Teac lcd2681fhdr, no stby

Try cleaning the top of the ic with alcohol It may show the numbers better. It might be a fan6753 ?????
Try replacing C132

[attainteddragon]

Re: Teac lcd2681fhdr, no stby

yeah, tried some iso then resorted to rubbing a tiny bit of thermal paste on it to highlight it a bit. i will try to see if i can get a pic of it with a different camera. my cannon doesn't do macro very well with the lens that i have.

[attainteddragon]

Re: Teac lcd2681fhdr, no stby

c132 was the one that i have already tested. blonde moment, didn't actually write down the location designator.

i think that you are right about it being a 6753. looking at the datasheet,
pin 5 and 6 have a low resistance to ground, so i will have to most likely order one.
i don't think that i have any laying around.

i'll update when i have it in.

[attainteddragon]

Re: Teac lcd2681fhdr, no stby

pics i got of the pfc ic.

[R_J]

Re: Teac lcd2681fhdr, no stby

c132 was the one that i have already tested. blonde moment, didn't actually write down the location designator.

i think that you are right about it being a 6753. looking at the datasheet,
pin 5 and 6 have a low resistance to ground, so i will have to most likely order one.
i don't think that i have any laying around.

i'll update when i have it in.

If pin 6 is low Ω to ground, check for a shorted diode (d107?) next to J53 jumper.
If pin 5 is low Ω to ground also check for shorted fet.

[attainteddragon]

Re: Teac lcd2681fhdr, no stby

D107 is good
lifted the fan chip and my low resistance on both pins is gone.
feeling confident on that chip being bad.

[Andrew F. Ali]

Re: Teac lcd2681fhdr, no stby

Yes it does appear to be the culprit here.