Welcome to EDAboard.com

Welcome to our site! EDAboard.com is an international Electronic Discussion Forum focused on EDA software, circuits, schematics, books, theory, papers, asic, pld, 8051, DSP, Network, RF, Analog Design, PCB, Service Manuals... and a whole lot more! To participate you need to register. Registration is free. Click here to register now.

Register Log in

Crt monitor clicking sound and image shrinking and expanding in loop, can someone help ?

RadeMkd

Junior Member level 1
Joined
Nov 5, 2020
Messages
19
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
170
Let's check the power supply to see if it's operating correctly.
So i did the test with a 240V 75W halogen bulb.
These is what i did :

connections.jpg

The result was :
-First the bulb was lit and then it started clicking.
-The bulb was blinking rapidly (at the rate of the clicking i think).
-Voltage at D817's cathode was between 72.4V - 74.9V (Fluctuating).

bulb.jpg

What's the purpose of the bulb ? prevent other components to fry ?

Regards,
Rade
 

Relayer

Full Member level 5
Joined
Jul 28, 2016
Messages
280
Helped
97
Reputation
194
Reaction score
62
Trophy points
28
Location
Hoppers Crossing, Australia
Activity points
2,953
These is what i did :
Spot on.

What's the purpose of the bulb ? prevent other components to fry ?
The purpose of the bulb is to apply a load to the main HT rail (80 volt). Without it, it can do
damage to the power supply.

-First the bulb was lit and then it started clicking.
-The bulb was blinking rapidly (at the rate of the clicking i think).
-Voltage at D817's cathode was between 72.4V - 74.9V (Fluctuating).
OK. Next step is to see if the horizontal output transistor is at fault.
Step 1: I need you to to place a shorting wire between the base and emitter of Q402, which is the horizontal
output transistor. The transistor should be located on a fairly large heatsink, very close the the flyback
transformer.
See picture below for transistor pinouts:



Once shorted, turn on the monitor to see if it still clicks.
If the clicking stops, then check the main HT rail again with the light bulb, but this time make sure L803
is reconnected. Measure the 80 volt rail.

Step 2: If it's still clicking, remove Q402 entirely from the circuit board.
Once again check the main HT rail with the light and make sure L803
is reconnected. Measure the HT rail again

If the monitor continues to click, then there's a very high probability that T402 (Horizontal Flyback Transformer)
needs to be replaced.
I know this is what you don't want to hear, but the above checks usually points to that tranny as more than
likely having shorted turns.
Please let us know how you get on.
Regards,
Relayer
 

    RadeMkd

    points: 2
    Helpful Answer Positive Rating

RadeMkd

Junior Member level 1
Joined
Nov 5, 2020
Messages
19
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
170
OK. Next step is to see if the horizontal output transistor is at fault.
Step 1: I need you to to place a shorting wire between the base and emitter of Q402, which is the horizontal
output transistor.
This is what i did :
-I reconnected L803.
-Placed a wire between base and emiter of HOT like this :

HOT.jpg

-Clicking stoped and there is no image.
-Reconnected the bulb :
-There is no clicking.
-Measured voltage at D817's cathode was 65.6V.
-Bulb is lit and not blinking.

You have already suggested to check the HOT previously using multimeter and it was ok.
Does this mean that, that particular test is not 100% accurate ?

Regards,
Rade
 

Relayer

Full Member level 5
Joined
Jul 28, 2016
Messages
280
Helped
97
Reputation
194
Reaction score
62
Trophy points
28
Location
Hoppers Crossing, Australia
Activity points
2,953
Does this mean that, that particular test is not 100% accurate ?
Both tests were to see if the flyback transformer was faulty.
There's a good chance that it's not.
I need you to measure the horizontal output transistor to see if it has shorted
or is open between the elements.
Start with setting your multimeter to diode check, and measure between the elements.
i.e. Base to emitter, base to collector, collector to emitter etc.
Please note the readings down and let us know what you get.
You should note that at two measurements, it will read around .600 plus.
If no shorts detected, then set your multimeter to it's highest ohms setting and do the same
test as above. As with the diode test, you'll get two measurements reading lowish ohms.
This is the punch-through test.
I'm certain that the horizontal output transistor is at fault, but if not, then I need you to lift
one leg of D402 and measure that the same way as above. Diode test and high ohms test.
Test this diode regardless.
If the horizontal output transistor measures faulty, then you need to replace it with the same
part number from a reputable supplier. DON'T purchase it from any Chinese sources.

Please let us know how you get on.
Regards,
Relayer
 

RadeMkd

Junior Member level 1
Joined
Nov 5, 2020
Messages
19
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
170
I need you to measure the horizontal output transistor to see if it has shorted
or is open between the elements.
I already did this test using multimeter but now i did it again, this is what i did :

HOT
-I disoldered the HOT from the board.

Multimeter at Diode mode:
-Base to emitter = 354
-Base to collector = 330
-Emitter to base = 1
-Collector to base = 1
-Emitter to collector = 1
-Collector to emitter = 1


Multimeter at ohmeter (max settings 2M):
-Base to emitter = 1
-Base to collector = 0.800 / 0.879 / 0.891 / 0.919 (I got different results when trying multiple times).
-Emitter to base = 1
-Collector to base = 1
-Emitter to collector = 1
-Collector to emitter = 1



D402
-Lifted one leg of D402
Diode mode :
-Red probe to cathode, Black to Anode = 310
-Red probe to Anode, Black to Cathode = 1

Ohmeter mode (2K):
-Red probe to Cathode, Black to Anode = 0.310

Ohmeter mode (2M max scale):
-Red probe to Anode, Black to Cathode = 1

Regards,
Rade
 
Last edited:

Relayer

Full Member level 5
Joined
Jul 28, 2016
Messages
280
Helped
97
Reputation
194
Reaction score
62
Trophy points
28
Location
Hoppers Crossing, Australia
Activity points
2,953
Hmm... It seems the HOT and D402 are OK.
Looks like we need to look elsewhere.
I need you to once again check the power supply, but this time, the other
voltage rails.
With the HOT's collector not connected. Place the light bulb on D817 carhode
and the other end on a ground point.
Measure the voltages on the following:
D817's cathode once again.
The cathode of D813.
The cathode of D814.
The collector of Q813.
The collector of Q811.
and lastly, the anode of D810, which should be a negative voltage.
Please note down those measurements.
Regards,
Relayer
 

RadeMkd

Junior Member level 1
Joined
Nov 5, 2020
Messages
19
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
170
I need you to once again check the power supply, but this time, the other
voltage rails.
L803 connected.
D402 connected.
HOT's base and emitter connected to board, collector is lifted not connected to the board.
Bulb is lit.
No clicking.

-D817 Cathode = 65.8V
-D813 Cathode = 50.2V
-D814 Cathode = 09.7V
-Q813 Collector = 09.7V
-Q811 Collector = 05.2V
-D810 Anode = -09.9V.

Regards,
Rade
 

Relayer

Full Member level 5
Joined
Jul 28, 2016
Messages
280
Helped
97
Reputation
194
Reaction score
62
Trophy points
28
Location
Hoppers Crossing, Australia
Activity points
2,953
All the voltage rails are fairly low for some reason.
What I'll get you to do, is to set up exactly as you did above, then I'll get
you to tweek the main HT rail to see if we can get it back to specification.
Once you've set up as per above, get a small flat bladed screwdriver and
turn VR801 (5k ohm variable resistor. B+ adjust) clock-wise, at the same time
monitor the voltage at the cathode of D817 to see if it rises. Turn the trim pot
slowly at the same time making sure you don't hear any noises coming from
the power supply. Attempt to turn the pot enough to get the main HT rail to
read 80 volts, but I doubt it will reach that figure.
This is more than likely not the cause of the clicking, but it is unusual that with
the HOT not affecting the circuit, the voltage rails should be reading close to
normal.
It seems we need to closely look at the horizontal stages, as well as the
protection circuits.
Please let us know how you get on.
Regards,
Relayer
 

    RadeMkd

    points: 2
    Helpful Answer Positive Rating

RadeMkd

Junior Member level 1
Joined
Nov 5, 2020
Messages
19
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
170
turn VR801
Did that and there was no change at all at both directions,
i switched it till the end with no effect. The voltage remained the same 65.8V at D817 Cathode.

Also, why when i tested the bulb method with the HOT properly connected, the voltage at D817's cathode was between 72.4V - 74.9V ?
and without the HOT's collector connected it's only 65.8V ?

Regards,
Rade
 

Relayer

Full Member level 5
Joined
Jul 28, 2016
Messages
280
Helped
97
Reputation
194
Reaction score
62
Trophy points
28
Location
Hoppers Crossing, Australia
Activity points
2,953
My apologies for the lateness of my reply.

Also, why when i tested the bulb method with the HOT properly connected, the voltage at D817's cathode was between 72.4V - 74.9V ?
and without the HOT's collector connected it's only 65.8V ?
Different types of loads. The bulb would have a specific load which is different to the HOT load
once connected.

I'll get you to reinstall the HOT and connect anything else desoldered.
Start the monitor up, check the 80 volt rail, at the same time adjust the trimpot of VR801.
I want to see if having everything connected may allow for a change in the main rail voltage.
Could you also take a picture of the screen once it's up and running. I need to see what you're
getting.
I have to admit at this point I'm starting to run out of other trouble-shooting ideas.
Please let us know how you get on.
Regards,
Relayer
 

RadeMkd

Junior Member level 1
Joined
Nov 5, 2020
Messages
19
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
170
My apologies for the lateness of my reply.
No worries.

So i placed the HOT properly.
Now it's clicking.

Voltage at rails without touching the VR801:

-D817 Cathode = 82V
-D813 Cathode = 54 - 56V
-D814 Cathode = 11.2V
-Q813 Collector = 11.2V
-Q811 Collector = 06.2V
-D810 Anode = -11.6V.
I guess these are good readings ?

VR801 adjust now works, it increases a bit the voltage.

Voltage at pin 2 of flyback is 80V - 110V (fluctuating). without HOT connected it was 50V (fixed).

Here is a pic :

20201221_171243.jpg

Regards,
Rade
 

Relayer

Full Member level 5
Joined
Jul 28, 2016
Messages
280
Helped
97
Reputation
194
Reaction score
62
Trophy points
28
Location
Hoppers Crossing, Australia
Activity points
2,953
Voltage at pin 2 of flyback is 80V - 110V (fluctuating). without HOT connected it was 50V (fixed).
Not surprising that it's fluctuating. It seems that having the HOT connected that it's giving the correct load,
especially since most of the PSU voltages returned to normal.

The picture you provided shows fairly gross pincushion distortion. There might be a possibility that this
section may be causing your woes, or could just be another symptom of the original fault.

At this point we'll try to correct the pincushion distortion.
I need you to measure the voltage at R412 (5k6Ω) . It should be around 11.6 volts.
You need to also check the voltage at R413 (750kΩ). It should be around 118 volts.

Please let us know what results you get.
Regards,
Relayer
 

RadeMkd

Junior Member level 1
Joined
Nov 5, 2020
Messages
19
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
170
I need you to measure the voltage at R412 (5k6Ω) . It should be around 11.6 volts.
You need to also check the voltage at R413 (750kΩ). It should be around 118 volts.
R412 = 11V
R413 = 88V - 92V (fluctuating).
G2 at neckboard is 22V.

Also heatsink where Q419 is placed and Q419 itself get very hot after like 15-20 seconds. It's untouchable.
The HOT is also getting very hot after a very short time. I don't know if this is normal ?

Regards,
Rade
 

Relayer

Full Member level 5
Joined
Jul 28, 2016
Messages
280
Helped
97
Reputation
194
Reaction score
62
Trophy points
28
Location
Hoppers Crossing, Australia
Activity points
2,953
G2 at neckboard is 22V.
I'll get you to check R912, which should be on the neck board.
Also measure the continuity of L911, which is in series with R912.
I'll get you to do a thorough visual inspection of ALL the capacitors
on the neck PCB. Make sure you can see both sides of the caps,
especially the 2kv types.
I have to admit that at this point I've definitely run out of other options.
Please let us know how you get on.
Regards,
Relayer
 

RadeMkd

Junior Member level 1
Joined
Nov 5, 2020
Messages
19
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
170
I'll get you to check R912, which should be on the neck board.
Also measure the continuity of L911, which is in series with R912.
I'll get you to do a thorough visual inspection of ALL the capacitors
R912 and L911 are ok.
I checked the caps all seem ok.
G2 wire disconected from the neckboard shows 22V, so it's not related to the neckboard i think.

Regards,
Rade
 

Relayer

Full Member level 5
Joined
Jul 28, 2016
Messages
280
Helped
97
Reputation
194
Reaction score
62
Trophy points
28
Location
Hoppers Crossing, Australia
Activity points
2,953
G2 wire disconected from the neckboard shows 22V, so it's not related to the neckboard i think.
A fair few of those caps have to do with the G2 voltage. That's why I wanted you to check them.

OK. I need you to monitor the G2 voltage while you adjust the screen adjustment.
The screen adjustment is one of two adjustments on the flyback transformer.
You'll have "FOCUS" and the other, "SCREEN".
Adjusting it one way will dim the picture to black. Adjusting it the other way will
cause the screen to grow much brighter and you should get retrace lines across
the picture.
Just monitor the G2 voltage, as I want to see if it varys in any way.
Please let us know how you get on.
Regards,
Relayer
 

RadeMkd

Junior Member level 1
Joined
Nov 5, 2020
Messages
19
Helped
0
Reputation
0
Reaction score
0
Trophy points
1
Activity points
170
OK. I need you to monitor the G2 voltage while you adjust the screen adjustment.
I already tried that and it does change the G2 a bit, +- 10V.
I think it's either the flyback or something on the board that's messed up.
When i press the front menu buttons it has an effect on the clicking.
Maybe an IC chip is messed up ... i don't know.
I paid 10€ for this monitor so it's not a big deal.
If it was a lcd i would trow it away immediately, but since it's a crt i just can't do it :)
I will still try to look for a solution on my free time.
In case i cannot fix it, Is there any reason to keep the tube ? Can it be used on other board ?
Thanks for all your help and happy holidays :)

Regards,
Rade
 

Relayer

Full Member level 5
Joined
Jul 28, 2016
Messages
280
Helped
97
Reputation
194
Reaction score
62
Trophy points
28
Location
Hoppers Crossing, Australia
Activity points
2,953
I think it's either the flyback or something on the board that's messed up.
My suspicions are on the flyback transformer as having an obscure fault.
I have had instances where it's actually the variable resistor on the focus pot that was the problem.
We drilled into it slightly and lubricated it, and it came good. Though it had to be replaced regardless.

In case i cannot fix it, Is there any reason to keep the tube ? Can it be used on other board ?
It would be rare that you would have a monitor requiring the same picture tube. The monitor doesn't have to
be the same model, as long as it uses the same tube type.
Unless you have excess storage space, I wouldn't bother keeping the tube.

Thanks for all your help and happy holidays :)
You're welcome, and I hope you have a very merry Christmas and a great New Year.
I'm sorry we couldn't nut your problem out.
Regards,
Relayer
 

Part and Inventory Search

Welcome to EDABoard.com

Sponsor

Top