Toshiba 42HL67US blows fuses.

[wickedwill]

My dad asked me to take a look at this tv and i am not really a tv repairman. i do work on computers so i a little familiar..

PROBLEM:
He states that tv worked fine before a power failure. when power was restored tv failed to work. he brought it to me.. i observed no red led when plugged in. so i took off back.. replaced fuse. plugged in and poof. fuse popped immediately.

not sure what to do next.. i suspect rectifier but there appears to be more than one.. help

[capkid]

Re: Toshiba 42HL67US blows fuses.

I could be wrong, but this seems like a time-consuming endeavor. You could be walking into a minefield of issues with a failure caused by a power outage. Unless you're looking to turn this into a learning experience and you're not pressed for time, I'd just buy a replacement power supply. I saw a couple used supplies for this particular TV on eBay for less than $50.

[wickedwill]

Re: Toshiba 42HL67US blows fuses.

I could be wrong, but this could be a time-consuming endeavor. Unless you're looking to turn this into a learning experience and you're not pressed for time, I'd just buy a replacement power supply. I saw a couple used supplies for this particular TV on eBay for less than $50.

well i am always eagor to learn a thing or two..and from what i can tell, this could teach me how to make a few dollars.. many lcd tvs in the garbage lately. suspect most may not be really hard to fix...hopefully..

[wickedwill]

Re: Toshiba 42HL67US blows fuses.

well i am always eagor to learn a thing or two..and from what i can tell, this could teach me how to make a few dollars.. many lcd tvs in the garbage lately. suspect most may not be really hard to fix...hopefully..

forgot to include picture of power board

[capkid]

Re: Toshiba 42HL67US blows fuses.

well i am always eagor to learn a thing or two..and from what i can tell, this could teach me how to make a few dollars.. many lcd tvs in the garbage lately. suspect most may not be really hard to fix...hopefully..

I thought the same thing when I first started fixing TVs; the fixes shouldn't be that hard..."probably just blown caps". I can't remember the last time I fixed a TV that only had blown caps.

I'd check the bridge rectifier(s) first, since your fuse is blowing.

[wickedwill]

Re: Toshiba 42HL67US blows fuses.

i am not sure which one is the rectifier(bridge) as i see two on the board.. one is attached to a heat sink.. the other is near fuse where ac comes in

[retiredcaps]

Re: Toshiba 42HL67US blows fuses.

i suspect rectifier but there appears to be more than one.. help

While possible, I have never seen more than one bridge rectifier on a power board. It is that long black 4 pin device just SE of the glass fuse.

With power off you want to see if it shorted between pins 1-2, 1-3, 1-4, 2-3, 2-4 and 3-4. Report all 6 ohms readings.

[retiredcaps]

Re: Toshiba 42HL67US blows fuses.

i am not sure which one is the rectifier(bridge) as i see two on the board.. one is attached to a heat sink.. the other is near fuse where ac comes in

The one attached to the heatsink is likely your power mosfet. You can see if it is shorted using the same test method I wrote for the bridge rectifier.

[wickedwill]

Re: Toshiba 42HL67US blows fuses.

The one attached to the heatsink is likely your power mosfet. You can see if it is shorted using the same test method I wrote for the bridge rectifier.

ok i am gonna test the one you said should be the bridge..the one that is attached to heat sing looks like the other one it has 4 leads also.. but i will check.. one question though you say i shoud check ohms.. my meter has diode meter. should i use that? if not and i use ohms.. what level should i set it at?

[retiredcaps]

Re: Toshiba 42HL67US blows fuses.

if not and i use ohms.. what level should i set it at?

If you have a manual meter, set it to two hundred (200). See this post (section on multimeter and shorted mosfet)

https://www.badcaps.net/forum/showpo...4&postcount=19

[wickedwill]

Re: Toshiba 42HL67US blows fuses.

With power off you want to see if it shorted between pins 1-2, 1-3, 1-4, 2-3, 2-4 and 3-4. Report all 6 ohms readings.

assuming 200k ohm settings...

pin 1-2, 131.1
pin 1-3, 133.0
pin 1-4, 00.1

pin 2-3, no number or 1
pin 2-4, 130.1

pin 3-4, 132.3


if u need me to include numbers for diode meter...

pin 1-2, 563
pin 1-3, 562
pin 1-4, 001

pin 2-3, 1399
pin 2-4, 563

pin 3-4, 562

hope this helps

[retiredcaps]

Re: Toshiba 42HL67US blows fuses.

pin 1-4, 00.1

Remove this component and retest out of circuit. If pin 1-4 still reads 0.1 ohms, then it is shorted (bad).

A shorted bridge rectifier and/or power mosfet will cause the fuse to go .

[retiredcaps]

Re: Toshiba 42HL67US blows fuses.

With power off

Just for your education, resistance readings are always done with power off and the device unplugged from the AC outlet.

[retiredcaps]

Re: Toshiba 42HL67US blows fuses.

Check the power mosfet as well. It is not uncommon to have multiple shorted components depending on the nature of the failure.

[retiredcaps]

Re: Toshiba 42HL67US blows fuses.

I can't remember the last time I fixed a TV that only had blown caps.

Currently, feedback according to most regulars and professional techs here on badcaps, the percentage of TVs fixed due purely to obviously bad caps is around 5% or less.

Knowing how to troubleshoot a SMPS power supply, IMHO, is a good lifelong skill to have since almost every modern consumer electronic device that is AC mains powered has one.

[wickedwill]

Re: Toshiba 42HL67US blows fuses.

ok got that rec out..

seems pin 1-4 whether i use red on 1 and black on 4..or reverse that.. gets no reading..

have ot checked the mosfet yet.. gettin late.. but will do first thing in morning if ness..

[tom66]

Re: Toshiba 42HL67US blows fuses.

Please clarify "no reading": what do you see on your meter?

[wickedwill]

Re: Toshiba 42HL67US blows fuses.

Please clarify "no reading": what do you see on your meter?

well i am a bit confused.. when i set multimeter to 200 ohm i not really gettin any readings at all, but when i set it to 200k i can get some numbers.

also when i set it to diode mode and check this is what i get IN DIODE MODE,

starting with red pin on the + terminal going left to right (+ ~~ -)

+=1
~=2 and 3
-=4

pin 1-2 nothing just a 1 on left side
1-3 same as 1-2
1-4 same as 1-2
red on 2
2-1, 554
2-3, no number
2-4 no number

red on 3
3-1 551
3-2 no number
3-4 no number
red on 4
4-1 1274
4-2 552
4-3 554

i hope this helps.. i cannot seem to get numbers when in ohms (200) just a quick flash

[multimeter]

Re: Toshiba 42HL67US blows fuses.

well i am a bit confused.. when i set multimeter to 200 ohm i not really gettin any readings at all, but when i set it to 200k i can get some numbers.

also when i set it to diode mode and check this is what i get IN DIODE MODE,

starting with red pin on the + terminal going left to right (+ ~~ -)

+=1
~=2 and 3
-=4

pin 1-2 nothing just a 1 on left side
1-3 same as 1-2
1-4 same as 1-2
red on 2
2-1, 554
2-3, no number
2-4 no number

red on 3
3-1 551
3-2 no number
3-4 no number
red on 4
4-1 1274
4-2 552
4-3 554

i hope this helps.. i cannot seem to get numbers when in ohms (200) just a quick flash

in addition to retired caps post ,another way you can test the bridge...

set meter to diode test

pins 1 and 2 should have reading one way when reversing leads

pins 2 and 3 should have no reading either way when reversing leads

pins 3 and 4 should have reading one way when reversing leads

[budm]

Re: Toshiba 42HL67US blows fuses.

Take the resistance reading of pad 1 and pad 4 where the rectifier was soldered to those pads, I believe you have shorted load.
The four pin device ont he heatsisnk looks like anothe bridge also.