Hanns-G HG281D, LCD Monitor no power

[selldoor]

By replace I meant put back the old one. - unlikely to be bust.
As long as its firmly in dont go overboard as it will have to come out again
to get the screw back.
Please can you update your profile with country and mains voltage.

[mmamuk]

I have a HG281DJ monitor which has no power light whatsoever. I picked it up from work. They replaced some capacitors to the Power Supply board but it still didn't work. So they dumped it because they didn't want to spend time diagnosing the problem. Anyway I picked it up to see what I could do with it. It is a 2008 model.

I came through to your site by searching for "HG281D repair". Anyway trawling through this forum has been a fascinating journey and I have learned lots.

PSON is always zero.

All pins are zero except for +5VSB which has 4.92 volts rock solid if not connected to the main board, but fluctuates between 4.15V and 4.60V when connected to the main board as does one of the pins on part U7 (on the main board).

I short circuited the PSON and +5VSB and lo and behold I could measure +12V on the 12V pins and +24V on the 24V pins. I had the main board disconnected for this exercise.

This suggests the Power Supply board is working fine and the problem is the main board. So the question is where do I go from here?

Any suggestions?

I have taken some photographs which I will download onto the site later on in the day.

Thanks.

[retiredcaps]

Originally Posted by mmamuk

I came through to your site by searching for "HG281D repair". Anyway trawling through this forum has been a fascinating journey and I have learned lots.

1) Thank you for doing some research and reading through the megathread. When people ask about this monitor, most, but not all, the problems have been documented and resolved for future people.

Recently, a couple of "noobs" can't even bother to read a 3 page post where the answers (how to test, part numbers, suggested suppliers) are in plain site.

All pins are zero except for +5VSB which has 4.92 volts rock solid if not connected to the main board, but fluctuates between 4.15V and 4.60V when connected to the main board as does one of the pins on part U7 (on the main board).

This suggests the Power Supply board is working fine and the problem is the main board. So the question is where do I go from here?

2) Excellent detective work so far. You may have a short somewhere on the main board. It took me 20 months to figure out, but I had a similar problem that might give you some clues? The below is only 24 posts.

http://www.badcaps.net/forum/showthr...994#post114994

And yes, I'm using the very same monitor to write this post. Notice that PlainBill had the correct diagnosis in the very first sentence in post #2.

3) The other possibility is that the 5V rail is failing under load (that is, when the logic card is hooked up). You can try hooking up an external load onto the 5V rail to see if it is steady or not.

4) Please follow the sig file below exactly when posting pictures.

[tom66]

Dropping voltage under load is a very common sign of bad caps, and I would replace them immediately with that symptom. If your main board was drawing enough current (probably >3A) to make the PSU output drop and the PSU was okay, something on the main board would start letting out the magic smoke quite quickly. (The t-con draws the most power from 5V.)

[retiredcaps]

Originally Posted by tom66

Dropping voltage under load is a very common sign of bad caps, and I would replace them immediately with that symptom.

That is exactly what Mishannya (the OP) found out with an ESR meter back on page 1 and 2 when I was helping him with the original problem.

Usually for this monitor, none of the caps *look* bad, but this monitor runs temperature hot and the caps may have dried out from the heat.

[mmamuk]

Thanks for the replies so far.

My JPGs vary in size from 1.9MB to 2.6MB, so I'll need to reduce them in size these before I can post them.

I think I need a hands on approach in resolving this issue, going forward.

I'm a mathematician / software engineer by profession and have minimal hands on electronic hardware diagnostics experience.

I don't appreciate the functionality of capacitors, inductors etc., due mainly to lack of knowledge and understanding of these, etc.

I can see this as a potential hobby, going forward, in particular that of resuscitating discarded electronic equipment. It all depends on whether I'm successful in repairing the current broken monitor.

On the surface of it it looks as if the problem is a simple one but its effects seem to be profound, in that one has a malfunctioning monitor which is totally out of service because of one potential minor setback somewhere.

I have minimal tools at my disposal, the main one being a multimeter, the one I got is SMART. Although it has FARADS as an option I didn't see anything functioning when I attempted to measure the capacitance of a capacitor.

How do I locate the 5V rail and how do I determine where the short circuit may be occurring?

Sorry if all this is a bit too basic for the more professionals on this thread.

[jetadm123]

Originally Posted by mmamuk

Thanks for the replies so far.


I have minimal tools at my disposal, the main one being a multimeter, the one I got is SMART. Although it has FARADS as an option I didn't see anything functioning when I attempted to measure the capacitance of a capacitor.

How do I locate the 5V rail and how do I determine where the short circuit may be occurring?

Sorry if all this is a bit too basic for the more professionals on this thread.

You should remove the cap from the board for proper measurement as other components on the board can cause erroneous readings. You might want to post a photo of your meter, so members can assist you with using it.

As for the 5V rail, members can usually point it out to you in a photo. Now, all we need are the photos......

[mmamuk]

Attached are the JPGs.

[jetadm123]

If you look underneath your power board, the voltage for each pin of each wiring harness should be silkscreened on the board.

Since you are getting a 5VSB voltage, then try measuring the voltage output of each voltage regulator (looks like they're labeled V-33S and V18S) located in the upper left of your first photo. They might be labeled something like 1117-1.8, where 1.8 indicates the DC output voltage.

[mmamuk]

Originally Posted by jetadm123

You should remove the cap from the board for proper measurement as other components on the board can cause erroneous readings.

Which CAP would you suggest removing? This would be a first for me as I've never removed a component from a PCB before.

What would be the purpose behind removing the CAP you had in mind?

A step by step approach at this stage would do me a world of good in terms of learning the art of Hardware Diagnostics.

Thanks for the response.

[selldoor]

Pictures are not really sharp enough for troubleshooting they need to look like this - good light is the key and no flash.
Examples of what is needed
http://www.badcaps.net/forum/attachm...1&d=1290283049

http://www.badcaps.net/forum/attachm...7&d=1280167246
In Pic 4 and I hope I am wrong all 4 ics look burnt - can you do a decent picture of just that corner

[jetadm123]

Originally Posted by mmamuk

Which CAP would you suggest removing? This would be a first for me as I've never removed a component from a PCB before.

What would be the purpose behind removing the CAP you had in mind?

A step by step approach at this stage would do me a world of good in terms of learning the art of Hardware Diagnostics.

Thanks for the response.

I'm not suggesting you remove any caps. You made a comment that you were not able to read a cap value off your meter and I was merely suggesting the proper way to read the capacitance value.

[mmamuk]

Originally Posted by jetadm123

Since you are getting a 5VSB voltage, then try measuring the voltage output of each voltage regulator (looks like they're labeled V-33S and V18S) located in the upper left of your first photo. They might be labeled something like 1117-1.8, where 1.8 indicates the DC output voltage.

They're also labelled as U7 and U8.

U7 from left to right reads:

4.09-4.33 Volts (fluctuating), 2.82-3.03Volts (fluctuating), 0

84 33
0625AL


U8 from left to right reads:
2.82-3.01 Volts (fluctuating), 1.56-1.70 Volts (fluctuating), 0.0

7F3L
17 18L

[mmamuk]

Originally Posted by selldoor

Pictures are not really sharp enough for troubleshooting they need to look like this - good light is the key and no flash.

I agree with you and I did have reservations about the quality of my photos. I'll re-do some or all of them without using the flash.

My digital camera has just run out of charge so now I have to wait until its charged up to take any additional shots.

I'm not sure that any of the photos I take are going to be any where near as good or crisp as the examples you've just shown.

In Pic 4 and I hope I am wrong all 4 ics look burnt - can you do a decent picture of just that corner

The ICs you refer to are on the Power Supply board and I think my diagnostics so far has indicated the problem is in the main board (comment#262). I may be wrong in my diagnosis though.

[mmamuk]

Originally Posted by jetadm123

Since you are getting a 5VSB voltage, ...

I was actually getting 4.92 Volts on the 5VSB pin. Is this a problem?

Also, the middle pin of U7 is not connected to the PCB. Is this deliberate?

[retiredcaps]

Originally Posted by mmamuk

They replaced some capacitors to the Power Supply board but it still didn't work.

As others mentioned, we need some higher quality photos, but from what I can see it looks like the power board has all Panasonic caps (T vent). So for now, let's assume the power board is working properly.

I have taken some photographs which I will download onto the site later on in the day.

Take your boards to a window ledge on a sunny day. Put your camera on macro mode for clearest and sharpest pictures.

[retiredcaps]

Originally Posted by mmamuk

I don't appreciate the functionality of capacitors, inductors etc., due mainly to lack of knowledge and understanding of these, etc.

Wiki is a good start for learning the basics of the above.

I can see this as a potential hobby, going forward, in particular that of resuscitating discarded electronic equipment. It all depends on whether I'm successful in repairing the current broken monitor.

This could be a difficult problem to find so I would not base your decision on whether this is a future hobby or not on this one lcd.

I have minimal tools at my disposal, the main one being a multimeter, the one I got is SMART. Although it has FARADS as an option I didn't see anything functioning when I attempted to measure the capacitance of a capacitor.

One retiredcaps bonus point for a picture of your multimeter. Measuring capacitance is not as important as measuring ESR on a SMPS board. However, we can assume that the new high quality Panasonic caps are all within spec and working properly.

[retiredcaps]

Originally Posted by mmamuk

How do I locate the 5V rail and how do I determine where the short circuit may be occurring?

The pin that measures 5V is your "rail". All other components that have continuity (which you can measure with your multimeter) are on that "rail". We need much better pictures of the logic board to see the components that might be on the 5V rail.

[retiredcaps]

Originally Posted by mmamuk

They're also labelled as U7 and U8.

U7 from left to right reads:

4.09-4.33 Volts (fluctuating), 2.82-3.03Volts (fluctuating), 0

84 33
0625AL

Since the 5V voltage is fluctating, the voltage regulator will not output the correct voltage (which is 3.3V in this case). It only outputs 2.82 to 3.03 which is not enough for the main board to work properly.

The 33 in the part number above denotes the expected output voltage usually +/- 1%.

[retiredcaps]

Originally Posted by mmamuk

I was actually getting 4.92 Volts on the 5VSB pin. Is this a problem?

Most 5V standby are "regulated". At 4.92, the voltage is 1.6% off which is okay. This figure also depends on the accuracy of your multimeter. If the voltage were 4.4V, then there is something obviously wrong.

Also, the middle pin of U7 is not connected to the PCB. Is this deliberate?

Yes. The "fat tab" and pin 2 are electrically connected.