Dell 1707FP no power

[PlainBill]

Re: Dell 1707FP no power

Before ordering these parts, based on the output voltages being under, can I assume that the processor is ok? (i know that both under voltages and over can damaged an IC but under is surely better than over?). Cause if the processor is damaged then I guess its probably economical to just find a replacement board.

Assumptions are dangerous. However, yes, if I had determined that the voltage regulator was defective, outputting too low a voltage I wouldn't hesitate to order a replacement part. Knowing what I know now, I would hesitate to replace one that had output too high a voltage.

PlainBill

[bob12345]

Re: Dell 1707FP no power

Before ordering these parts, based on the output voltages being under, can I assume that the processor is ok? (i know that both under voltages and over can damaged an IC but under is surely better than over?). Cause if the processor is damaged then I guess its probably economical to just find a replacement board.

[PlainBill]

Re: Dell 1707FP no power

Yeah its strange there was no voltage on the U902, i checked it a couple of times when I tested. Does this mean a possible processor fault - ie the processor not telling it to turn on as you mentioned?

I think that's what is happening. After all, the panel itself takes a fair amount of power. Why not reduce the energy consumption by turning off the power to the panel at the same time you turn off the inverters.

PlainBill

[bob12345]

Re: Dell 1707FP no power

The two voltage regulators are 'jelly bean' parts - available from a number of ventors; sometimes with different part numbers, all serving the same function. The ST datasheet is for the equivalent part from a different vendor. The ST parts have a higher current rating.

That DOES bring up an interesting point. Why weren't you able to detect an input voltage for U902? If that is a 3.3V regulator, it must be fed from the 5V supply. Doh!! Maybe it's switched off until commended on by the processor?

I also wouldn't consider doing anything with U404. Again, it appears it isn't receiving the proper voltage, so it's inactive.

PlainBill

Yeah its strange there was no voltage on the U902, i checked it a couple of times when I tested. Does this mean a possible processor fault - ie the processor not telling it to turn on as you mentioned?

[PlainBill]

Re: Dell 1707FP no power

I'll try and tackle the removal and testing of those parts as you mentioned during the week. In the mean time I think I'll order some replacements for the above. I'm assuming as the original parts are likely to be tricky if not near impossible to get hold of, compatible ones of the same rating (voltage), current output, package type, basically the same or better than the specs in the datasheet would do the job? Do you think its worth replacing that U404 considering the details of its part number are pretty poor (DF64?).

Also the LD1117A - is this likely to be a similar datasheet

Once again PB, thanks for all your help, very much appreciated!

The two voltage regulators are 'jelly bean' parts - available from a number of ventors; sometimes with different part numbers, all serving the same function. The ST datasheet is for the equivalent part from a different vendor. The ST parts have a higher current rating.

That DOES bring up an interesting point. Why weren't you able to detect an input voltage for U902? If that is a 3.3V regulator, it must be fed from the 5V supply. Doh!! Maybe it's switched off until commended on by the processor?

I also wouldn't consider doing anything with U404. Again, it appears it isn't receiving the proper voltage, so it's inactive.

PlainBill

[bob12345]

Re: Dell 1707FP no power

There are some errors in your list. Not surprising, considering the size of the IC, and the propensity to conserve space by omitting characters.

The AS1117R-33 is here.

For the AS117L-18, use the same datasheet, it's probably from a different vendor.

The LD1117A again is a similar part. It may again be a 3.3 v part, or it may be an adjustable regulator.

The next step requires finesse. Starting with the AS1117R-33 I'd remove the part and test it with 5V in, and a 25 ohm load. If the output was wrong, I'd replace the part with a new one. If the output was right, I'd try to determine why the output was overloaded, perhaps by removing the AS117L-18.

We've been seeing a number of these recently, but with the output voltage too high. That usually kills the processor or it's support chips.

PlainBill

I'll try and tackle the removal and testing of those parts as you mentioned during the week. In the mean time I think I'll order some replacements for the above. I'm assuming as the original parts are likely to be tricky if not near impossible to get hold of, compatible ones of the same rating (voltage), current output, package type, basically the same or better than the specs in the datasheet would do the job? Do you think its worth replacing that U404 considering the details of its part number are pretty poor (DF64?).

Also the LD1117A - is this likely to be a similar datasheet

Once again PB, thanks for all your help, very much appreciated!

[PlainBill]

Re: Dell 1707FP no power

I'm in fact having trouble even trying to find datasheets from the part number of these components!

There are some errors in your list. Not surprising, considering the size of the IC, and the propensity to conserve space by omitting characters.

The AS1117R-33 is here.

For the AS117L-18, use the same datasheet, it's probably from a different vendor.

The LD1117A again is a similar part. It may again be a 3.3 v part, or it may be an adjustable regulator.

The next step requires finesse. Starting with the AS1117R-33 I'd remove the part and test it with 5V in, and a 25 ohm load. If the output was wrong, I'd replace the part with a new one. If the output was right, I'd try to determine why the output was overloaded, perhaps by removing the AS117L-18.

We've been seeing a number of these recently, but with the output voltage too high. That usually kills the processor or it's support chips.

PlainBill

[bob12345]

Re: Dell 1707FP no power

I'm in fact having trouble even trying to find datasheets from the part number of these components!

[bob12345]

Re: Dell 1707FP no power

Bingo!!! U 601 is a 3.3 volt regulator; it's output is 1.24V; U602 is a 1.8 volt regulator; it's output is .4 volts and it's getting it's input from U601. With those voltages the processor won't run. I'm not sure about U902; I think it provides power for the panel.

PlainBill

PB do you suggest replacing all those parts? Ie the U404, U601, U602 and U902? Its strange there is no voltage across the U902 - a result of the other faulty components down the line?

[PlainBill]

Re: Dell 1707FP no power

So to verify I checked the mounting hole at the top left, resistance is low, as you said around 0.5-1ohm, the voltage relative to the negative cap terminals was indeed 0 so confirmed that as GND reference.

So measurements relative to GND at the respective pins (layout as before):
U404:
Pin 1: 0V
Pin 2: 0V
Pin 3: 1.24V

U601:
Pin 1: 0V
Pin 2: 5.21V
Pin 3: 1.24V

U902:
Pin 1: 0V
Pin 2: 0V
Pin 3: 0V
Pin 4: 0V

U602:
Pin 1: 0V
Pin 2: 0.4V
Pin 3: 1.24V
Pin 4: 0.4V


Part numbers of components (as read from top to bottom on each device):

U601:
A1
AS117R-33
B0606

U902:
LD117A
L33ATB

U602:
A1
AS1117L-18
B0548


Thanks

Bingo!!! U 601 is a 3.3 volt regulator; it's output is 1.24V; U602 is a 1.8 volt regulator; it's output is .4 volts and it's getting it's input from U601. With those voltages the processor won't run. I'm not sure about U902; I think it provides power for the panel.

PlainBill

[bob12345]

Re: Dell 1707FP no power

Ohhh, my head hurts. These numbers aren't making sense to me. OK, let's try to make some sense of what is going on here. In the upper left corner of the board is a mounting hole, which seems to be designed to contact the metal mounting screws. That SHOULD be ground. Verify by measuring the resistance to the - lead on several of the caps, please. (This should be low - under 1 ohm).

Set the meter on DC volts, and with the power on measure the voltage from ground to the pins of U404, U601, U602, and U901. ALSO list the part numbers of U601, U602, and U902, please.

PlainBill

So to verify I checked the mounting hole at the top left, resistance is low, as you said around 0.5-1ohm, the voltage relative to the negative cap terminals was indeed 0 so confirmed that as GND reference.

So measurements relative to GND at the respective pins (layout as before):
U404:
Pin 1: 0V
Pin 2: 0V
Pin 3: 1.24V

U601:
Pin 1: 0V
Pin 2: 5.21V
Pin 3: 1.24V

U902:
Pin 1: 0V
Pin 2: 0V
Pin 3: 0V
Pin 4: 0V

U602:
Pin 1: 0V
Pin 2: 0.4V
Pin 3: 1.24V
Pin 4: 0.4V


Part numbers of components (as read from top to bottom on each device):

U601:
A1
AS117R-33
B0606

U902:
LD117A
L33ATB

U602:
A1
AS1117L-18
B0548


Thanks

[PlainBill]

Re: Dell 1707FP no power

Thanks for the info PB,

As for the voltages:

I've measured them relative to each pin (probes across pin 1 - 2 for example) on the 4 components - pins as per the attached image.

U404:

Pin 1 - 2 = 0V
Pin 1 - 3 = 1.24V
Pin 2 - 3 = 1.24V

Voltages between pins 1-3 and 2-3 on the U404 seems to start at 1.24 then drop off to 0, bit unstable but perhaps showing the operation as you described.

U601:

Pin 1 - 2 = 5.2V
Pin 1 - 3 = 1.24V
Pin 2 - 3 = 3.96V

U902:

Pin 1 - 4 = 0V
Pin 2 - 4 = 0V
Pin 3 - 4 = 0V
Pin 1 - 2 = 0V
Pin 1 - 3 = 0V
Pin 2 - 3 = 0V

U602:

Pin 1 - 4 = 0.4V
Pin 2 - 4 = 0V
Pin 3 - 4 = 0.84V
Pin 1 - 2 = 0.4V
Pin 1 - 3 = 1.24V
Pin 2 - 3 = 0.84V

The middle pin of the cluster of 3 (between pins 1 and 2) on the U602 doesn't seem to be connected to the board - i assume this is connected as pin 3.

Ohhh, my head hurts. These numbers aren't making sense to me. OK, let's try to make some sense of what is going on here. In the upper left corner of the board is a mounting hole, which seems to be designed to contact the metal mounting screws. That SHOULD be ground. Verify by measuring the resistance to the - lead on several of the caps, please. (This should be low - under 1 ohm).

Set the meter on DC volts, and with the power on measure the voltage from ground to the pins of U404, U601, U602, and U901. ALSO list the part numbers of U601, U602, and U902, please.

PlainBill

[bob12345]

Re: Dell 1707FP no power

If I'm correct, it's a reset controller. A quick background: Processors often have internal charge pumps, etc that require a finite time to stabilize after the chip receives power. Plus of course, the power supplies themselves require time to stabilize. The common way to do this was with a resistor/capacitor network holding the processor in reset until the cap charged. The problem is the timing was not consistent, and the relatively slow rise time of the reset line would cause problems. It also doesn't reset quickly in case of a power glitch. Thus the reset controller. That busy little circuit holds a comparator, an oscillator, a counter, and a driver. When the power comes on the driver holds the processor in reset. Once the comparator senses the supply is above a preset level (90% of nominal supply voltage, it allows the oscillator to drive the counter. Once the desired delay has been reached, the driver releases the reset and the processor starts.

Measure the voltage on the three pins of U404. Also, there are three voltage regulators to investigate. Measure the voltage on all three pins of U601, U602, and U902.

PlainBill

Thanks for the info PB,

As for the voltages:

I've measured them relative to each pin (probes across pin 1 - 2 for example) on the 4 components - pins as per the attached image.

U404:

Pin 1 - 2 = 0V
Pin 1 - 3 = 1.24V
Pin 2 - 3 = 1.24V

Voltages between pins 1-3 and 2-3 on the U404 seems to start at 1.24 then drop off to 0, bit unstable but perhaps showing the operation as you described.

U601:

Pin 1 - 2 = 5.2V
Pin 1 - 3 = 1.24V
Pin 2 - 3 = 3.96V

U902:

Pin 1 - 4 = 0V
Pin 2 - 4 = 0V
Pin 3 - 4 = 0V
Pin 1 - 2 = 0V
Pin 1 - 3 = 0V
Pin 2 - 3 = 0V

U602:

Pin 1 - 4 = 0.4V
Pin 2 - 4 = 0V
Pin 3 - 4 = 0.84V
Pin 1 - 2 = 0.4V
Pin 1 - 3 = 1.24V
Pin 2 - 3 = 0.84V

The middle pin of the cluster of 3 (between pins 1 and 2) on the U602 doesn't seem to be connected to the board - i assume this is connected as pin 3.

[PlainBill]

Re: Dell 1707FP no power

A better pic - Is that device a voltage regulator of some sort?

If I'm correct, it's a reset controller. A quick background: Processors often have internal charge pumps, etc that require a finite time to stabilize after the chip receives power. Plus of course, the power supplies themselves require time to stabilize. The common way to do this was with a resistor/capacitor network holding the processor in reset until the cap charged. The problem is the timing was not consistent, and the relatively slow rise time of the reset line would cause problems. It also doesn't reset quickly in case of a power glitch. Thus the reset controller. That busy little circuit holds a comparator, an oscillator, a counter, and a driver. When the power comes on the driver holds the processor in reset. Once the comparator senses the supply is above a preset level (90% of nominal supply voltage, it allows the oscillator to drive the counter. Once the desired delay has been reached, the driver releases the reset and the processor starts.

Measure the voltage on the three pins of U404. Also, there are three voltage regulators to investigate. Measure the voltage on all three pins of U601, U602, and U902.

PlainBill

[bob12345]

Re: Dell 1707FP no power

A better pic - Is that device a voltage regulator of some sort?

[bob12345]

Re: Dell 1707FP no power

We may have a winner!!! What is the part number for U404 (three pin device to the left of the gm5621-LF).

PlainBill

If my eyes aren't play tricks on me, the part# is DF64

[PlainBill]

Re: Dell 1707FP no power

I'm dreading that the logic board is dead, probably hardest to source/repair i'm assuming! Here are two pictures of either side of the logic board (model is a 1707FPt). Nothing appears to be burnt out visually.
Sorry about the blur in the second pic, camera doesn't like to focus with no flash in macro mode.

We may have a winner!!! What is the part number for U404 (three pin device to the left of the gm5621-LF).

PlainBill

[bob12345]

Re: Dell 1707FP no power

I'm dreading that the logic board is dead, probably hardest to source/repair i'm assuming! Here are two pictures of either side of the logic board (model is a 1707FPt). Nothing appears to be burnt out visually.
Sorry about the blur in the second pic, camera doesn't like to focus with no flash in macro mode.

My mistake the monitor is a 1707FPf not t.

[bob12345]

Re: Dell 1707FP no power

One thing is apparent; another can be inferred.
1. The power supply is working.
2. You have very good ears.

As I've said repeatedly, the power LED is controlled by the processor on the logic card. It's time to post pictures of the logic card and see if we can find the problem.

PlainBill

I'm dreading that the logic board is dead, probably hardest to source/repair i'm assuming! Here are two pictures of either side of the logic board (model is a 1707FPt). Nothing appears to be burnt out visually.
Sorry about the blur in the second pic, camera doesn't like to focus with no flash in macro mode.

[PlainBill]

Re: Dell 1707FP no power

I've measured the voltage from ground (or what I think is ground - please correct me if i'm mistaken) - the three pins on the right of the (pins 0 - 2) connector CN853 (PSU -> Logic card) which appear to be connected to the ground track of some nearby caps and that track also goes to the chassis mounting screw hole so I assume thats a suitable ground location (see attached underside pic). The voltages relative to these GND pins (right to left as shown on underside pic):

Pins 0-2: GND (0V)
Pin 3: 0V ---- (as expected as this appears to be connected to the 12V optional speaker attachement - not attached)
Pin 4: 5.18V
Pins 5-7: 5.21V
Pins 8-9: 0V ---- (appear to go to one of the inverter transformers T2?)

All parts where connected: LCD panel, inverters, logic board (but not the usb header board)

No ticking noise heard now, only the constant buzz/humm of something.

Thanks for all your help so far!

One thing is apparent; another can be inferred.
1. The power supply is working.
2. You have very good ears.

As I've said repeatedly, the power LED is controlled by the processor on the logic card. It's time to post pictures of the logic card and see if we can find the problem.

PlainBill