Technosonic 1908

[sienoki]

Another project im hoping to fix..
This lcd tv i got from a friend to try and fix..no power lights no nothing dead.. has a ticking noise from transformer..after googling the psu (MSDV1901-ZC01(B) there was a common fault with the 2 schotty diodes on the heatsink..so i replaced them with MBR20100CT-20a-100v..still same issue and ticking noise remains

[Scenic]

Re: Technosonic 1908

check for shorts on the output(s) and replace the startup cap (usually 47uF 35-50V).
That's usually the first thing I try for ticking powersupplies.
If that's not it, look up the datasheet on the SMPS controller IC and start checking that one.

[sienoki]

Re: Technosonic 1908

check for shorts on the output(s) and replace the startup cap (usually 47uF 35-50V).
That's usually the first thing I try for ticking powersupplies.
If that's not it, look up the datasheet on the SMPS controller IC and start checking that one.

Is the start up cap usually in the psu area if so mine was 50v 22uf i replaced that 1 but no joy..where would i start testing now..thx

[sienoki]

Re: Technosonic 1908

where will that IC controller be..thx

[bbjunkie]

Re: Technosonic 1908

Is the start up cap usually in the psu area

See attached photo.

Controller is usually on the underside. Small surface mount IC

Post a pic of the underside, and the number on any chips close to the startup cap on the opposite side of the board.

I'm not the best person to be giving advice, I've got a PSU ticking at present and cant locate the source of the problem!

[PlainBill]

Re: Technosonic 1908

You're going to have to give us a little more to work with. I really prefer that the picture cover the entire board.. including the edges.

The controller could be the device fastened to the heat sink, it could be on the bottom of the board, or it could be on the top of the board, but in the shadows. It will be in the neighborhood of the very large cap.

PlainBill

[sienoki]

Re: Technosonic 1908

where will that IC controller be..thx

The 3 blue disc caps are c103..103m-1kv..c102..101k-1kv..c114..472z-y1 250v
how do i measure those..thx

r101 & r102 both 105 resistors measure.948m
r104..104 resistor..94.5k
r121..104 resistor..94.5k
r110..470 resistor..47.0
c109 & c106 yellow box caps.22k275v..MCY/HT BOTH MEASURE 1.816m
thx guys sorry for the poor pics im having to use my phone at moment..the circled cap was the 1 i replaced..theres no smds on underside of board..the ic attached to the heatsink has 6 legs & will need to desolder as i cant see any numbers on it clearly

[sienoki]

Re: Technosonic 1908

The 3 blue disc caps are c103..103m-1kv..c102..101k-1kv..c114..472z-y1 250v
how do i measure those..thx

r101 & r102 both 105 resistors measure.948m
r104..104 resistor..94.5k
r121..104 resistor..94.5k
r110..470 resistor..47.0
c109 & c106 yellow box caps.22k275v..MCY/HT BOTH MEASURE 1.816m
thx guys sorry for the poor pics im having to use my phone at moment..the circled cap was the 1 i replaced..theres no smds on underside of board..the ic attached to the heatsink has 6 legs & will need to desolder as i cant see any numbers on it clearly

I removed the big cap to get a good view of ic..it reads F1G45-CW0765R
also when i first changed the schotty diodes i kind of overheated the pads abit..so i added a trace..

[sienoki]

Re: Technosonic 1908

I removed the big cap to get a good view of ic..it reads F1G45-CW0765R
also when i first changed the schotty diodes i kind of overheated the pads abit..so i added a trace..

Whats this 4 legged item between yellow cupoid cap & large cap..
Ive to far only changed the start up cap would replacing all the caps give me any standby by light or power to backlights etc..or is my issue situated only within the psu area of the board..thx

The transformer or within that area has stopped ticking now but still dead..if i desoldered the transformer how can i test it to make sure its not dead..thx

[tom66]

Re: Technosonic 1908

That's a bridge rectifier.

-

What do the output voltages measure at?

[sienoki]

Re: Technosonic 1908

That's a bridge rectifier.

-

What do the output voltages measure at?

Am i testing the bridge rectifier with power on & on 20v setting on my multimeter..thx

[tom66]

Re: Technosonic 1908

Am i testing the bridge rectifier with power on & on 20v setting on my multimeter..thx

Use diode test.

BUT...

If the bridge rectifier is dead the fuse will blow or the power supply will not work at all.

It is probably not the cause of your problem.

[selldoor]

Re: Technosonic 1908

I am butting in here just on the side of safety.
I believe that the Bridge Rectifier is in the HOT part of the board
and it turns the 250v AC into around 370v DC so if you set your meter on 20v there will be smoke.
I am not sure which pins are AC and which are DC - it might say on the board? or you could get a data sheet for the part number.

I think you can test it power OFF as well but not as a voltage but as a diode Take a multi-Meter and switch it to Ohm x 1
Test between one of the "~" and "+" legs.
You should get either an almost-zero reading in one direction, and when you reverse the test probes, you should get an almost infinite reading.
Now try the same between this "~" leg and "-".
Same as above.
Now repeat the same tests with the other "~" leg, and "+", and then "-".
Same as above.
If you either get almost zero or almost infinite in BOTH directions, then the rectifier burnt out.

Reading previous bits it is unusual for the blue ceramic caps to fail and same goes for the box caps and even the BIG 400v or 450v cap

[sienoki]

Re: Technosonic 1908

I am butting in here just on the side of safety.
I believe that the Bridge Rectifier is in the HOT part of the board
and it turns the 250v AC into around 370v DC so if you set your meter on 20v there will be smoke.
I am not sure which pins are AC and which are DC - it might say on the board? or you could get a data sheet for the part number.

I think you can test it power OFF as well but not as a voltage but as a diode Take a multi-Meter and switch it to Ohm x 1
Test between one of the "~" and "+" legs.
You should get either an almost-zero reading in one direction, and when you reverse the test probes, you should get an almost infinite reading.
Now try the same between this "~" leg and "-".
Same as above.
Now repeat the same tests with the other "~" leg, and "+", and then "-".
Same as above.
If you either get almost zero or almost infinite in BOTH directions, then the rectifier burnt out.

Reading previous bits it is unusual for the blue ceramic caps to fail and same goes for the box caps and even the BIG 400v or 450v cap

When testing the legs of the rectifier from bottom side with power on it keep on tripping my fuse box..so im gonna leave this 1 as i dont want to blow myself up..thx

With the fluke 77 series II multimeter

I know my limits so thx guys for your help in troubleshooting this set but im gonna give him it back

[selldoor]

Re: Technosonic 1908

Good Idea!! (not blowing yourself up- not the edit) as Tom says probably not the problem

I removed the big cap to get a good view of ic..it reads F1G45-CW0765R

Almost missed this - I have attached what I think is the data sheet for it.
(or its equivalent)
I dont know enough to suggest how to test it but Plainbill or the others
will.

[sienoki]

Re: Technosonic 1908

I am butting in here just on the side of safety.
I believe that the Bridge Rectifier is in the HOT part of the board
and it turns the 250v AC into around 370v DC so if you set your meter on 20v there will be smoke.
I am not sure which pins are AC and which are DC - it might say on the board? or you could get a data sheet for the part number.

I think you can test it power OFF as well but not as a voltage but as a diode Take a multi-Meter and switch it to Ohm x 1
Test between one of the "~" and "+" legs.
You should get either an almost-zero reading in one direction, and when you reverse the test probes, you should get an almost infinite reading.
Now try the same between this "~" leg and "-".
Same as above.
Now repeat the same tests with the other "~" leg, and "+", and then "-".
Same as above.
If you either get almost zero or almost infinite in BOTH directions, then the rectifier burnt out.

Reading previous bits it is unusual for the blue ceramic caps to fail and same goes for the box caps and even the BIG 400v or 450v cap

When measuring this rectifier in dioide mode with above sequence i get .512 then .OL the reverse is .512 an almost zero?..thx

[selldoor]

Re: Technosonic 1908

That's half the test -looks good to me- picture worth a thousand words:
http://www.youtube.com/watch?v=dqkT6hF0O3E

Just found this