VX922 with FSP035-1PI01 PSU

[Sparky]

Plug in the monitor and get nothing except a quiet tick...tick...tick...tick...tick

Had a few bugling caps, so I recapped it.

tick...tick...tick...

Checked diodes and the resistors on the primary side. Looks good. Thought maybe the small 1kV 102k ceramic cap was bad, so swapped it.

tick...tick...tick...

Seems tapping around the transformer/resistor/small cap/diode area makes the ticking change pace for a moment. Not sure why. Kept tapping trying to see if there was a particular spot that caused it, then touched the wrong thing and BOOM blew the fuse

Replaced the fuse. BOOM. Fuse blew again. Too small oops, 2A not 1A

Anyway. Anyone ever ran into this before? Can't seem to pinpoint the problem. Possibly the transistor? Markings are 542MZ and CEF04N6 I believe.

Or maybe if someone has one of these PSUs for this monitor I could buy it cheap? I know I could put an external brick on the monitor but I'd like to keep the power button working.

[PlainBill]

Re: VX922 with FSP035-1PI01 PSU

Plug in the monitor and get nothing except a quiet tick...tick...tick...tick...tick

Had a few bugling caps, so I recapped it.

tick...tick...tick...

Checked diodes and the resistors on the primary side. Looks good. Thought maybe the small 1kV 102k ceramic cap was bad, so swapped it.

tick...tick...tick...

Seems tapping around the transformer/resistor/small cap/diode area makes the ticking change pace for a moment. Not sure why. Kept tapping trying to see if there was a particular spot that caused it, then touched the wrong thing and BOOM blew the fuse

Replaced the fuse. BOOM. Fuse blew again. Too small oops, 2A not 1A

Anyway. Anyone ever ran into this before? Can't seem to pinpoint the problem. Possibly the transistor? Markings are 542MZ and CEF04N6 I believe.

Or maybe if someone has one of these PSUs for this monitor I could buy it cheap? I know I could put an external brick on the monitor but I'd like to keep the power button working.

I've seen it a couple of times. The tick - tick -tick is the power supply trying to start, but failing. One possible culprit is the small cap (typically 22-47uF, 50V) next to the main transformer. Another is shorted transistors in the inverter, but that's less likely.

PlainBill

[Sparky]

Re: VX922 with FSP035-1PI01 PSU

That's what I thought on the small cap (10uF 50V in this case) but replacing that didn't help.

[PlainBill]

Re: VX922 with FSP035-1PI01 PSU

That's what I thought on the small cap (10uF 50V in this case) but replacing that didn't help.

Check the diodes on the secondary. A shorted diode would do that too.

PlainBill

[Sparky]

Re: VX922 with FSP035-1PI01 PSU

Diode seems to be checking out OK but I'm not entirely sure what the numbers on my meter for the diode setting mean. lol sad I know but it spits out something like 530 on the large one, and 760 on the little glass one. 530 and 760 of what? Beats me. Trying it with the leads reversed show nothing, so they are only working one way.

[PlainBill]

Re: VX922 with FSP035-1PI01 PSU

Diode seems to be checking out OK but I'm not entirely sure what the numbers on my meter for the diode setting mean. lol sad I know but it spits out something like 530 on the large one, and 760 on the little glass one. 530 and 760 of what? Beats me. Trying it with the leads reversed show nothing, so they are only working one way.

The diode test function applies a voltage to the leads through a resistor. The number you see is the voltage across the leads as you touch the diode.

Oh, solder shorts can cause this problem too. Even a shorted power transformer.

PlainBill

[Sparky]

Re: VX922 with FSP035-1PI01 PSU

OK, must be in mV then. Makes sense now.

If I had a new transistor I'd try replacing it, but I don't, and I am not sure about just blowing away more money on this thing. Maybe I'll just rig up an external power brick for it.

[Sparky]

Re: VX922 with FSP035-1PI01 PSU

Well interesting thing today. Finally dug up a power brick that has enough oomph to run the LCD. Removed the caps on the secondary side and put in a power socket, connected the 12V brick to the board... nothing. Found that there is a direct short somewhere on the PCB on the secondary side.

So all this time I thought it was on the primary side or part of the switching circuit, and here it looks like I was wrong. But now to find out what the heck IS wrong...

[Sparky]

Re: VX922 with FSP035-1PI01 PSU

Does anyone have any clues what I need to be looking for? I'm lost.

[PlainBill]

Re: VX922 with FSP035-1PI01 PSU

Does anyone have any clues what I need to be looking for? I'm lost.

You're looking for a short. Try the 'divide and conquer' approach. Is teh short on the 5V or the 12V supply. If it's the 12V supply, is there a jumper you can pull that will isolate the inverter? Did you create a solder short when replacing a cap?

PlainBill

[Sparky]

Re: VX922 with FSP035-1PI01 PSU

Well, yeah, a short I know that much. But nothing seems apparent as to where it is. The LCD only has a 12V supply.

Guess I'm just in a brain lock, sorry I'll check for the jumpers and see if I can isolate it.

[Sparky]

Re: VX922 with FSP035-1PI01 PSU

OK Pulled the jumper to the inverter section, no short on the inverter side.

Kept tracing and realized there isn't much else on the 12V side at all... pulled the main transformer and the direct short is gone. About 99k ohms between the +12V and ground.

Well I guess unless I can get a new transformer from somewhere I'd best use the external brick which should work now.

[PlainBill]

Re: VX922 with FSP035-1PI01 PSU

OK Pulled the jumper to the inverter section, no short on the inverter side.

Kept tracing and realized there isn't much else on the 12V side at all... pulled the main transformer and the direct short is gone. About 99k ohms between the +12V and ground.

Well I guess unless I can get a new transformer from somewhere I'd best use the external brick which should work now.

That would indicate the output diode on the SMPS is shorted.

PlainBill

[momaka]

Re: VX922 with FSP035-1PI01 PSU

Kept tracing and realized there isn't much else on the 12V side at all... pulled the main transformer and the direct short is gone.

It's normal for a transformer to measure shorted with a DMM, so that's probably not the problem. Post some pictures of the top and underside of the power board if possible.

[Sparky]

Re: VX922 with FSP035-1PI01 PSU

/facepalm

You're right. I feel so stupid right now.

The MBR10100CT I thought was a transistor. But it isn't. 10A 100V schottky diode. Pins 1 and 2 are a direct short on this one.

Digikey doesn't have one in stock but West Florida Components does. I'll probably order from them seeing as I don't have any spare parts like this around here.

Thanks guys for putting up with me. As is pretty obvious, I'm fairly new to doing troubleshooting at this level.

[PlainBill]

Re: VX922 with FSP035-1PI01 PSU

/facepalm

You're right. I feel so stupid right now.

The MBR10100CT I thought was a transistor. But it isn't. 10A 100V schottky diode. Pins 1 and 2 are a direct short on this one.

Digikey doesn't have one in stock but West Florida Components does. I'll probably order from them seeing as I don't have any spare parts like this around here.

Thanks guys for putting up with me. As is pretty obvious, I'm fairly new to doing troubleshooting at this level.

So??? I have it on good authority that even Krankshaft wasn't born knowing how to use a DMM, he had to learn. At least you ARE learning. I've known 'Electronics Technicians' who were only capable of swapping boards - and then only if they happened to grab the right end of the screwdriver.

PlainBill

[Sparky]

Re: VX922 with FSP035-1PI01 PSU

Well well...

Pulled the diode and fed external 12V power. Voila, it works.

Disassembled some gateway LCD with a bad panel and it had the necessary diode, woot! Pulled it, put it in the Viewsonic, it checks out good now.

Except from my tinkering around I've developed another short someplace on the primary side as it pops the fuse as soon as I plug it in So now I need to track that down. But other than that, I think we're good.

[Sparky]

Re: VX922 with FSP035-1PI01 PSU

FIXED

Bridge rectifier was shorted for some reason, not sure why as it wasn't when I first picked up the monitor, but I replaced that with the rectifier from the bad Gateway (same series rectifier even) and voila! It works!

I'm happy

[PlainBill]

Re: VX922 with FSP035-1PI01 PSU

FIXED

Bridge rectifier was shorted for some reason, not sure why as it wasn't when I first picked up the monitor, but I replaced that with the rectifier from the bad Gateway (same series rectifier even) and voila! It works!

I'm happy

I'm happy that you're happy. Did it cross your mind that 'Sparky' is not an appropriate name for someone trying to REPAIR electronics?

PlainBill

[Sparky]

Re: VX922 with FSP035-1PI01 PSU

lol, well I was given that nickname years ago when I first started playing with electricity (I was 10 at the time) and blew a few fuses, melted a few wires, sent sparks flying...

The name stuck