Tv won't come on
to all from Tom Arnold, WA6OVP
Repair of computer monitors or flat panel TV’s.
Recently my wife's 27-inch AKAI (LCT21AS) 27-inch flat panel HDTV with DVD
player quit working. Years ago, when I had an analog computer monitor quit
operating; Joe Fadden WA6DDF had mentioned to me, that often computer monitor
problems were caused by the monitor's power supply. Joe also said these power
supply problems were often caused by failed electrolytic capacitors. Joe said
he was able to fix many computer monitors by just changing all of the power
supply electrolytic capacitors. Rather the fix that failed monitor, I just a
bought a new one.
The inoperative HDTV had been bought at COSTCO and had already been returned
once to a COSTCO repair center for repairs. Cost to ship and insure the HDTV
was 67 dollars. We received back a new HDTV set. Turn around time was over a
month, with many long distance telephone calls being required. The new HDTV
worked for about three months after it was received. When the returned HDTV
failed, it trapped a DVD disc that had been left in the HDTV DVD player. The
new HDTV failure symptoms were the same as the original HDTV failure. The red
led indication would not change to green when the remotes power on button was
pushed. There was no picture and no sound. The remote is required to operate
the TV set.
My wife's HDTV with internal DVD player was very expensive. Worse yet, the
trapped DVD disc was the movie Flash Gorden Space Soldiers 1936. A local TV
shop wanted 85 dollars to look at the failed HDTV; repairs were 75 dollars
labor an hour plus parts. I quickly figured out that if I could fix the problem
it would save a lot of time and money.
I checked the Internet to determine if other AKAI owners had similar problems
with their HDTV sets. There were lots of AKAI 27 inch and 32 inch HDTV set
owners listing problems. Without exception all of the complaints concerned the
HDTV power supply PC board and failed electrolytic capacitors.
Most of the AKAI HDTV sets worked just great and that many had been sold
worldwide. There were some AKAI HDTV sets that did have power supply problems.
Most of the AKAI HDTV set owners were not very pleased with either AKAI or the
COSTCO response to the inoperative HDTV power supply problem.
All electrical power was removed from the HDTV set. The HDTV was placed face
down on a workbench with a piece of cardboard to protect the display screen.
The HDTV back panel cover was removed. There were many screws of several
different sizes. The power supply PC board was separate from the rest of the
set's components and was easily identified. The power supply PC board contained
several different individual different voltage power supplies. Three
electrolytic capacitors located on the PC board had obviously failed. The tops
of these three capacitors were puffed out. Often when electrolytic capacitors
fail they get over heated and the top of the capacitor is puffed out displaying
an over pressurized appearance. The power supplies on the PC board were of the
switching type. Switching type power supplies are also used in computer
monitors to save money and weight.
Supply PC Board Removal:
The power supply PC board was mounted to the HDTV back panel with several
screws. These screws were removed. There also several multi-pin connectors
attached to the PC board. These connectors were numbered with a black felt
marker to ensure correct reinstallation. The connectors were Hot-glued in
place. A sharp knife was used to remove the hot glue. The connectors were
The three suspect failed capacitors were easily removed. The three capacitors
were each 1000 ufd and rated at 16 working volts. The other power supply PC
board electrolytic capacitors were visibly checked. Three new capacitors were
installed, they were rated at 1000 ufd at 25 working volts. On the PC board the
three electrolytic capacitors were in just one of the power supply circuits and
were identified as EC18, EC19, and EC20.
New Electrolytic capacitors:
These were low impedance / high reliability radial lead polarized aluminum
capacitors, they have a plus and minus connection pins. Correct installation of
any polarized capacitor is required. The three new electrolytic capacitors were
specifically designed and rated for service in switching type power supply
circuits. Switching type power supply electrolytic capacitors need to be both
very robust and designed for use in high frequency circuits. General-purpose
aluminum electrolytic capacitors should not be used in switching type power
supplies, if capacitors designed for switching power supplies can be obtained.
The PC board was reinstalled without the electrical connectors to the PC board
being hot glued. The HDTV back panel cover was refastened. Watched episodes one
through five of Space Soldiers. It was well worth the time and three
electrolytic capacitors to fix the problem. The repairs saved a lot of time and
money. The repair was very simple and not the least challenging. It took longer to remove and then reinstall
the HDTV back cover panel than it took to replace the three failed capacitors.
types of repairs should not be attempted without a complete understanding of
the dangers involved with working on electrical equipment, especially working
around power supplies and charged capacitors. Proper desoldiering and
soldiering techniques need to be used.
Flat screen computer monitors and TV sets do fail. Repairs of electronic
equipment can be very expensive. When your computer monitor or flat screen TV
does fail, you might consider a visible inspection of the equipments power
supply. A simple repair might save you a lot of time and money.
Aug 12, 2008 |
Akai LCT2785TA 27 in. LCD Television