Hitachi 35UX85B TV - Dead with periodic "Chirping" sound

[tman]

A neighbor moving out left me this non-functional Hitachi 35UX85B, now
to get it to work!!! Upon Power-up the relay clicks, but there is no
audio, video (raster), or visible LED's on the front. This is
accompanied by an intermittent chirping sound (~1 - 2 sec. interval).
The "Chirp" is coming from the Power Block in the vicinity of T-902 and
is audible in a quiet room (sounds like there's an agitated mouse in
there....but there isn't). All fuses (2) check out fine. Upon
Power-down the "Chirping" will persist another 8 - 10 secs. after the
relay shuts off power. Boards look good as well, no obvious fried
components/connections, shorts or dry joints.

I downloaded the service manual and it has all the schematics and
specs. but does not give much help in the troubleshooting flowcharts.
Before I cause too much havoc with my Fluke and soldering iron, does
anyone have a good idea of what are the likely suspects?

Mucho thanks for any help.

 

[Art]

Troubleshoot with your trusty DMM then post any and all diagnostic results
you actually have produced. Suggest paying attention to the higher current
circuits of the set, such as the SWPS, Deflection, Etc. A bit of tutorial
reading may also be necessary for you to safely proceeded.

 

[ray13]

Not much to go on there. But look at a shorted horizontal output
transisitor. The chirping is the P.S. trying to start then the over
current sense kicks it off. Needless to say once the current drops it
try's to do it again ad nausium.

Then there are a few things the can cause the transistor to short. Like
bad connections on the drive xformer, bad hold down cap, and bad
flyback transformer.

But then you could have a bad supply too.

 

[Asimov]

"tman" bravely wrote to "All" (17 Oct 05 22:57:10)
--- on the heady topic of "Hitachi 35UX85B TV - Dead with periodic "Chirping" sound"

tm> From: "tman" <[email protected]>
tm> Xref: core-easynews sci.electronics.repair:345572

tm> A neighbor moving out left me this non-functional Hitachi 35UX85B, now
tm> to get it to work!!! Upon Power-up the relay clicks, but there is no
tm> audio, video (raster), or visible LED's on the front. This is
tm> accompanied by an intermittent chirping sound (~1 - 2 sec. interval).
tm> The "Chirp" is coming from the Power Block in the vicinity of T-902
tm> and is audible in a quiet room (sounds like there's an agitated mouse
tm> in there....but there isn't). All fuses (2) check out fine. Upon
tm> Power-down the "Chirping" will persist another 8 - 10 secs. after the
tm> relay shuts off power. Boards look good as well, no obvious fried
tm> components/connections, shorts or dry joints.

tm> I downloaded the service manual and it has all the schematics and
tm> specs. but does not give much help in the troubleshooting flowcharts.
tm> Before I cause too much havoc with my Fluke and soldering iron, does
tm> anyone have a good idea of what are the likely suspects?

tm> Mucho thanks for any help.


Sure, from what you describe it seems like the switching power supply
is trying to start up into a dead short, fails, turns off, and then
keeps trying: chirp, chirp, chirp.

You will need to check the h-out Q, as a short there will definitly
load down the smps. If it isn't the hot, then locate the v-out etc.

First consider that a dead short is something pretty obvious to
locate. Once the short is found, then you have to determine what its
causes were and repair the defective circuitry. Sometimes a dead short
is just a symptom of deeper problems. Keep in mind a new replacement
hot will blow in about 3.5 milli-seconds unless the defect is found.

Finding a dead short should be child's play with your Fluke, but it's
the other steps that might be trickier, depending on your ability. An
esr meter might be helpful to locate faulty electrolytic capacitors.
Good luck and be careful around high voltage electronics.

A*s*i*m*o*v

.... You mean 15" sparks are SUPPOSED to come out of this thing?!?

 

[Guest]

The full service manual for this unit can be found at>>>
http://fletchersite.com/hitachi2.html

 

[kip]

Get your Credit Card out....

 

[Rich Webb]

A neighbor moving out left me this non-functional Hitachi 35UX85B, now
to get it to work!!! Upon Power-up the relay clicks, but there is no
audio, video (raster), or visible LED's on the front.

[snip...snip...]

Dumb suggestion (since you've probably already done this) but try
unplugging it for a few minutes and not just hitting the power switch.
I've an ancient JVC set that occasionally has symptoms very much like
you describe and a "cold boot" always does the trick.

 

[Tony Magon]

s.com.au

 

[[email protected]]

tman:
You have to perform some troubleshooting at your end and post the
testing and meter reading results then maybe you can get some more
specific suggestions. As with any dead set, usually the very first
things to investigate are the power supply and horizontal deflection
circuitry.
Since you have the manual and schematics.... and your Fluke... you are
way ahead of anyone here on the newsgroup.... open'er up and get going.
If you still do not know how to proceed then you should visit the
website for this newsgroup at
http://www.repairfaq.org/
there, with some searching, you will find a wealth of troubleshooting
tips, repair information, component testing methods and IMPORTANT
safety information that will help you to stay away from dangerous and
lethal electrical shock hazards inside your television.... note that
even when the television is unplugged from the AC power that these
hazards can still be present.... be very careful.
You have confirmed what seems to be a regular topic with newbie
postings for repair help.... components and parts that "look" good can
be very bad and must be tested... and a schematic and manual are of
very little use and do not provide troubleshooting help to the novice
repair person... a skilled and experienced tech who can fix the
majority of equipment without a schematic will find the them very
helpful in tough dog repairs.
electricitym
..
..
..

 

[James Sweet]

The full service manual for this unit can be found at>>>
http://fletchersite.com/hitachi2.html

You've got a shorted component causing the power supply to shut down.
Start by checking the rectfier diodes on the output of the power supply
and also check the HOT. You can also often disconnect outputs of the PSU
to track down which section the short is in.

 

[Livewire]

I had the same problem twice. The first time it happened was Nov 2004.
It cost me $344 for in home service to get it fixed. It just happened
again in Sep 2005. It was the same problem. There are 2 high voltage
capacitors in the power supply section, C714 & C715 that can
short, they may be blue in color, mine were. They are located on the
main board on the right side of the TV when looking at it from the
back. Most likely you will find at least one of them shorted. You
will probably need to remove them from the board to get an accurate
measurement.

I have a technical background as a radio repair tech, no experience
with TV, but I was comfortable making an attempt at fixing this
myself before dishing out a lot of money to the repair shop. There is
very high voltage (thousands) produced inside the TV from the flyback
transformer so be careful to make sure the CRT is disharged before
tinkering around. Since this is a high voltage problem, most likely
everything is discharged. The way I discharged the CRT was with an
insulated screwdriver with a jumper lead to ground. It was already
discharged as there was no popping noise when I tried it.

The original part # is 0244889. There is a substitute they are using
now Part # 0244729. The substitute part is larger in size, maybe to
handle the heat better. These can be found at several sites on line.
I purchased mine at www.partstore.com They are $1.83 ea. If you find
one of the caps shorted I would recommend replacing both of them.
They are the same part 2000v 2200pf ceramic caps.

Since I fixed this problem, I have another problem. I have a buzzing
sound in the audio when you have any kind of screen overlay like the
guide or Tivo menus. I do not here it while watching TV. Don't know
if it's related to the other problem or not. If anyone has any
suggestions. I'm not sure I want to open the set up again though.

Good luck, hope this helps.

 

[[email protected]]

The buzzing is due to the routing of the wiring and Hitachi has put out
a bulletin on it.

Open the tv up and move the wiring around to see if the buzzing changes.