lp2407 aka fpd2485W No Power

[PlainBill]

Re: lp2407 aka fpd2485W No Power

Here are my test values on the voltage regulators.

------- Pin 3 Pin 4

Chip 1 - 5 ---- 3.3
Chip 2 - 1.3 ---- .5
Chip 3 - 5 ---- 1.3
Chip 4 - 5 ---- 3.3
Chip 5 - 3.3 ---- 1.8

Whoops!!! We have a problem. The voltage out of chip 3 (U605) is incorrect. It should be 3.3 volts. Digikey has the equivalent part available as AP1117E33GDICT-ND. It's rather expensive at $.56 each.

PlainBill

[knoxrebel]

Re: lp2407 aka fpd2485W No Power

A little confused about chip 2, wasn't able to find a data sheet on it. How do we know what the output voltage should be?

[PlainBill]

Re: lp2407 aka fpd2485W No Power

A little confused about chip 2, wasn't able to find a data sheet on it. How do we know what the output voltage should be?

It's included in the part number - AS117L-18. The 18 indicates it's a 1.8 volt fixed output regulator. These are 'jelly bean' parts, available from a number of manufacturers. The original part may have been the National Semiconductor LM117, but the part has gone through many refinements by various manufacturers. The essential characteristics are output accurate to +- 1%, 1A output current, low (1.2 V or less) drop out. You notice that IC2 gets it's input from IC3. IC3's output voltage is too low.

PlainBill

[knoxrebel]

Re: lp2407 aka fpd2485W No Power

Replaced that voltage regulator and now the monitor is powering up and displaying video. Just waiting for the replacement caps for the video board. There is still a low pitched buzzing sound on the power board, is this something i should be concerned about?

[knoxrebel]

Re: lp2407 aka fpd2485W No Power

1 month later: still working great. Repair success.

[justincase102]

Re: lp2407 aka fpd2485W No Power

After recapping my power supply, I thought my feeble attempt at repairing my monitor was lost. The power supply wasn't the problem. But by successfully recapping the power supply and not losing a limb in the process, I found the confidence to push ahead. This thread saved me as Plainbill's diagnostic steps to test the 5 regulators on the signal board lead me to find that I had two bad regulators. I'll report back after installing the 3.3v regulators. Thanks to knoxrebel and PlainBill for helping diagnose.

[drdenner]

Re: lp2407 aka fpd2485W No Power

I have the same issue- no signs of life at all from the monitor. I noticed a few bulging caps on the power supply, inverter and signal board and replaced them all. I also replaced ALL the caps on the power supply just to be sure. I did make a small error in ordering caps so for the 2x 450uf 35v 125C i got the same but rated for operating temp 105C, installed them anyway.

When I plug in the power supply, I've measured 164v across the big 450v cap and I checked the fuse and its ok obviously.

However, when I check the voltage coming off the power supply (blue area in http://i.imgur.com/X9yaF.jpg)
I'm getting nothing, 0v, from all leads.

I'm not sure what my next step should be, any advice would be greatly appreciated. I'm close to sending it in somewhere or try and order new power supply if possible.

[PlainBill]

Re: lp2407 aka fpd2485W No Power

I have the same issue- no signs of life at all from the monitor. I noticed a few bulging caps on the power supply, inverter and signal board and replaced them all. I also replaced ALL the caps on the power supply just to be sure. I did make a small error in ordering caps so for the 2x 450uf 35v 125C i got the same but rated for operating temp 105C, installed them anyway.

When I plug in the power supply, I've measured 164v across the big 450v cap and I checked the fuse and its ok obviously.

However, when I check the voltage coming off the power supply (blue area in http://i.imgur.com/X9yaF.jpg)
I'm getting nothing, 0v, from all leads.

I'm not sure what my next step should be, any advice would be greatly appreciated. I'm close to sending it in somewhere or try and order new power supply if possible.

There are several possibilities. The chief ones are

1. A cap was put in backwards - don't laugh, it happens.

2. You formed a solder bridge between the leads of a capacitor.

3. The SMPS controller has died.

I'd suggest you investigate the first two yourself. If you don't find anything, take good, sharp, well lit pictures, one of the top and one of the bottom of the power supply and attach them to your next post using 'Manage Attachments'. From that we can suggest the next troubleshooting steps.

PlainBill

[drdenner]

Re: lp2407 aka fpd2485W No Power

Thanks Bill,

1. Checked the polarity on the caps. All look ok.
2. Checked for cap solder bridge shorts using DMM. Also look all good (pretty easy soldering actually)
3. No idea what SMPS is.

attached are the pics

[retiredcaps]

Re: lp2407 aka fpd2485W No Power

3. No idea what SMPS is.

3) SMPS = switch mode power supply.

PlainBill is interested in the SMPS controller (IC). It looks like it is mounted on the small pcb board that is mounted vertically next to the biggest cap.

On that board should be a 8 pin IC. A picture of that board will help.

4) Did you change the little cap next to the big 150uF, 450V cap as well? I know you wrote "ALL", but some people may missed that one.

What is the DC voltage across that little cap?

5) I see one Panasonic replacement and I think the others are Nichicon? Is that correct?

[drdenner]

Re: lp2407 aka fpd2485W No Power

3) SMPS photo attached
4) Indeed I did change that small cap,
15.87v DC across it.
5) There are 2 Panasonic caps (the 10uf 50v and 1000uf 25v), the rest are Nichicon.

[retiredcaps]

Re: lp2407 aka fpd2485W No Power

4) Indeed I did change that small cap,
15.87v DC across it.

Datasheet is at

http://pdf1.alldatasheet.com/datashe.../SG6902SZ.html

It looks like 16V DC is the typical startup threshold (min = 15, max = 17V DC). So it looks like the voltage across the small cap is okay.

You can try to carefully measure the voltage on Vdd. Try not to short out the pins as the chip as a lot of pins.

[drdenner]

Re: lp2407 aka fpd2485W No Power

Ok so I measured the voltage on the IC and its 15.87v also.
But something weird happened the first time I tried- I think I may have shorted it accidentally, but then the power supply started humming and I measured voltage coming off of it, 5v and 23v. I turned it off and then on, but again no voltage.

[retiredcaps]

Re: lp2407 aka fpd2485W No Power

I think I may have shorted it accidentally, but then the power supply started humming and I measured voltage coming off of it, 5v and 23v.

Solder bridge? See area in red.

[drdenner]

Re: lp2407 aka fpd2485W No Power

Ya but those were intentional since in those spots the trace came off the board so I just tested to make sure the trace was joined to a neighbouring pin and bridged the pins for a better connection. They were already joined electrically. I know the basics of electronics.

[drdenner]

Re: lp2407 aka fpd2485W No Power

When I was testing the voltage on the SMPS the first time something happened and the power supply started working. I might have shorted pins 15 and 16 but i'm not really sure

[PlainBill]

Re: lp2407 aka fpd2485W No Power

When I was testing the voltage on the SMPS the first time something happened and the power supply started working. I might have shorted pins 15 and 16 but i'm not really sure

Bad solder joint on the daughterboard?

PlainBill

[drdenner]

Re: lp2407 aka fpd2485W No Power

No, the daughterboard looks fine.

[jetadm123]

Re: lp2407 aka fpd2485W No Power

No, the daughterboard looks fine.

Try checking transistors Q811 and Q812 for shorts. With power off and your meter set to resistance, place your probes across:

E-B
B-C
E-C

[mcintoshtc]

Re: lp2407 aka fpd2485W No Power

Good Morning,

This is my first time posting on this forum, so I apologize if I'm not following protocol. I am kind of a novice when it comes to component level repair, but I used to do a lot of power jack repairs on laptops a few years back, so I am very comfortable with a soldering iron.

I am having the same issue that knoxrebel was. My unit was turning on until recently and now it does nothing when I plug it in except make some noise. I would describe the sound as being similar to turning on an old CRT monitor, but quieter. I's coming from the power board near the big capacitor. It may be normal and may have happened ever since I bought it and just never noticed it, but I thought I would at least mention it.

I do not notice any bulging from the capacitors, and I don't see anything that looks unusual.

I ran through the diagnostics that PlainBill had knoxrebel go through and these are the results that I got back:

voltage across big cap(yellow circles) (C854) - 160v

voltages to inverter board (blue circle):
0
0
0
5.1
0
0
26.3
26.3

voltages across regulators (3 - 4)
chip 1: 5.1 - 3.3
chip 2: 1.25 - .42
chip 3: 5.1 - 1.3
chip 4: 5.1 - 4.1
chip 5: 3.3 - 1.8

Based on PlainBill's response to knoxrebel's voltages, I know that the voltage regulator labeled at chip 3 is bad, but chip 4's voltage is also a little off and the voltages to the inverter board is slightly off too.

Is chip 4 within tolerance or does it need to be replaced too?

Are the voltages coming from the power board within tolerance, or do I have a problem there too?

Thanks for the help!

- T