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Author Topic: China MIN DONG TV-MD 14/22 repair  (Read 784 times)

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perjmolsen

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China MIN DONG TV-MD 14/22 repair
« on: January 12, 2019, 04:23:10 pm »
Hi

Trying one more time with a China chassis repair.  :applaud:
Again just to learn the basics and to kill the time waiting for pats to my NANO MS9-SU29 repair.
This chassis where also put on the shelf, because back in 2008 i burned it by mistake because i turned the wrong pot (the knob which adjust the horizontal frequency).

So it died - no neck glow or anything after my mistake.

The Yoke spec for this chassis is:
VR:  11.8 ohm
HR: 2.14 ohm

I have pulled a TV apart, the pins is a match, and checked the tube:
VR: 11.2 ohm (yellow / blue)
HR: 1.9 ohm (red/white)

So this time  I have one  compatible monitor for testing  ;D

I began to test and change parts, hoping to find some defects - and i found a couple defective  :applaud:
The parts that i have tested is marked with color in this sheet. -> https://www.dropbox.com/s/ssfd4c0xpl66ste/Rep%20log%20Min%20dong%20md%2014-22.xlsx?dl=0

I have changed the parts marked by green, because they where dead.

So my plan is now to put in the parts that i have pulled out and tested OK - and connect it to the monitor and see what the status is...
Or do i need to test/check anything before?
This chassis i can be used with 220V
« Last Edit: January 12, 2019, 04:25:36 pm by perjmolsen »

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Re: China MIN DONG TV-MD 14/22 repair
« Reply #1 on: January 12, 2019, 04:24:05 pm »
Pictures of the chassis

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Re: China MIN DONG TV-MD 14/22 repair
« Reply #2 on: January 13, 2019, 06:37:14 am »
Status with all components in.. Nothing...

I tried to see if there where any volts at the big 10 ohm ceramic resistor, but 0V.
There is also no neck glow or any high voltage sound.

So i guess i need to remove the HOT (BU2520DF) the transistor mounted at the heatsnik next to the flyback, and then test for volt at the flyback...
But how to i figure out witch leg i need to de solder at the flyback in order to test B+?

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Re: China MIN DONG TV-MD 14/22 repair
« Reply #3 on: January 13, 2019, 08:07:55 am »
Remove the HOT and connect the lightbulb to the middle pad.

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Re: China MIN DONG TV-MD 14/22 repair
« Reply #4 on: January 13, 2019, 08:27:03 am »
Remove the HOT and connect the lightbulb to the middle pad.

Thanks :)

But 0V :(

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Re: China MIN DONG TV-MD 14/22 repair
« Reply #5 on: January 13, 2019, 08:40:43 am »
Just noticed a thing....

A cap is missing... seems top have broken off due to corrosion...
Now the question... what type could that have been..  ::)

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Re: China MIN DONG TV-MD 14/22 repair
« Reply #6 on: January 13, 2019, 09:37:46 am »
A ceramic cap (like the blue ones) across frame ground and secondary ground. Low capacity (1n to 4.7n) and 400V or 1KV.

Suck all the solder from the yellow pin on the flyback and connect the bulb to the trace and a ground point and lift the jumper in the white circle.

If still no voltage check that you have around 300VDC across the legs of the big cap with green top and if you have voltage there it could be a bad voltage regulator IC (5-pin IC screwed to the heat sink).
« Last Edit: January 13, 2019, 09:44:20 am by princess prin prin »

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Re: China MIN DONG TV-MD 14/22 repair
« Reply #7 on: January 13, 2019, 10:22:51 am »
A ceramic cap (like the blue ones) across frame ground and secondary ground. Low capacity (1n to 4.7n) and 400V or 1KV.

Suck all the solder from the yellow pin on the flyback and connect the bulb to the trace and a ground point and lift the jumper in the white circle.

If still no voltage check that you have around 300VDC across the legs of the big cap with green top and if you have voltage there it could be a bad voltage regulator IC (5-pin IC screwed to the heat sink).

Hi

Big thanks for all your information :)

I have done as you say, but no volt.
I can massure 298V across the big 150uf 400V ud cap.
I have also tried to change the cap to a new one - but same result.

So it might be the 5 legged IC KA2S0765 - I have already changed it but i might be defect - i think that i have some more laying around.

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Re: China MIN DONG TV-MD 14/22 repair
« Reply #8 on: January 13, 2019, 11:06:51 am »
Halleluja  :cheers:

I got 113 V now

What i did

Changed the KA2S0765 IC one more time
Also changed the small cap (47uf 50v) after the big cap- the old one measured (45uf esr 1.1 ohm)

Powered it on and now I have 113V at the yellow circle at the flyback.

SO.... Then i think that i need to put it back in reverse order?
1.
Solder the yellow pin back at the flyback
Connect the jumper
Test if i have B+ at middle leg where HOT need to be put in

If test OK then

2.
Put HOT back in

Test if i got static and picture ?

« Last Edit: January 13, 2019, 11:08:42 am by perjmolsen »

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Re: China MIN DONG TV-MD 14/22 repair
« Reply #9 on: January 13, 2019, 12:25:06 pm »
Don't connect the jumper yet. Do the lightbulb test at the HOT collector (with HOT out of circuit). If you have steady light and b+ voltage put the HOT back in and reconnect the jumper and test the chassis. Don't keep the yoke connected to the chassis.

The horizontal inductance on the label seems quite high for the resistance. I would expect it to be half of that.
« Last Edit: January 13, 2019, 12:26:47 pm by princess prin prin »

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Re: China MIN DONG TV-MD 14/22 repair
« Reply #10 on: January 13, 2019, 02:11:57 pm »
Don't connect the jumper yet. Do the lightbulb test at the HOT collector (with HOT out of circuit). If you have steady light and b+ voltage put the HOT back in and reconnect the jumper and test the chassis. Don't keep the yoke connected to the chassis.

The horizontal inductance on the label seems quite high for the resistance. I would expect it to be half of that.

OK :)

Status.

1. I connected the light bulb to the middle leg at the hot (with the HOT out) - NO light 0V
2. Put solder on the yellow marked pin at the flyback, so it now where solder in, still with connected light bulb to middle pin at the HOT (still with the HOT out) - A light for 1 sec came on.?!? but when out quickly If i tried a second time to turn on  no light - only light for at short time the first time i turned it on.

3. Removed the solder at the yellow marked pin at the flyback, moved the wire to the pad of the yellow marked pin at flyback - and i still have 113V...

What do that tell?... is my flyback dead?

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Re: China MIN DONG TV-MD 14/22 repair
« Reply #11 on: January 13, 2019, 03:08:20 pm »
Measure the resistance across middle pad of the HOT and ground. Is it very low/zero ohm?

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Re: China MIN DONG TV-MD 14/22 repair
« Reply #12 on: January 13, 2019, 03:38:10 pm »
Measure the resistance across middle pad of the HOT and ground. Is it very low/zero ohm?

Yes OL/zero ohm between middle pad at HOT and the ground
(when testing i have not solder the yellow marked pin)
« Last Edit: January 14, 2019, 02:39:30 am by perjmolsen »

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Re: China MIN DONG TV-MD 14/22 repair
« Reply #13 on: January 14, 2019, 03:35:02 am »
Suck solder off the flyback pin connected to the middle pad of the HOT, i.e. the pin just below the yellow one. Then measure resistance across that pin and ground. If it's 0 ohm the flyback is bad (primary and secondary windings are shorted). If the resistance is very high/infinite, measure the resistance across the middle pad of the HOT and ground.

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Re: China MIN DONG TV-MD 14/22 repair
« Reply #14 on: January 14, 2019, 04:06:25 am »
Suck solder off the flyback pin connected to the middle pad of the HOT, i.e. the pin just below the yellow one. Then measure resistance across that pin and ground. If it's 0 ohm the flyback is bad (primary and secondary windings are shorted). If the resistance is very high/infinite, measure the resistance across the middle pad of the HOT and ground.

Hi

Well both are reading OL (and i have checked that there is ground to the point) :)

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Re: China MIN DONG TV-MD 14/22 repair
« Reply #15 on: January 14, 2019, 05:56:10 am »
If you touch the multimeter probes with each other what reading do you get?

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Re: China MIN DONG TV-MD 14/22 repair
« Reply #16 on: January 14, 2019, 06:04:57 am »
If you touch the multimeter probes with each other what reading do you get?

I get 000.0 if i hold the probes together

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Re: China MIN DONG TV-MD 14/22 repair
« Reply #17 on: January 14, 2019, 07:23:48 am »
That's zero ohm which would point to a short. OL is the opposite, infinite resistance. So from the previous tests there's no short in the flyback or in the collector line. How did you test the HOT and what readings did you have?

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Re: China MIN DONG TV-MD 14/22 repair
« Reply #18 on: January 14, 2019, 07:32:50 am »
Hi

I tested the HOT (BU2520DF) in my china tester

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Re: China MIN DONG TV-MD 14/22 repair
« Reply #19 on: January 14, 2019, 07:44:47 am »
Desolder the other flyback pin connected to the HOT collector and repeat the tests. Also when you put the probe on the chassis make sure the points are squeaky clean and not covered with flux. Clean with q-tip and alcohol in case. And don't put the tip of the probe in the hole but on the pad or some other points connected to the pad.

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Re: China MIN DONG TV-MD 14/22 repair
« Reply #20 on: January 14, 2019, 08:19:25 am »
Hi

I have cleaned up around the flyback and took another reading, with a closer ground.

Still OL between ground and HOT collector and ground
Still OL between HOT collector pad and the first flyback pin

Tested with the other pin connected to HOT collector at first i got resistance starting from 36.84 ohm and it counted up... but suddenly OL
And when i test it again I still get OL...?!?
 

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Re: China MIN DONG TV-MD 14/22 repair
« Reply #21 on: January 14, 2019, 08:58:42 am »
Counting flyback pins clockwise you desoldered 10, 11 and 12. Resolder 10 and 11 but not 12 and connect the light bulb to the Hot collector pin. Does the light stay on?

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Re: China MIN DONG TV-MD 14/22 repair
« Reply #22 on: January 14, 2019, 09:58:50 am »
Sorry.. but no cigar 0V  :'(
( I have also checked the bulb- it is not blown)

You need to know I appreciate all your help  :)

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Re: China MIN DONG TV-MD 14/22 repair
« Reply #23 on: January 14, 2019, 01:44:09 pm »
I have tried to massure between pin 10 and 12 and got this.
I guess that is OK?
 

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Re: China MIN DONG TV-MD 14/22 repair
« Reply #24 on: January 15, 2019, 04:18:39 am »
Did you still have the yoke connected to the chassis during the test? Disconnect.

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Re: China MIN DONG TV-MD 14/22 repair
« Reply #25 on: January 15, 2019, 11:12:21 am »
Hi   :cheers:

I can not remember, but i think that i had it connected.
I have now disconnected the yoke and also the bulb and got this reading


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Re: China MIN DONG TV-MD 14/22 repair
« Reply #26 on: January 16, 2019, 10:12:55 am »
I think pins 9, 10, 11, 12 are the primary winding of the flyback. 9 ultimately goes to the 8-pin header to the neckboard so it's likely to be the video B+ (200V supply for the RGB amps), 10 is the B+ and either 11 or 12 is the HOT collector. There should be a very low resistance (or continuity) across each other and very high or infinite resistance with all the other flyback pins. Once this is confirmed, desolder pin 9 and resolder pins 10, 11, 12 and do the lightbulb test on the HOT collector with the chassis disconnected from the tube/yoke. If it fails try it again after desoldering one by one C20 and the two big polypropylene caps conncted to it (those just below the yoke header). At somepoint it cannot fail as there's nothing else connected to that line.

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Re: China MIN DONG TV-MD 14/22 repair
« Reply #27 on: January 21, 2019, 04:47:16 am »
I think pins 9, 10, 11, 12 are the primary winding of the flyback. 9 ultimately goes to the 8-pin header to the neckboard so it's likely to be the video B+ (200V supply for the RGB amps), 10 is the B+ and either 11 or 12 is the HOT collector. There should be a very low resistance (or continuity) across each other and very high or infinite resistance with all the other flyback pins. Once this is confirmed, desolder pin 9 and resolder pins 10, 11, 12 and do the lightbulb test on the HOT collector with the chassis disconnected from the tube/yoke. If it fails try it again after desoldering one by one C20 and the two big polypropylene caps conncted to it (those just below the yoke header). At somepoint it cannot fail as there's nothing else connected to that line.

Hi

Sorry for the delay this time :) And thanks for your tips Princess prin prin, I have made some progress (i think)  ;D

Test conditions: HOT is out, Jumper is lifted and nothing connected to the chassis.
Started testing de-soldering pins at the flyback except the input at pin 10 and also the ground pins where connected.

I am loosing my 113V when i connect the 1 pin on the flyback, all other legs connected, there is 113V at HOT middle pad.

If I look at the other side where pin 1 is connected there is a big CAP - It might be shorted?
Trying to pull that out and see what reading i get from it
« Last Edit: January 21, 2019, 06:45:30 am by perjmolsen »

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Re: China MIN DONG TV-MD 14/22 repair
« Reply #28 on: January 21, 2019, 05:04:54 am »
Update

Tested the big cap at pin1 - an 100uf 200V cap.
It does not seem to be bad.

I measure it to 90 uf  ESR 0.43 ohm

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Re: China MIN DONG TV-MD 14/22 repair
« Reply #29 on: January 21, 2019, 05:28:22 am »
Hmm...

Put in a new 100uf 200V cap - soldered the pin1 at flyback to pcb
Just light for a second... ???

Again if i remove the solder at pin1 - my volts is back... why?!? :)
« Last Edit: January 21, 2019, 05:33:07 am by perjmolsen »

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Re: China MIN DONG TV-MD 14/22 repair
« Reply #30 on: January 21, 2019, 10:34:52 am »
There are no indications that the flyback is shorted and you have a stable B+ and a good HOT so it's time that you connect the chassis to the tube and check the voltages that come out of the flyback.

This is what I gathered from examining your pics:



Pin 1 connected to + of electrolytic cap (- to ground) is unclear especially since the cap is rated 200V and there are no voltages that high on the secondary side of the flyback.
pin 2 flyback pulse/AFC to pin 13 of sync/V-H oscillator IC (a clone of HA11235)
pin 3 (heater voltage 6.3AC) to neckboard.
pin 4 (25V?) to vertical deflection transistors.
pin 5 (12V) to pin 6 of sync/V-H oscillator IC (a clone of HA11235)

It's unclear what pin is ABL (the other end of the EHT), either 1 or one of the grounded pins.

Check if you have something from the flyback pins. Not directly on the pins, the voltages become DC after the diodes. There are handy points on parts side if you follow the traces.