Hanns G monitor with new caps

[Pyarone]

I have a Hanns-G HH251 with the notorious symptoms of the screen going black with the power light still solid green about 2 seconds after powering on every time.

I replaced all small capacitors one day, and on the 3rd try it stayed on for about half an hour, then it went to occasionally staying on for about 45sec.

The next day, I replaced the big fat 400v 150mfd. This time it turned on and stayed on first try, looked great, about 30min later it lapsed back to dying about 50% of the time, the other 50% it stays on for about 45sec before dying.

I don't really know that much about capacitors, is it possible that they're burning out on me during that half hour period? Is there a problem because I didn't replace them all at once?

[mariushm]

Re: Hanns G monitor with new caps

Can you make a picture of the boards pointing out what you replaced?

It's possible there's a bad solder connection somewhere which only causes problems when the monitor warms up to a certain degree, so then the inverter stops working.

It's also possible there's a poor wire connection to one of the lamps, which causes the inverter circuit to stop providing power to the lamps.

[retiredcaps]

Re: Hanns G monitor with new caps

I have a Hanns-G HH251 with the notorious symptoms of the screen going black with the power light still solid green about 2 seconds after powering on every time.

2 seconds to black can be

a) bad caps
b) bad ccfls
c) bad ccfl wiring (especially the return wiring)
d) bad secondary windings on the inverter transformer

More details starting with post #19 at

https://www.badcaps.net/forum/showthread.php?t=10419

Also, see budm's Inverter tester using old CFL

https://www.badcaps.net/forum/showthread.php?t=19987

[Pyarone]

Re: Hanns G monitor with new caps

Here are photos of the two boards. Every capacitor is new from a local shop, I also added new thermal compound I got from best buy under the 3 laying down, but it's oozing everywhere.

retiredcaps, Thanks for that link, I didn't think of the search phrase 2 seconds to black.

Edit; Update: After cooling off, I hooked it back up and it's working so far on the first power up, it's been about 10min, so it does seem to be related to heating up. Also, there is no image revealed by flash-light.

[mariushm]

Re: Hanns G monitor with new caps

There's several problems here.

I see some capacitors that say NRS on them - I'm not from US but I think those are from Radioshack or some other shop, which are not really suitable for the way these capacitors are used here.
These are circuits running at high frequencies and need capacitors that can handle high ripple and have low impedance - these sold at local shops often can't handle it.

The monitor should work with them for a while as you can see, but you can't tell how long they'll last until they crap out.

Second... the pictures are a bit too far away so it's hard to tell how well you soldered them - you should try to use macro mode on the camera and get everything closer to the camera.
This being said, it looks to me like you need a bit of a soldering tutorial - please watch this when you have time: http://www.youtube.com/watch?v=fYz5nIHH0iY

I may be wrong as it's hard to tell but it seems to me ( in the last picture you attached) that the three capacitors in a line and the 2 right above them have very little solder.
The best soldering is when you can see the tip of the lead and there's a small dome of solder below it.

If there's bad soldering there, it could explain the heat issue.

The two lone capacitors on the bottom side of the board in the first picture are important for the inverters (those two rectangular things) which send power to the lamps.

Proper series of capacitors for this would be

Nichicon HM ,
Panasonic FM, FR
United Chemi Con KZE, KY
Rubycon ZLJ, ZLK

Badcaps store might have some, but may not have 25v or 35v rated capacitors you need. If so, try Digikey.com , newark.com (or farnell.com if you're not in US - it's branded as newark only in US), rs-online.com etc

[Pyarone]

Re: Hanns G monitor with new caps

Thanks for the video link, I found it to be a suitable review. I'll recheck all my joints, but I'm quite confident those are fine. Sorry about the low photo quality, the only camera I have is on my phone.

The two laying down capacitors you mentioned are indeed of questionable quality I have to admit, after I got them home I noticed they aren't even the same brand. I may look for better replacements for those positions. The shop I'm getting them from isn't like a Radio Shack, it's a wholesale electronic supply warehouse, but evidently they sometimes have random junk mixed in.

Do you think the quality of the thermal compound I'm using might be causing problems?

Edit; Update: By running the monitor caseless and face-down, I've identified a slight buzzing noise that occurs only when it's in the blacked out state, and it seems to be coming from one of the transistors right next to the 3 black capacitors in a line on the power supply board. Will attempt testing.

[Pyarone]

Re: Hanns G monitor with new caps

Update: Actually, after further examination, I now think the sound is coming from the big transformer, will try testing that.

[ben7]

Re: Hanns G monitor with new caps

Update: Actually, after further examination, I now think the sound is coming from the big transformer, will try testing that.

You are getting AC ripple on the transformer. Try another new primary cap. What brand is the current one, that you put in?

[Pyarone]

Re: Hanns G monitor with new caps

The biggest one? I think it's a Tech-cap, my shop didn't have that one in a Nichicon.

[ben7]

Re: Hanns G monitor with new caps

The biggest one? I think it's a Tech-cap, my shop didn't have that one in a Nichicon.

A 'Tech-cap'?

That sounds VERY fishy, I would suggest getting a better cap!

[Pyarone]

Re: Hanns G monitor with new caps

Ok, I'll look into ordering one, thanks!

Edit; Update: I put the old Taicon primary cap back on, and I've had another change of symptoms. Now it stays on for right about 30min every time, then dies. No more 2 seconds to black, just having to restart it every half hour or so. I'm thinking maybe redo the solder joints on that transformer? The only thing I can think of that's different now than before I replaced the primary is the solder joints.

[Undead]

Re: Hanns G monitor with new caps

Do you think the quality of the thermal compound I'm using might be causing problems?

Unless I'm mistaken, the stuff under the 3 that are lying down should be a type of caulking that glues them in place and not a thermal compound.

[Pyarone]

Re: Hanns G monitor with new caps

Ok cool then it shouldn't matter. Thanks!

[ben7]

Re: Hanns G monitor with new caps

Ok cool then it shouldn't matter. Thanks!

It does matter!

They need to be kept cool, and they are already bolted to the heatsink.
The grease helps make the thermal resistance between the heatsink and the diode much less, making more heat flow from the diode into the heatsink, keeping everything cooler.

[Pyarone]

Re: Hanns G monitor with new caps

That's what I assumed, and why I added new thermal compound, but Undead said that the board didn't originally have thermal compound, it was just a caulking to hold the cap in place. Well the solder connections on those caps aren't in danger just sitting on my desk, I don't plan to ship the monitor anywhere, so they don't actually need that extra support.

Unless you're saying the caulking was an insulator to keep heat from the board from heating up the caps? Neither those 3 caps nor anything near them are heating up much during operation, so I'm pretty sure they're safe.

[mariushm]

Re: Hanns G monitor with new caps

You have to distinguish caulk/elastic glue from thermal paste. One is not conducting electricity while the thermal paste may conduct electricity.

The white stuff by the big capacitor and the white stuff just under the transformer over a blue disc capacitor is caulk, it's like a glue to hold the components on place and to prevent vibrations.

If you look to the D260, D261 ... the transistors (or whatever they are... the things in TO220 package ... all of them are screwed down to those metal strips with a foil between them and the metal.
That foil can be just to transfer heat, but it can very well be to isolate the back side of the chip from the metal. If you mess with that foil and put thermal paste there, you might make contact between the metal on the back of the chips and the metal bar, and you cause shorts.

As the monitor works now fine, it's unlikely this is an issue.

But look at the picture, in particular at the L shaped heatsink on the left.

Under the screws of the TO220 device on the right side there IS a plastic ring - those plastic rings are usually placed there to keep the screw centered, preventing it from touching the metal of the package. That chip might be insulated from the heatsink because the back side has some voltage (or something different than what other chips attached to the same heatsink have).

The chip on the left side, on the opposite side of the heatsink, doesn't have that plastic ring, so the chip is probably screwed straight to the heatsink, maybe because on that package the metal tab is connected to Ground.

Now if this is correct and you would have made the chip on the right touch the metal, you would have a short there.

So be careful in the future. If there's thermal pads or silicon pads for insulation, you usually don't want to mess with them.

The capacitors at the bottom, layed horizontally... probably had some of that gunk to keep them from hitting the pcb. Now it looks like it's some thermal paste there or something thin there... it's a bit dangerous to see it go all the way to that inverter there ... there's 700-1400v inside that transformer. If that's thermal paste, it may not be rated to not conduct electricity at such high voltages. I'd clean that area a bit better.

[Pyarone]

Re: Hanns G monitor with new caps

Ok, will do, thanks.

Edit:

As the monitor works now fine, it's unlikely this is an issue.

It works fine until it's been on for about 30min right now, then it goes black. If I restart it right then, it lasts only a minute or two. Have to let it cool down before it will stay on for half an hour again. And this is identical with both the original primary cap and the new replacement. I'm really confused. ><