HANSS 19" fuse keep blown

[newbie1]

Hi Guys,

I need your advise on how to proceed with this monitor.. Starting to lose my patience with it..

Model : HX191D

Background : Owner says the house had a power surge. I am not sure whether this caused it or the surge caused the monitor to breakdown

Fault : No Power LED.

What i did:
1) Check fuse. It is open. Change the fuse to Fuse #1. Plug it in then 'Pop'. Fuse #1 blown.

2) Check Bridge Rectifier (KBP206G). It is shorted. Found one KBP210 from old PSU/monitor. Replaced it & and the blown fuse #1 with Fuse #2. Plug it in then 'BOOM'. Thermistor (SCK103) blown. Together with Fuse #2.

3) Check Bridge Rectifier. It is no longer shorted. Replaced blown Thermistor & Fuse #2 with Fuse #3. Plug it in then 'Pop'. Fuse #3 blown again.

4) Check Bridge Rectifier. It is no longer shorted. Check Thermistor. No blown signature & resistance reads 9.1 ohms (spec is 10 ohms). Check inverter controller (LD7575PS) and there are no shorting between all the pins to Gnd (Pin 4). Replaced blown Fuse #3 with Fuse #4. Plug it in then 'Pop'. Fuse #4 blown again.

Stumped..

What else that i did/observed:
Unplugged & check the resistance of the following, with ohms set to lowest 200 :
1) D821, Q801 - not shorted on all the pins with each other
2) T801 - some pins are shorted to each other. Unsure whether it should be shorted. They are group in Red. See attached photo.
3) T901 & 902 - some pins (Pins 1-6 to be exact) are shorted to each other. Unsure whether it should be shorted. They are group in Red as well. See attached photo.
4) F802 is replaced with a jumper. But i am not sure whether this is intended to be that way.

Question/s :
Is blown fused caused by components in the Power board ONLY?! Or do i have to check the Logic card or could be caused by the panel?

Hope somebody can guide me further on my next step. Thanks as usual guys...

Edit 1 : Need to highlight that i have not recapped the board, except 1 (replaced it with a Panasonic FM). Also i did check most of the diode, that i can see all over the board, & shows no shorting on the diodes. Hope i did not missout any of them

[jetadm123]

Re: HANSS 19" fuse keep blown

Hi Guys,

I need your advise on how to proceed with this monitor.. Starting to lose my patience with it..

Model : HX191D

Background : Owner says the house had a power surge. I am not sure whether this caused it or the surge caused the monitor to breakdown

Fault : No Power LED.

What i did:
1) Check fuse. It is open. Change the fuse to Fuse #1. Plug it in then 'Pop'. Fuse #1 blown.

2) Check Bridge Rectifier (KBP206G). It is shorted. Found one KBP210 from old PSU/monitor. Replaced it & and the blown fuse #1 with Fuse #2. Plug it in then 'BOOM'. Thermistor (SCK103) blown. Together with Fuse #2.

3) Check Bridge Rectifier. It is no longer shorted. Replaced blown Thermistor & Fuse #2 with Fuse #3. Plug it in then 'Pop'. Fuse #3 blown again.

4) Check Bridge Rectifier. It is no longer shorted. Check Thermistor. No blown signature & resistance reads 9.1 ohms (spec is 10 ohms). Check inverter controller (LD7575PS) and there are no shorting between all the pins to Gnd (Pin 4). Replaced blown Fuse #3 with Fuse #4. Plug it in then 'Pop'. Fuse #4 blown again.

Stumped..

What else that i did/observed:
Unplugged & check the resistance of the following, with ohms set to lowest 200 :
1) D821, Q801 - not shorted on all the pins with each other
2) T801 - some pins are shorted to each other. Unsure whether it should be shorted. They are group in Red. See attached photo.
3) T901 & 902 - some pins (Pins 1-6 to be exact) are shorted to each other. Unsure whether it should be shorted. They are group in Red as well. See attached photo.
4) F802 is replaced with a jumper. But i am not sure whether this is intended to be that way.

Question/s :
Is blown fused caused by components in the Power board ONLY?! Or do i have to check the Logic card or could be caused by the panel?

Hope somebody can guide me further on my next step. Thanks as usual guys...

Edit 1 : Need to highlight that i have not recapped the board, except 1 (replaced it with a Panasonic FM). Also i did check most of the diode, that i can see all over the board, & shows no shorting on the diodes. Hope i did not missout any of them

You may be getting ahead of yourself. Have you tried checking the components between the fuse and the bridge rectifier for shorts? You still have the coil L805 and large yellow cap next to it and other componenents to check. If you have a schematic of another monitor take a look at it and you'll see what I mean. Many of the manufacturers use a similar circuit design from the input fuse to the bridge rectifier.

[PlainBill]

Re: HANSS 19" fuse keep blown

Don't forget on the other side of the bridge rectifier. The switching FET could be shorted.

One method of saving fuses (and time) is to hook a 120V light bulb across the fuse position. This limits the current, and allows troubleshooting (CAREFULLY!!!) with power applied.

PlainBill

[momaka]

Re: HANSS 19" fuse keep blown

2) T801 - some pins are shorted to each other. Unsure whether it should be shorted. They are group in Red.

Normal. The pins on the left you circled are connected to the auxiliary winding of the transformer. Once the PSU starts up, the second pin provides power to the PWM controller (that's the one you labeled as inverter controller).
The other two pins are connected to the primary winding of the transformer.
They appear shorted (with a multimeter) because the number of windings in the transformer is usually small.

3) T901 & 902 - some pins (Pins 1-6 to be exact) are shorted to each other. Unsure whether it should be shorted.

Normal, same reason as above.
If you check the secondary side of those transformers, though, you should get a high resistance, usually around 1000 Ohms.

4) F802 is replaced with a jumper. But i am not sure whether this is intended to be that way.

If this is how it came from the factory, then yes, this is how the manufacturer intended it to be (this practice, however, is usually done to save money for the manufacturer, so from the designer's perspective - no this was not intended to be this way). But let's leave that alone for now and assume it is normal.

Question/s :
Is blown fused caused by components in the Power board ONLY?!

Not necessarily, but it your case it most likely is.

Check resistance between (+) and (-) on the big primary cap. If it's shorted, then there's a short on the primary somewhere. If not shorted, check the rest of the primary side - particularly D886? R833 and the 3 other resistors around it.

Definitely try PlainBill's suggestion - it will save you a lot of fuses and frustration.

[newbie1]

Re: HANSS 19" fuse keep blown

thanks for all the replies..

@jetadm123 - oops.. ok.. I had rechecked the large yellow cap, but it is not shorted. The coil L802 & L805 pins are shorted as shown in the red circle in the photo attached. Do let me know if i miss out any other component from the Fuse to the Bridge rectifier..

@PlainBill - Is the Switching FET Q801 (with a S-D-G pin)? If yes, the pins are not shorted to each other. As for the 'lightbulb' testing, don't mind me asking you further questions, as I have never done it before .. Some of them might be stupid, by the way, hope you are not mad.. .. Do not want another 'fireworks' happening in the household.. lol..
So here goes:
1) what safety precaution must i be aware of?
2) i am staying in a 220-230V are so should i be using a 220-230V bulb?
3) the bulb should be in what wattage range & what is the type i.e normal fluorescent glass bulb?
4) so i solder the bulb across the fuse & start measuring voltages, right?. So which component voltages should i be starting with?

@momaka - many thanks for your explanation on the transformer pins. I did checked resistance between (+) and (-) on the big primary cap but it is not shorted. D806 (not D886) is not shorted as well.

Another thing i would like to clarify. I have attached a photo of a resistor R811. It measure 1.0 ohm in circuit. But i could not figure out what is the correct resistance should it be. It is color coded as Brown-Gray-Blue-Green. This is the proof why i could not get an Electronic Engineering degree. ..

[Rtech]

Re: HANSS 19" fuse keep blown

R811 should be very low, color coded 0.56 ohms.

[PlainBill]

Re: HANSS 19" fuse keep blown

thanks for all the replies..

@jetadm123 - oops.. ok.. I had rechecked the large yellow cap, but it is not shorted. The coil L802 & L805 pins are shorted as shown in the red circle in the photo attached. Do let me know if i miss out any other component from the Fuse to the Bridge rectifier..

@PlainBill - Is the Switching FET Q801 (with a S-D-G pin)? If yes, the pins are not shorted to each other. As for the 'lightbulb' testing, don't mind me asking you further questions, as I have never done it before .. Some of them might be stupid, by the way, hope you are not mad.. .. Do not want another 'fireworks' happening in the household.. lol..
So here goes:
1) what safety precaution must i be aware of?
2) i am staying in a 220-230V are so should i be using a 220-230V bulb?
3) the bulb should be in what wattage range & what is the type i.e normal fluorescent glass bulb?
4) so i solder the bulb across the fuse & start measuring voltages, right?. So which component voltages should i be starting with?

@momaka - many thanks for your explanation on the transformer pins. I did checked resistance between (+) and (-) on the big primary cap but it is not shorted. D806 (not D886) is not shorted as well.

Another thing i would like to clarify. I have attached a photo of a resistor R811. It measure 1.0 ohm in circuit. But i could not figure out what is the correct resistance should it be. It is color coded as Brown-Gray-Blue-Green. This is the proof why i could not get an Electronic Engineering degree. ..

Right, use a light bulb that matches your line voltage. I have a socket with two wire leads I use for these tests. For initial testing, I usually use a 25 or 40 watt bulb. When the circuit is working I move up to a 75 or 100 watt bulb. In part, it's a guide. If it glows a full brightness, something is seriously wrong. If it doesn't glow at all, and the device isn't operating, something is wrong. Like I forgot to plug in the power cord. If it glows brightly for a fraction of a second, then gets dim and the device is working, I know I've fixed it.

PlainBill

[jetadm123]

Re: HANSS 19" fuse keep blown

Yes, Q801 is the switching fet. I'm guessing you don't have a schematic of another LCD monitor, since you missed a lot of what I asked you to do. Measure the points circled in yellow. There looks to be resistors connected to the bridge, R802, 803 and 812. They're probaby ok, but check them anyway. Also, check to see if there are any other non-electrolytic caps around the bridge rectifier and check them for shorts.

[momaka]

Re: HANSS 19" fuse keep blown

Upon closer inspection of the inverter section, it looks like the two MOSFETs under transformers T901 and T902 may have overheated a bit. Can you post a zoomed-in picture of that area?

Also, what resistance do you get between ground and either of the two rightmost pins of T901 and T902?

Lastly, try the light bulb trick as PlainBill suggested, and if the light bulb glows, remove L801, then give the power supply another try with it disconnected from the rest of the monitor.

3) the bulb should be in what wattage range & what is the type i.e normal fluorescent glass bulb?

Go with regular incandescent light bulb. Fluorescent ones take too long to light up and they probably won't work well if there's a slight voltage drop from the power supply.

4) so i solder the bulb across the fuse & start measuring voltages, right

No, not exactly. If the light bulb glows, obviously there is a short somewhere across some component, and it's probably not a good idea to keep feeding it power.

[newbie1]

Re: HANSS 19" fuse keep blown

Thanks Rtech. How do you read them, by the way? Correct me if am wrong.. I am always thinking that the first 3 are indicating the ohm value & the fourth is the tolerance.

Apologies Jet. I do have schematic of other monitors but not this one. I guess you can blame me for being LAZY, or IGNORANT,... or BOTH. I did set my ohm meter to 200 & measure R802, 803 & 812 and could not find any shorting among them. Also same result with C801, C802 & C803.

Momaka, i have attached the photo as you requested. Pins 5-6 are all shorted together but the rest are not shorted to each other. Resistance i get between ground and either of the two rightmost pins of T901 and T902 is ERRATIC. Setting to 2000k it start with a reading of 200 then decreasing steadily. I am not sure what does the reading means. For the record the secondary winding resistance for both T901 & T902 are 374 ohms & 376 ohms respectively.

PlainBill, i nervously did the 'bulb test'. I will try to describe as close as possible what happened and is happening now.

The first time, bulb glows bright for a moment then dim, Power led turns on AUTOMATICALLY, but i unplugged before the backlight turn-on. Sorry was nervous that's why i turned it off.. gheesz..
The second time i plugged again, bulb glows bright then suddenly 'BOOM'. Something sounded 'POP', bulb is no longer dim/ON, Power led is off. I dissembled & checked the Power board but could not visually see any components burning/chipped off. Measured resistance on the Thermistor is still 10 ohms. Bridge rectifier, Switching FET are also not shorted. So i re-assembled again.
After that, I later cooled it for a while.

NOW, when i plugged again. The below is happening in the following order :
1) Bulb glows bright for a moment & turns-off;
2) Power led light up automatically;
3) Backlight turns-ON for a few sex;
4) Bulb glows bright for a moment AGAIN & turns-off;
5) Backlight & Power led turns-OFF;
6) After a moment, Power led light up automatically AGAIN;
7) "Goes back to #1"

....and the cycle continues... I tested it for 3 cycles.

Questions :
1) Is the CCFL drawing the EXCESSIVE current?
2) If the fault lies in the inverter section, what are the remote chances of me finding the shorted component? Is it as remote as me having the playboy playmates as my one night stand partner?.. heh..
3) What do i do next?

[alexanna]

Re: HANSS 19" fuse keep blown

With everything unplugged and discharged .Use an ohmmeter and from the solder pads of the fuse, do you see a low resistance reading to ground.
Remember there are different grounds on the board use the hot side ground.
REMEMBER UNPLUGED AND EVERY THING DISCHARGED.

[newbie1]

Re: HANSS 19" fuse keep blown

thanks Al. But by saying 'Hot side' Ground, do you mean the -ve point of the Big Cap or the mounting screw?.

Any other things to measure/try?. thanks guys

[alexanna]

Re: HANSS 19" fuse keep blown

The negitive lead of the large cap should be tied to the ground i am talking about

[alexanna]

Re: HANSS 19" fuse keep blown

I was going to try step by step to try to find out why the fuse is shorted to ground

[newbie1]

Re: HANSS 19" fuse keep blown

The negitive lead of the large cap should be tied to the ground i am talking about

With resistance setting to 200, no shorted at either of the fuse solder pads to either of the negative of the Big cap or to the Gnd (mounting screw).

[alexanna]

Re: HANSS 19" fuse keep blown

One more ground I should have had you check. The ground and the neutral wire at the AC plug on the power supply. [Without the power cord plugged in to the wall.]
I am hoping that somewhere along the line we will find something going to ground that shouldn't be.

[alexanna]

Re: HANSS 19" fuse keep blown

A few more things that I would check,
If you've already checked them my apologies.
The center leg of the switching FET for a ground to the neg lead of large cap.
The two outer legs of the FET, only one should show a low ohm reading to ground.

[momaka]

Re: HANSS 19" fuse keep blown

The negitive lead of the large cap should be tied to the ground i am talking about

Nope.
Negative lead of the large cap is floating, as is the positive. You cannot use a ground to measure anything on the primary side because everything is floating relative to ground.

1) Is the CCFL drawing the EXCESSIVE current?

Possibly. Or it could also be that there's a problem with the inverter somewhere. Either way, if this is the case, the inverter should safely shut down, not blow fuses. This is why I wanted to you to remove L801 because L801 feeds power to the inverter.
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.

2) If the fault lies in the inverter section, what are the remote chances of me finding the shorted component?

Can't say at this point. Are you optimist or pessimist?

[newbie1]

Re: HANSS 19" fuse keep blown

Guys, thanks for still helping me on this..

Nope.
Negative lead of the large cap is floating, as is the positive. You cannot use a ground to measure anything on the primary side because everything is floating relative to ground.

Thought so too.. Usually i measure voltages of the primary side with respect to the -ve lead of the Big cap instead of the Ground (screwhole)

Nope.
Possibly. Or it could also be that there's a problem with the inverter somewhere. Either way, if this is the case, the inverter should safely shut down, not blow fuses. This is why I wanted to you to remove L801 because L801 feeds power to the inverter.
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.

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?

FYI, to rule-out the panel/CCFL causing the failure, I swapped another 19" panel/CCFL before I did the 'remove-the-L801' test above. Same result. So can i safely say the CCFL/Panel is not causing the blown fuses?.

Nope.
Can't say at this point. Are you optimist or pessimist?

Usually, I am optimist.. But after having 2 monitors unrepairable due to logic card/processor being faulty, I am not so sure now. ..

[PlainBill]

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