HP no backlight

[davg]

Re: HP no backlight

Thanks jetadm123 it appears from the schematic that the plus side of C122 (which was lifted) goes to pin 8 of Q104 so should I connect these two points?

[jetadm123]

Re: HP no backlight

A lifted pad/trace on a circuit board is considered unreliable and should be repaired using point to point wiring. Solder one end of a wire to the lifted lead of C122 and the other end to solder a pad at the other end of that trace.

[davg]

Re: HP no backlight

I have carefully looked over the board and I am unable to see any thing that looks like a grn? I did discover a lifted trace on C122 but it is still contacting. Not sure where I go from here?

[davg]

Re: HP no backlight

Thanks guys I will go over the board again to be sure there are no shorts caused by my soldering. I will report back

[budm]

Re: HP no backlight

I would suggest you to recheck all your works just to be sure.

[jetadm123]

Re: HP no backlight

As retiredcaps mentioned earlier, the lack of VDD reading around 5V could indicate a possible short. When you soldered in the new caps in the inverter section, did you make sure that there were no solder bridges that might cause a short?

Also, if you continue going through the flowchart, you'll see that very few of your voltage readings meet the suggested values for I101. It's understood that since you don't have a scope, you cannot perform some of the steps.

[davg]

Re: HP no backlight

Thanks jetadm123 yes I did replace C102. I could remove it?? I am getting slight a humming on the board as I indicated earlier and I can't tell where it is coming from but it is close to one of the transformer. T101 or T102. What does that indicate? Should that be a concern?

[jetadm123]

Re: HP no backlight

Here are my thoughts so far:

I looked at the datasheet for the OZ9938 and the min VDD is 4.5V. If the OZ9930 is similar, then your VDD is too low. I'm wondering if that .6V difference is enough to cause it not to operate?

When you said you changed all the caps, do you also change C102? If not, try changing it and see what happens.

C102 appears to be a filter cap to protect VDD against voltage spikes/noise. If you don't have a spare cap for C102, for testing purposes, leave C102 off the board and see if VDD increases. If not, then something could be wrong with the OZ9930.

[davg]

Re: HP no backlight

The voltage across C102 is 3.91v Grn to + 3.91 and Grn to - 0 v I have no idea where the first reading came from I thought I may have read C105 but there is 2.5 v across that one. sorry

[jetadm123]

Re: HP no backlight

If you're still seeing .9V across C102, it sounds like it's shorted to ground. I would try changing it to see what happens.

[davg]

Re: HP no backlight

pin 8 is reading 0.780 megohms

[budm]

Re: HP no backlight

OK, is pin 8 = 0.780 Ohm or 780 Ohms? if it is 0.780 Ohms, then there is short circuit around pin 8.
VDD pin also seems low at less than 100 Ohms.

[jetadm123]

Re: HP no backlight

Can you read C102 again. It's "+" leg is sharing VDD and should also read 3.2V.

[davg]

Re: HP no backlight

Thanks budm with black prob on GRN screw the read as follows pin 1- 0L pin 2- 0L pin 3- Grn 0
pin 4- 0L pin 5 0L pin 6- 93.0 ohms pin 7-119 ohms pin 8 .780 mohms
Jetadm123 R105 22ohms C102 reads 16.30 mohms one way 0L the other Un plugged no power
Plugged in power on connected to running computer R102 reads 5 v one side 3.2 v other side and C102 reads .9volts one side and 0 other side and across C102 is .9 volts

[budm]

Re: HP no backlight

Can I get the resistance reading of each pin of the PWM IC OZ9930 and Ground?

[jetadm123]

Re: HP no backlight

I see what you mean. Since they say "pin", it sounds more like a test point, but I'm not sure. However, I think most members agree it's an inverter problem and I would go on to the next step, checking pin 6 of I101. You read 3.8V versus the suggested 5V (I don't know what the min VDD is for the OZ9930). The flowchart says to check R105 and C112. I think it's a typo and they meant C102 instead of C112, since C112 is not part of the VDD circuit.

[davg]

Re: HP no backlight

Thanks jetadm123 I have been away but will get some readings as soon as I get back on track. Question on the trouble shooting page check voltage on pin C112 is that across the cap c112?
Thanks budm truly appreciate it. This f2105 do have lines but they are shadows of the objects on the desktop and a very slow refresh rate. Takes the mouse for ever to move from one point to the other? I will start another thread on that one later

[budm]

Re: HP no backlight

davg, I hope if you do not mind, I post your pictures of the boards on my Photobucket.
By the way, the HP F2105 are know for having bad lamp assemblies and bad LCD panel (vertical lines), I had done 5 of them, all with bad lamp assemblies.
http://s807.photobucket.com/albums/y...HP/HP%20F2105/

[jetadm123]

Re: HP no backlight

Thanks budm for the service manual, it helps a lot.

davg- on the VS19 service manual, go to page 15 for troubleshooting the inverter circuit and try taking some of the recommended voltage measurements.

[davg]

Re: HP no backlight

Thanks retiredcaps these two points are reading .458k and .454k
Thanks budm great information and will require much study. Great troubleshooting section. Don't put away your HP pictures yet because I have a HP f2105 that I have been trying to find a service manual for if I may be so bold??