troubleshooting a tv power supply

R!f@@

Joined Apr 2, 2009
9,918
Something is bothering me, anyways, if it is used in an TV, then I got nothing more to say.
How are doing with measurements.
 

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johndoe45

Joined Jan 30, 2010
364
i'm not home. how do i check the filter capacitor. my DMM has a capacitance mode. is that a good enough test? alright. just saw your message before.
how many filter capacitors are there? just that one big one. so your saying if i desolder the bridge and leave FET out and the fuse blows it is the filter cap for sure? or probably
 
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R!f@@

Joined Apr 2, 2009
9,918
the line filters are the disc type blue colored caps. that are located at the input and near the inductors
But they seldom go bad, I think you have a leaky bridge
 

Thread Starter

johndoe45

Joined Jan 30, 2010
364
alright. thanks for your help. i'll go ahead and just buy a bridge rectifier anyway and try it out after i desolder and put power on and test voltage at two middle pins. it is like $2.75. and those capacitors how do i test them? just the capacitance test on my DMM?

one more thing. what solder gun would you suggest?

so if i had a PCB that worked. I could disconnect any component and turn on the power and the fuse won't burn? it only burns out if there is a short or defective component?
 

R!f@@

Joined Apr 2, 2009
9,918
Hmmm. That depends on your budget.
What types can you get.
Any thing around 24V 50W that can do 450°C max , with a variable temp control and have replaceable tips will be good.
I use hakko. By far they have given me years of faithful service.
Would you believe my soldering Iron is like a decade old and still works like new.
That's quality. And that will give you better performance

PS leave the line filters for now...caps will be OK
 

R!f@@

Joined Apr 2, 2009
9,918
Disconnecting components and doing what I do comes with experience.
You just cannot take out a component.
What if you take out a safe guard component.

One should know how the circuit works and does if one is going to repair it.

If you are not sure then don't tackle any thing high voltage.

I am telling you what to do cause I am confident that if you follow my lead you can fix it.
 

Thread Starter

johndoe45

Joined Jan 30, 2010
364
thats pretty good. I will have to check them out. going to bed. thanks for your help. i've learned so much and can you help me with these last two questions. tried asking robotics team for help at my school but were kind of not helping me too much cause i'm a Mechanical Engineer.

is the capacitance test good enough to test a capacitor?

and if i desolder anywhere on a working PCB will the fuse blow when i turn the power on? or does a fuse blow only when there is something wrong like a short?
 

R!f@@

Joined Apr 2, 2009
9,918
is the capacitance test good enough to test a capacitor?
Depends on the capacitance meter you use, I use a fluke one. And it has given my money's worth

and if i desolder anywhere on a working PCB will the fuse blow when i turn the power on? or does a fuse blow only when there is something wrong like a short?
Like I said, You should know what you are doing.
Fuses are there to protect the wiring in case of a short.
And yes fuse will blow if a short occurs respective to that fuse.

Just taking out a component might not blow the fuse, but it depends on what you are taking out. Besides they are there for a reason ;)
 

Thread Starter

johndoe45

Joined Jan 30, 2010
364
Rifaa. I took out the bridge rectifier and fuse didn't blow. does that mean the problem could be beyond the rectifier or it is the rectifier. i messed up the board when desoldering the rectifier. sucks. maybe it will still work. here is a picture.

voltage was at about 52 AC at the bridge rectifier at both points even though board was messed up a little at copper part. piece of actual board chipped off when getting bridge out. probably temp and bad desoldering technique. third time i took that bridge out.

there is not that much copper left on any of them. and as you see a piece of the board came off but the voltage could still be read in the half circle :(

could i super glue the chipped piece or just solder the new bridge rectifier in and make sure it is touching the half.

i need to get a new solder gun asap and get a finer tip.

what is the proper way to desolder?
what i do is heat up the solder and then put wick on top then heat up the wick. but can't seem to pick up all solder so i heat each pin up as fast as i can then try to wiggle the component out. as you can see the board chipped. :mad:
 

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R!f@@

Joined Apr 2, 2009
9,918
yeah! I can see that.. So leave the bridge out till I finalize every thing.
You can use single strand wires to complete the copper tracks, you do fine. you are applying too much pressure due to poor soldering iron.
Soldering takes a lot of practice to perfect.

The Voltage at the inner two pins of the bridge should be same as the mains voltage.
Keep the bridge out. And confirm this voltage for me.
By the way I suggest that you throw the old bridge away and get a new one.
 

R!f@@

Joined Apr 2, 2009
9,918
Big problem.....checking the pics.

weller is good, try to get the specs.
and yes you need to use a desoldering pump
 

R!f@@

Joined Apr 2, 2009
9,918
See the Pic.
The points indicating zero resistance. leave the bridge out
Power disconnected...cap discharged
measure the resistance between the 2 marked arrow heads.
One is connection from Neutral to Bridge
Other is Live to Bridge
Both should give 0Ω resistance..period.
Check fuse for 0Ω.
Tell me the unidentified component.
 

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johndoe45

Joined Jan 30, 2010
364
with fluke 117 fuse reads 0.3 Ω on auto range (don't know why. even when i touch just probes together its 0.2-0.3)

2nd pin from top is 1.1 Ω
3rd pin from top 1.2 Ω

analog meter they are all 0 Ω
but the other to go up and down from 1 to zero because of copper ring loss. if i go right in front of the bridge pins on the trace it is zero

unidentified component looks like wire. labeled PTH1 on board
 
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johndoe45

Joined Jan 30, 2010
364
yes i did.

analog meter they are all 0 Ω
but the other two go up and down from 1 to zero because of copper ring loss. if i go right in front of the bridge pins on the trace it is zero

unidentified component looks like wire. labeled PTH1 on board
 

R!f@@

Joined Apr 2, 2009
9,918
So every thing seems OK.
With the bridge out and power connected
measure the AC voltage as shown.
Confirm the 120VAC at both connector and the bridge pin
 

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johndoe45

Joined Jan 30, 2010
364
at connector 52 VAC and bridge 52 VAC

put probes in outlet. 123 VAC

i also left cable in outlet and measured voltage at the other end and was 123 VAC. so the cable is fine.

maybe resolder the big clump at connector???? (one nearest to top in picture in previous post-copper came off when the black burn marks happened. like 1/8th of it. not like the bridge ones)
 
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R!f@@

Joined Apr 2, 2009
9,918
Is the power cable OK.
Check the connector, use common sense to find this fault
Check connector, re solder the connections, do what is necessary to get the proper voltage
 
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