Viewsonic VP201b power supply option

[bioray]

Trying to troubleshoot the power supply on this display. No power out of the switching power supply. Removed all caps and checked and found all in specs. The specs for the power supply are 18vdc 3.3a. I found a 18.5vdc 4.9a external supply. Would this fry the other boards in the display if I were to use it? I have a bench power supply to test the display and it worked great on 18vdc bench power. Just worried about the extra .5v

[PlainBill]

Re: Viewsonic VP201b power supply option

Trying to troubleshoot the power supply on this display. No power out of the switching power supply. Removed all caps and checked and found all in specs. The specs for the power supply are 18vdc 3.3a. I found a 18.5vdc 4.9a external supply. Would this fry the other boards in the display if I were to use it? I have a bench power supply to test the display and it worked great on 18vdc bench power. Just worried about the extra .5v

The extra .5 volts shouldn't kill it, but why not just repair the original supply? They don't get much simpler than that one.

PlainBill

[bioray]

Re: Viewsonic VP201b power supply option

I would like to repair the supply. When I checked the caps the values were within about 10%. The shockley diodes checked good as well. Kinda of stuck at this point, that's why I was going to rig up an external supply. Any pointers would be appreciated!

[sam_sam_sam]

Re: Viewsonic VP201b power supply option

Here is what I would tell you if the power supply is more than 2 years old I would recap this power suply

I have a lot of switching power supply a litte over two years old and every one of the the caps when BAD POP there tops on them

When YOU say they are " within about 10% " Is this Over or Under if under REPLACE them they are no good

[PlainBill]

Re: Viewsonic VP201b power supply option

I would like to repair the supply. When I checked the caps the values were within about 10%. The shockley diodes checked good as well. Kinda of stuck at this point, that's why I was going to rig up an external supply. Any pointers would be appreciated!

I use a two step process for checking power supplies. Step 1 is to check the voltage across the main power supply cap (the 100uF, 450 volt one). It should read 1.4 x your line voltage - 120VAC in yields 165 VDC across the cap.

If that is correct, I check the voltage across the startup cap. It's a small 22uF to 47uF cap near the power FET. It is often overlooked. If that cap is bad, the power supply won't start. CAREFULLY measuring the voltages on the SMPS controller also will help. And of course, look up the datasheet for the SMPS controller.

Pictures help us help you.

PlainBill

[bioray]

Re: Viewsonic VP201b power supply option

Thanks for some direction. I will check those readings tomorrow. A bad cap might just explain the fact that the output voltage slowly ramps up when a/c is applied. Again thanks for the direction! I will report back with what I find.

[PlainBill]

Re: Viewsonic VP201b power supply option

Thanks for some direction. I will check those readings tomorrow. A bad cap might just explain the fact that the output voltage slowly ramps up when a/c is applied. Again thanks for the direction! I will report back with what I find.

That might be a bad startup cap or a bad mains filter cap, but what I would check first is the current sense resistor.

Incidentally, the service manual for this monitor is available at Elektrotanya.

PlainBill

[bioray]

Re: Viewsonic VP201b power supply option

A little help please with locating the components. Current sense resistor, power cap, starter cap.

Thanks

[bioray]

Re: Viewsonic VP201b power supply option

The caps measured as follows 150uf =127uf 47uf=30uf 150uf=127uf 680uf=621uf taicon and nichison caps

[PlainBill]

Re: Viewsonic VP201b power supply option

A little help please with locating the components. Current sense resistor, power cap, starter cap.

Thanks

R114=current sense resistor.
C101 is the main filter cap.
C105 is the startup cap.

Some people (I WAS one of them) ignore the small electrolytic caps. C105 and C106 should both be checked and replaced if there is any question about their condition.

Plainbill

[PlainBill]

Re: Viewsonic VP201b power supply option

The caps measured as follows 150uf =127uf 47uf=30uf 150uf=127uf 680uf=621uf taicon and nichison caps

Either there is a problem with your meter, or all of those caps are under spec, the 47 uF seriously so.

PlainBill

[bioray]

Re: Viewsonic VP201b power supply option

The resistor checked good @.4ohm rated 0.36ohm. c105 reads 15uf should be 22. and c101 reads 127uf should be 150uf. Checked my meter with some new caps in my shop it seemed to be accurate. Fluke 179 has always worked good for me. C106 is a surface mount, just don't think that i will be able to take that one off to check.. Thanks for the tips. All these caps reading low might just be my problem? maybe? got a reading of 2.5vdc when power supply was loaded and it ramped up to 18vdc when unloaded. Please excuse my A.d.d When a thought comes to mind i have to put it down.

[PlainBill]

Re: Viewsonic VP201b power supply option

The resistor checked good @.4ohm rated 0.36ohm. c105 reads 15uf should be 22. and c101 reads 127uf should be 150uf. Checked my meter with some new caps in my shop it seemed to be accurate. Fluke 179 has always worked good for me. C106 is a surface mount, just don't think that i will be able to take that one off to check.. Thanks for the tips. All these caps reading low might just be my problem? maybe? got a reading of 2.5vdc when power supply was loaded and it ramped up to 18vdc when unloaded. Please excuse my A.d.d When a thought comes to mind i have to put it down.

I seem to have misread the schematic. If C108 is a small electrolytic cap, check it. Low capacitance on these caps can cause problems.

A quick history. We've known for a couple of years that a bad startup cap will prevent the monitor starting. Some time ago a friend gave me a Samsung 17" LCD TV / Monitor that would not power up. The only sign of activity was a clicking sound about every second or two from the speakers. This TV had an external 12V 4.5A power brick, so the first test I performed was to test the output under load. I use an 1157 automobile lamp as a 2 Amp load, and the power supply worked perfectly.

After many false leads, I discovered the TV worked perfectly when hooked to a bench supply, so I turned my attention back to the power brick. All the filter caps had an ESR that was slightly high. Ordinarily, that would not be a problem, but the problem was obviously the power brick, so I replaced them, and that didn't help. The next step was to dig out some of the glue and free the startup cap. Replacing that fixed the power supply.

Obviously, the startup cap was working well enough to keep the supply working at a light load, but not well enough to keep it working under full load. I've got a few theories of why this was the case, but the experience confirmed my opinion - ALWAYS replace the one or two small caps next to the SMPS controller.

PlainBill

[bioray]

Re: Viewsonic VP201b power supply option

C108 is reading low as well. This display is 5years old after all. I guess all the years of use has taken its toll on the caps.

[bioray]

Re: Viewsonic VP201b power supply option

Replaced caps on the power supply. Got correct voltage out. Back lights come on and I get a solid blue screen with no graphics or characters displayed. Reseated ribbon cables to no avail. The monitor worked before repairing the power supply. After repair and reassembly I now get a solid blue screen. Getting aggravated with the display. Any ideas. Has to be logic board.

[jsog]

Re: Viewsonic VP201b power supply option

Check the capacitors on the processor board. Also make sure the button cable is connected at both ends.

[mcof]

Re: Viewsonic VP201b power supply option

I know this is an old thread but it's coming up on google and I have a few things to add.

1) The monitor will happily run on the HP 18.5V 3.5A supplies
2) If you crack off the plastic casing it will fit in place of the original power board, barely (see image)

Recapping my board didn't quite do the business so I decided to go this route since used laptop supplies are dirt cheap and work out of the box. Used the back ends of crimp connectors to interface with the C6 power pins and the rest is just solder and heatshrink. Ignore the black connector, should have re-used the original. If anyone else does this remember to strap the earth and connect the hot wire (should be the blue one) through the switch.

[Folxs]

Re: Viewsonic VP201b power supply option

Hi, thanks for sharing information, that this is 18V power supply 3.3A - how did You found it?
That info helped me troubleshoot my power supply. (I got sign on it 15V2A so I thought, that it is 15V 2A but it was not!)
In my case that cap 22uF 50V was measuring 2uF so I replacement it and that works just fine.