HP L1702 goes on and off

[PCBONEZ]

Re: HP L1702 goes on and off

CapXon KM are General Purpose [GP].
To compare GP caps look at the Ripple Current ratings

Other series of CapXon are rated near FC or even FM so if you have any you will need to look up the data sheets for those.
It's not uncommon to have a few high grade caps mixed in with GP caps for specific apps on a PCB.

I would attach the KM data sheet but file size limit is too low here.
[Gezz, the file is only ~196k.]

CapXon's site is hard to search but you can look up their data sheets with creative use of Google.
Example for KM series: Put this into Google > site:capxongroup.com KM < as so:

http://www.google.com/#hl=en&q=site%...fp=Q5rYJf3FIq4

If you need to find a different series just change "KM" to the series you want the data sheet for.

Even though KM are general purpose I would upgrade to something that is at least a basic grade of low ESR which you'll know because data sheet at least shows ESR in the table.
Reason is the caps are much better and cost difference is usually nil.
.

[PCBONEZ]

Re: HP L1702 goes on and off

If you compare Ripple for the KM to FC and FM in the 1000uF 6.3v from earlier you can easily see how widely specs vary between caps.

KM = 430 mA
FC = 755 mA
FM = 1290 mA
.

[Qwertyco]

Re: HP L1702 goes on and off

Well, here I am back to square one!
3a pico fuse is fine, checked soldered connections on the board and re-flowed quite a few.
Plugged it all in and . . . . . . There is LIGHT!, and windows, and my desktop, then, flicker and gone again!
Back lights come on for between 2 and 30 seconds, gently flickering all the time then go off again.
Right back to where I started.

ps. the only cap i DIDN'T change was the big boy!

the screen just stayed on for about two minutes this time.

[EGuevarae]

Re: HP L1702 goes on and off

ps. the only cap i DIDN'T change was the big boy!

Rarely Fails. You probably have a bad lamp in there. Did you notice any strange noise when the lamp flickered?

[Qwertyco]

Re: HP L1702 goes on and off

It seems to be Ok for two or three seconds, then off go the lights, no flickering or noise.

Occasionally it stays on for a minute or two, gently flickering, then goes off, still no noise.

[Bobdee]

Re: HP L1702 goes on and off

It seems to be Ok for two or three seconds, then off go the lights, no flickering or noise.

Occasionally it stays on for a minute or two, gently flickering, then goes off, still no noise.

Hello again
I agree with Eguevarae that its probably a bad lamp
This link is a good read its not your monitor but still applies
https://www.badcaps.net/forum/showpo...&postcount=296
One to four will help you find out if its top lamps or bottom,but read whole link to get a good understanding of inverter problems

replacing lamps is not that hard but very good care is needed
bob

[EGuevarae]

Re: HP L1702 goes on and off

It seems to be Ok for two or three seconds, then off go the lights, no flickering or noise.

Occasionally it stays on for a minute or two, gently flickering, then goes off, still no noise.

See this post on this very same thread.

[Qwertyco]

Re: HP L1702 goes on and off

This may seem strange, but it seems to be getting better by itself!
I've seen it working fine for over an hour now, no flickering, no problems at all.
It still looses the backlights, but the time period before this happens is massively improved.
. . . and I haven't done anything to it lately!

[PCBONEZ]

Re: HP L1702 goes on and off

Electrolytic caps can 'come and go' like that before they finally croak so you might not be home-free.

On the other hand...
There is characteristic of electrolytic caps that people don't talk about much anymore.
Electrolytic caps used to be called "self healing capacitors".
Ripple Currents damage the oxide layer [that is the actual dielectric] more or less by making pits (thin spots) in the layer.
Time also takes it's toll. [next paragraph]
Applying DC voltage [in the correct polarity] rebuilds [makes thicker] that oxide layer and refills the pits.
It works the same way as electroplating something only we are plating out an oxide.
[Note: In electroplating the solution is also called the Electrolyte. It's the same process.]

The oxide layer on caps that haven't been used [no DC applied] thins over time by dissolving into the electrolyte. [Shelf life issue.] As long as the electrolyte isn't shot the layer can be rebuilt through a process called "reforming". Reforming is basically applying a DC voltage in the correct polarity and increasing it incrementally until it's slightly higer than the rated voltage. [No, I dunno specific values, just how the process works.]
- Some of your caps your may be reforming to some degree. [Especially if this thing has been sitting in a closet for a couple years.]
But, don't count on that being a permanent fix unless you've fixed the other problems.
.

[Qwertyco]

Re: HP L1702 goes on and off

Electrolytic caps can 'come and go' like that before they finally croak so you might not be home-free..

Thats very interesting.

Could it be that the new Caps I fitted have been lying on the shelf for a long time, and are now 'Waking Up' ?

The person I got it from claimed it worked fine, but he hadn't used it for a while.

It does seem to keep going for longer and longer between blackouts.

[Qwertyco]

Re: HP L1702 goes on and off

Quick update:
gentle flicker on first startup last night, then performed faultlessly for two hours before I switched it off !

[Qwertyco]

Re: HP L1702 goes on and off

Quick update:
gentle flicker on first startup last night, then performed faultlessly for two hours before I switched it off !

I now declare this monitor FIXED!
running faultlessly.
Still not sure why it got better and better, unless it was the 'self repairing' caps thing!
Thanks for all your help guys!
I've been inspired now, I have two more monitors to attempt repair now,
Time for a new thread I think . . . . .

[EGuevarae]

Re: HP L1702 goes on and off

I now declare this monitor FIXED!
running faultlessly.
Still not sure why it got better and better, unless it was the 'self repairing' caps thing!
Thanks for all your help guys!
I've been inspired now, I have two more monitors to attempt repair now,
Time for a new thread I think . . . . .

Go for it! We're help to help or give you ideas.

[alsim]

Re: HP L1702 goes on and off

Hey, Thanks for Pic# 1 posted by Qwertyco.
That is the same board as my monitor. I needed to identify resistor R125. Mine was burnt and couldn't see all the color bands in order to replace it. Your Pic was perfect.

[Maxxarcade]

Re: HP L1702 goes on and off

Well, let me add another one to the mix. HP 1702 LCD... Backlight only comes on for about 1 second. I've replaced all caps and checked solder joints to no avail. Both lamps seem to be coming on, but could they still be the problem? I only paid $25 for the monitor, but i was hoping the toasted caps would be the only problem...

I think my boards are different than other I've seen in previous posts.

[dobber]

Re: HP L1702 goes on and off

Ok, So I got a L1702 in and it gets video and loses it like everybody else. So I change out all the caps, and find that it is still doing the same thing. So I was asking at work, and found that one of our Slot Techs has one and it has the same issue after all the caps were changed. Is there a posability that they may have a bad Transformer on them causing this problem, or is there another route I should take.

[eckertb83]

Re: HP L1702 goes on and off

Ok, So I got a L1702 in and it gets video and loses it like everybody else. So I change out all the caps, and find that it is still doing the same thing. So I was asking at work, and found that one of our Slot Techs has one and it has the same issue after all the caps were changed. Is there a posability that they may have a bad Transformer on them causing this problem, or is there another route I should take.

Mine is doing the same after re capping the board (all caps) and the backlight.
What else is there to check?
Sorry to bring up an old thread, but seemed better that starting a new one.

Thanks for the help

[jetadm123]

Re: HP L1702 goes on and off

Mine is doing the same after re capping the board (all caps) and the backlight.
What else is there to check?
Sorry to bring up an old thread, but seemed better that starting a new one.

Thanks for the help

The fact that it "loses video" is rather vague. Please give a more detailed description of the symptoms. Does it power off after a few seconds, or after several minutes? Does the power led and backlights stay on, but no video? Is it completely dead after it loses video? Asking us to second guess what you're seeing usually results in no help. More info only helps us help you.

Several different power supplies were used on this monitor and good focused photos of your entire power supply (top and bottom shots) and logic board are required for members to point out things for you to check. Use the manage attachment button to post your photos.

[eckertb83]

Re: HP L1702 goes on and off

Ok sorry about that mine does not lose video. Monitor comes on then a few seconds the screen goes black. If i hold a flash light to the screen i can see everything. I've all ready recapped the inverter board and new backlights. The led stays on and green. I will post pics shortly as I have to take it apart again.

[alexanna]

Re: HP L1702 goes on and off

Would you also see if you can read the number of the 16 pin IC on the back left side of the board.And on the connector going to the logic board , are any pin voltages identified?