How can I test non-polarized capacitor?

[chth96]

I desoldered samwha NF capacitor(50v 5.6uf) from PCB circuit of 29inch CRT TV which have symptoms of no display after I heard sound of inrush of current to TV whenever I switch on this television.
I measured ESR value of this non-polarized capacitor(samwha NF capacitor 50v 5.6uf) by means of MESR-100 ESR meter and It displayed 0.3 ohm

And When I measured its capacitance with digital multimeter and LCR-T4 Mega328 meter, It displayed 10uf from DMM and 8uf from LCR-T4 meter.
I found catalogue of samwha capacitor(samwha-catalogue_3.pdf file), which is attached to this thread, but there is no Tan(δ) in the characteristic entry(page 135) which is essential for ESR calculation.
Is this non-polarized capacitor(samwha NF capacitor 50v 5.6uf) defective?

[R_J]

Usually, a cap with that rating in a crt tv is in the horz. yoke return path, if it was bad, you would likely have a narrow picture.

[chth96]

Usually, a cap with that rating in a crt tv is in the horz. yoke return path, if it was bad, you would likely have a narrow picture.

Is it means that this non-polarized capacitor(samwha NF capacitor 50v 5.6uf) has nothing to do with symptoms of no display after I heard sound of inrush of current to TV?

[R_J]

Is it means that this non-polarized capacitor(samwha NF capacitor 50v 5.6uf) has nothing to do with symptoms of no display after I heard sound of inrush of current to TV?

Thats what I suspect, can you post the make and model or service manual? or maybe post some pictures of the board.

[chth96]

Thats what I suspect, can you post the make and model or service manual? or maybe post some pictures of the board.

partnumber on the surface of main PCB and small PCB is

MC-7CA(MAIN) 6870VM0056C(6) 980424 L.W.G(0)

MC-7CA(CPT) 6870VS0167A(1) 971014 K.J.B(0)

and model number of This LG CRT TV is CN-29H3

Frankly speaking,I posted a thread about this CRT TV in the reddit forum.But It seems that there is no way to find the culprit of no display symptoms.
https://www.reddit.com/r/Electronics...6707_regulator

[stj]

does the iinside of the tube neck glow?

[chth96]

does the iinside of the tube neck glow?

I have desoldered PC817 Optocoupler from PCB of this CRT TV and tested it by following below youtube tutorial.
https://www.youtube.com/watch?v=SPSwvVpMrvc
I confirmed that a led light turned on, But unfortunately, When I measure its resistance of pin 3 and pin 4 with10k ohm range of analogue meter, I saw that It display two reading of low resistance when checking both way.
I think that following youtube tutorial spoiled PC817 Optocoupler, So I need to find any local store where sells it.

[stj]

you can find optocouplers inside almost every switching psu including ones in lcd monitors

[chth96]

you can find optocouplers inside almost every switching psu including ones in lcd monitors

I purchased LITEON LTV817 D grade. But PC817 Optocoupler, which was defective, was C grade and made in Sharp corperation.
Is it Okay to replace C grade PC817 from Sharp corperation with D grade LITEON LTV817?

[stj]

maybe - try it

[chth96]

does the iinside of the tube neck glow?

I finally soldered LITEON LTV817 D grade on the PCB circuit of 29inch CRT TV and switched on this CRT TV.
It still displayed black screen. And It seems that it doesn't glow inside of the tube neck at all...
and Moreover, After switching on I measured voltage of this big capacitor(160v 100uf) on the cold side,which seems to be B+ filter capacitor,It was measured only 37-38 voltage in DC Voltage mode of analogue meter,But before I replaced opto-coupler with LITEON LTV817 D grade,It was measued nearly 45 DC voltage..

[stj]

low B+ could be a short circuit on the HV side,
if you look at the trace for B+ you usually have a link or inductor that couples the HV section,
you can desolder that and put a 40w 240v lamp across the B+ cap as a load - then test it again.

[chth96]

low B+ could be a short circuit on the HV side,
if you look at the trace for B+ you usually have a link or inductor that couples the HV section,
you can desolder that and put a 40w 240v lamp across the B+ cap as a load - then test it again.

Thank you very much for reply.
I roughly draw most of flyback transformer's soldering point and its nearby components on the circuits.
I noticed that B+ soldering point is coupled to three carbon resistor(R432,R437,R831) and C829 is the big capacitor.
Should I isolate B+ soldering point by desoldering these three carbon resistor(R432,R437,R831) from circuits In order to connect 240v lamp and test it?
And where should I solder 240v lamp on the bottom of PCB?

scan0008.jpg (640×379) (ibb.co)

[stj]

is this similar?
check the H46 schematic - L853 inductor left of the transformer

or H90?
lift R402

[R_J]

This is likely the schematic. I would replace the small electrolytics in the power supply primary, they are likely weak. C812, C810, C811
This tv power supply is always running when it is plugged in so those caps take a beating. C810 is right next to R807 which would cook that poor electrolytic

[chth96]

Thank very much for reply.
there is no inductor left or right to the transformer.
I saw H46 or H90 schematic which you have attached, But it seems that it is totally different to the circuits which I tried to repair.

And I saw MC-7CA schematic and at least It is somewhat similar to STR-S6707 area in the circuits.
You can compare STR-S6707 area in the MC-7CA schematic to my drawing of circuits which contains resistor and capacitor near STR-S6707.

I already have measured ESR ohm value of all capacitor with ESR meter(MESR-100) and checked most of diode and carbon resistor in the STR-S6707 area and I replaced C810(25v 470uf Korea chemicon KME) and C811(25v 220uf samwha RG) which has higher ESR ohm value(C811 was measured over 70 ohm)
But it won't repair black screen symptom..

[chth96]

The strange thing is whenever I measure the DC voltage of pin#9 of STR-S6707, It is measured 6.4V.
As far as I know,It should be measured at least 7.6V in order to go On-State Voltage.
I doubted any diode near STR-S6707,So I checked it using analogue meter(x10 ohm) But It showed only one reading with the correct and opposite polarity of probe.

[R_J]

What is the voltage across C812? it needs to be at least around 9vdc to supply the regulator transistor Q800 collector. Q800 base should measure 7.5vdc, if not ZD808 may be leaky and not zenering at 7.5vdc I would have also replaced C812

If Q800 collector is over 9v and the base is 7.5v and the emitter is only 6.4v, Q800 may be bad

[chth96]

What is the voltage across C812? it needs to be at least around 9vdc to supply the regulator transistor Q800 collector. Q800 base should measure 7.5vdc, if not ZD808 may be leaky and not zenering at 7.5vdc I would have also replaced C812

If Q800 collector is over 9v and the base is 7.5v and the emitter is only 6.4v, Q800 may be bad

Thank you very much for reply.

I just have measured DC voltage of C812 by placing red probe to positive terminal of C812 and placing black probe to negative terminal of C808 in HOT area(400V 470uf the biggest capacitor in the circuit).
It was measured 10.8DCV.

And I measured cathode of ZD808,It was measured 7.1DCV and Q800(C3852A) base was also measured 7.1 DCV.
Q800(C3852A) collector was measured 10.8DCV.and pin#9 of STR-S6707 was measured 6.4DCV.

I desoldered C812 and I check it with LCR T4 meter. Its capacitance was still within 10% tolerance(23uf) and Its ESR value was lower(0.5 ohm) than reference value.

By the way it was written B.75 on the surface of ZD808 zener diode.
Is It Okay to purchase any zener diode which has specification of 7.5V?

[chth96]

I replaced ZD808 zener diode with 1N4737,But it won't repair black screen symptom,and there is no difference between these zener diode in measuring cathode voltage(7.1Vdc)
I think that I need to connect a 40w 60w bulb to B+ soldering point of Flyback transformer,But I don't know the process to substitute for the Flyback's B+ Load with a blub in detail.