How to test Flyback Transformer Without taking it off the Board

If your HP z74 CRT monitor is not turning on, there could be several potential causes. Some common causes of power failure in CRT monitors include:

• A faulty power supply: The power supply is responsible for providing power to all the components of the monitor, so if it is not functioning properly, the monitor will not turn on. You can test the power supply by using a multimeter to measure the voltage at the output connectors. If the voltage is not within the expected range, the power supply may need to be replaced.
• A faulty flyback transformer: The flyback transformer is a critical component of a CRT monitor, as it converts the high voltage AC input from the power supply into the low voltage DC output required by the other components of the monitor. If the flyback transformer is faulty, the monitor will not turn on. You can test the flyback transformer by using a multimeter to measure the voltage at the output terminals. If the voltage is not within the expected range, the flyback transformer may need to be replaced.
• A faulty or blown fuse: The fuse is a safety device that protects the monitor from damage due to excessive current. If the fuse is blown, the monitor will not turn on. You can test the fuse by using a multimeter to measure the resistance across the fuse. If the resistance is very high or infinite, the fuse is blown and will need to be replaced.

To diagnose the specific cause of the power failure on your HP z74 CRT monitor, you may need to open the monitor and perform some basic tests using a multimeter. This will help you identify the specific problem and take the appropriate steps to fix it. It is important to note that working on electronic equipment can be dangerous, so if you are not familiar with electronics repair, it is best to seek the assistance of a qualified professional.

My rca D52W20BYX1 model # F045C10AB would turn off and then back on, then it wouldn't turn at all it looked like sparks inside the foam screen below and there was a crackling noise, we took off the front foam screen and it looks like a tube is hanging down in the center.

how do you remove the fly back

I am unable to give any specific advice but if there is voltage or power to the Line Output circuit then its possible a short or load exists on the flyback transformer which causes a shutdown in this circuit.
I am afraid practise and knowledge of a particular model is a great help to find its faults.
The Flyback transformer (if like I remember) will have sub power supplies from it to drive audio, frame etc so a short on these will cause problems, also the rectifier diodes to these can fail you may need to remove one end of a diode for accurate testing.
Another failure point in power supply rails is capacitors which go open circuit this makes their voltage line unstable, also on the capacitor problem list are those around its flyback circuit that act as snubbers to tune it, these were at my time little blue capacitors of several KV which had a habit of shorting or change value.
Any of these will disturb a balanced start up cause a spike and shutdown.
Without particular knowledge of a model and its circuit I am unable to help further, I would look for shorts on Diodes and components, disconnect supply rails to audio and frame if they come from the flyback transformer (these are the heaviest loads and will only serve those particular circuits) then it will possibly capacitors gone o/c (I used to carry a cap tester years ago which used a 555 ic easy and robust).

Hope this helps in some way...

there is a possibility of a shorted turn of the flyback transformer. To test. short B-E together on the horizontal output transistor and connect 60W globe across C-E. measure voltage across lamp - if it comes up to 135v then you have a short either in the horizontal circuit or secondary circuit off the flyback transformer or even the transformer itself.