Tough "Dog", Curtis Mathes/Samsung TV model CM27001S

Check for high ESR caps in the power supply and horiz output stages.

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JANA _____

I have a Curtis Mathes/Samsung TV model CM27001S (mfg. 11/01) in my shop. I now have SM (.PDF file)

The TV will turn on. There is around 27KV (measured) for the CRT. There is vertical deflection and good sound, but just as the picture begins to show, the TV turns off. Note: This happens every time you turn on the TV.

Note: Regulated B+ is 130V (measured).

I unplugged the CRT pcb and the TV stays on. I plugged it back onto the CRT and turn "screen" (FBT) to minimum. I turn on the TV and it says on, but when I turn up the "screen" slowly, just as the picture begins to show, TV turns off. Note: I tested the CRT and it is AOK. If I turn the "screen" all the way up, then turn on the TV, I can see a good picture just for moment, but the TV turns off. I scoped FBT with "screen" turned all the way down. Very good FB pulses which doesn't change at the point the TV turns off (by advancing the "screen"). The "Xray" circuit is not the cause (tested). I put a "pull up" (via bias box) on the ABL line to "hold up" the voltage which would drop (viewed on scope) at the moment the picture starts to show, but the TV still turns off.

Did you have one of these sets with the same symptom? What caused it?

Thanks in advance, Brad

Before you type your password, credit card number, etc., be sure there is no active keystroke logger (spyware) in your PC.

How much high voltage does it have maybe it's high,is the screen voltage in a normal range or is it excessive.

Hi,

In response to your replies, I did check caps for high ESR on the chance that when the picture begins to show, a "load" is placed on the regulated B+.

When the picture begins to show, a "load" is added to the HV trippler and FBT. Is it possible this "load" causes a "breakdown" in FBT? Note: I don't see evidence of this on the scope as I advance the "screen".

I thought about making a HV "dummy" load to substitute for the picture tube as a test, but I don't know what the current is (normal brightness current).

If I fix this "DOG", I will post an "Update".

Brad

snipped-for-privacy@verizon.net (Brad) wrote in news: snipped-for-privacy@news.verizon.net:

Find the monitored leg of the HVT and check there, for a voltage change at the time the picture appears.

Take a closer look at the abl detect is the dag on the tube above ground this also may be monitored.

Hope this helps, been out of this type of work for several years.

R!!

Hi,

Here is additional information on what I have tried in response to additional suggestions. Please see my other postings below for the "full story"..

I opened the ABL line and put a 10K resistor from the FBT ABL pin to ground. The ABL line, now isolated, will be unaffected by FBT/HV trippler "effects". The ABL circuit has a 79K resistor to regulated B+ and a 6.8K resistor to ground which will keep the voltage constant on the now isolated ABL line. With "screen" turned all the way down, the TV stays on. As I slowly advance the "screen", I see a good quality picture for a split second, then the TV shuts off. Please note: The "Xray" circuit (excessive HV shutdown) was already eliminated.

I hope one of you had a similar experience with this brand of TV.

Thanks in advance, Brad

snipped-for-privacy@verizon.net (Brad) wrote in news: snipped-for-privacy@news.verizon.net:

Have you found what is exactly causing the shutdown ?

Overcurrent shutdown ?

X-Ray Protect ?

The "Xray" circuit (excessive HV shutdown) was already eliminated

Are you sure some of those circuits are very tricky...

ABL Protect ?

Is the dag grounded on the tube or above ground ?

Power supply problem all sources ?

Possibly even vertical circuit problem ?

Before you dismiss I had a Zenith with this problem, a resistor had changed value causing a shutdown, looked like a horiz. problem had a slight driveline through the picture from top to bottom.

I don't have a diagram but I would check all the scan derived sources very carefully.

Roll the over for awhile...

R!!

Hi,

I checked all those items you have listed.

This "Tough Dog" has been upgraded to "Super Dog". Please search for "Super Dog" (another post) which has more information.

Brad