HANNSPREE HF289H Black Screen No Power

[selldoor]

Ok easy bits first

TCon board white oblong Fuse F400 near socket at top of picture (4 of7)
Inverter board Pic (3of 7) left hand bottom- white oblong fuses F1 & F2

Can you test them- (Power off) meter on 20 ohms probe on each end report result - should be same as touching probes together.

I checked the big capacitor underneath the metal plate and it was reading 280vDC
Hmm!I think that is either too high or too low - did you have your meter on DC? - can you check it again.

[welch_41]

Good news and bad new -
I checked those fuses and they read like you expected. Then I reread the big capacitor (using a different multimeter thinking that maybe I had a bad one), huge mistake. It caused an arch and burned the board. Caught me off guard and caused the dogs to jump. I'm not sure if I fried that capacitor because now I'm not getting any reading. You can see the burn in the attachment.

[welch_41]

Out of fear that I might have killed this board, I did some extensive searching and found a reseller that has a few of these power supplies available for sale. Should I go ahead and drop the coins on buying a replacement?

[selldoor]

Wow! - I am an optimist and think the board might be repairable, but it is your call.
I can only suggest what happened either you got the polarity wrong or had your meter on the wrong setting.

"I'm not sure if I fried that capacitor because now I'm not getting any reading."

If you are using the same meter that was involved its just as likely you fried the meter. It may have a fuse you can replace?

If you can clean up the damage zone with meths or isopropyl alcohol and take another pic we can look at repair. If you get a meter to work test the two resistors and the diode D106 - also test the traces for continuity from
(it looks like R129 to the D106)

[welch_41]

I'm usually and optimistic but just as a safety net, I ordered a new power supply. However, I'm still going to see if I can repair this cooked unit to resale or have as a backup. I'll check the flow of electricity between the numbers that you pointed out while re-posting a clean photo of that blemish. Thanks.

[retiredcaps]

Originally Posted by selldoor

If you are using the same meter that was involved its just as likely you fried the meter. It may have a fuse you can replace?

As selldoor suggested your multimeter may be fried. Post a picture of it and the probes. Some people use their probes when they are falling apart or have obvious cut/nicks in the wiring.

[welch_41]

I was hesitant on using the multimeter because it was free from Harbor Freight. For those of you that don't know what Harbor Freight is, it's a tool/hardware store that offers the cheapest items that you can buy at your own risk. I can take some pictures of the multimeter and post later. It seems fairly new without any cracks or breaks. So how would I check to see if it were fried?

[retiredcaps]

Originally Posted by welch_41

I was hesitant on using the multimeter because it was free from Harbor Freight.

1) My first multimeter that I bought was a sort by lowest price ebay "Harbor Freight like" style multimeter for 99 cents. It arrived, thankfully, DOA. After I took it apart, I decided to spend more. When you see how badly they are put together and the potentially high voltage you are measuring (possibly up to 400V DC on SMPS with a PFC), you will quickly change your mind.

2) Pictures of that 99 cent multimeter.

http://www.badcaps.net/forum/showpos...4&postcount=25

3) Note in picture

http://www.badcaps.net/forum/attachm...0&d=1275345583

that single thin strand of jumper wire (the Volt jack in the middle) that is barely soldered on could be carrying 400V DC. And YES, it arrived like that. There were no modifications done by me.

4) Recently I was attempting to repair a LG 22 inch monitor. It was made in 2008. As such, most modern LCDs have a SMPS power supply where there is a bleeder resistor that discharges the large filter capacitor in a few minutes once the lcd is unplugged.

I hooked up my Fluke to monitor the large filter cap and was TOTALLY SURPRISED that the voltage stayed at 165V DC after I unplugged the power. I left it overnight. The next morning the large filter cap was still at 155V DC. I finally used a 100K ohm resistor to discharge the large filter cap. Had I not checked or used a cheap multimeter that gives false readings, I would have had a nasty surprise.

5) 2 years later I now have several used Fluke multimeters that I got a very good prices. One of the latest purchases was a Fluke 27.

In addition, I couldn't resist another ebay bargain today so I have another coming. Hmm, which one to sell now?

[selldoor]

Originally Posted by welch_41

So how would I check to see if it were fried?

Open it up and look for a fuse or burnt bits. Post a pic and we will have a look.

Initial test - Make sure it has a fresh battery in and put on ohms

- probably shoiuld have a 1 on the left side of screen.

Touch probes together should go to 0.00 or very close.

Switch to volts DC and measure a 1.2v or 1.5v 9v or 12v batteries.- (do you call them batterys or cells?).

Back onto ohms check a couple of resistors on your boards see of the results match the color ring code.

Then the big test meter on 600VAC plug in your power board and test the mains voltage in.

[welch_41]

Well I got the new power supply and have hooked it up. I checked the big cap and is reading 165dcv with no source plugged in and doesn't change if I hit the power button. However, it does jump up to near 400dcv with a video source plugged in but eventually goes down to 280dcv.

[welch_41]

Oh and it still won't turn on. Should I start looking at the main board or am I getting ahead of myself?

[retiredcaps]

Solid steady 5V DC standby is essential to any modern electronic/consumer device. Is it present and steady on the main board?

[welch_41]

Before I called it a night, I checked the 5vsb pin on the power supply and it was steady around 2.75dcv. However, I didn't check on the main board. I'll give that a shot today and report back.

[retiredcaps]

Originally Posted by welch_41

Before I called it a night, I checked the 5vsb pin on the power supply and it was steady around 2.75dcv. However, I didn't check on the main board. I'll give that a shot today and report back.

Nothing is going to work with 5V standby at 2.75V DC.

Try this with your replacement power board.

1) Disconnect the main board from the power board?

2) What is the 5V standy reading?

3) Are you still using that HF multimeter that is possibly damaged?

[welch_41]

Originally Posted by retiredcaps

Nothing is going to work with 5V standby at 2.75V DC.

Try this with your replacement power board.

1) Disconnect the main board from the power board?
I disconnected all wires from the main board.
2) What is the 5V standy reading?
The SB5V is now reading 4.94v without the main board connected.
3) Are you still using that HF multimeter that is possibly damaged?

I've reverted back to my Radio Shack multimeter.

[retiredcaps]

Post 262 and on are applicable to your situation since you get 4.9V DC rock solid without the main board connected. See

http://www.badcaps.net/forum/showthr...=11329&page=14

[welch_41]

Thank you for the help. I will sift through that thread and the ones that run off from it. I know that people mention buying caps from digikey but is there any issue with using Radio Shack parts outside of paying a premium?

[selldoor]

Originally Posted by welch_41

Thank you for the help. I will sift through that thread and the ones that run off from it. I know that people mention buying caps from digikey but is there any issue with using Radio Shack parts outside of paying a premium?

Unless they have a special offer on good brand caps in the size you need
which is unlikely.
Most of the caps they sell are not low esr and are not suitable for this application. They might work but not for long. They are ok for resistors.

[welch_41]

Please excuse my ignorance but how do I tell the specs of these capacitors. I've looked around the web for a clear explanation but haven't seen anything...which makes it hard to order replacements from DigiKey.

[retiredcaps]

Originally Posted by welch_41

Please excuse my ignorance but how do I tell the specs of these capacitors.

The most important parameters are

a) voltage
b) capacitance
c) diameter of cap
d) height
e) esr
f) ripple

For example, EC905 is a 470uF, 25V cap. Now measure the height and diameter. For esr and ripple, see the megathread as I instructed, I wrote instructions just less than 24 hours ago.