Acer AL1923 repair

Background

The Acer 1923 monitor is a 19" LCD panel of about 2006/2007 vintage. This monitor has given light to moderate service over the past 7 years, has not generally been left on 24/7 more likely doing 4-6 hours at a stint several times per week. A rough calculation something north of 11,000 hours of operating time.

The unit has performed well, except for recently over period of two weeks, it failed to start on several occasions, and when operating had wavy lines across the screen, which disappeared after a few minutes. The false starts increased in frequency until the monitor would not start no matter what was done to the power or controls.



The AL1923 died on 3pm on 10th February 2014.

Disassembly

The first step to repair was disassembly...
Editors note: Any half-arsed service technician, would tell you the first steps to repair are to accurately record the symptoms, and go find the service manual, interestingly the service manual was located two weeks after the repair was complete...



Remove the four screws from the stand and release the back cover, reveals a metal shield over the power and video PCBs (per the picture).
Remove another four screws holding down the shield, to reveal the PCBs take careful note of the orientation of the four plugs for the LCD back-light (per the photo, the left side of the photo is the top of the monitor)



To release the shield requires the careful removal of the metallised tape (which also must be some sort of shielding), the tape is difficult to remove in one piece.



Removal of the panel connector and console connector presents little problem if you note the orientation before removal. Tip the shield upside down to reveal the PCBs, the small one with external connectors is the video board, and the larger one is the power supply.

First step in diagnosing the problem was a detailed visual inspection of the two boards by removing the 7 screws, juggling the connectors and disconnection the power header between boards. Tricky but not too difficult.

A close visual inspection means with a magnifying glass, looking for burnt components, blown fuses, bulging capacitors, loose connectors etc etc .

Repair

The video board (pictured below), had no visible signs of stress.



The power supply is a pretty straightforward beast (pictured below), and from the top everything looked pretty normal....



But from the side things became much more obvious, five of the largest capacitors were bulging,
a sure sign of stress in the power supply, (see photo below), specifically they were :

C261 470uF 25V 105c

C263 470uF 25V 105c

C241 1000uF 10V 105c

C244 1000uF 10V 105c

C242 470uF 10V 105c



A quick check with and ESR meter (Effective Series Resistance), confirmed all the suspect capacitors are well out of specification which meant they had to be replaced, desoldering and measuring their values confirmed both.
For example in the picture below the 1000uF capacitor under test has a paltry 30uF up it's sleeve.
The ESR for a 1000uF at 10V at 2.76 ohms, is 25 times the expected value !



As bad luck would have it.. I did not have one new capacitor of correct ratings on hand, whilst I had some of the values, I did not have the voltages or temperature ratings. I resorted to scrounging around, cutting about 20 capacitors out of two old PC switch mode power supplies, and managed to cobble together some reasonable replacements

I replaced the faulty capacitors with the following values which seemed close enough...
for a power supply the capacitance seems less critical, especially if higher, but for voltage and temperature need to be the same or of a higher rating.

C261 560uF 35V 105c

C263 560uF 35V 105c

C241 2200uF 10V 105c

C244 2200uF 10V 105c

C242 1000uF 10V 105c



As you can see, the replacements look pretty good, I re-established the goop holding the components together using dobs of hot glue...

Reassembly

The reassembly went together with only minor one hitch, a trap for punters ...
the new capacitors are slightly taller than the old ones, and pushing up against the case.
Fortunately Acer had preempted this and placed a thick piece of black plastic between the
components and the metal shield. I made this more secure using duct tape, (per the photo),
and did not screw everything down quite as tight to avoid flexing the PCB.



and voila ..! it works a treat !

General Observations

On one hand, this was a reasonably predictable fix, LCD monitors are notorious for defective capacitors in the power supply, on the other hand it was a bit lucky, I just leapt in, no service information, no schematic and no real understanding of what to expect.

Since then I have found the service manual for a AL1923W model, which appears useful, slightly different but as all the components match up, I have included the schematic below and a link to the service information

Further Information

schematic
user manual
service manual

This content is published under Attribution-Noncommercial-Share Alike 3.0 Unported license.