HANSS 19" fuse keep blown

[newbie1]

Re: HANSS 19" fuse keep blown

At this point you haven't even established if the power supply is working!!! There is a 7(8?) pin cable that connects the power supply to the signal card. Fasten the power supply in place. Use one of the mounting screws for the power supply as ground. Measure the voltage on each pin of that cable.

PlainBill

...

Sorry about that, Chief...

With one of the L801 leg lifted & using the bulb as fuse, I applied power. But no reading could be seen on any of the 9 pins of the cable linking to the signal card, with DMM volt set to 20. On the Big cap it reads 326V & VCC (Pin 6) of PWM controler (LD7575PS) is 13V.

should i resolder L801 & re-measure?.. thanks, Chief

[newbie1]

Re: HANSS 19" fuse keep blown

Since you missed my earlier suggestion, I'll repeat it again.
1) remove L801
2) connect the monitor in series with the light bulb (as you've already done before)
3) see if the power LED stays lit.

If you get the Power LED to turn on and stay turned on, feed the monitor with a video signal from a computer and use a flashlight to see if there is a faint image on the screen.
If yes, then we have it narrowed down to the inverter.
If not, post what results you got.

for the record, this is the L801 leg that i lifted. Hope this is the right inductor that I was told to remove.

[PlainBill]

Re: HANSS 19" fuse keep blown

for the record, this is the L801 leg that i lifted. Hope this is the right inductor that I was told to remove.

I'll admit it, I'm lazy. I haven't identified what L801 does. Looking back, I missed some solid evidence at post #10. The behavior where the power LED, lamp, and backlights were cycling was normal considering there was a (relatively) high resistance in the AC input. My $.03 worth (inflation).

Reconnect L801, double check everything for stray solder, etc. Hook everything together and apply power. If the process above repeats itself, remove the lamp and insert a fuse. You certainly have fixed whatever was causing the fuse to blow.

If you REALLY want to be super cautious, as an intermediate step replace the present lamp with the highest wattage lamp you have available and test BEFORE installing the fuse. If they cycle time gets longer, it is definitely preforming normally.

PlainBill

[newbie1]

Re: HANSS 19" fuse keep blown

I'll admit it, I'm lazy. I haven't identified what L801 does. Looking back, I missed some solid evidence at post #10. The behavior where the power LED, lamp, and backlights were cycling was normal considering there was a (relatively) high resistance in the AC input. My $.03 worth (inflation).

Reconnect L801, double check everything for stray solder, etc. Hook everything together and apply power. If the process above repeats itself, remove the lamp and insert a fuse. You certainly have fixed whatever was causing the fuse to blow.

If you REALLY want to be super cautious, as an intermediate step replace the present lamp with the highest wattage lamp you have available and test BEFORE installing the fuse. If they cycle time gets longer, it is definitely preforming normally.

PlainBill

PlainBill.. .. you are my saviour,, as always..

I reconnect L801. Removed the test lamp. Hook everything together put in the fuse (i still have extra so i skipped being overly cautious) and apply power.

IT WORKS!!!... ..

In Summary
Fault : Blown fuse, bridge rectifier shorted, blown thermistor
Cause : unknown?
Repair procedure : Not sure what i did to fix the blown fuse
Lesson learnt : How to do the 'bulb test'..... PRICELESS!!!

By the way, is the bulb test applicable for all devices (TV, fridge, etc) that is having repeated blown fuse?.

thanks a gazzilion, Captain.. .. & not forgetting the other guys as well,.. Momaka, jetadm123, Rtech, Alexanna.. appreciate it..

[PlainBill]

Re: HANSS 19" fuse keep blown

PlainBill.. .. you are my saviour,, as always..

I reconnect L801. Removed the test lamp. Hook everything together put in the fuse (i still have extra so i skipped being overly cautious) and apply power.

IT WORKS!!!... ..

In Summary
Fault : Blown fuse, bridge rectifier shorted, blown thermistor
Cause : unknown?
Repair procedure : Not sure what i did to fix the blown fuse
Lesson learnt : How to do the 'bulb test'..... PRICELESS!!!

By the way, is the bulb test applicable for all devices (TV, fridge, etc) that is having repeated blown fuse?.

thanks a gazzilion, Captain.. .. & not forgetting the other guys as well,.. Momaka, jetadm123, Rtech, Alexanna.. appreciate it..

Here is a tentative analysis of the failure and recovery.
A voltage spike caused the bridge rectifier to short. As in all good designs, the thermistor failed while protecting the fuse, in sympathy the fuse also blew. Replacing the bridge rectifier, fuse and thermistor would have fixed it.

The light bulb in series with the AC line meant that the monitor was getting less than 100 volts AC when the backlights etc were on. This resulted in the SMPS shutting down, at which time the main filter cap recharged and the process started again.

The 'series light bulb' trick can be used any time you have a device that blows a fuse. Ideally, the current drawn by the bulb should be much greater than the normal current demand of the device being repaired.

To address a specific example, the light bulb could be used on a refrigerator that blows the fuse every time it is plugged in. By disconnecting portions of the appliance you can identify where the excess load is. (Possible culprits could be the compressor, the defrost heater, or the relay for the icemaker, for example). Because an electric motor has a very high starting current, you would not expect to see the bulb glow brightly when the motor started, then get dimmer.

PlainBill

[newbie1]

Re: HANSS 19" fuse keep blown

D#@$ IT!!!..
After I 'ignore it' for a few days & decided to reassembled the whole unit including the back cover, the new fuse blew again once the monitor is plugged...
B^!@#$$%!!!!!

I will tear it apart later & go through the whole troubleshooting process again..

[momaka]

Re: HANSS 19" fuse keep blown

I am sorry about missing this test. I was searching for the L801 for sometime now & finally found it under the white 'glob' beside the transformer. Duh!.. I removed one leg of it & conduct the 'bulb' test again with everything hooked up. The following happened:
1) Bulb light up for a sec & dim/off
2) Power led DIDN'T turn on
3) I unplugged the mains
4) Re-plugged the mains
5) "goes back to #1"
so why doesn't the LED turn-on?

Why doesn't it turn on? Because apparently I need glasses, that's why.
More precisely, I misread the numbers of the coils in the picture. What should have been removed was L901, not L801. Removing L801 disconnects the primary winding of the transformer from the MOSFET - of course it's not going to turn on. Good thing you posted that picture in post #22.

Sorry about the screw up.

Try removing L901 and repeat the procedures I mentioned in post #18. Then also measure the voltages on the power supply connector (P902?) as per PlainBill's suggestions in post #19.
This will test whether or not the power supply is functioning correctly.

[coolre]

Re: HANSS 19" fuse keep blown

Hi guys ..got tht same model monitor ..but mine no blown fuse , fet transistor etc the only prob no power no green led on ..already re caps even there was no bluged or blown caps ..the only thing is tht i got only 4-6v on pins 6 in LD7575ps ..is that PWM controller faulty ? On a workable monitor same model i got 12-15v on pin 6 ..pls help me troubleshooting it more thnx a lots

[jetadm123]

Re: HANSS 19" fuse keep blown

Hi guys ..got tht same model monitor ..but mine no blown fuse , fet transistor etc the only prob no power no green led on ..already re caps even there was no bluged or blown caps ..the only thing is tht i got only 4-6v on pins 6 in LD7575ps ..is that PWM controller faulty ? On a workable monitor same model i got 12-15v on pin 6 ..pls help me troubleshooting it more thnx a lots

4-6V on the VCC pin is not enough to turn the LD7575 on.


1) Did you also change the small startup cap connected to pin 6?

With power off:

2) Check the diode, resistor value and any other component connected to pin 6 for possible shorts or out of range values.

[coolre]

Re: HANSS 19" fuse keep blown

4-6V on the VCC pin is not enough to turn the LD7575 on.


1) Did you also change the small startup cap connected to pin 6?

With power off:

2) Check the diode, resistor value and any other component connected to pin 6 for possible shorts or out of range values.

Already swap diodes n the small caps from the working one to cross verify.. still getting the 4-6v on pin6 vcc .all other reading same value as on working one .. is the ld7575ps still good ?

[coolre]

Re: HANSS 19" fuse keep blown

4-6V on the VCC pin is not enough to turn the LD7575 on.


1) Did you also change the small startup cap connected to pin 6?

With power off:

2) Check the diode, resistor value and any other component connected to pin 6 for possible shorts or out of range values.

Pls see attach pics (ive used the 1 available here) Yellow mark are the parts i interchange on a working one ..the red mark is where the 4-6v reading happens

[PlainBill]

Re: HANSS 19" fuse keep blown

Pls see attach pics (ive used the 1 available here) Yellow mark are the parts i interchange on a working one ..the red mark is where the 4-6v reading happens

If R844, R838, R805 read the proper values, the SMPS controller is bad. It's not uncommon to find them bad.

PlainBill

[coolre]

Re: HANSS 19" fuse keep blown

If R844, R838, R805 read the proper values, the SMPS controller is bad. It's not uncommon to find them bad.

PlainBill

ok thnx Plainbill ..already placed an order online for the ld7575ps will keep updated once i get it and work it out have a nice weekend all

[coolre]

Re: HANSS 19" fuse keep blown

Hi there again... got the LD7575 replace it Bingo Monitor back to life