Author Topic: Sourcing a replacement transformer, LCD TV repair.  (Read 5469 times)

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Offline boba3

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Re: Sourcing a replacement transformer, LCD TV repair.
« Reply #25 on: September 25, 2018, 09:28:20 am »
the f601 fuse is ok.
in pins 3-5 of the ic601 there is no power supply.
what are the legs to check on the part of the primary? on the part of the primary there are 5 feet
 

Offline boba3

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Re: Sourcing a replacement transformer, LCD TV repair.
« Reply #26 on: September 25, 2018, 09:35:05 am »
looking at the tracks from f601 it goes through fb601 then goes to pin 5 of t601.
between gnd and pin 5 of t601 I have 320v
 

Online wraper

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Re: Sourcing a replacement transformer, LCD TV repair.
« Reply #27 on: September 25, 2018, 09:57:05 am »
what are the legs to check on the part of the primary? on the part of the primary there are 5 feet
One leg which goes to FB601, another which goes to IC601. If there is no power on pin 5, then first check if there is no short to ground. Then check components connected to it. As IC blew up, very likely there was high voltage applied to that pin through IC and something could blow up as well.
 

Offline boba3

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Re: Sourcing a replacement transformer, LCD TV repair.
« Reply #28 on: September 25, 2018, 10:10:32 am »
on the foot connected to FB601 and the ic601 there is no power supply.
pin 5 of ic601 is not short-circuited with gnd
 

Online wraper

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Re: Sourcing a replacement transformer, LCD TV repair.
« Reply #29 on: September 25, 2018, 10:15:58 am »
on the foot connected to FB601 and the ic601 there is no power supply.
I was meaning measuring winding resistance between those points.
 

Offline boba3

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Re: Sourcing a replacement transformer, LCD TV repair.
« Reply #30 on: September 25, 2018, 10:20:53 am »
sorry, about 1.5 ohm
 

Offline boba3

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Re: Sourcing a replacement transformer, LCD TV repair.
« Reply #31 on: September 25, 2018, 10:24:38 am »
is it normal that there is no power supply to pin 5? who gives him power?
 

Online wraper

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Re: Sourcing a replacement transformer, LCD TV repair.
« Reply #32 on: September 25, 2018, 10:35:07 am »
is it normal that there is no power supply to pin 5? who gives him power?
First small current is provided through R630, R631 from high voltage (path 1). This is so standby PSU can start, when it starts, then it powers itself fro auxiliary winding of T601 (path 2). If voltage on pin 5 never rises, either those resistors or R609 are open or something leaks the current to GND so voltage never rises.

 

Online wraper

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Re: Sourcing a replacement transformer, LCD TV repair.
« Reply #33 on: September 25, 2018, 10:36:52 am »
sorry, about 1.5 ohm
winding should be ok.
 

Offline boba3

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Re: Sourcing a replacement transformer, LCD TV repair.
« Reply #34 on: September 25, 2018, 10:50:43 am »
before R630 I have 78v, between R630 and R631 I have 38v, between R631 and R609 I have 38mv
 

Online wraper

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Re: Sourcing a replacement transformer, LCD TV repair.
« Reply #35 on: September 25, 2018, 11:29:04 am »
Well, something is leaking current to ground.
 

Offline boba3

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Re: Sourcing a replacement transformer, LCD TV repair.
« Reply #36 on: September 25, 2018, 12:04:25 pm »
I removed ic601 but at pin 5 I have 0.8v.What should I check?
 

Online wraper

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Re: Sourcing a replacement transformer, LCD TV repair.
« Reply #37 on: September 25, 2018, 12:25:51 pm »
First of all semiconductors connected to it, capacitors as well. I would start with ZD604, C613, D603. Just note that you should not power it on without ZD604 as something else may blow up due to possible overvoltage, or temporarily replace it with say 12V or similar zener diode and power on. You could also remove R607 to disconnect a large part of the circuit (to exclude it as a cause), just do that with IC601 still absent from the circuit.
« Last Edit: September 25, 2018, 12:27:24 pm by wraper »
 

Offline boba3

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Re: Sourcing a replacement transformer, LCD TV repair.
« Reply #38 on: September 25, 2018, 01:06:06 pm »
I removed ic601 from the board, to the pin ho0,8v, I replaced c613, I removed R607and I still have 0.8v to pin 5.
I checked zd604 and d604 but both of them are not open and are not shorted. do you advise me to replace them anyway?
 

Offline boba3

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Re: Sourcing a replacement transformer, LCD TV repair.
« Reply #39 on: September 25, 2018, 01:07:32 pm »
I try to take off the R616?
 

Online wraper

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Re: Sourcing a replacement transformer, LCD TV repair.
« Reply #40 on: September 25, 2018, 01:14:06 pm »
I try to take off the R616?
It won't change anything. It's part of the circuit you should not bother with.
 

Offline boba3

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Re: Sourcing a replacement transformer, LCD TV repair.
« Reply #41 on: September 25, 2018, 01:20:34 pm »
what do you suggest me?
 

Offline boba3

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Re: Sourcing a replacement transformer, LCD TV repair.
« Reply #42 on: September 25, 2018, 01:22:48 pm »
I try to take off the R609?
 

Online wraper

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Re: Sourcing a replacement transformer, LCD TV repair.
« Reply #43 on: September 25, 2018, 01:24:34 pm »
I removed ic601 from the board, to the pin ho0,8v, I replaced c613, I removed R607and I still have 0.8v to pin 5.
I checked zd604 and d604 but both of them are not open and are not shorted. do you advise me to replace them anyway?
If you removed R607 and problem still remains, you have a very small number of parts remaining. Diodes and zener should properly check as diode, conducting in one way only.
You could also remove D603, just in case it's leaky. And then remove remaining components one at a time and check how it works. Just as I said, replace ZD604 zener with something else to avoid damage by over voltage. If you don't have any, take ZD605 and place it instead of ZD604 temporarily.
 

Online wraper

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Re: Sourcing a replacement transformer, LCD TV repair.
« Reply #44 on: September 25, 2018, 01:25:10 pm »
 

Offline boba3

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Re: Sourcing a replacement transformer, LCD TV repair.
« Reply #45 on: September 25, 2018, 02:13:52 pm »
Yes, the diodes control them in diode mode and lead only one way. I removed the zd 605 and put it in place of the ZD604. I removed D603. now in pin 5 I have nothing, I have 13v between R631 and R609
 

Online wraper

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Re: Sourcing a replacement transformer, LCD TV repair.
« Reply #46 on: September 25, 2018, 02:23:05 pm »
I have 13v between R631 and R609
I don't really get it. They are directly connected together, how there can be 13V between them?
EDIT: I guess you mean 13V between point they connect and GND.
« Last Edit: September 25, 2018, 02:25:07 pm by wraper »
 

Online wraper

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Re: Sourcing a replacement transformer, LCD TV repair.
« Reply #47 on: September 25, 2018, 02:26:55 pm »
If you have 13V on one side of R609 and zero on other, then R609 would need to be failed open. But it contradicts previous measurments.
 

Offline boba3

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Re: Sourcing a replacement transformer, LCD TV repair.
« Reply #48 on: September 25, 2018, 02:35:08 pm »
yes I mean 13V between point they connect and GND.
what value should the R609 have?
 

Offline boba3

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Re: Sourcing a replacement transformer, LCD TV repair.
« Reply #49 on: September 25, 2018, 02:39:03 pm »
putting the ZD604 and ZD605 back to their original position I find on one side of the r609 I have 13v and on the other side 0.9v
 


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