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Monitor Philips CM11342

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
 
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.

www.crcindustries.ca

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 www.crcindustries.ca
 
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
 
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
 
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
 
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.
 
Hi Guys,

I am off on a new repair project for a CM11342 Philips Monitor with a dead screen.

All rail voltages (+128, +9, +5, +12, +28) are ok.
The 27V is missing at C2541 like in the previous monitor. I did all the necessary checkups but did not find any bad components.

I noticed that:

- 23.4V is missing at the junction of C2547 and D6548 and D6546.
- 13.4V is missing at the junction of T7526 and R3530 and R3526 and C2526
- 12.8V is missing at the junction of T7526 and T7530.
- 6.5V is missing at the junction of T7530 and R3536 and C2532.


Any tips ?

Thanks,

Shad
 
You should have approximately +128V on C2520.

You should also have approximately +125V on C2514.

These could have higher-voltage spikes on them if the high voltage is present - so just take sensible precautions.

Dave
 
Hello Dave,

I measured the voltage across C2520 and it read 128V. Across C2514 it read 128V.

What else to check ?


Shad
 
The voltage on C2520 is good - power to the line/horizontal oscillator section.

The voltage on C2514 is good - it indicates that the primary winding of the line output transformer is OK (between pins 3 and 5).

So, we are looking at a faulty T7512 (line driver transistor) or this transistor is not being driven correctly.

Can you check the voltage across C2512? It should be about +28V.

Can you also check the voltage across R3514? It should be about 1V - but start off with your measurement equipment at a high voltage reading range (>128V) and select a lower range as required to read 1V. I would only change ranges with the measuring equipment NOT connected to the monitor though.

Another thought: Can you read the voltage across C2514 with your measuring equipment set to AC (not DC). Again, expect a potential high voltage (128V).

Dave
 
Last edited:
Hello Dave,

I am back from a business trip to Germany.
I am using a multi-meter for the voltage readings. I have ordered an oscilloscope but I didn't receive it yet.

- Voltage across C2512 is +28V
- Voltage across R3514 is 0.0mV
- Voltage across C2514 is 128V DC and 76V AC

What can we conclude here ?


Thanks,

Shad
 
I am suspecting that the line oscillator and high voltage drive to the high voltage transformer primary winding is OK.

C2512 being 28V indicates that the fusible resistor R3512 is OK.

I can't get too excited about the voltage at R3514 being non existent.

Because we have both a healthy DC reading of 128V AND an AC reading at C2514, I am making an educated guess that that the driver transistor (T7512) and the primary coil winding (between pins 3 and 5) are all OK. It would, however, be much easier to confirm this with an oscilloscope...

The next thing to ascertain is why we are not getting any -27V across C2541.

With the monitor off (and discharged) can you measure the resistance between pins '8 and 9' and '9 and 10' of the high voltage transformer please.

Dave
 
Hello Dave,

I measured the resistance across pins 8, 9, 10 of the High Voltage Transformer (5510) as follows:

Between Pin 8 and 9: it is continuously increasing as it reached 800 KOhm rising gradually
Between Pin 9 and 10: 0.2 Ohm


Shad
 
Between pins 9 and 10 is the key resistance. So the winding is not open circuit.

Can you measure the AC voltage between pins 9 and 10 now (with the power ON). Be careful though. It should be fairly low voltage (50 VAC or so) but it is around circuitry with high voltages.

Dave
 
With the power on, voltage reading between pins 9 and 10 is 4.00 VAC and sometimes 7.50 VAC.
 
OK, that seems low, but we must remember that your multimeter is not expecting an AC voltage at that frequency either!

The fact that there is some voltage there at all perhaps indicates that we have an operational line oscillator driving the high voltage transformer primary (as we suspected in a previous post).

Can you now check the DC voltage between pin 9 of the transformer and each end of R3540 in turn.

Dave
.
 
Voltage between PIN 9 of transformer and each end of R3540 is 0.55V DC
 
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