Monitor Philips CM11342

[daver2]

4M4 is supposed to be 15V.

Check potentiometer R3583 and the voltages around the two transistors 7580 and 7585.

Look for bad solder joints or varying voltages +28A on the two resistors.

Dave

 

[bburley]

It is possible that the TDA3653 Vertical IC could be going bad as it warms up. I used to use a can of "Freeze Spray" to cool down parts to see if the temperature change would affect the problem.

CRC Freeze Spray, 283g

Aerosol coolant system that instantly freezes surfaces to -60°F, dissipating heat & cooling equipment. It also assists in locating thermal intermittent components, failures & shorts. Safe to use on sensitive components & all surfaces finishes.

www.crcindustries.ca

 

[daver2]

I was thinking a similar thing. I would spray transistors 7580 and 7580 also.

Use freezer spray designed for electronics work, not medical from a chemist.

Dave

 

[shad]

GREAT NEWS ! Monitor is up and running with no faults finally !

The culprit was the vertical line IC 7560 (TDA3653) which was causing the screen to collapse into a single horizontal line.
I replaced it and made sure to apply thermal paste for the cooling. I tested it for the past days and all is good !

Dave and Bburley, thank you so much for all your help and hints.
I learned quite a lot from you guys. Appreciate it !

I have ordered online an oscilloscope as it would be a crucial tool for future repairs.
The question is how to use the scope for testing the board ? Are there specific points where i should take readings with the scope ? I noticed wave forms mentioned on page 17 of the the service manual.

Shad

 

[daver2]

The basic things are to check the power rails and any oscillators to make sure they are all functioning correctly. You can now 'see' the power rails - so you can vary the timebase to look for any ripple (50/60/100/120 Hz) or noise (much faster timebase settings). Switching to AC coupling and increasing the sensitivity will mean you can see the noise and ripple.

If the service manual has oscilloscope traces, then YES, check these points out. The manual should describe the oscilloscope setting (timebase and expected voltages). Compare what you have with what should be there - bearing in mind that the manual will describe the waveforms under certain video conditions.

An oscilloscope is an invaluable tool.

Dave

 

[bburley]

Service manuals will sometimes show the waveforms that you should expect but you can also sometimes see typical or very similar waveforms that may be shown in component datasheets when they show a typical application circuit for that component.

As you gain experience and more electronics knowledge you will often know roughly what to expect. You may not know when it is exactly correct but it shouldn't be too hard to know when it is way off or something is very wrong.