Acer AL1914 Dead

[Tiny1000]

Hello this is my first post so be gentle please

The story so far - A Friend got five of these monitors from work all with the same symptoms: Dead no response from the front controls or LED - He changed C914 (1000uf) & C915 (1000uf) which got two of the monitors working and gave the rest to me . Before he gave then to me he put a working power board in each one. Two worked fully and one had a white screen (not too bothered about this one at the mo) So I know that the two remaining monitors would work with a good power supply board. I changed all the electrolytic capacitors apart from the large one by the ac power supply (these are only general purpose caps I had at home, which are really just for test purpose and will be changed if I can get the monitors working). I have also changed a few other components (marked with red dots in the pictures) but all with no success. Any help with where to go now would be appreciated

[PlainBill]

Re: Acer AL1914 Dead

Hello this is my first post so be gentle please

The story so far - A Friend got five of these monitors from work all with the same symptoms: Dead no response from the front controls or LED - He changed C914 (1000uf) & C915 (1000uf) which got two of the monitors working and gave the rest to me . Before he gave then to me he put a working power board in each one. Two worked fully and one had a white screen (not too bothered about this one at the mo) So I know that the two remaining monitors would work with a good power supply board. I changed all the electrolytic capacitors apart from the large one by the ac power supply (these are only general purpose caps I had at home, which are really just for test purpose and will be changed if I can get the monitors working). I have also changed a few other components (marked with red dots in the pictures) but all with no success. Any help with where to go now would be appreciated

My first suggestion was to turn them over to someone competent. But that is unfair, especially in view of the number of poorly working items I managed to convert to non-working.

First step: CAREFULLY!! Measure the voltage across the large cap. It should be about 1.4 times the AC line voltage and stable.

Next step: Check the output voltages.

PlainBill

[Tiny1000]

Re: Acer AL1914 Dead

Thanks PlainBill, The large cap is about right at 340v but I have no output voltages at the plugs - I tested from the earth connection to each of the connections in the plug and only got 0 volts

[PlainBill]

Re: Acer AL1914 Dead

Thanks PlainBill, The large cap is about right at 340v but I have no output voltages at the plugs - I tested from the earth connection to each of the connections in the plug and only got 0 volts

340 volts? I take it you live in an area where line voltage is 240 volts?

Measuring from earth ground may not be reliable. I've taken the liberty of marking up the picture of the bottom of the board. VERY IMPORTANT!!! The area outlined in red is at line voltage. It will hurt if you touch it when the power is applied. Correction: YOU will hurt!!

Set the meter to the 20 VDC range and measure from the ground pad outlined in black to what should be the 5 V output outlined in red. If (as I expect) you get 0 volts, what is the part number of the SMPS controller (outlined in blue)?

PlainBill

[Tiny1000]

Re: Acer AL1914 Dead

England 240V - Spot on - 0 volts between the two pads - IC109 SG6841SZ - Cheers

[PlainBill]

Re: Acer AL1914 Dead

England 240V - Spot on - 0 volts between the two pads - IC109 SG6841SZ - Cheers

Got it! It's a System General Green-mode PWM power supply controller.

First steps are with power off. What are the color bands on R907? It's the green bodied resistor just above the yellow transformer. Now, what is it's resistance (measured with the DMM)?

Second step is with power on, be careful. From the - lead (upper lead in the picture) of the large capacitor what are the voltages at each end of R907?

PlainBill

[Tiny1000]

Re: Acer AL1914 Dead

R907 Brown Black Green - 994 ohms
Now this was a bit strange - when I first tried Maybe I didn't have a great connection but the reading was climbing into the 300v range then the display seemed to zero out - then at one end it was 0.473v and the other was 0.5047

[PlainBill]

Re: Acer AL1914 Dead

R907 Brown Black Green - 994 ohms
Now this was a bit strange - when I first tried Maybe I didn't have a great connection but the reading was climbing into the 300v range then the display seemed to zero out - then at one end it was 0.473v and the other was 0.5047

Something very strange, indeed. That resistor should read 100K ohms, not 1K. One end should go to the + lead of the large cap, the other to pin 3 of the SG6841S. It provides start up power for the SG6841S. It may be a good idea to look the board over carefully for bad solder joints.

PlainBill

[Tiny1000]

Re: Acer AL1914 Dead

Sorry PlainBill Typo mistake 994 m ohms

[Tiny1000]

Re: Acer AL1914 Dead

typing lessons needed 0.994 m ohms Sorry (read this 3 times before submitting)

[PlainBill]

Re: Acer AL1914 Dead

typing lessons needed 0.994 m ohms Sorry (read this 3 times before submitting)

Thank you. After considerable thought I realized that Brown, Black, Green is 10 followed by 5 zeros; or 1 Megohm. .994 is well within normal tolerances.

Now do you have any answers to the disappearing voltage?

PlainBill

[Tiny1000]

Re: Acer AL1914 Dead

Well after taking you're advice with the dry joints, I re-soldered everything that was even slightly suspect. Re-tested the voltage on the 1m resistor - The side closest to the transformer was 164v the other side 4.78v (starting to enjoy this!!)

[PlainBill]

Re: Acer AL1914 Dead

Well after taking you're advice with the dry joints, I re-soldered everything that was even slightly suspect. Re-tested the voltage on the 1m resistor - The side closest to the transformer was 164v the other side 4.78v (starting to enjoy this!!)

Something is not right. From the negative side of the large capacitor to one side of the resistor you should read 340 volts. To the other side you should read something much lower; the SMPS controller won't start until the voltage reaches 16 volts.

The datasheet is here.

PlainBill

[kc8adu]

Re: Acer AL1914 Dead

follow the trace from + of the primary cap to that group of 3 smt resistors and that lytic they lead to.check carefully.
if all ok replace the 6841.have needed to replace quite a few of those.

[Tiny1000]

Re: Acer AL1914 Dead

Just in case I had a quick look on the internet and i'm having trouble finding where I can buy 1 or 2 of the SG6841SZ ic's any ideas - Cheers

[Bobdee]

Re: Acer AL1914 Dead

Just in case I had a quick look on the internet and i'm having trouble finding where I can buy 1 or 2 of the SG6841SZ ic's any ideas - Cheers

There are some on ebay (international sellers) see link
http://shop.ebay.co.uk/?_from=R40&_t...All-Categories

[Tiny1000]

Re: Acer AL1914 Dead

Thanks Bobdee - Guess what - I won't be getting them from China (postage more than the ic and the ic 3 time the price from the USA!) lol

[Bobdee]

Re: Acer AL1914 Dead

Thanks Bobdee - Guess what - I won't be getting them from China (postage more than the ic and the ic 3 time the price from the USA!) lol

One here at £4-16p from states all in
http://shop.ebay.co.uk/i.html?_nkw=S...41SZ&_osacat=0

[kc8adu]

Re: Acer AL1914 Dead

digikey

[Toasty]

Re: Acer AL1914 Dead

Mouser.com:
http://mouser.com/ProductDetail/ISL6...WrqemkHA%3d%3d

Only 938 left and will be dropped when stock is depleted.

Digikey is all non-stocked and all no-stock.