Home Theater Forum and Systems banner

1 - 7 of 7 Posts

·
Registered
Joined
·
3 Posts
Discussion Starter #1
My problem began with green bowing at the top and bottom of the screen. I have read many posts on multiple forums and chose to make the repairs myself. I upgraded my ICs to the stk394-160's but did not replace the resistors as they all looked good and the ones that came in my kit weren't banded like the originals. I reinstalled the board and found all three colors bow on all sides.

Not sure where to go next.
 

·
Plain ole user
Joined
·
11,121 Posts
Start by checking your power supplies to the ICs, the resistors, and checking your work to be sure that you did not bridge solder joints. Check the nearby solder conections on the board for ring cracks or powdery looking solder and resolder any that are suspect, particularly any larger heat producing parts.

Read the first 10 posts of the convergence sticky very carefully.
 

·
Registered
Joined
·
3 Posts
Discussion Starter #3
Thanks. Based on your advice in the early threads I examined the board very carefully and it looks pristine. All the resistors tested good but I checked them after the IC's were installed and I had expected to get altered readings while in the board. Since your post, I removed the board again and rechecked my soldering. I re-did a couple of posts just to be safe and I went ahead and replaced the resistors RK42,46,50,54,58,62. The old resistors tested okay once removed.

I reinstalled the board and have the same results. I wasn't clear on my initial post...the screen bows at the top and bottom and the colors are out of convergence. When I press the blue button to reach the service mode, the grids that come up have the red flashing, as you suggested, and it is here where the grid lines bow on all sides. I can toggle between the coarse, medium and fine screens and I can toggle between the color selections but I cannot get the thumbstick to adjust any of the colors.

When the problem first appeared, Magic Focus failed on green and gave me a 4 in lower right. After the install it failed on Red. Now when trying to run Magic Focus I get a static screen with cross hatches which show the colors out of alignment but I can affect no changes.

I do not know how to check the power supply to the IC's.

Any help is appreciated.
 

·
Plain ole user
Joined
·
11,121 Posts
You should have +/- 24v to 30v on the appropriate pins of the ICs. Look at the schematic or the STK datasheet to see which pins those are. Measure the voltages carefully so that you do not short the pins together. If there is no power to the chips there will be no correction.
 

·
Registered
Joined
·
3 Posts
Discussion Starter #5
I'm clearly in over my head now as I'm not familiar with circuitry and voltage testing procedures.

I cannot locate a datasheet for the STK394-160. My service manual shows the DC voltage on Pin 5 at 31 and Pin 10 at 27.2 but I don't know which to test. Nor do I know where to place the second probe on my meter to complete the reading.

How is the power supply checked at the IC pins while the board is installed? The board is the furthest right in the cabinet with the heatsink shielding the IC's between it and the cabinet wall.

My ignorance is clearly showing. Also, are there fuses I should be testing or is the process you've recommended a determining factor in whether or not to move in that direction.

Your patience is appreciated.
 

·
Plain ole user
Joined
·
11,121 Posts
There are pico fuses in the power supply.

There is no datasheet for the STK394-160 but there is one for the STK392-110 in the convergence repair thread. The pins are identical.

You can use a probe that allows you to reach the pins or you can stand the boards up on the front edge to get to the pins to troubleshoot,
 

·
Registered
Joined
·
9 Posts
I just completed the repair of a 53UWX10BA yesterday. I purchased the Hitachi kit(JT22052) from our normal supplier. I pulled the convergance board and removed the STK392-110 IC's that were there. After I removed the IC's, I then checked the resistors already soldered into the board. They were all good*. I installed the new STK394-160E IC's, checked my work, then installed the board. Using a digital picture from my cellphone, I dressed the cabling as it was before disassembly. I applied power and signal through the component inputs and was greeted with picture and sound. The convergance was off a bit but I wanted to let it "cook" a bit before I ran the DCAM procedure on it. After about 1/2 hr, I stepped back about 10-12 feet and looked at the screen. What I saw kinda blew my mind. From the center of the screen going to the right...I had perfect picture! Zero, I mean no distortion or convergance problem at all. But, from the center of the screen going to the left...completely different story! All 3 colors divulged by almost 2" at the far left edge of the screen! Tried running the Magic Focus and it cleared up by only a little.

"All the resistors were good*." As in none were charred or open.

As I stared at the distorted screen....that came back to me. The resistors used in the circuit are supposed to be 5% tolerance. I flashed back on when I checked the resistors. The 1.5 ohm measured 1.6 ohm and so forth. All the resistors were within .1-.2 of what they should be.......COLD! .2 ohms difference on a 1.5 ohm resistor comes out to be right at 7.5%....out of tolerance!

I powered off the set and again removed the board, then changed all the resistors, then installed it again, keeping the same cable arrangement as before. Crossed my fingers and powered it up again. Once again was greeted with picture and sound, but..now I had just a small difference in the convergance. I used a laser thermometer we have at the shop to check how hot the new IC's were getting. After about 1/2 hour they were stable at 85 degrees C. I held my breath and pushed the Magic Focus button..... it took about 20 seconds for it to run through the routine, but when it was done...I had perfect picture...all the way across! I let it run for about 3 hours to make sure it was stable and had to make no more adjustments to it. Going to have another happy customer because they wanted it back for the New Year's Games.

This episode taught me a lesson...if you have new parts...USE THEM! Trying to save myself some time resulted in my having to in effect, do the job twice!! Low ohm resistors being .1-.2 ohms off what they're banded require replacement. Luckily, I didn't damage the new IC's in my haste to get the job done.

Lesson learned!!:sweat:
 
1 - 7 of 7 Posts
Top