Clicking sound in CRT TV, any speculations of what's the problem?

[eagle1109]

Hello,

I got a new problem


Now the CRT takes time to switch ON.

It starts with the usual clicking sound, then the clicks speed increases.

After that the CRT switches ON.

What could that be?

Thanks,

 

[chuckey]

I would think that some resistor has drifted in value and needs to be warmed up before the circuit works properly. It looks as though its around where you were working last time. You could try freezer spray to cool components when the set is working. Or you could measure the voltages while it is clicking, turning it off and letting it cool down before its working. This way you wilol have a record of the voltages in the faulty state. Then turn it on and let the set warm up and repeat the measurements. Now you shoulod be able to figure out what the fault nis.
Frank

 

[RichardHead]

It could also be that the bleed-on electrolytic capacitor is drying out and its value decreasing. With the lower value the start up circuitry depletes its charge before the output and feedback has had time to build up. Try replacing the cap with a decent 105 deg rated one. Good luck.

 

[retrogear]

The feedback circuit is always negative feedback based. The primary side circuit should supply all the power needed to initially power on, then as the secondary sample voltage comes up, the feedback
voltage will be returned to the primary to reduce power. That's power regulation in it's simplest terms. Slowly powering on would probably be a component on the primary side. I would measure DC voltage across each capacitor on the primary side. If the DC slowly comes up on one of those caps, it could be the problem. Also I see a series thermistor RT802 on the main DC input which could be suspect.

Larry G

 

[RichardHead]

I wasn't referring to the voltage feedback loop, rather the feedback to power the primary side controller.

 

[retrogear]

Richard - yes, I was expanding on what you were saying. I think we both agree the problem is most likely on the primary side

 

[eagle1109]

I would think that some resistor has drifted in value and needs to be warmed up before the circuit works properly. It looks as though its around where you were working last time. You could try freezer spray to cool components when the set is working. Or you could measure the voltages while it is clicking, turning it off and letting it cool down before its working. This way you wilol have a record of the voltages in the faulty state. Then turn it on and let the set warm up and repeat the measurements. Now you shoulod be able to figure out what the fault nis.
Frank

OK, there are different resistors I have in the primary and secondary areas.
The one I suspected was the R836 10k ohm 5W and R808 22K ohm 5W which are ceramic resistors, because they get warm when the CRT is working.

We changed the RT801 which is the degaussing resistor, with another one from another monitor and place it again.

Now the CRT won't start at all, and the monitor is flickering with of course with the clicking sound.

Now, I don't know if it's a capacitor or a resistor or try to continue checking the low voltage I get at D833 which get the original voltage after I disconnect L843.

I'm planning to disconnect the degaussing coil and try with the resistors and capacitors or continue checking after L843.

The semiconductor part should be OK I guess.

It could also be that the bleed-on electrolytic capacitor is drying out and its value decreasing. With the lower value the start up circuitry depletes its charge before the output and feedback has had time to build up. Try replacing the cap with a decent 105 deg rated one. Good luck.

The main capacitor has 320V now, I think it was 328V. Would 8V affect the system?

Do you also suspect caps on the secondary area?

The feedback circuit is always negative feedback based. The primary side circuit should supply all the power needed to initially power on, then as the secondary sample voltage comes up, the feedback
voltage will be returned to the primary to reduce power. That's power regulation in it's simplest terms. Slowly powering on would probably be a component on the primary side. I would measure DC voltage across each capacitor on the primary side. If the DC slowly comes up on one of those caps, it could be the problem. Also I see a series thermistor RT802 on the main DC input which could be suspect.

Larry G

OK

What I did yesterday.

I was checking voltages at the secondary side, so I have 3 output rectifying diode.

I was having low and unstable voltage at D833 with values ranging from 8-5V, so I disconnected the anode of D835 and the voltage was the same.

Then I returned it and disconnected L843, then the voltage got back to the original value which is 15V.

Now, I think there's a short or faulty component after this coil.

Regards,

 

[retrogear]

You'll have to chase it down by desoldering IC401 the 9v regulator next. It seems the 12V goes elsewhere too.

 

[eagle1109]

I guess

 

[eagle1109]

Hello

Here're my updates

1. One of the monitors is working perfectly, all voltages are good. Except the monitor is not glowing up!

I may change the flayback transformer, the monitor. What could be other possible failures?

2. How to read thermistor code, because I want to order a lot from Aliexpress?

This is the one I have in our model.