Repairing Mitsai TV

[dark666]

Hi to all.

Im repairing a mitsai TV, it's the first time i find a TV with this problem althou i've heard about it.

When i turn the TV on the tube stays all black with a thick white very bright line across the screen.
The line is located between the middle and the botton of the screen.

I've heard that this could be caused by bad capacitors that are used to strech the picture to the tube size.

What could cause this?


Thanks

 

[Nigel Goodwin]

I've heard that this could be caused by bad capacitors that are used to strech the picture to the tube size.

No, as there's no such thing

Most common cause is a dry joint on the scan coil connector, or the the frame output IC. Sometimes resoldering will cure it, other times the chip will have been damaged as well and require replacing.

 

[dark666]

i'm no longer near the TV. I spend most of my time from place to place.

Tomorrow i'l check for dry joints and resolder, if not i'l replace the IC.
I'l post the results.

Thanks

 

[dark666]

I resolder the dry joints on the TV.

While resoldering i found a burnned black resistor near the flyback transformer.
Browsed arround the internet and found a electronic forum from my country councerning the same problem on the same tv model.
Since Mitsai is a very cheap and popular brand here in my country i give it a shot.

I found out that the resistor is a 10ohm resistor.
Also in the forum said that if that particular resistor is burnned the TDA1771 IC is also burnned and if i replace only the resistor the resistor will burn again.

The IC is the Vertical Deflection IC.
Is it possible to test the IC to see if its burnned?

Thanks to all.

 

[Nigel Goodwin]

I resolder the dry joints on the TV.

While resoldering i found a burnned black resistor near the flyback transformer.
Browsed arround the internet and found a electronic forum from my country councerning the same problem on the same tv model.
Since Mitsai is a very cheap and popular brand here in my country i give it a shot.

I found out that the resistor is a 10ohm resistor.
Also in the forum said that if that particular resistor is burnned the TDA1771 IC is also burnned and if i replace only the resistor the resistor will burn again.

The IC is the Vertical Deflection IC.
Is it possible to test the IC to see if its burnned?

Stick a resistor in and watch it smoke - just change the IC, the dry joints have killed the chip, and the chip failing often takes out the resistior (it acts as a fuse).

 

[dark666]

I encountered a small problem while replacing the IC and resistor.

The resistor is in a tight spot, and removing the resistor i damaged lead of a diode.
I tested the diode and the diode is fine, the problem is i can put the diode back in its place because one of the leads as become smaller.

Either way, the diode is a BYV36C PH, I couldnt find the same diode on any shop but i found a BYD34M PH, in the store they told that the BYD34M would do the job in replacing the damaged one.
I can find the DataSheet for the BYV36C but not for the BYD34M.

In the store they told me that the only diference was that the BYV36C works at 600V and the BYD34M is for 1000V.

Will this work?

Thanks

 

[Nigel Goodwin]

Try it and see, or just solder a longer wire on the original diode.

 

[dark666]

hi again.

I placed the resistor, IC and the new Diode on their place.

I turn on the TV, I have audio but no picture, the white line that was across the screen is no longer there, the screen is just all black.

What can i do now?

 

[Nigel Goodwin]

Measure the voltages around the new IC, or (if you can) check it's output with a scope.

 

[dark666]

Found it.

I found a broken solder on wire that connects the mainboard to the small PCB on the back of the tube,
I probaly broke it while removing the PCB, this TV doesnt have connectors, all the wires are soldered to the PCB, tie only connectors are the AC cord, Degaus coil and mono speaker.

I resolder all solders on the tube PCB, also had a couple of dry joints on 6 transistors on the tube PCB.

It work now, i have audio and picture. Im adjusting the flyback focus and sharpness, as the picture looks a little blurry.


Another thing it looks the picture has too much red, I found no adjusting resistors for colors.

Any idea about the picture being red and blurry?

Thanks

 

[dark666]

I lost picture again.

Worked ok for about 5 min, now its black again, audio but no picture.

 

[dark666]

Got picture again. LOL

I found the problem i just don't know how it is called, not in english at least.
Its like this, there are 3 wires from the flyback transformer, 1 goes to the top of the monitor with that large rubber connector, 1 is soldered to the tube PCB and the other goes to the same connector as the tube.
Now, the wire that goes to the connector of the tube keeps geeting loose, there is a small button that disconnects the wire but the button apears to be very loose.

I already cut the wire, stripped the insulation and reconnect the wire in its place but it looks loose, i don't think its gonna last long until it gets loose again.

Any ideas on how to prevent/repair this?

Thanks