Gateway LP2407 Monitor Burnt

[mren]

Hi everyone, I came here for your help.

My 24" Gateway LP2407 is about 4 years old, It's been working fine until yesterday. The screen suddenly went off and the circuit breaker on house panelboard also jumped.

Now the monitor has no power. I opened it and saw the blown fuse, so I went out and bought the same fuse and replaced it.

But when I pluged in the power code, the fuse is blown immediately, with "pop" sound and smell.

I did buy two fuses for backup, but I really don't want just blow it again before identifying the real problem.

By looking at the power supply board, I noticed that the T851 transformer has some kind of burnt, brown resin like stuff (red circled on picture), it also smells burnt. Yes, the fuse burnt mark also can be seen, other than that, the board look clean, all caps seem OK.

Since I could not plug in power, so can't really measure anything. Is there any way to measure the transformer off power? Or is there any other possible shorted on board?

Thank you.

[selldoor]

Re: Gateway LP2407 Monitor Burnt

Test your Bridge rectifier - D850 on your board Black rectangular
with one end slanted


Bridge rectifier test

a) put your multimeter in diode test mode
b) put your red lead on plus + pin side and the red lead on adjacent ~ pin
- record reading
c) reverse the leads - recording reading


Then repeat the test on the other two pins

b) put your black lead on negative - pin side and the red lead on adjacent ~ pin - record reading
c) reverse the leads - recording reading

[mren]

Re: Gateway LP2407 Monitor Burnt

Thank you very much selldoor, please see the readings inline.

Test your Bridge rectifier - D850 on your board Black rectangular
with one end slanted


Bridge rectifier test

a) put your multimeter in diode test mode
b) put your red lead on plus + pin side and the red lead on adjacent ~ pin
- record reading
1
c) reverse the leads - recording reading
980 - 1012

Then repeat the test on the other two pins

b) put your black lead on negative - pin side and the red lead on adjacent ~ pin - record reading
1
c) reverse the leads - recording reading
880 - 927

[tom66]

Re: Gateway LP2407 Monitor Burnt

Test across the ~ and ~ pins too - should read open circuit (single "1".)

[multimeter]

Re: Gateway LP2407 Monitor Burnt

Thank you very much selldoor, please see the readings inline.

your bridge is fine,just check the 2 ~ pins should show "1" both ways

[selldoor]

Re: Gateway LP2407 Monitor Burnt

when you have done that report result then
On the heatsink to the left of the transformer (By the way they often look like that) there are two transistors can you read the part numbers off them? Have you taken them off? as one looks to have an isolation washer and the other doesnt (perhaps that is correct- depend on the transistor) .
Also can you test the green component between the two transistors - meter on ohms 2000. if it goes off scale try ohms 20000.

Also not much of a test but first meter on
600vDC check across the legs of the BIG cap (should be less than 10v) just checking it has discharged from high voltage) then meter on ohms 2000 check across legs just to make sure its not shorted.

[mren]

Re: Gateway LP2407 Monitor Burnt

Test across the ~ and ~ pins too - should read open circuit (single "1".)

Only one direction reads "1", the other way around reads about 800.

[mren]

Re: Gateway LP2407 Monitor Burnt

Results are inline.

when you have done that report result then
On the heatsink to the left of the transformer (By the way they often look like that) there are two transistors can you read the part numbers off them? Have you taken them off? as one looks to have an isolation washer and the other doesnt (perhaps that is correct- depend on the transistor) .

P71222 / K3469
1H06SF / RHRP1560
No they are still on board.


Also can you test the green component between the two transistors - meter on ohms 2000. if it goes off scale try ohms 20000.

Result: 5

Also not much of a test but first meter on
600vDC check across the legs of the BIG cap (should be less than 10v) just checking it has discharged from high voltage) then meter on ohms 2000 check across legs just to make sure its not shorted.

My multimeter only has 200 or 1000 on VDC, so I use 200, it reads 0.02, on ohms 2000, starts with some number around 800 then down to 1.

[selldoor]

Re: Gateway LP2407 Monitor Burnt

Only one direction reads "1", the other way around reads about 800.

Looks like it is leaking, that is between the two~~ isnt it?

You will need to take it out and test out of circuit, to make sure but it looks bust.

[Rtech]

Re: Gateway LP2407 Monitor Burnt

Having a look at the readings he took,just did not look right !!! so taking 3 different fully working and tested monitor and TV Power supplies I measured, in the same way,as you normally would, and all show readings of either *1* 0r OL,as they should and 0.5 approx,with the leads reversed, which is the normal voltage drop across a diode,He then should have got *1* across the AC input as advised and does not,so it looks as though the Bridge needs to come out and be tested again,but would seem to have failed.

[mren]

Re: Gateway LP2407 Monitor Burnt

Looks like it is leaking, that is between the two~~ isnt it?

You will need to take it out and test out of circuit, to make sure but it looks bust.

OK took it out and the test results are same. Between two ~ ~, only one way reads "1", reverse reading is around 800.

[Rtech]

Re: Gateway LP2407 Monitor Burnt

Change it !!

[mren]

Re: Gateway LP2407 Monitor Burnt

Change it !!

I will, but I have to buy the replacement first.
Is there anything else I need to test? Is that the cause of blown fuse?

[tom66]

Re: Gateway LP2407 Monitor Burnt

Most likely, it has a shorted internal diode. Just the bridge should be all you need to replace.

[mren]

Re: Gateway LP2407 Monitor Burnt

Thank you all guys, you are all genius! Thank you, thank you, thank you!

After replaced the D850 bridge rectifier, the monitor now works again! I can't believe I fix it, with all your helps (I only fixed one HP printer before by replacing the bad caps, but I know computer hardware and software well, and I'm an IT professional).

The original rectifier is 706V, but the electronics shop here only got 606V, it seems OK.

So the total cost of repair is less than $10. The 5A/250V fuse @ $2.5 ea, bought two and blown one, 606V rectifier @ $2.30.

Case closed. Now I can watch the Olympic closing ceremony peacefully.

[selldoor]

Re: Gateway LP2407 Monitor Burnt

Well done! Higher would have been better then lower but if its working- great.
After the olympics you might want to consider upgrading the middle size caps
to give the monitor a bit longer life.