Hp 1955

[terminatorX]

The hp 1955 (Benq 48.L1A02.A00) the monitor was just totaly dead.
So I opened it and removed the power board. So I found out that one of the three pins on the power cable connector was blown. If you look at the "green" side its the left pin. the center pin was loose and the right pin had cracked solder. So I resoledered it. I think I did I decent job on that but it didn't help at all. The power led didn't go on. also here is no bulging on capacitators or something similar. What do you think, could it be both the C5707 transistors and the picofuse maybe?

[PlainBill]

Re: Hp 1955

Don't post pictures inline. It seriousl inconveniences retiredcaps and pisses me off.

No, it's not the picofuse, and it's not the c5707s.

Let's do this logically. What is the voltage across the large cap? On the top view there is an 8 pin IC partially obscured the green wire. What is the part number of that IC?

PlainBill

[terminatorX]

Re: Hp 1955

Thanks for respons. Just want to emphasize that I'm a real newbie.
Can I check the large cap without current running through? Not really in the mood of killing my self if do something wrong...
Ic part number should be 1200AP40,CPBC, 0449 close to a spot called IC601.

[retiredcaps]

Re: Hp 1955

Can I check the large cap without current running through?

No.

Not really in the mood of killing my self if do something wrong...

1) Assuming your mains AC is 110 to 120V AC and you have a manual range multimeter, set it to 200V DC. Yes, set it to DC.

2) Plug your black probe into the COM jack. Plug your red probe into the Volts jack.

3) Put your red probe on the positive leg of the capacitor. Put your black probe on the negative leg of the capacitor.

4) If it is working properly, we expect a stable DC voltage reading somewhere in the 165V to 170V DC range.

120 mains AC x 1.414 (rectified) = 169.68V DC

[terminatorX]

Re: Hp 1955

Nope the AC is 230V. Don't know how to determine which leg is positive or negative (or even if that matters). Just to make clear....should I plug in the board to the wall as is or mount it back to the screen first?

[selldoor]

Re: Hp 1955

Please can you update your profile with at least the country you are in.

The previous instructions need amending accordingly
TAKE EVEN GREATER CARE

1) Assuming your mains AC is 230AC and you have a manual range multimeter, set it to 600V DC. Yes, set it to DC.

2) Plug your black probe into the COM jack. Plug your red probe into the Volts jack.

3) Put your red probe on the positive leg **of the capacitor. Put your black probe on the negative leg of the capacitor. YES IT DOES MATTER

4) If you rectify 230 volts AC RMS with bridge rectifier, without Filter capacitor, the meter will read 230 X 1.414 Volts = 325.22 Volts exactly.

So If it is working properly, we expect a stable DC voltage reading somewhere in the 320V to 350V DC range.

** The capacitor probably has a white or pale blue stripe down one side
with - - - - - - minus signs in it the leg on the same side as the stripe
is the negative. Note both legs are high voltage.

The monitor does not have to be rebuilt and I believe for this test the power board can stand alone. Do not rest it on anything metallic and do not touch it other than with the probes. Do not let them slip off the legs and do not touch the board after the test until it has been switched off for at least 5 minutes.

If you have any time for reading read this:https://www.badcaps.net/forum/showthread.php?t=10419 there are revisions within it so start at
post 18 .It will give you advanced insight into what further tests may be required.

[terminatorX]

Re: Hp 1955

Thanks for your good help!

If you rectify 230 volts AC RMS with bridge rectifier, without Filter capacitor, the meter will read 230 X 1.414 Volts = 325.22 Volts exactly.

Not really sure what this is about...AC RMS....

To be exactly sure what I'm doing. I don't really se an adequat marking for +/- so would it be a good guess to say at the side where there are those minus marking should be the minus pin?

[selldoor]

Re: Hp 1955

Yes - I believe that is what I said?
[Quote]
** The capacitor probably has a white or pale blue stripe down one side
with - - - - - - minus signs in it the leg on the same side as the stripe
is the negative.[Quote]

[terminatorX]

Re: Hp 1955

Hahha sorry read that part quickly, thought you meant the actual pin was suppose to have a marking....

But you still didn't describe what AC RMS rectifier ...filter capacitator...is.
Kind of why I quoted it and wrote

Not really sure what this is about...AC RMS....

[terminatorX]

Re: Hp 1955

Never mind I did the testing. I have a semi automatic DMM. The capacitator showed 0.5V to verify the plausability of the test I also tested my hp 1940 powerboard that I also have a problem with that is in another thread it showed a very stable 325V.
Knowing this what do you belive is the reason the power connector blew it's two soldering points? Is it really the capacitor that is boken maybe the current is inhibited somewhere else...

[PlainBill]

Re: Hp 1955

1. Benq is notorious for shoddy soldering

2. The pins of the power connector can receive a lot of stress when the power cord is plugged in..

3. The fuse in the power supply would blow long before any excessive load would destroy the solder on the pins of the power connector.

Resolder the pins!!!

PlainBill

[terminatorX]

Re: Hp 1955

Ok...
So would you say the capacitator is bad? Do you want me to resolder the power connector pins? I just did that.....

[PlainBill]

Re: Hp 1955

Ok...
So would you say the capacitator is bad? Do you want me to resolder the power connector pins? I just did that.....

Let's walk through this. I'm seeing references to another monitor, don't do that. It's hard enough as it is.

1. What is the voltage across the large cap?

2. Using the minus (-) lead of the large cap as ground, what are the voltages on the pins of the NCP1200AP40? Do this carefully.

PlainBill

[Krankshaft]

Re: Hp 1955

For easier troubleshooting I've attached the main switcher IC datasheet.

Post the readings Plainbill suggested and we'll get a better handle on the status of the IC.

[selldoor]

Re: Hp 1955

Ok...
So would you say the capacitator is bad? Do you want me to resolder the power connector pins? I just did that.....

No Not the power connector pins - the pins of all the components ringed in red on the earlier picture.

I understand you to say that the voltage across the Big cap is 0.5v.

Whilst it could be the cap, this may be due a fault in the bridge rectifier
which I will mark in a picture. This should be tested initially with the power OFF, with your meter on a test diode setting.
Take a multi-Meter and switch it to Ohm x 1
Test between one of the "~" and "+" legs.
You should get either an almost-zero reading in one direction, and when you reverse the test probes, you should get an almost infinite reading.
Now try the same between this "~" leg and "-".
Same as above.
Now repeat the same tests with the other "~" leg, and "+", and then "-".
Same as above.
If you either get almost zero or almost infinite in BOTH directions, then the rectifier burnt out.

If the rectifier has gone the fuse will probably also be blown - can you test it. (POWER OFF) Can you post any numbers on the Rectifier and the fuse.

[terminatorX]

Re: Hp 1955

So PlainBills and Krankshafts part.
Weird part is that i retested the large cap voltage and it fluctuated around 1.4XX volts instead what I said before around 0.5V.

Hope I done this properly.
Pin 8 had about the same voltage as the large cap voltage and pretty much the same fluctuation. They were more or less synchronized.
Pin 7 read -0.008 but also fluctuating. Pin 6 about 0.203. Pin 5-1 read stable zero (pin 3 read actually 0.001) To mention when started reading it read a value that increased when retested it started about the same initial value increasing the same way. All fluctuating values were like this.


Selldors part:

I followed:
http://www.youtube.com/watch?v=dqkT6hF0O3E

and pretty much got the same reading maybe just below what was on the vid.
For some reason it doesn't seem to work ohm way. If I have low ohm reading it all read "OL"when I set it to M(ega I suppose) ohms then it starts to read and one direction is always reading a bit higher.

So I don't know why it's not matching with diode testing...

when You say fuse do you mean the picofuse?

Just to mention nothing has been soldered out of the board yet.

[selldoor]

Re: Hp 1955

I followed:
http://www.youtube.com/watch?v=dqkT6hF0O3E

and pretty much got the same reading maybe just below what was on the vid.
For some reason it doesn't seem to work ohm way. If I have low ohm reading it all read "OL"when I set it to M(ega I suppose) ohms then it starts to read and one direction is always reading a bit higher.

So I don't know why it's not matching with diode testing...

.

My turn to not understand- Can you post the actual readings with what leads on what pins.

when You say fuse do you mean the picofuse?

No ,I mean the mains fuse - I have marked what I think is a fuse It will probably say on the board and on the fuse but cant see. (This is why good clear photos are important)

Have you resoldered the joints yet?

[terminatorX]

Re: Hp 1955

Have not resoldered yet will maybe do that at weekend.

Ok so i hope this is right. When I talk about the rectifier I mean; (+,1,2,-) pins.

Using the DMM in diode mode i get:
Red on leg + and black on leg1= OL
Red on leg 2 and black on leg - =OL
Black on leg + and red on leg 1= 0.495
Black on leg 2 and red on leg - =0.506
Red on leg 1 and black on leg 2 =OL
Black on leg 1 and red on leg 2= OL

But when using in ohm mode it's just really weird. To mention it does work properly since I tested it on a couple of resistors on the board and right values where displayed.

Here are a couple of values it's more values at one reading because my DMM show different values when setting range...

Red on leg + and black to both leg 1 and 2 =2MΩ
Black on leg + and red on leg 1= 34.67kΩ, 145.1kΩ, 0.642MΩ and 2.07MΩ
Black on leg + and red on leg 2= 39.7kΩ, 165.9kΩ, 0.72MΩ and 2.28MΩ
Red on leg - and black on leg 2= 40.21kΩ, 166.5kΩ, 0.738MΩ and 2.42MΩ
Red on leg - and black on leg 1= 40.49kΩ, 167.5kΩ, 0.739MΩ and 2.39MΩ

By the way, how should I test the fuse before resoldering?

[jayoung]

Re: Hp 1955

Set the DMM on 200 ohm scale and put one probe on each leg of the fuse. You should get a reading less than 1 ohm (same as touching the two probes together).

[selldoor]

Re: Hp 1955

Hmm! test fuse?? Whilst looking for an easy way to show this I noticed that this board has a switch. When you were testing the BIG Cap
was it definitely switched on?
If it was can you test the switch. - same as the fuse but obviously resistance when on and none when off.