HP vs17e turns on for 3 seconds then goes off

[riget]

Hi all, my HP lcd monitor vs17e turns on for about 3 seconds then turns off, I can see with a torch what's on the screen so it's the backlights?
I found this site: http://www.instructables.com/id/Repairing-a-vs19e/ that shows the problem with a similar lcd, I've change a few capacitors but it's still the same, none of the capacitors looked bad.
Any one know any known faults, I'll take some pics later.
Thanks.

 

[riget]

On this pic I changed the 5 caps on the left, and the one at the top.

A pic of the back

What is this chip? and should the centre leg be disconnected like that?
It doesn't look burnt, just looks like it's never been connected.

 

[(*steve*)]

On this pic I changed the 5 caps on the left, and the one at the top.

Sounds like a good move. Were they replaced with low-ESR capacitors?

Were you able to measure the ESR of the capacitors you removed?

Was there any change in behaviour at all?

What is this chip? and should the centre leg be disconnected like that?
It doesn't look burnt, just looks like it's never been connected.

It could be almost anything (I can't make out any markings on the case)

But the tab is connected to the centre pin in these packages. It's not unusual for the centre pin to be like this.

edit: When the backlight is on, does it appear at all pink in hue?

 

[riget]

Sounds like a good move. Were they replaced with low-ESR capacitors?

Were you able to measure the ESR of the capacitors you removed?

Was there any change in behaviour at all?

I can't measure the esr, I only have a standard multimeter, the one's I replaced with had a slightly higher voltage as recomended on another site.
no change at all in behaviour.

It could be almost anything (I can't make out any markings on the case)

But the tab is connected to the centre pin in these packages. It's not unusual for the centre pin to be like this.

edit: When the backlight is on, does it appear at all pink in hue?

I'll take a look at the markings and let you know later, so that centre pin not being connected can be normal?
Picture is fine for about 3 seconds, doesn't look pink.
Thanks.

 

[(*steve*)]

I'll take a look at the markings and let you know later, so that centre pin not being connected can be normal?

Perfectly normal.

Picture is fine for about 3 seconds, doesn't look pink.

"Pink" is apparently a symptom of failure of the lamp. I can't confirm it though.

I have had a display go pink before it died and it exhibited the same symptoms. It was lit (although dim) for a few seconds before the backlight went off.

 

[riget]

On the chip it says: UTC LD1117AL 33AjeTLDF
but if the centre pin not connected is normal I don't think it's the problem.

Can anyone tell me what area of the board I should be looking at for the inverter? Or is it anywhere?

 

[(*steve*)]

it's an LD1117. It id a 3.3V 1A low dropout regulator (lead free). It must be either TO253 or TO263 package because, as you can see from the datasheet, these don't have the centre pin connected. My guess is that it's a TO263 because the pad layout on the board appears to allow for either this package or the functionally equivalent TO263-3 (which has the full centre pin).

The inverter is the entire left hand side of the board (as viewed from your first component side photograph).

 

[riget]

Cheers steve, after a bit of checking with my ohm meter, I'm going to change the cap at the top, just right of centre, it's 1000uf 16v, I've ordered the same of ebay, it just gave me different readings with the ohm meter, not sure if it could give me the fault I've got but I'm enjoying trying to get it to work.
Thanks
pete.

 

[(*steve*)]

Are you replacing them with low ESR capacitors?

 

[riget]

Hi m8, this is what add says:

Radial Capacitor 16V 1000uF 105°C EXR
Low impedance
Dimension 10mm x 21mm
Lead spacing 5mm
Lead free /RoHS comliant
These are quality capacitors, new stock

 

[riget]

I got the cap today, fitted it, but the old one gave me the same reading as the new one when not on the board, I'm not using a proper tester so hoped it still could be faulty.
I turned it on and at first it gave the same fault, went off after 3 seconds, I tried a few times and it stayed on the first time in about 3 months of trying, I've tried it several times now and it's working every time.

 

[Resqueline]

Maybe the ESR got a little lower with the first few tries and came inside tolerable levels. It will increase as the cap ages though, so it may fail in a few months/years from now depending on use.
A rough way to compare ESR is to charge up the cap with a 9V battery, and then short it with a screwdriver. The more sparking the better ESR.
There are really big differences between caps when it comes to ESR, even between low-ESR types. You'll need to check the manufacturers data sheets to know. You also need to be suspicious about counterfeit/relabeled caps when buying on eBay. Even reputed computer manufacturers have been hit by the fake plague.

 

[(*steve*)]

As Resqueline suggests, ESR decreases with increasing temperature.

If some capacitor is marginal, it may have it's ESR drop below some critical value after some time operating.

If the problem recurs after the equipment as been off for some time (and presumably cooled) then you might start to suspect that.

 

[(*steve*)]

This may be of interest. Incidentally, it is the same ESR meter as the one I use.

Worth every cent. (and it's not very expensive as a kit either).

 

[riget]

Cheers guys, I don't think it's ok, I've had to turn it off and on again to get it to stay on, but this is the first time it's stayed on, so as I only changed that 1 capacitor it must be something to do with that.
I'll look into getting an esr meter, as I'm getting more into doing electrical repairs, thanks for the link.

 

[55pilot]

I would be shocked if the cap you have replaced had anything to do directly with your problem. The cap is part of the input side of the voltage regulators and unlikely to directly impact the drivers. What you have experienced is likely the result of physical manipulation of the board during the repair and installation process.

The failure you are describing is likely because the safety circuit in the CCFL driver is kicking in. It either thinks that one or more of the bulbs is not present or that they are drawing too much current.

Looking at the pictures, this looks like a really crude CCFL driver. The two rectangular black blocks with yellow sides are transformers, quite likely set up as Royer transformers. Each transformer drives two bulbs. The bank of diodes in between them near the edge of the board looks for the maximum voltage and trips the safety circuit if the voltage stays too high for too long.

On the back side of the board in this area, there is an 8 pin black chip, which is likely an op-amp, comparator or ASIC that does the comparison. Are there any components in that area that look damaged? Do any of the small glass diodes look damaged? Are the sense resistors next to the transformers OK? Is any pin not soldered down well?

Lastly, one really dumb question. Have you looked at the bulbs and made sure that all 4 light up? Since the safety circuits are all tied together, if one bulb fails, the whole circuit will shut down, even though the other 3 bulbs are functioning properly.

Working with circuits like this can be frustrating when you do not have the schematics or the tools to actually dig into it and find the problem. If I had the schematics and the required tools along with this board in front of me, I would have likely diagnosed and fixed the problem in less time than it took for me to read this thread and post this message.

---55p

 

[(*steve*)]

The 2 most common problems with these inverters are the caps and the CCFL tubes.

It's often really hard to see the CCFL tubes without lots of disassembly. They're also extremely fragile and will break if you look at them the wrong way.

Be careful.

edit: Let me add to that -- the tiny inverter boards in laptops often die in more spectacular ways. Some have the evidence of past pyrotechnics.

 

[55pilot]

Let me add some more up and coming "most common" ways for things to die: Tin whiskers and unreliable solder joints. They are a byproduct of lead free solder mandated by the EU's RoHS (Reduction of Hazardous Substances) directive that went into effect a few years ago.

The lead free solder is just as bad for the environment as the lead based solder and is far less reliable. It does not have the mechanical strength. It is susceptible to tin whiskers (google it if you do not know about it). It requires much higher temperatures to solder the parts in manufacturing. The exposure to higher temperatures reduces life of the components.

The end result is that electronics made in the last few years are going to start failing much sooner than their predecessors, all because of unreliable solder joints and shorts on the board due to tin whiskers.

Welcome to the new and improved world!

---55p

 

[(*steve*)]

I fear tin whiskers more on boards that have very fine pitch SMD components. Incidentally, it is highly likely that this board is "lead free".

I agree that the lead free solder is problematic in many ways. It is no longer a simple case of looking for "dry joints".

However there are now a bewildering array of lead free solders, all having their own set of problems. It is essentially impossible to predict what sort of issues a board will have because it's almost impossible to know what sort of solder was used.

You even have to ask -- what solder will I use to repair this board? Frankly, I use my tried and true lead containing solder. Will mixing the solder have implications (beyond technically breaching ROHS)? I have very little idea. If it's fixed, at least it's better than it was...

 

[55pilot]

Frankly, I use my tried and true lead containing solder. Will mixing the solder have implications (beyond technically breaching ROHS)? I have very little idea. If it's fixed, at least it's better than it was...

I do not deal with repair much, so I can not say much form that aspect. But I can tell you from the original manufacturing angle. Professional manufacturing departments are unwilling to mix lead and lead free solder because the mixture it creates has pretty bad properties. This is for industries that are exempt from RoHS. Certain military ICs are available only in lead based packages and it is creating a havoc because they are having problems when they mix those with RoHS parts on the same board and try to use automated manufacturing.

As for the legality of what you are doing, it MAY actually be legal. At least an early draft of the RoHS directive exempted repairs, so you could legally repair a RoHS board with lead solder. I do not know if that survived into the final rule.

---55p