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Author Topic: kortek ki-2-vo brand chassis repair help - only high voltage  (Read 1590 times)

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perjmolsen

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kortek ki-2-vo brand chassis repair help - only high voltage
« on: January 07, 2020, 05:39:55 pm »
Hi

I have this Kortek ki-2-vo  chassis that I am trying to repair.

I have checked the fuses they are all OK, also change a couple of caps because that looked bad, but where OK when I tested them.
Changed:
c610   47uf 160v
c612   22uf 160v
c706   10nf 250v
c703   470uf 25v

Tested OK
q702   D1399
d703   Diode
Fuses

When I power it on, I hear the normal static high voltage sound on the CRT, and I can also feel the static on the CRT
Nothing happens when I turn up the screen voltage.
I cannot see any neck glow, is that possible with high voltage?

I assume that my flyback is working because I can hear the static turn on sound, and also I get a big POP when i discharge the annode.

How do I tackle this repair?  :notworthy:

Can I test for heater voltage by putting the red probe to the "H" on the neckboard? and netative to chassis ground
and the screen volt at the "screen" on the neckboard?

Or is there a better way?
« Last Edit: January 07, 2020, 05:55:04 pm by perjmolsen »

princess prin prin

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Re: kortek ki-2-vo brand chassis repair help - only high voltage
« Reply #1 on: January 08, 2020, 05:42:31 am »
The flyback generates the heater voltage (H) and the video B+ voltage (BH). They're on the header with the red/black/white wires running from the main chassis to the neckboard. You can measure H on the neck socket and ground. it's an AC voltage around 6V. BH is a DC voltage in the 180-200V range. If H is not present, check R706.

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Re: kortek ki-2-vo brand chassis repair help - only high voltage
« Reply #2 on: January 08, 2020, 08:41:16 am »
Check the connection on the neck board. I had a monitor with similar issues, and the problem was with the connection from the fly back to the neckboard.
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Re: kortek ki-2-vo brand chassis repair help - only high voltage
« Reply #3 on: January 08, 2020, 03:00:30 pm »
The flyback generates the heater voltage (H) and the video B+ voltage (BH). They're on the header with the red/black/white wires running from the main chassis to the neckboard. You can measure H on the neck socket and ground. it's an AC voltage around 6V. BH is a DC voltage in the 180-200V range. If H is not present, check R706.

Hi

I have tried to see if there is 6V AC Heater volt, on the "H" point at the neck socket (ground to chassis) = 0V
Tested R706, tests OK.

Also tested for DC B+ on BH, (ground to chassis) = 0V

So It must be a bad flyback then....?

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Re: kortek ki-2-vo brand chassis repair help - only high voltage
« Reply #4 on: January 08, 2020, 03:01:38 pm »
Check the connection on the neck board. I had a monitor with similar issues, and the problem was with the connection from the fly back to the neckboard.

Hi :)

I have re-solder the connections but still no luck

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kortek ki-2-vo brand chassis repair help - only high voltage
« Reply #5 on: January 08, 2020, 03:10:53 pm »
You donít have any sparks by the flyback, do you?
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Re: kortek ki-2-vo brand chassis repair help - only high voltage
« Reply #6 on: January 08, 2020, 03:13:48 pm »
You donít have any sparks by the flyback, do you?

No, no sparks

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Re: kortek ki-2-vo brand chassis repair help - only high voltage
« Reply #7 on: January 09, 2020, 03:30:23 am »
Hi

Just an update -
The Fly is model KFS-60291, I have orderd a new replacment HR 8508 today, lets see if that brings back life

I will keep you updated :)

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Re: kortek ki-2-vo brand chassis repair help - only high voltage
« Reply #8 on: January 09, 2020, 04:59:07 am »
If high voltage comes and then goes it can be the x-ray protection that shuts down the horizontal drive. Lift one side of D541 near the HA11235 and see if you get a picture. If you do, switch the monitor off quickly. The x-ray adjustment pot is broken so it may be sending a voltage high enough to trigger the protection.
« Last Edit: January 09, 2020, 05:12:09 am by princess prin prin »

perjmolsen

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Re: kortek ki-2-vo brand chassis repair help - only high voltage
« Reply #9 on: January 09, 2020, 07:53:01 am »
If high voltage comes and then goes it can be the x-ray protection that shuts down the horizontal drive. Lift one side of D541 near the HA11235 and see if you get a picture. If you do, switch the monitor off quickly. The x-ray adjustment pot is broken so it may be sending a voltage high enough to trigger the protection.

Super I did not know that :notworthy:
I will try to test  :D and keep you updated

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Re: kortek ki-2-vo brand chassis repair help - only high voltage
« Reply #10 on: January 09, 2020, 11:42:13 am »
DAMM!!!!!!  :applaud:

NOW I GOT PICTURE!  :applaud:

Lifted D541 near the HA11235

So, it is x-ray protection... possibly the pot RV537
So now i just need to figure out what type/ohm RV537 is, and then how to adjust x-ray??

Is adjusting x-ray just turn the pot down, and try to see if the monitor turns on? and then adjust it up until it do not turn on, and then a hair back?

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Re: kortek ki-2-vo brand chassis repair help - only high voltage
« Reply #11 on: January 09, 2020, 01:14:10 pm »
I pulled out the RV537 - It is a 5k
Tried to turn it and see what the meter said... it jumped arround...

I have a sh..t load of 472 pot's  ;D

I guess that is OK to put a 4.47 pot in..

How to adjust the x.ray?  :notworthy:

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Re: kortek ki-2-vo brand chassis repair help - only high voltage
« Reply #12 on: January 09, 2020, 01:23:36 pm »
Put in the new pot, and the diode in again.
Tried to adjust the new pot, but I am unable to get the monitor to turn on... :notworthy:

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Re: kortek ki-2-vo brand chassis repair help - only high voltage
« Reply #13 on: January 09, 2020, 02:53:36 pm »
The pot may just have a broken rotor and not be the problem. This is when a high voltage probe would be necessary to see if the anode voltage is excessive when the protection is disabled. If it's not within the normal range you need to find out what is causing it to go too high. Either B+ too high or faulty flyback capacitor.

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Re: kortek ki-2-vo brand chassis repair help - only high voltage
« Reply #14 on: January 09, 2020, 03:06:11 pm »
I have not tested b+ if I look at the scematic to the flyback it says 115v at pin2 is that what my b+ needs to be?

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Re: kortek ki-2-vo brand chassis repair help - only high voltage
« Reply #15 on: January 10, 2020, 05:07:58 pm »
Some updates..

New HR8508 fly mounted, chassis still go to x-ray protection  :hissy:

Tested the big resistors
The big resistor with the blue wires connected, volt 149 on both sides. Tested resistor 169 ohm, and it is a 170 ohm so that is OK.
The other big resistor with blue and yellow wire, volt 115V on yellow wire, and 145 on blue wire. It is a 300 ohm and test as 300 ohm, so OK.


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Re: kortek ki-2-vo brand chassis repair help - only high voltage
« Reply #16 on: January 10, 2020, 05:22:18 pm »
odd that the chassis would use that flyback, its almost a ms2030 clone chassis
do you have the actual original schematic?

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Re: kortek ki-2-vo brand chassis repair help - only high voltage
« Reply #17 on: January 10, 2020, 05:35:34 pm »
odd that the chassis would use that flyback, its almost a ms2030 clone chassis
do you have the actual original schematic?

Hi Grant
No, schematic I have tried to find one but no luck.
If i search the web, I can find this chassis Nanao-MS720L1 it looks just like mine, but neither that I can find any schematic either
http://www.jomac.net.au/wp-content/uploads/2006/02/Kortek_Copy-of-Nanao-MS720L1.jpg

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Re: kortek ki-2-vo brand chassis repair help - only high voltage
« Reply #18 on: January 10, 2020, 06:08:06 pm »
i doubt thats the right flyback

perjmolsen

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Re: kortek ki-2-vo brand chassis repair help - only high voltage
« Reply #19 on: January 10, 2020, 06:10:49 pm »
Well some positive progress now  :applaud:

I have changed nearly all the electrolytic caps (the one with the blue dots changed)
And turned on the power, and picture witout x-ray shutdown - BUT I am unable to get the picture black, it is like the screen volt is to high.

As I remember with the x-ray protection turned off yesterday, the picture where possible to get nearly good, so can it now be my new fly that is causing this issue?

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Re: kortek ki-2-vo brand chassis repair help - only high voltage
« Reply #20 on: January 10, 2020, 06:12:07 pm »
i doubt thats the right flyback

I think you are right.. I am swapping out the new fly now to the old one...

Do not open the beer yet  ;D

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Re: kortek ki-2-vo brand chassis repair help - only high voltage
« Reply #21 on: January 10, 2020, 06:34:04 pm »
Well...

Now we open beer....  :cheers:

Positive, with the old fly KFS-60291 I am able to adjust the brightness  :applaud:
BUT... since I have changed caps the picture is to far to the one side and I am unable to move it back with H-pos pot.

Can it be the wrong cap I have mounted in spot  C501, I have put in a 47uf 50V, BUT when I looked again at the caps that i have removed it seems that is has to be a 4.7uf 50V... :banghead:

So do not drink that beer yet

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Re: kortek ki-2-vo brand chassis repair help - only high voltage
« Reply #22 on: January 10, 2020, 06:46:55 pm »
DAMMIT....  :banghead:

changed the c501 cap to the 4.7 uf 50V still the picture is moved to one side...  :hissy: :hissy:

Now drink beer anyway...  :hissy: :cheers:

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Re: kortek ki-2-vo brand chassis repair help - only high voltage
« Reply #23 on: January 10, 2020, 07:15:04 pm »
Ran thru the caps that I had changed, just to be sure that I had put the right ones in..

It seemed that "somone" had put a 10uf  in where a 33uf should had been. :banghead:

In C512 I had put a 10uf in, original it where a 33uf, so swapped it out and turned on power... AND back to x-ray protection!!!!!!!!!!  :banghead: :hissy: :hissy: :hissy: :hissy: :hissy:

Now I go to bed..!!

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Re: kortek ki-2-vo brand chassis repair help - only high voltage
« Reply #24 on: January 11, 2020, 06:32:35 am »
i would suggest checking any tantalum caps, there is one next to the sync processor

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Re: kortek ki-2-vo brand chassis repair help - only high voltage
« Reply #25 on: January 11, 2020, 07:03:30 am »
i would suggest checking any tantalum caps, there is one next to the sync processor

Will do, a tantalum cap, it is the blue ones, right?
I have pulled blue tantalum cap next to HA11235, the reading on the cap is 2.2 35 I guess that means 2.2nf 35V
It reads 2130nf, so that is good right?

I have also pulled out and tested all the polyester caps around flyback,to me they all look OK
c711 - 434J (0.43uf) TESTS: 417nf
c709   - 332J 1600V (3.3nf / 3300pf) TESTS:   3147 pf
c712 - 104K 200V (100nf)   TESTS: 99.90pf
c706   - 152J 1600V (1.5nf / 1500pf) TESTS: 1496pf
c705   - 392J 1.6KV (3.9 nf) TESTS: 3925pf
c704   - 533K 200V TESTS: 57.05nf

« Last Edit: January 11, 2020, 07:06:20 am by perjmolsen »

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Re: kortek ki-2-vo brand chassis repair help - only high voltage
« Reply #26 on: January 11, 2020, 07:19:06 am »
that is ok

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Re: kortek ki-2-vo brand chassis repair help - only high voltage
« Reply #27 on: January 11, 2020, 07:56:35 am »
What's the voltage at the cathode of D541 with anode lifted? What diode is it? If the voltage is higher than the zener breakdown voltage the diode becomes conductive and the voltage arrives at the HA11235 which shuts down.

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Re: kortek ki-2-vo brand chassis repair help - only high voltage
« Reply #28 on: January 11, 2020, 09:23:16 am »
Hi

Is is 41,6V with the annode lifted.
The diode is 1N5 242. I have also tested the diode with a leg lifted, it tests OK
« Last Edit: January 11, 2020, 09:24:49 am by perjmolsen »

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Re: kortek ki-2-vo brand chassis repair help - only high voltage
« Reply #29 on: January 11, 2020, 11:13:57 am »
That's a 12V zener so no wonder it's conductive when 41V is applied to it. The monitor uses a flyback derived secondary voltage for x-ray protection. The circuit is designed so that an anode voltage potentially dangerous (well above 25KV for a 20" tube) generates a secondary voltage high enough to make D541 conductive so that the voltage can go to the HA11235 which detects it as too high and stops outputting the signal that drives the HOT and hence the flyback. You have not measured the anode voltage so we don't know if the protection circuit is working as it should or if it's faulty/incorrectly adjusted. The protection circuit is very simple so you can easily check if all parts are good. If they are and if the adjustment pot that forms a voltage divider with R542/R541 is set to maximum resistance and the protection still kicks in, that would point to the anode voltage being actually too high. On the other hand the b+ seems correct and the caps that could make the anode voltage too high (C705 etc.) seems good too. I don't see a damper diode so it must be in the HOT. Check that too.
« Last Edit: January 11, 2020, 11:57:41 am by princess prin prin »

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Re: kortek ki-2-vo brand chassis repair help - only high voltage
« Reply #30 on: January 12, 2020, 03:01:14 pm »
Hi

I have now pulled out every component in the x-ray circuit, all components test as they are specified.
Also pulled out the HOT (D1399) according to the datasheet is has a damperdiode build in, it also tests OK

 :hissy: :notworthy:

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Re: kortek ki-2-vo brand chassis repair help - only high voltage
« Reply #31 on: January 13, 2020, 03:10:37 am »
You're not using the original tube are you? The inductance of the horizontal coil may not match the value required by the chassis.

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Re: kortek ki-2-vo brand chassis repair help - only high voltage
« Reply #32 on: January 13, 2020, 03:46:49 am »
You're not using the original tube are you? The inductance of the horizontal coil may not match the value required by the chassis.

Hi

I think that is is the original monitor, but I will check later today.
I got three monitors and chassis for free, the seller had marked them so that the chassis and monitor where paired.