Dell E178fp repair

[mathog]

Dell E178fp intercepted on the way to e-waste, manufactured in 2007.
Initially at power on the DELL warm up screen would appear dimly for a second or two and then it would blank. At best, other times it would just start black. Disassembled and found the power supply and video board shown front and back in the attachments. The PS board had 4 Capxon electrolytic capacitors of which the biggest two (c203 and c204 on the right side) were domed and one of the smaller ones (c16, near F151 at the left) had blown its plug. Replaced them with Panasonics. Reassembled, and it powered up and lit.

However, the image has problems (see the attachment). The video board has 2 X Teapo 330uF 16V, 8 X G-Luxon 22uF 25V and 1 X Teapo 100uF 25V. Is the image defect shown consistent with some or all of these being bad? They all look ok, but as I understand it, none of these are very good capacitors. Measured the voltage at pin 1 on the power supply and it was 5.1, which is the value stamped on the motherboard. So I think the PS board is OK now and this problem is either in the video board, or I suppose it could be in the panel itself. The horizontal lines follow the color rectangle around the screen and appear in all positions. The Moire pattern is from the camera image, it isn't visible by eye.

[Wizard]

Re: Dell E178fp repair

You're not done and what kind of panasonic capacitors was used? FC, etc?

Need to replace the rest of capacitors ( group of violet caps) and check the rest on the mainboard.

Be easy with these white ribbon cables, they are delicate.

Cheers, Wizard

[mathog]

Re: Dell E178fp repair

You're not done

Clearly

what kind of panasonic capacitors was used? FC, etc?

FM.

Need to replace the rest of capacitors ( group of violet caps) and check the rest on the mainboard.

I don't have this board with me, but if memory serves I didn't replace those because they still looked good and were from an OK manufacturer. By "mainboard" are you referring to the video board? None of the caps there are visibly deformed, but neither Teapo nor G-Luxon has a stellar reputation. I don't have an ESR or any other kind of capacitance meter. All I can check is if the caps are shorted.

Seemed to me the display glitches remaining were probably from problems on the video board, since the horizontal lines correspond to video signal changes, and that's all on the video board.

Will try to be careful with the white ribbon cable.

Thanks.

[Wizard]

Re: Dell E178fp repair

The way it looked shows me there is noise that is not cleaned up or poor voltage.

This is ideal to go all the way to recap the power supply if don't have ESR meter, just swap out these four on that power supply.

I'll just wait.

Cheers, Wizard

[mathog]

Re: Dell E178fp repair

I don't have this board with me, but if memory serves I didn't replace those because they still looked good and were from an OK manufacturer.

Better than OK. The are all Nichicon: two HD and two PW.

[mathog]

Re: Dell E178fp repair

Progress report.

Replaced all the caps on the video board. Reassembled, powered on, nothing. Inspected and noticed the connector between the PS and video board was off one row (that is, 4 on one side were hanging out into the air, and the other 4 were plugged into the holes where the first ones were supposed to be. My bad, hopefully that didn't blow anything up permanently. Reassembled correctly this time. Power on (with no video input). Nothing, not even a back light. After a while though the Dell warm up screen came up for a while. It was still a little noisy, but just a bit on the left edge of the box that wanders around the screen this time, not lines all the way across like before. However it didn't stay on, but turned off after a while. Maybe that's normal - I've never had this monitor in working condition.

I could easily have damaged the video board replacing those caps as it was very, very hard to get the solder out of the through holes once the caps were out. Couldn't do it with a solder sucker, a Radio Shack desoldering iron, or solder wick. Eventually resorted to heating up a resistor lead, pushing it through the hole, wiping the solder off the far side with the iron, and repeat until the hole cleared. TEDIOUS. Overheating of nearby components is a distinct possibility. As are solder bridges, although I didn't see any. (My eyesight is crappy these days though, and the video card is pretty densely packed, so the odds of me seeing a small solder bridge are not great.)

Guess I'll try plugging in a video source that's umm, expendable, just in case it handles real video input OK (I really don't care if the warm up screen looks right if the normal display correct.) Also replacing the last few caps on the PS.

[llphat]

Re: Dell E178fp repair

Apologies for digging out such an old thread, I have recently come across an E178FP which does not power up. Opening up and checking the PCB, there were no obvious bad caps or burnt areas. There was no voltage across pin 1 which should be be 5.1V when on.

The only obvious thing is when I measure across ZD2 which gives 0.001V (in circuit) which surely does not sound right - is this the culprit?

Oh if ZD2 does turn out to be blown, is there a way to find out the values from the marking on the component?

[Rtech]

Re: Dell E178fp repair

What is the other letters in the model code after the FP /c/,v/,b etc ??

[llphat]

Re: Dell E178fp repair

The model is E178FPv the boards are similar to the images posted in the first post.

Fuses checked OK and there is a ~330V voltage across the big cap at the bridge exit.

[retiredcaps]

Re: Dell E178fp repair

What is the DC voltage across C4? That is the startup cap for the SMPS. It should be steady and not fluctuating.

[tmcw]

Re: Dell E178fpV repair

Apologies for digging out such an old thread, I have recently come across an E178FP which does not power up. Opening up and checking the PCB, there were no obvious bad caps or burnt areas. There was no voltage across pin 1 which should be be 5.1V when on.

The only obvious thing is when I measure across ZD2 which gives 0.001V (in circuit) which surely does not sound right - is this the culprit?

Oh if ZD2 does turn out to be blown, is there a way to find out the values from the marking on the component?

Another E178FPv here, exact same boards, observations and symptoms (no 2 seconds, or any sign of life) as yourself, though ZD2 measures "OL" both ways on mine.

My first thoughts were with the startup cap C4, so I replaced that with a Panasonic FM 47uF/50V, but there are no changes from that.

C160 looked coupled to pin 1, so I changed that as well (it was giving some bizarre behaviour when probed, so it looked suspect, will check the ESR later). Anyway, on pins 1-8, I'm now getting the following...

1, 2: 5.19v
3, 4: GND
5: NC
6: 5.11v
7: 3.5v
8: 0v

... but still no visible signs of life, not even from the LED on the button panel.

Did you pursue it any further?

I know the other Capxons will need to be replaced, but should I be seeing other signs of life before they need replacement?

Should pin 8 be registering a voltage change if the on/off button is switched on and off? How best to test this?

[retiredcaps]

Re: Dell E178fpV repair

though ZD2 measures "OL" both ways on mine.

Are you measuring ZD2 with the diode test function or resistance function on your multimeter? I always use diode test.

... but still no visible signs of life, not even from the LED on the button panel.

No power LED suggests something is wrong on the main/logic board. A good place to start is with the voltage regulators.

[tmcw]

Re: Dell E178fp repair

Yes, I went back and retested the ZD2, and got 0.01 both ways on diode test. I had to scratch one of the pads to get a reading, must be a bit of oxidation there.

Found another thread on this monitor since (https://www.badcaps.net/forum/showthread.php?p=152680) and went back and tested the button panel, but it seems to be functioning correctly. Buttons (cheap clicky things, like mobile phone contacts) all register out to the logic board, and I even got to see the orange and yellow LEDs to light up when testing them for continuity to ground. Is that bad for them?

I might be able to get a similar working monitor to transplant and test, at least rule out the logic board, but might help troubleshooting the power board.

[retiredcaps]

Re: Dell E178fp repair

Yes, I went back and retested the ZD2, and got 0.01 both ways on diode test.

Remove ZD2 and test out of circuit to verify it is shorted. In circuit measurements can cause false readings sometimes.

[tmcw]

Re: Dell E178fp repair

Yep, did that, I guess it's fine, "OL" one way, 0.737 the other way.

[selldoor]

Re: Dell E178fp repair

ok - so do you want to put off further tests until you know if you are getting the similar working monitor?

[tmcw]

Re: Dell E178fp repair

It might be a while (couple of weeks) before I can get the same model monitor, so if you have any suggestions, feel free to suggest them.

I additionally changed the rest of the electrolytic capacitors (except the large line filter), and tested the rest of the zeners and the bridge rectifier (out of circuit), and they're all ok. But the set still shows no sign of life.

[retiredcaps]

Re: Dell E178fp repair

It might be a while (couple of weeks) before I can get the same model monitor, so if you have any suggestions, feel free to suggest them.

I repeat, voltage regulators as per post #12.