Dell E171FP No power

[PlainBill]

Re: Dell E171FP No power

I measured the voltages again this time using the gnd pin from the device to measure relative voltage levels.

Note: Inverter board is not connected for any of the measurements. Same as in previous post.

With logic board connected:
Pin1: 167.8V DC
Pin2:
Pin3: 11.45
Pin4: 0.061
Pin5: 4.96


With logic board NOT connected:
Pin1: 168V DC
Pin2:
Pin3: 18.24
Pin4: 0.331
Pin5: 4.96

I'm not sure where the problem is occurring. Obviously, the 'power switch' is getting less voltage with the logic card attached. Looking at the application note for it, the recommended Vcc is 24 volts. That MAY be a false clue.

First, is there any label, printing, etc. on the board indicating it's output voltage and current rating? Second, if the 5V output is rated at more than 2.5 Amps, buy Radio Shack Catalog #: 271-131. This is a package of two 1 ohm resistors. Connect them in series from the 5 volt output to Gnd. Then with the logic card disconnected, plug the power supply in and measure the output voltages.

PlainBill

[Welchs101]

Re: Dell E171FP No power

The only voltages i see on the board is a general 250V/3.15A which is the same rating i see on the fuses.

The board appears to be the exact same as this one
http://www.lcdrepair.us/1504fp-power.html

I dont know if that helps or not.

Regarding the "1 ohm" resistors.....where do i connect them?

[PlainBill]

Re: Dell E171FP No power

The only voltages i see on the board is a general 250V/3.15A which is the same rating i see on the fuses.

The board appears to be the exact same as this one
http://www.lcdrepair.us/1504fp-power.html

I dont know if that helps or not.

Regarding the "1 ohm" resistors.....where do i connect them?

Hook them in series (end to end), then hook one end of the string to the + side of one of the 2200 uF cap, and the other end to the - side of the same cap.

PlainBill

[Welchs101]

Re: Dell E171FP No power

ok, i think i understand.

Its going to take me a day or two to get the resistors.

What is it i am looking for once i do put the resistors in? What will i be measuring or looking for?

[PlainBill]

Re: Dell E171FP No power

ok, i think i understand.

Its going to take me a day or two to get the resistors.

What is it i am looking for once i do put the resistors in? What will i be measuring or looking for?

You'll be measuring the output of the power supply. I'm sort of guessing here. Most monitors of that era had power supplies rated at about 3 Amps. If yours puts out 5V with a two ohm load (2.5 Amps) we can be pretty sure it is working right. Then the problem is on the logic card.

PlainBill

[Welchs101]

Re: Dell E171FP No power

thanks! that makes sense.

[Welchs101]

Re: Dell E171FP No power

ok. I have the two 1ohm 10watt resistors. They are big.....guess they might need to handle a large current!

I am attaching a pic to show you how i set it up based on what you had said. Want to make sure i have it setup correctly.

Procedure:
1) Make sure power supply board is NOT connected to logic board.
2) Plug in power cord to power supply
3) Measure voltages at the connector as i have done in previous posts.
4) record voltages and post to bad-caps

Is this the correct procedure?

[Welchs101]

Re: Dell E171FP No power

ok. I assumed it was connected correctly and went ahead with what i thought was the procedure.

Here are the voltages i measured. Note: Logic board was disconnected. Setup as shown in the previous picture except i decided to solder the two resistors together instead of using the banana clip.


Voltages measured at connector:
With logic board NOT connected and two resistors in parallel with 220uF cap:
At 1: 4.96V DC
At 2: 0.089V DC
At 3: 0.004V DC
At 4: 0.004V DC
At 5: 0.004V DC
At 6: 26.58V DC
At 7(Blue): 26.57DC


I was surprised by the 26V DC voltage on pin 6 and 7. Had not seen this before.

Any comments?

[PlainBill]

Re: Dell E171FP No power

ok. I assumed it was connected correctly and went ahead with what i thought was the procedure.

Here are the voltages i measured. Note: Logic board was disconnected. Setup as shown in the previous picture except i decided to solder the two resistors together instead of using the banana clip.


Voltages measured at connector:
With logic board NOT connected and two resistors in parallel with 220uF cap:
At 1: 4.96V DC
At 2: 0.089V DC
At 3: 0.004V DC
At 4: 0.004V DC
At 5: 0.004V DC
At 6: 26.58V DC
At 7(Blue): 26.57DC


I was surprised by the 26V DC voltage on pin 6 and 7. Had not seen this before.

Any comments?

Several.

You did a good job. The hookup was correct, and you proved that the power supply is working correctly.

26 volts on the 12 volt line is a little surprising; I expected it to be in the 14 - 18 volt range. Obviously, the transformer has fairly loose coupling.

I'm not optimistic about being able to repair the logic board. There are also questions about the various outputs of the power supply. If you want to continue I will need good quality pictures of the back of the power supply, and of both front and back of the logic board.

PlainBill

[Welchs101]

Re: Dell E171FP No power

I am enclosing what i think are good pics of frnt/bck of logic and power supply board.

I wanted to ask you another question if i may. See the pic titled Measure points. There are two devices highlighed in a red box. One of them (on the left) is a two terminal diode, the other is a 3 terminal schottky diodes.

When i measure the "resistance" across the diode it starts out around 50ohms and increases. It does this regardless of which probe i put where. I have a video of me measuring it so you can see the multi-meter readings.........is there a way to post this video so you can see it?

[PlainBill]

Re: Dell E171FP No power

I am enclosing what i think are good pics of frnt/bck of logic and power supply board.

I wanted to ask you another question if i may. See the pic titled Measure points. There are two devices highlighed in a red box. One of them (on the left) is a two terminal diode, the other is a 3 terminal schottky diodes.

When i measure the "resistance" across the diode it starts out around 50ohms and increases. It does this regardless of which probe i put where. I have a video of me measuring it so you can see the multi-meter readings.........is there a way to post this video so you can see it?

The voltage increase like that is normal - the meter is charging the main filter caps.

On the logic board I have identified 5 ICs. I believe these are all voltage regulators. What are the part numbers of them?

PlainBill

[Welchs101]

Re: Dell E171FP No power

I have included pics as well because i am notorius for looking at a partnumber and getting it wrong.

From what i can tell with magnifying glass:
Part1)
26AT
LBBB

Parts2)3)4)
BA033
2B 29

Part5)
7805C
NLEC239


If this does not answer your question or you need more info just let me know.

[PlainBill]

Re: Dell E171FP No power

I have included pics as well because i am notorius for looking at a partnumber and getting it wrong.

From what i can tell with magnifying glass:
Part1)
26AT
LBBB

Parts2)3)4)
BA033
2B 29

Part5)
7805C
NLEC239


If this does not answer your question or you need more info just let me know.

26AT is unknown (Darn!)

BA033 is a 3.3V regulator
MC7805C is a 5V regulator

The four parts identified all have the same input / output configuration. Referring to IC104, pin 1 is the pin closest to the camera; the pin closest to R337. The same position applies to IC103. It is also the input pin. With an ohmmeter check if pin 1 of IC103 is connected to pin 1 of IC104, IC403, and IC404.

Another test is to check which pins of the power supply connector are connected to pin 1 of these ICs.

PlainBill

[mathog]

Re: Dell E171FP No power

ok. I have the two 1ohm 10watt resistors. They are big.....guess they might need to handle a large current!

Back in the day for low value test resistances we used 120V incandescent bulbs like this:

1 Ohm = 100W bulb
2 Ohm = 60W bulb
3 Ohm = 40W bulb

Just put them in a lamp, clip the power to the lamp plug, and away you go. For the amount of power they could dissipate these were much, much cheaper than the equivalent high power resistor.

[PlainBill]

Re: Dell E171FP No power

Back in the day for low value test resistances we used 120V incandescent bulbs like this:

1 Ohm = 100W bulb
2 Ohm = 60W bulb
3 Ohm = 40W bulb

Just put them in a lamp, clip the power to the lamp plug, and away you go. For the amount of power they could dissipate these were much, much cheaper than the equivalent high power resistor.

There are a couple of problems with that idea. For example, a 60 watt 120 Volt bulb has a resistance of 240 ohms at operating temperature. That's a pretty light load for a 5 Volt supply. But, you say, the resistance of a cold filament is much less. Did you ever check the resistance of one of the bulbs when cold? I just did - 17 ohms. Still not much of a load for a 5 Volt supply.

I DO have it on excellent authority (the ARRL) that an appropriate wattage bulb makes a serviceable dummy load when tuning a ham transmitter (provided you remove the base first).

PlainBill

[Welchs101]

Re: Dell E171FP No power

ok.

Pin1 of IC403, IC404 and IC104 are all connected together.


Pin7 of the connector is connected to only pin1 of IC103.


Note: All of the metal on the back of the ICs are shorted.

[PlainBill]

Re: Dell E171FP No power

ok.

Pin1 of IC403, IC404 and IC104 are all connected together.


Pin7 of the connector is connected to only pin1 of IC103.


Note: All of the metal on the back of the ICs are shorted.

I take it then that pin 1 of IC403, IC404, and IC104 are NOT connected to any pin (I would have expected pin 1) of the connector?

All of the metal 'shorted' is to be expected. That is the ground pin.

Does any pin of IC105 connect to the connector? Does any pin of IC105 connect to pin 1 of IC403, IC404, IC104?

Here's what's going on here. Something on the logic board is loading down the 5 volt output of the power supply. We know it's not IC103, it gets power from the 12V supply. So we're on a hunt to establish WHERE the power is disappearing, and hopefully it will be a replaceable part.

Another set of things to try. With the logic board hooked to the power supply, measure the voltage on pins 1 and 3 of IC403, IC404, and IC 104. You can use the tab on any of them as ground. Also, check the voltage on every pin of IC105, again using the tab of IC403 etc as ground.

PlainBill

[Welchs101]

Re: Dell E171FP No power

Yes, pin 1 of IC403, IC404, and IC104 do not appear to be shorted to any pin of the connector.

IC105: No of the pins of this device are shorted to any of the pins of the connector. However, pin1 and pin2 of IC105 are shorted together.

With logic board connected:
IC105:
Pin1: 3.367V DC
Pin2: 3.367V DC
Pin3: 2.5V DC
Pin4: 0.71V DC

IC404:
Pin1: 4.72V DC
Pin2:
Pin3: 3.368V DC


IC403:
Pin1: 4.73V DC
Pin2:
Pin3: 3.37V DC

IC104:
Pin1: 4.73V DC
Pin2:
Pin3: 3.368V DC

IC104:
Pin1: 7.72V DC
Pin2:
Pin3: 5.02V DC

[PlainBill]

Re: Dell E171FP No power

Yes, pin 1 of IC403, IC404, and IC104 do not appear to be shorted to any pin of the connector.

IC105: No of the pins of this device are shorted to any of the pins of the connector. However, pin1 and pin2 of IC105 are shorted together.

With logic board connected:
IC105:
Pin1: 3.367V DC
Pin2: 3.367V DC
Pin3: 2.5V DC
Pin4: 0.71V DC

IC404:
Pin1: 4.72V DC
Pin2:
Pin3: 3.368V DC


IC403:
Pin1: 4.73V DC
Pin2:
Pin3: 3.37V DC

IC104:
Pin1: 4.73V DC
Pin2:
Pin3: 3.368V DC

IC104:
Pin1: 7.72V DC
Pin2:
Pin3: 5.02V DC

At this point I don't have a clue what is drawing the extra power from the 5 Volt supply. About all I can suggest is trying to find other ICs that are connected to it.

PlainBill

[Welchs101]

Re: Dell E171FP No power

ok.....thanks Bill! I really appreciate your help. If i figure anything out i will post an update.