HP1955 Board Burnout - Is it Fixable?

[harveywilson]

Recently, to my alarm, my HP1955 monitor started smoking when turned on. I quickly removed the power and put it outside to cool down.

I was going to ditch it, but wondered if it might be fixable. When I removed the back, I could see that smoke had come from the melting plastic of two transistors and the capacitor (?) between them. I have included a photo of the area:





I'm not electronics expert, but I can wield a soldering iron so I thought I'd seek help from this forum. I would appreciate any help in identifying what has caused this fault, and what parts should be replaced in order to fix the problem (and where I might be able to get them from).

Thanks,

Harvey Wilson

[retiredcaps]

Re: HP1955 Board Burnout - Is it Fixable?

When I removed the back, I could see that smoke had come from the melting plastic of two transistors and the capacitor (?) between them.

This is a Benq board so the Q808 and Q809 are likely C5707 transistors. If they melted, I would also check with a multimeter the picofuse (PF701), Q805, Q812, Q815, Q816.

Q805 and Q812 are likely to be FU9024.

You must also resolder all the pins on the transformers.

Sellers on ebay offer repair kits. Search for "c5707 kit".

In addition, most here will suggest you recap all the capacitors with quality caps using Panasonic, Rubycon, or United Chemicon.

PS. Insert pics like this

https://www.badcaps.net/forum/showthread.php?t=1868

[PlainBill]

Re: HP1955 Board Burnout - Is it Fixable?

Retiredcaps beat me to it. Follow his instructions.

PlainBill

[harveywilson]

Re: HP1955 Board Burnout - Is it Fixable?

Thanks for the replies, and sorry about the pictures.

I can find the C5707's on a local auction site, so no problem there.

Q815 and Q805 are "J598" - not sure where to get those.

The picofuse is intact.

I'm also not sure where to get a replacement for the grey R75 MKP capacitor that has heat damage.

[alexanna]

Re: HP1955 Board Burnout - Is it Fixable?

To me the melting of the c5707 looks scary.
What is the amprage rating of pf701,And did it go open?
What dose the back of the board look like?
Al.

[harveywilson]

Re: HP1955 Board Burnout - Is it Fixable?

Here's the back of the board


I can see heat damage to the solder joints of Q805, 808 and 809.

And pf701 has 5 A printed on it.

[alexanna]

Re: HP1955 Board Burnout - Is it Fixable?

5 Amps seams like a hell of alot 17" are only using 2a fuses.
When I have substuted a 3a fuse for testing it got hot but never caused smoke.Some one needs to verify correct amprage of that fuse,I am afraid were going to have a fire.
Al.

[harveywilson]

Re: HP1955 Board Burnout - Is it Fixable?

That's what worried me at the time.

Do you recommend replacing the fuse with 3A?

[alexanna]

Re: HP1955 Board Burnout - Is it Fixable?

No not at this time lets see if someone can find the correct specs.
I dont think it will take long
Al.

[retiredcaps]

Re: HP1955 Board Burnout - Is it Fixable?

That's what worried me at the time.

Do you recommend replacing the fuse with 3A?

I have had 5 Benq boards at one point or another and all have been 3A/125V picofuse. NEVER seen anything higher.

And I think I will suggest that it is mandatory that you change all the electrolytic caps given the age of the monitor and how it went up in smoke.

[retiredcaps]

Re: HP1955 Board Burnout - Is it Fixable?

Q815 and Q805 are "J598" - not sure where to get those.

The picofuse is intact.

I'm also not sure where to get a replacement for the grey R75 MKP capacitor that has heat damage.

You may not have to replace Q815 and Q805 if they are not shorted. Test with your multimeter set on ohms. With power off and monitor unplugged,

put black on pin 1, red on 2 - read ohm
put black on pin 1, red on 3 - read ohm
put black on pin 2, red on 3 - read ohm

All the reading should be well over 500 ohms or so.

Repeat test as above, but with diode checker. After the 3 readings, reverse the leads so you should have 6 readings in total.

From what I'm learning the grey capacitor can take a lot of abuse. I accidentally touched the side of it with a solder iron and it still works.

[retiredcaps]

Re: HP1955 Board Burnout - Is it Fixable?

I have had 5 Benq boards at one point or another and all have been 3A/125V picofuse. NEVER seen anything higher.

Just searched through this forum and found this (even the same smoked c5707)

https://www.badcaps.net/forum/showth...hlight=5a+fuse

It looks like 5A is the correct picofuse value for this monitor.

[alexanna]

Re: HP1955 Board Burnout - Is it Fixable?

If the 5a fuse was original,And it caused that much damage and did not open,I wonder if there was a safty recall?
Call me chicken, but I would see if it could handel a 2or3a fuse.
Al.

[pedro]

Re: HP1955 Board Burnout - Is it Fixable?

The manufacturer will have selected 5A for a reason. The fuse *isn't* intended to prevent the 2SC5707 flameout - semiconductors die several orders or magnitude faster than fuses. I have repaired many of these Benq/Acer configurations and never felt the inclination to fiddle with the fuse rating.

What often happens is the transistor providing the PWM drive the the inverter pair fails, which causes the 5707's to overheat and die.

[PlainBill]

Re: HP1955 Board Burnout - Is it Fixable?

The failures on these monitors are quite well understood. A bad solder joint on the transformer will cause one of the C5707's to short, resulting in the other shorting. This will often cause the associated mosfet to short, and MAY cause the fuse to blow.

Transistors are encased in self-extinguishing plastics. There is no reason to get into a panic about a little smoke. Do a little math, alexanna. If the transistors short with a fairly high resistance - say 10 ohms - you have 2.5 amps at 12 Volts - 30 watts being dissipated. Yes, it's going to stink. No, it's not going to set the room on fire.

The cap SHOULD be replaced if there is any physical damage. .22 uF, 160 volt. The two bipolar transistors (C5707) and the FET above it (FU9024N).

PlainBill

[harveywilson]

Re: HP1955 Board Burnout - Is it Fixable?

Thanks PlainBill, I'm going to try and find the parts and give that a go. Just one further question; the FET on my board is marked J598, is the FU9024N an equivalent part?

Harvey

[seanc]

Re: HP1955 Board Burnout - Is it Fixable?

I might re-acquire my BenQ QT73 and replace the two other transistors attached to the heatsink, they test shorted, I just hit the point whether I wondered if it was worth it.

It has new 2SC5707s, some caps, resoldered transformers and pico fuse.

[retiredcaps]

Re: HP1955 Board Burnout - Is it Fixable?

I just hit the point whether I wondered if it was worth it.

Used 19 inch LCDs sell anywhere from $40 CDN to $70 CDN on craigslist/kijiji. Once in a while, I see a 19 inch LCD sell for $20, but they often get snapped up quickly.

Used 17 inch LCDs sell anywhere from $30 CDN to $50 CDN on craigslist/kijiji.

[seanc]

Re: HP1955 Board Burnout - Is it Fixable?

Used 19 inch LCDs sell anywhere from $40 CDN to $70 CDN on craigslist/kijiji. Once in a while, I see a 19 inch LCD sell for $20, but they often get snapped up quickly.

Mine's a 17", but yeah, maybe I'll rescue it.

If nothing else, I can donate it to someone in need

[PlainBill]

Re: HP1955 Board Burnout - Is it Fixable?

Thanks PlainBill, I'm going to try and find the parts and give that a go. Just one further question; the FET on my board is marked J598, is the FU9024N an equivalent part?

Harvey

Yes, according to a quick look at the datasheets.

PlainBill