Dry joint on 28" Hitachi wide screen TV?
 

Hi All,

A mate has given me his 5yr old 28" Hitachi wide screen TV and it
comes with an intermittent fault where it just cuts out.

Apparently if it does this you can *sometimes* switch it back on with
the remote and sometimes not.

He said if it fails to come back on, lifting one corner and dropping
it (gently?) often sorts it out?

I had a quick word with the guy in the local electrical shop today and
he suggested this was not an unknown fault on that and smaller models
in the range and of that age.

So, before I start tapping about all over the place looking for dry
joints, any TV gurus out there have any idea if there is a 'common'
area that I could start with please?

If I do get it all sorted I will probably give it to my elderly Mum /
Dad.

All the best ..

T i m

Failure to come on suggests PSU as a likely candidate, though not the
only one.

But you need to be aware of the various dangers in TVs before poking
about. Theres caps that store mains V, live lines on boards, 25kV EHT,
with storage in the tube, and one or 2 HT lines as well for eg focus
(maybe a few kV) etc. Plenty of ways to cook.

NT

On 19 Jan 2005 14:33:26 -0800, wrote:

Failure to come on suggests PSU as a likely candidate, though not the
only one.

I thought it might be around that area but other things (like
overvoltage to the HT) can cause TV's to shutdown can't it?

But you need to be aware of the various dangers in TVs before poking
about. Theres caps that store mains V, live lines on boards, 25kV EHT,
with storage in the tube, and one or 2 HT lines as well for eg focus
(maybe a few kV) etc. Plenty of ways to cook.

Hi and thanks for the reminder ;-)

I can remember watching an old-school TV engineer re-joining the
broken turn on the mains dropper resistor with his fingers with the
set still on .. ;-( (only 240 I know but that still tingles g)

If this wasn't (potentially ouch) a (free) nice 28" TV I wouldn't go
there out of choice ..

I have fixed a few swiched mode PSU's in my time but don't bother with
PC ones any more (too cheap).

All the best ..

T i m

T i m wrote:
Hi All,

A mate has given me his 5yr old 28" Hitachi wide screen TV and it
comes with an intermittent fault where it just cuts out.

Apparently if it does this you can *sometimes* switch it back on with
the remote and sometimes not.

He said if it fails to come back on, lifting one corner and dropping
it (gently?) often sorts it out?

I had a quick word with the guy in the local electrical shop today
and
he suggested this was not an unknown fault on that and smaller models
in the range and of that age.

So, before I start tapping about all over the place looking for dry
joints, any TV gurus out there have any idea if there is a 'common'
area that I could start with please?

If I do get it all sorted I will probably give it to my elderly Mum /
Dad.

All the best ..

T i m

Look around the flyback transformer. I was told (by the man who
repaired one of my TVs with this kind of fault) that the amount of
copper in that area makes a very efficient heatsink and makes reliable
soldering difficult.

MBQ

Hi All,

A mate has given me his 5yr old 28" Hitachi wide screen TV and it
comes with an intermittent fault where it just cuts out.

Apparently if it does this you can *sometimes* switch it back on with
the remote and sometimes not.

He said if it fails to come back on, lifting one corner and dropping
it (gently?) often sorts it out?

I had a quick word with the guy in the local electrical shop today and
he suggested this was not an unknown fault on that and smaller models
in the range and of that age.

So, before I start tapping about all over the place looking for dry
joints, any TV gurus out there have any idea if there is a 'common'
area that I could start with please?

If I do get it all sorted I will probably give it to my elderly Mum /
Dad.

All the best ..

T i m

Out 28" hitachi did exactly the same - it was rented so an engineer (!?)
came out and knew exactly where to look, he just remade a couple of joints
(I couldnt tell you where on the board though) and it has been find since -
he said it was a common fault.

On Thu, 20 Jan 2005 13:44:16 -0000, "a" wrote:

So, before I start tapping about all over the place looking for dry
joints, any TV gurus out there have any idea if there is a 'common'
area that I could start with please?


Out 28" hitachi did exactly the same - it was rented so an engineer (!?)
came out and knew exactly where to look, he just remade a couple of joints
(I couldnt tell you where on the board though) and it has been find since -
he said it was a common fault.

Hmm, I re-soldered all the main joints today and now I have a *dead*
telly ;-(

The problem is I may have 'firmed up' the intermittent fault?

I have spoken to an ex TV repair mate and he might pop in to point me
in the right direction, or get one of his TV repair mates to sort it
for me. ;-(

All the best ..

T i m

oh :( do crosspost this lot to sci.electronics.repair.

NT

I thought it might be around that area but other things (like
overvoltage to the HT) can cause TV's to shutdown can't it?

HT overvoltage would be a PSU fault. If you mean EHT overvoltage...

On second thoughts it might not be set up like that, I dont do tv
repairs any more. SMPSUs can be a right pain now with their overzealous
protection schemes, so youre right its not necessarily a psu fault.
Just a question of starting where things are most likely. Thats the way
when you cant divide and conquer, and with todays overprotected psus
you often cant.

Its good you know the risks, i just never know whos going to read these
posts on a public ng.


NT

On another note, regular readers here may remember me rambling on
about
a sony TV suffering from green screen/flyback lines/PSU shutdown.

I used to bash it hard, it was getting worse. Cassandras prophesised
that it would finally fail as the tube was going.

In fact, for some unexplained reasn, it has performed flawlessly for
the
last 6 months.

Perhaps a tube short burnt out or fell off? Burning shorts out is a
standard repair after all, and the associated psu shutdown suggests
possible high fault current. Who knows :)

I once experimentally ran a Sony tube fairly heavily overvoltage
(heater +70%, drive V increased, and 10% EHT boost), and it did this
fairly regularly. The tube would arc over and so on. It was the only
tube I saw that turned PAL into Never The Same Colour Twice :) Dont
think I'd do that sort of thing now though :)


NT