Philips TV-set Matchline 6720 distorted picture, no sound

[Quibus]

Hi All,

I'm hoping someone can help me get this Philips Matchline 6720 TV that
was given to me, back to work again.
It still had sharp and crisp picturequality, both from the tuner and
from the 2 external Scart-sources, all TV-channels were available and
selectable, and all frontside buttons were functional.
It did have these 2 errors:
- segments of the 2-digit channeldisplay worked erratic.
- there was no sound on the 2 built-in loudspeakers, although sound
_was_ present (without any distortion) on the headphone jack.

I resoldered the PCB of the channeldisplay, and (just in case) the
flyback and HOT as well. I also removed and reseated the M5M8050 on
the controller board.
After reassembly this display works fine, but now all of a sudden the
picture is distorted on all TV-channels and on the ext. sources. It
looks as if there is no sync available. The picture looks to roll off
sideways with every scanline further down the screen. When switching
on Teletext I can vaguely recognize the image it is supposed to
display.

Does anybody have a suggestion how to get image again, and how to
restore sound? Are there any specific area's that need resoldering?
I have already checked my soldering with a looking-glass, but found no
accidental errors. I have also checked the horizontal PCB at the base
and the vertical HV PCB for bad solderjoints, but they all appear to
be in order.

Thanx in advance, Quibus

 

[Jerry G.]

Without being able to troubleshoot your set, using the schematic diagram, it
would be impossible to suggest an exact cause. It sounds like the sync, and
the scans are being effected. I would suspect that in your soldering work,
you jumpered or bridged some traces or connections where parts are soldered
on to the board. If this is the case (most likely), there is also a good
chance some components were also damaged from the bridging (shorting).

It is also possible that even though the power is off, if there is still
some charge left from the supply or in any of the caps, when bridging
circuits, it is still possible to do some damage to sensitive components.
The last thing I would do in any set, is go in to it with a soldering iron
and solder up the set, "as like a bull in a china shop!".

Your original fault of having segments not displaying properly would be from
the display segments themselves (if this module uses an external segment
display), such as if this set uses a segment display module or some numeric
LED displays, or the driver(s) to them, or the logic circuitry behind the
drivers, or the uPC (circuit) itself. With proper troubleshooting, as per
following up the signal paths with a scope and DVM, this could all be
determined and serviced.

Now you will have to fix the created fault, and then properly service the
fault you started out with, if this would be feasible.

--

Jerry G.
=====


<Quibus> wrote in message Hi All,

I'm hoping someone can help me get this Philips Matchline 6720 TV that
was given to me, back to work again.
It still had sharp and crisp picturequality, both from the tuner and
from the 2 external Scart-sources, all TV-channels were available and
selectable, and all frontside buttons were functional.
It did have these 2 errors:
- segments of the 2-digit channeldisplay worked erratic.
- there was no sound on the 2 built-in loudspeakers, although sound
_was_ present (without any distortion) on the headphone jack.

I resoldered the PCB of the channeldisplay, and (just in case) the
flyback and HOT as well. I also removed and reseated the M5M8050 on
the controller board.
After reassembly this display works fine, but now all of a sudden the
picture is distorted on all TV-channels and on the ext. sources. It
looks as if there is no sync available. The picture looks to roll off
sideways with every scanline further down the screen. When switching
on Teletext I can vaguely recognize the image it is supposed to
display.

Does anybody have a suggestion how to get image again, and how to
restore sound? Are there any specific area's that need resoldering?
I have already checked my soldering with a looking-glass, but found no
accidental errors. I have also checked the horizontal PCB at the base
and the vertical HV PCB for bad solderjoints, but they all appear to
be in order.

Thanx in advance, Quibus

 

[Quibus]

Without being able to troubleshoot your set, using the schematic diagram, it
would be impossible to suggest an exact cause. It sounds like the sync, and
the scans are being effected. I would suspect that in your soldering work,
you jumpered or bridged some traces or connections where parts are soldered
on to the board. If this is the case (most likely), there is also a good
chance some components were also damaged from the bridging (shorting).

It is also possible that even though the power is off, if there is still
some charge left from the supply or in any of the caps, when bridging
circuits, it is still possible to do some damage to sensitive components.
The last thing I would do in any set, is go in to it with a soldering iron
and solder up the set, "as like a bull in a china shop!".

Your original fault of having segments not displaying properly would be from
the display segments themselves (if this module uses an external segment
display), such as if this set uses a segment display module or some numeric
LED displays, or the driver(s) to them, or the logic circuitry behind the
drivers, or the uPC (circuit) itself. With proper troubleshooting, as per
following up the signal paths with a scope and DVM, this could all be
determined and serviced.

Now you will have to fix the created fault, and then properly service the
fault you started out with, if this would be feasible.

Jerry,

Thanks for your reply.
In fact I did not create a new fault when I resoldered the
channeldisplay PCB. Both problems were induced by dry solder joints in
several connectors on the base PCB. Problems were solved by
resoldering them, although I did the entire PCB as other solder joints
didn't look very convincing either. Not a single component was
defective.

The set is fully working now. Nice one as well, although already 20
years old it features stereo with 2 built in loudspeakers, 2 separate
scart input jacks, one of which even has RGB input.
So, it shows once again: if in doubt about the quality of solder
joints, resolder them anyway. It might take a while, but why overlook
the most obvious and simplest fault.

BTW: this set has a _lot_ of connectors on the various PCB's. I now
understand why Philips developed the I2C-bus later on...

Grtz, Quibus