Dead but clicking Hanns-G HC194D?

[Mafi]

Please be patient with me this is my first post.

A little Background on this. I had been having issues with this monitor waking up from sleep mode. I have two of these side by side. One was HDMI and the other DVI connected. Recently this HDMI one would wake and it would keep trying various resolutions blinking on and off before finally coming back on. I discovered if I shut it off and back on it would usually lock in and work fine right away. This was for several weeks. I came home to have it not come on but I could hear a ticking sound from inside and it wouldn't come wake up.

I pulled it apart to discover that I had partly recapped it at some point years ago. I have no idea why I only did 6 of them and not the other other 6. I don't see any obvious bad caps but obviously I don't trust the other 5 and the big 100uf 400v one either. With PS board unplugged from everything I powered it up and I could hear the ticking sound coming from the transformer about once a sec. I checked the outputs and was getting 4.98v on the +5 volt but only about 6.3v on the +12 and that was bouncing around.

The caps c101 and 102 as well as those down the right side of the pics are Panasonic FMs I put in some time ago. Image 8 shows the legs on the large cap and I had some kind of baked on dust on the left one that almost made me think it could have been leaking. It was likely just normal dust but some of it in there seemed to be almost granular. could be nothing but it just seemed weird to me so I thought I would mention it.

At a minimum I plan to try and replace the caps I missed before but I am wondering if there is a better way to proceed. I do not know theory so consider me an idiot who can barely solder. Having said that if anyone can help guide me I would appreciate it. I am sorry the pictures are so poor, I miss real cameras instead of cell phones.
I hope you can help
-Adrian

[Per Hansson]

Re: Dead but clicking Hanns-G HC194D?

Normally this would be the small startup cap on the primary side that is dead (C8 or C10).
However I can visually see that the small green caps inside the heatsink (C62 for example) are bulging.
So just replace all caps you did not replace the last time.

[Mafi]

Re: Dead but clicking Hanns-G HC194D?

Thanks for replying. I think it may be a result of my terrible pictures but I will go after them first and see where I stand. They didn't seem to be bulging to me, or at least not near as bad as the ones I have seen in the past. I will let you know after I get them replaced. I was afraid it was something more like bad transformer or a diodes and was figuring I could get all of the parts in one order. Would you recommend that I replace the big 100uf 400v one as well since I have it apart?

-Adrian

[Per Hansson]

Re: Dead but clicking Hanns-G HC194D?

Yes if you anyway need to order the parts do replace the main 400v capacitor too.
They do go bad, especially when the unit has a PFC booster stage.

[momaka]

Re: Dead but clicking Hanns-G HC194D?

I concur with Per here - just replace all of the electrolytic caps that you didn't replace the first time around (including the very small ones on the primary side - i.e. one being the startup cap.) The two green ones near one corner of the secondary heatsink definitely look bulged to me. And here is the thing: caps don't have to look extremely bulged or leaking to be bad. Even the slightest bulge is an indication that excess gas (Hydrogen) has already built up inside the cap from the electrolyte breaking down, which means the cap is failing.

As for the big cap - you don't really need to replace it in this case, as this PSU does not have an APFC circuit... but if the cost of $2-3 extra doesn't matter to you, then you might as well get a replacement for it too. With that kind of recap, this monitor will very likely function well past its relevant useful life.

Now while at it, also take a peek at what's on the video/logic board of the monitor, in terms of electrolytic caps. There may be a few more small caps on there that probably could also benefit from being replaced, as video/logic boards always have at least one or more linear regulators... and those often run hot too. I usually only replace the small caps near the voltage regulators on logic boards, if the regulators looked like they were running hot. If not, I forgo changing them.

[Mafi]

Re: Dead but clicking Hanns-G HC194D?

Well, I just got my 6 caps and soldered them in. I even replaced the large one. I plugged in the board and I could hear the ticking still and when I checked the output connections I am getting 6.21-6.25 on the 12v pins and 4.98 on the 5v pins. so nothing really different. I did not put it all together yet. I thought I would see if you had any more input. I was able to isolate the ticking sound though it seems to be coming from the transformer. Any thoughts?

[momaka]

Re: Dead but clicking Hanns-G HC194D?

OK, try this: disconnect PSU board from the logic/video board, then plug in the PSU board into the wall and check those output voltages again. Are the 12V and 5V rails stable and close to their nominal values?
- If not, desolder one side of jumpers WJ11, WJ12, WJ13, & WJ14 and try the above procedure again. These jumpers should disable power going into the inverter MOSFETs. If you only get 12V rail to be stable after this, there may be an issue with the CCFL inverter circuit.

Also, does this monitor happen to have an audio input/output or any built-in speakers? Reason I ask is because sometimes those use the 12V rail... so trying to see if there's an issue with that (circuit is typically located on the video/logic board.)

[Mafi]

Re: Dead but clicking Hanns-G HC194D?

Sorry I should have clarified. I had the PS board by itself when I plugged it in. It was not connected to anything when I took the voltage readings on the connectors. I will desolder one side of each of the 4 jumpers and see what I get. Yes it does have built in speakers but since it wasn't connected that should rule out the video/logic board right? Thanks again for all the guidance.

[Mafi]

Re: Dead but clicking Hanns-G HC194D?

Ok I desoldered the one side of the four jumpers mentioned and I am still getting the same results. The only thing I can add is that I had my test leads clipped onto the output pins for the 12v and ground and as I plugged it in I noticed the voltage on my meter first flashed ~10 and then quickly worked its way down to about 6.43V. It was still 4.99 on the 5V pin. Sorry life got in the way a bit so it took a bit to get it done. Where to next?

[Mafi]

Re: Dead but clicking Hanns-G HC194D?

Hello? Is there anyone out there that can help me zero in on my issue? We've ruled out a few things but now that I am deeper into it I could really use some help...

[R_J]

Re: Dead but clicking Hanns-G HC194D?

In post #6 you say you replaced 6 capacitors, Which ones? the board has location numbers. I suspect you did not replace the two startup ones.

[Mafi]

Re: Dead but clicking Hanns-G HC194D?

RJ, Thanks for replying. I replaced C5, C8, C10, C57, C59, C62. [At some point a while back (years) I had replaced C51, C52, C54, C56, C101, C102.] So at this point there are no original electrolytic caps on the board. I was still getting the ~6.43v on the 12v side at the CN101 connector. It currently has jumpers WJ11,12,13,14 disconnected to remove the Inverter section as suggested by Momaka in post #7 but it had no effect. That's why I am stuck. So I open to any suggestions.

[Mafi]

Re: Dead but clicking Hanns-G HC194D?

Hello?? Anyone?? I now have a board pulled apart with caps replaced and jumpers disconnected and I have made no progress. Can anyone chime in as to what to do next?

[CapLeaker]

Re: Dead but clicking Hanns-G HC194D?

How do you turn the power supply on? Are you forcing it, or are you plugging the main board back in? If you are turning the PSU on with the main board, I suggest you force it on without the main board.

[R_J]

Re: Dead but clicking Hanns-G HC194D?

What is the number on IC53? I believe this is a scr that is there for protection, it should have a couple resistors connected to it's gate and then two zener diodes, one connected to the +5v and one to the +12v.

[Mafi]

Re: Dead but clicking Hanns-G HC194D?

Thanks for replying. Capleaker, I have been just plugging the PS board in by itself and those are the readings I am getting. Is there something I am missing? I am just reading CN101. I see there is a marking that says On/Off as well as one that says ADJ. I have no idea how this works.

RJ, IC53 is a KIA7812A which seems to be a 3 terminal voltage regulator.

[Mafi]

Re: Dead but clicking Hanns-G HC194D?

I just checked the IC53 and seem to get input of 7.6V in with 6.2V out. Hopefully that helps a bit. I am guessing that means I am not getting the proper voltage since that regulator is supposed to be 12v out.

[stj]

Re: Dead but clicking Hanns-G HC194D?

if the 5v is good and both voltages are from the same transformer,
logically either the 7812 regulator has an internal fault dragging the voltage down, or you need to look at what is between the regulator and the transformer feeding power into pin1
it could be as simple as a bad rectifier diode.

[Mafi]

Re: Dead but clicking Hanns-G HC194D?

Just curious can the 7812 be tested in place? like could I supply 12v from a battery to the input and see what I get out? The thought just occurred since I have a motorcycle battery charging right next to it on my work area. Obviously I am getting further from abilities in trying to trace back further on the board to see what could be causing the 6.3v on the 12v.

[Per Hansson]

Re: Dead but clicking Hanns-G HC194D?

You might be able to do that but it could cause more damage too.
Better would be to lift the input leg of the 7812
Then power it up and see what voltage you have on the input then.