ACER AL1713m no power

[PlainBill]

Re: ACER AL1713m no power

Tutorial time for Welchs101, retiredcaps, and anyone else.

Look at the schematic on the last page of the service manual that Welches101 provided. D850 is the bridge rectifier, AC comes in on pins 2 and 3, DC goes out on pins 1 and 4. AC power is a sine wave. For 120 VAC, the live wire goes from approximately +170 volts to -170 volts relative to neutral. When the live wire is positive, current flows from pin 3 to pin 1 of D850, and into the positive pin of C854. The negative side of C854 is returned to the neutral wire through pins 4 and 2 of D850. When the live wire is negative current flows from the neutral wire, through pins 2 and 1 of D850, and into the positive lead of C854. The negative side of C854 is returned to the live wire through pins 4 and 3 of D850. That means the positive terminal of C854 varies from -1V (one diode drop) to +168V with respect to neutral. Neutral is tied to ground at your home fuse or circuit breaker box. Note that there are two different ground symbols. The circuitry between D850 and T850 is referred to as live or hot ground.

Now on to the low voltage at pin 3 of U850. Note R855 and R857 connect pin 3 of U850 to the positive side of C854. U850 contains a constant current source that takes this voltage and uses it to charge C857 on pin 7. This takes about a second when power is applied.

When C857 gets charged above about 16 volts U850 starts sending pulses to Q850, which in turn grounds T850 pin 5. Since T850 pin 3 is tied to + 168V, this generates voltage in the secondary windings, (pins 8&9, 6&7, and 10. This also generates voltage in the tertiary winding of T850, pins 2 and 3. Those pulses are rectified by D852 and passed through R856 where they charge C857.

U850 is an SG6841. A common mode of failure is a high leakage, so the voltage on pin 7 never reaches 16 volts. Replace it. Also, C857 takes a lot of stress, replace that also.

PlainBill

[retiredcaps]

Re: ACER AL1713m no power

Any comments on the 4.52V? Anyone have any ideas on what i should do next?

Don't know for sure, but usually there is a startup/run capacitor near the SMPS. It is 22uF to 47uF/25V to 50V. If you have an ESR meter, check that cap.

It provides the "startup power" to the SMPS. It could be bad and explain the 4.52V?

[Welchs101]

Re: ACER AL1713m no power

Any comments on the 4.52V? Anyone have any ideas on what i should do next?

Does this mean the U850 device is bad.......i would not think so since pin 3 is the Vin which is an input and not an output. I would think the problem is more "upstream" from the U850...........

[Welchs101]

Re: ACER AL1713m no power

ok.

I remeasured the voltage on pin3 and this time i used as "ground" the "-" lead of the "big" cap in the power supply.

I measured 4.52V. Again, its not the 16V as indicated in the document.


also, a little learning for me, why did i have to use the "negative" lead of the big cap.....why couldnt i just use the "ground" from where i plug in the power cord? I thought the 16V was 16V to ground.......i guess it might not be relative to this ground.......

[newbie1]

Re: ACER AL1713m no power

Schematics aren't better than sex, but are almost as good as chocolate.

PlainBill

LMAO! ROFL! LOL!.. this, for me, will be the quote of the century....

[bonney]

Re: ACER AL1713m no power

this is O2micro's product guide

[PlainBill]

Re: ACER AL1713m no power

1. The part number for the SMPS controller is on the schematic.

2. When measuring DC voltages on the 'Hot' side of the power supply use the negative lead of the large capacitor as ground, or in this case, pin 1 of the SG6841 (which is tied to ground) can be used.

3. At this point I would not worry about the 10 ohm resistor.

4. Yes, R852 is good.

PlainBill

[alexanna]

Re: ACER AL1713m no power

Is u850 the SMPS controller?
Al.

[Welchs101]

Re: ACER AL1713m no power

ok......thanks. WHere should i measure the voltage from. Can you indicate on the picture where i should probe? Thanks.

[alexanna]

Re: ACER AL1713m no power

I measured the voltage on pin3 of the U850......i measured DV volts of (-78.1V). From the documentation the voltage is supposed to be 16V.......so something is wrong......right?

I measured the pin3 voltage with power to the board and everything connected EXCEPT the speakers.

It sounds like your making a mistake I have made in the past, ,there is a hot [hurt]side of the PS and a cold [low voltage side].To me it sounds like when you were measuring pin #3 you had the negative lead of your DVM hooked to the wrong ground point.
Al.

[Welchs101]

Re: ACER AL1713m no power

I measured the voltage on pin3 of the U850......i measured DV volts of (-78.1V). From the documentation the voltage is supposed to be 16V.......so something is wrong......right?

I measured the pin3 voltage with power to the board and everything connected EXCEPT the speakers.

[Welchs101]

Re: ACER AL1713m no power

Hi Bill,

Yes, i did toggle the "on/off" button but the LED still did not light up. But please keep helping me.........

I did check the connector between the power supply board and the logic board. I actually forgot to include this information in my original post. I am getting "0V" on all pins for connector CN852.

Regarding Resistor R852.I see what your saying.........from the schematic it does appear to be 0.2ohm/1watt..........so this means the resistor is ok. RIght?

For R1. I did find that i have two resistors in my "spare parts bin" that are 10ohm resistors. (both i bought from radio shack years ago). I have one that 10ohm and 1/2watt (5% tolerance) and another that is 10ohm Metal oxide resistor 1watt with 5% tolerance. I can give you the web site that i found the reference to 10ohm if you like....

http://www.fixya.com/support/t2659080-acer_al_1713

I will check the voltage value on U850 pin 3 and get back to you.

How did you know again inverter controller was a OZ99R? Where is this on the front or the back of the power supply board?

thanks again for your help!

[PlainBill]

Re: ACER AL1713m no power

Whoo, boy.

Let's start with troubleshooting theory. If a car runs out of gas, the normal first step is to add gas to the tank. You have done the equivalent of that, well done. If the car does not start do you start taking apart the engine, or do you check to see if the gas is getting to the engine?

Next point. The power LED is controlled by the processor on the logic card. Take a working monitor, turn if off by the power button, then unplug it. Plug it back in, and the power LED will still be off until you hit the power button. I assume you did try hitting the power button, if I'm wrong, let me know and I'll quit helping you.

So there are three possible reasons for the 'no power light' symptom. No power, no processor, no brains. Note that I am assuming the third case does not apply to you. (Some others I'm not so sure about.)

The next step ALWAYS is to check the connector between power supply and logic board for proper voltages. If the voltages are not present, you PROBABLY have a power supply issue. If the voltages are present, you have a logic card issue (unless you forgot to hook up the cable to the front panel).

It helps to know the standard resistor values. 938 is not a standard value. I read the resistor as red, black, silver, gold. This looks like a fusible resistor.

The service manual. Schematics aren't better than sex, but are almost as good as chocolate. R852 is shown on the last page of the service manual. .2 ohm, 1 watt, fusible. No chocolate for you.

R1 is disturbing. It's on page 45 of the Service Manual. It provides power to the inverter controller. No, that won't cause the 'No power LED' problem.

But the inverter controller seems to be an OZ99R. I haven't been able to find a datasheet for that one, but the schematic will help. You can have chocolate - two M&Ms.

If there is no power, check the voltage on pin 3 of U850.

PlainBill

[Welchs101]

Hi, I have an ACER AL1713m which does not turn on.

What i have learned and what information I have gathered.

1) When i plug in power to the monitor the LED does NOT come on.
2) I opened the monitor and found the following capacitors which were "bulging". I replaced the "bulging" capacitors.
C867:1000UF/16v => replaced with 1000uF/25V
C862: 1000uf/25v => replaced with 1000uF/25V
C865: 470Uf/25v => replaced with 470uF/25V
C22 and C6: 220uF/25V => replaced with 220uF/35V

3) I found resistor R1 was burned.
From online literature I found that this resistor is supposed to be 10ohms,1/4watt. The resistor is visually burned up. I had trouble getting solder to “stick” to the holes which hold the resistor in place. I cleaned as best I could. Also, cleaned the leads of the resistor. I measured the resistance of R1 and it measured 13ohms. I re-soldered this resistor and put it back into the pcb. I would like a replacement but don't have one. With resistor R1 in place (although burned...see enclosed pics) the LED on light does NOT come on.

4) I found an ACER troubleshooting document (also enclosed) online.
If you look at page 26 it says that if no led lights comes on then check the "Q.P.I". I dont know what this is but if you jump to page 30 of the document it says to check device U850. I did not check this device as yet but I did look at some of the resistors R855, R857 and R852. According to the document i should check these resistors if there is a problem with U850.....i went ahead and assumed U850 would have a problem and looked at the resistors R855, R857 and R852. What i found was that resistor R852 measured only 0.5ohms. This seemed strange since the color band (i think....someone please confirm) says the resistance should be 938ohms. I dont have a replacement resistor for R852 but i think i should get one.

Help:
1) I know i should replace R1 but given that it still measures 13ohms.......i would think that with R1 in place as it is now i should at least get the LED to come on. Is this thinking flawed?

2) R852: Did i read the resistor color band right? is the resistance 938ohms? I measure 0.5ohms. Could this 0.5ohms cause the LED not to come on or do you think there are other issues?

Any help you can give or direction to trouble shooting would be helpful.