Hanns-G HG281D, LCD Monitor no power

[DIODE]

Re: Hanns-G HG281D, LCD Monitor no power

Hello I am a new member, please excuse any lapse in ediquet, I have not posted before.

I have similar problem with I-INC IF281D

Monitor will not turn on, complelty dead, no blue power light, if computer left on and connected, over last week or so the monitor will occasionsly come to life for hours, then die, no blue power light and no standby amber light.

U7 reading 0, 2.2v 4.2v (from memory, measured this 2 nights ago.)

Earlier in this thread I saw reference to replacing C603,606 and 707 based on similar symptoms.

Q1 - With 120 vac connected would anyone know what voltage should be present across the power on switch.

Q2 - Is there an accessable service manual/schematic of this monitor.

Q3 - If C603,606 and 707 defective (low uf value) should a significant ripple be measured across each?

Any helpful comments would be much appreciated, not a big fan of land fill contributions.
Dan

[DIODE]

Re: Hanns-G HG281D, LCD Monitor no power

Updated reading on U7 on Video input connection board
U7 - pin 1 - 0v
U7 - pin 2 - (center) 2.4v to 3.2v (with Fluke meter recording min/max)
U7 - pin 3 - 3.6v to 5.1v (with Fluke meter recording min/max)
Dan

[retiredcaps]

Re: Hanns-G HG281D, LCD Monitor no power

Updated reading on U7 on Video input connection board
U7 - pin 1 - 0v
U7 - pin 2 - (center) 2.4v to 3.2v (with Fluke meter recording min/max)
U7 - pin 3 - 3.6v to 5.1v (with Fluke meter recording min/max)
Dan

What is the part number for U7?

A picture of U7 and its surrounding components uploaded to this forum following my sig file instructions EXACTLY would help.

[DIODE]

Re: Hanns-G HG281D, LCD Monitor no power

Picture of board referenced in last message
Dan

[DIODE]

Re: Hanns-G HG281D, LCD Monitor no power

U7 part number reads top furthest from the pinsas follows:



84-33
0631AL


Thanks for the assitance
Dan

[retiredcaps]

Re: Hanns-G HG281D, LCD Monitor no power

U7 part number reads top furthest from the pinsas follows:
84-33

1) The suffix, -33, denotes the proper output voltage. So it should be 3.3V DC. Since your input voltage is fluctuating from 3.6 to 5.1V, this indicates the problem may lie elsewhere. For example, you may have a bad cap that is not bloated.

2) On the connector from the main board to the power board, measure the voltages of all the connectors and see if one is fluctuating from 3.6 to 5.1V. If yes, that implies there is a problem on the power board. If the voltages are stable (namely the 5V), then the problem lies on the main board.

PS. Curiousity. Which Fluke?

[DIODE]

Re: Hanns-G HG281D, LCD Monitor no power

Thanks Retired Caps

Fluke 85 , have two of them, had them for a long time,can't kill them.

I think I did see a weak 5v on the PS connector, I'll work backwards and post results.

Thanks again
Dan
BTW I could not find a data sheet for U7 using that PN in Motorola or Fairchild cross refernce lists , is ther another more generic PN for it? What is it?

[retiredcaps]

Re: Hanns-G HG281D, LCD Monitor no power

Fluke 85 , have two of them, had them for a long time,can't kill them.

Jealous! Especially given how expensive they are in Canada. It is like Fluke Canada doesn't even acknowledge the dollar parity for the last few years.

I think I did see a weak 5v on the PS connector, I'll work backwards and post results.

As a test, you can disconnect the main board and see if 5V standby is solid or not. If it is solid, then something on the main board may be dragging down the 5V standby rail.

BTW I could not find a data sheet for U7 using that PN in Motorola or Fairchild cross refernce lists , is ther another more generic PN for it? What is it?

Two years ago I had no idea what a voltage regulator was. Now I even know the darn part numbers. Try 1084-33.

http://www.digchip.com/datasheets/do...ber=AIC1084-33

[Arioch5]

Re: Hanns-G HG281D, LCD Monitor no power

Hello all,
...
I decided to disassemble the monitor again and take a close look at the logic board.
There were signs of heating near the two voltage regulators.
After looking closely at C80 and C83 I found they were "Xunda" brand "RK" series, 100uf/16 volt.
I don't trust these kind of less known brands. I did repair a lot of PCC boards and also some monitors and the failing caps were nearly always less known, mostly Chinese caps.

...

I decided to take the risk, even if it would show some improvement then at least I could try to get better caps later on.
I was pretty sure the problem was C80 and C83 on the logic board, but didn't want to replace blindly all of them. I wanted to know which caps were causing the problem.
Finally I replaced C80 and C83 both 100uf/16V and also C13 and C14 both 10uf/25V because they were near by and probably stressed by heat already.

Thank You!

Sorry to interrupt but I just wanted to let everyone know this worked for me as well. I have the same monitor as my work was disposing of it due to a wavy image for the first 5-10 minutes after power up and the buttons on the display not fully functional (could not adjust brightness stuck on 100).

After inspecting the power/logic boards I found the logic board had clear signs of heat damage by the regulators as described above. I do not own an ESR meter so I replaced all 7 capacitors in this region of the board last night. After the repair the monitor turns on and has no wavy image instantly and the buttons work again. Total cost was about $15 as I ordered spare capacitors and had to buy some solder weave.

Thanks BadCaps.net I'm really going to enjoy my new monitor!

The only bad experience I had was that the ground pins on these capacitors do not seem to have thermal reliefs so it's a royal PITA to get the ground pins out/in.

[DIODE]

Re: Hanns-G HG281D, LCD Monitor no power

OK I tested the 5v supply to the main board. This is the 5vsb (Stand By 5v) without connection to the main board the voltage is rock staedy at 5 volts, connect the main board the and the 5vsb fluctuates 3.6 to 5.1. The 5vsb is rated for 1.5 amps (per lable on PS see attached pics) so I measure the current flow while connected to the main board and it's darwing 40 ma. So me thinks the 5vsb in the power supply is wonky, not outputing anywhere near 1.5A , I poke around with the meter and trace the 5vsb to D701 and C701(see attached pics). With the main board disconnected I measure 5 volts across c701 (+ to -) and 5 volts across D701 (anode to cathode)?? so I'm thinking if D701 is suppose to be a regular silicon power diode it's deveope a little reisitance (no pun intended) to conducting @ 0.7 voltage drop. I have not worked on switching power supplies Is there anyone that knows if D107 for this PS is a zenier or ????

Dan

[retiredcaps]

Re: Hanns-G HG281D, LCD Monitor no power

So me thinks the 5vsb in the power supply is wonky, not outputing anywhere near 1.5A , I poke around with the meter and trace the 5vsb to D701 and C701(see attached pics).

You can try jumping the power board on like so

https://www.badcaps.net/forum/showpo...1&postcount=45

This will rule out the main board dragging the power supply down.

PS. No pics in post #190.

[DIODE]

Re: Hanns-G HG281D, LCD Monitor no power

Sorry about the lack of pics, stuggling to get file size lower, finally uploaded
Dan

[budm]

Re: Hanns-G HG281D, LCD Monitor no power

If the 5V SB is fluctuating with only 40ma current draw, then you need to get this section working first. I use 6v lamp as a load for 5VSB testing, you can get 6v 250ma from Radio Shack, that way you will not have plug/unplug it from the main board, I also use 12V 10~20Watts car lamp for testing the 12V section, and 2 12v in series for the 24v section, this way I can test the power supply by itself.

[retiredcaps]

Re: Hanns-G HG281D, LCD Monitor no power

the 5vsb fluctuates 3.6 to 5.1.

BTW, since I was the first person to help on this thread way back in Sept 2010, Mishannya had the same problem with fluctuating 5V standby. With an ESR meter, Mishannya found dry caps with high ESR and changed them out.

You may want to consider this strategy as well. Details in the first two pages of this megathread.

[DIODE]

Re: Hanns-G HG281D, LCD Monitor no power

You can try jumping the power board on like so

https://www.badcaps.net/forum/showpo...1&postcount=45

This will rule out the main board dragging the power supply down.

PS. No pics in post #190.

I looked at the link re 1 to 3 k resistor connect 5vsb to 5vmain, I will try that but I think the 5vmain is not on until the monitor is turned on and that needs the 5vsb to turn on, I'm thinking I need to pull D701 and test it, I may cut one of it's leads so not to heat it and lose the symptom of defect, D107 is sort of behaving like a diode in series with a 400-1k ohm resistor, if in fact it is an ordinary si power diode.
And thanks for the suggestions
Dan

[DIODE]

Re: Hanns-G HG281D, LCD Monitor no power

If the 5V SB is fluctuating with only 40ma current draw, then you need to get this section working first. I use 6v lamp as a load for 5VSB testing, you can get 6v 250ma from Radio Shack, that way you will not have plug/unplug it from the main board, I also use 12V 10~20Watts car lamp for testing the 12V section, and 2 12v in series for the 24v section, this way I can test the power supply by itself.

Thanks for those suggestions budm, I was also considering using 3 x 1.5v bateries in series to get the 5vsb up so the 5vmain could be switched on. If I only had a schematic of this I could manully start the 5vmain and jump it through a 1k to 5vsb......

Little guys hockey parctise in 4.5 hrs, I'll post tomorrow thanks again

Dan

[budm]

Re: Hanns-G HG281D, LCD Monitor no power

I just looked at the pictures of the power supply you have posted, I really suspect those caps to be bad, see PDF. You can try heating them up with hair dryer to see if the lamp will light up steadily, unless the caps are really dried out.

[retiredcaps]

Re: Hanns-G HG281D, LCD Monitor no power

I looked at the link re 1 to 3 k resistor connect 5vsb to 5vmain,

I think you misunderstand. We are suggesting to jumper 5V SB and PS_ON. PS_ON is a signal generated by the main board that is usually 3V or slightly higher. PS_ON tells the power supply to turn on.

It is likely jumpering PS_ON to GND on an ATX power supply.

PS. Have a look at post #194 first before jumpering. You may have missed it while you were posting and it is saying ths same thing as budm in post #197.

[DIODE]

Re: Hanns-G HG281D, LCD Monitor no power

So after exhausting all the other tests I dusted off the scope and found intermitant/flaky AC power going to D701 Anode, Attached pics (sorry about the quality). The AC supply frequency to D701 is varying between 4 K Hz and 9 K Hz going low to high on at about 45ms intervals (based on frequency counter - Fluke 85 and looking at the DC waveform) I could not sync the scope to clearly see the AC faveform attache pic as good as it gets - "AC Voltage....

The DC that varies from 3.2v to 5v is shown in pic "DC on D701 Cathode, 1v per div, 0v @ bottom 10ms per second per horizontal division. Ther looks about 4.5 horizontal divisions , this is where I get the 45ms of 9k/4k AC frequency shift, the AC freq rate of change on anode D701 is the same rate of DC fluctuation on the D701 cathode , you'd agree if you could see it here.

Also attached is repeat of pic from previous post showing D701
All of the above tests were connected with power on and all circuits/boards connected where they should be.

So I am thinking it is a flaky high frequency AC power supply feeding the D701anode!

Anyone out there skilled with debugging power osciliators, or know which componets make this circuit oscilate?

Any all/suggestion are most welcome- thanks in advance
Dan

[budm]

Re: Hanns-G HG281D, LCD Monitor no power

That 8-pin IC is the all in one SMPS IC, get the P/N and then you can see how simple it is being used. I still suspect the DC filter caps in the Primary side where the IC is.