CRT based RPTV Convergence Repairs - Page 10 - Home Theater Forum and Systems - HomeTheaterShack.com

 
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post #91 of 305 Old 02-24-08, 03:40 PM Thread Starter
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Re: CRT based RPTV Convergence Repairs

If a fuse has blown, it is unlikely that changing it will solve the problem. I am not very familiar with that convergence circuit, but if you look for the largest heat sinks, you will likely find the ICs if it has them. Some of the RCA sets have discrete transistors rather than IC outputs.




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post #92 of 305 Old 02-24-08, 08:04 PM
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Re: CRT based RPTV Convergence Repairs

Quote:
lcaillo wrote: View Post
Further repair would take some troubleshooting...at this point I would be verifying the info that you gave above and likely getting out my scope if it is correct. My guess is that you missed something in the repair, or perhaps you do not have complete info on how to adjust the convergence.
The set I'm working on is a 55" Samsung HCM5525W. After taking it apart a second time, I closely examined the board around the STKs. I found two pico fuses that I hadn't noticed before. I found them by the marking on the underside of the board. They were both green and looked like resistors without the indentifying bands. I ohmed both of them, and one was open. It was labeled FD101S on my board. So I replaced it, and finally I was able to correct the convergence. The fuse probably blew when the STKs went out, and burnt the resistors.

For those who are having trouble correcting convergence after replacing the convergence ICs, look for a sine wave symbol on the underside of the board. That indicates a fuse, and is usually soldered on the board like a resistor.

Thanks again lcaillo!
post #93 of 305 Old 02-24-08, 10:42 PM
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Re: CRT based RPTV Convergence Repairs

nice write up!!
 
post #94 of 305 Old 02-25-08, 03:57 PM
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Re: CRT based RPTV Convergence Repairs

The line is not perfectly horizontal, it angles downward. I am in the customer convergence menu with the cross hairs using the remote to move the lines. Access by the convergence button on the TV's control panel.

If I move the line up or down it is still angled. Since the other lines are perfectly horizontal they can not lie on each other to create the white. Does the service menu offer addtional options.
post #95 of 305 Old 02-25-08, 05:30 PM Thread Starter
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Re: CRT based RPTV Convergence Repairs

Sounds like you moved the blue yoke. You need to get the service and training info to go through the convergence alignment. I don't recall on that unit specifically whether there is a tilt adjustment or not, but again, my guess is that you just twisted the yoke.




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post #96 of 305 Old 02-26-08, 11:14 PM
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Brief story: got lazy, and got convinced to call repair shop (did not have schematics at time), after $400 and only one visit had the Magnavox 51MP392H/17 fixed with replacing the STK392-120s due to convergence issue. About 1 month went by and then (while watching) set would power down and after a few seconds power up, CRTs would start to illuminate then power off again. could only stop this by unplugging set. Now it became my challenge to fix. If this would have happened after I did the initial fix certain person with significant influence in household would have NEVER let me live it down. Got schematics (SAMS) started checking, replaced the power MOSFET, power control IC for the MOSFET and a few diodes etc.... no luck. Did not consider infant mortality initially but it was the problem, the STK392-120s needed replacement, the supply voltage as measured on the ICs never recovered as the set was trying to power up. As a result of checking for bad resistors, caps or open circuits I discovered the two STKs were not connected to the supplies as the schematic indicated. One had +35VDC, -35VDC and a -22VDC supply connection the other only a +35 and -35 supply connection. All supply voltages come from same winding (different taps) on transformer per the schematic. The discrepancy bothered me, decided to change board (removed existing jumper, installed "custom jumper" on pwb) so both STKs have 3 supply voltages. The two application notes on the data sheet (for the STKs) did not closely match the configuration in the set. Been working now for two months no problems. Bought the STKs from a site that promised genuine Sanyo parts I also recommend this. Now why post this.. 1) to share the experience. 2) possibly someone can answer the question was this modification I made good, bad or indifferent, and why. Do I recommend others do similar??, no not without further understanding of the longer term effects of the modifications I made.
post #97 of 305 Old 02-27-08, 05:03 AM Thread Starter
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Re: CRT based RPTV Convergence Repairs

My suspicion is that you did not modify the circuit at all. A problem on these sets that I have on these sets is that techs will crack a trace on the board. It was likely not easily visible or even just partly cracked when he serviced it, then with thermal cycling eventually cracked, trashing the chip. Could also be that he just used a cheap copy for the replacement parts. What you did should be fine if it conforms to the design intent for the IC.

The lesson that I would take from this is that there are lots of pitfalls with any repair. Be very careful not to damage boards and use known OEM parts unless there is a very good reason to do otherwise. Finally, never assume that mistakes are not waiting to happen with every action you take. One must be very careful working on these boards. Some of them can be very fragile. Some are well made and easy. Assume nothing.




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post #98 of 305 Old 03-01-08, 02:10 AM
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Re: CRT based RPTV Convergence Repairs

Hello all
I am working on a friend's pioneer tv (don't have the model number) and the red convergence would not properly align. I have replaced the two STK392-110's with STK394-250A's (from ACME) and none of the color's will adjust now (previously, all were adjustable). All resistors are unburned and within spec, capacitors appear fine as well. The mute circuitry seems different, according to this thread as well as the datasheets. As I've read here, all colors bowed (as they now are) was attributed to no power to the STK's, but I would assume that the chip's output being muted would also cause the same problem? The 250A's datasheet states 'high' input on pin 2 for unmute, whereas the pcb has pin 2 grounded...Just want to make sure that cutting the trace and tying the pin to 5V may solve the problem, driving out to his house takes a while.
post #99 of 305 Old 03-01-08, 05:50 AM Thread Starter
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Re: CRT based RPTV Convergence Repairs

I do not recommend making modifications to the circuit. The STK392-110 should be replaced with STK392-150 or STK394-160, not the chip that you used. It is always best to use exact replacement parts. Pioneer replaced the -110 chips with the -150 and -180 versions. We know that the best solution is to use the STK394-160 from Hitachi and from using it in many other sets to replace the STK392-110. While the STK-394-250 appears to be the same except for the mute circuit, there is simply no good reason to take chances with circuit redesign in the field. Save yourself some headaches and get the right parts.




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post #100 of 305 Old 03-20-08, 06:28 PM
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Re: CRT based RPTV Convergence Repairs

O.K. I've got the dreaded convergence problem on a Hitachi 53UWX10BA. Had it fixed (?) about 14 months ago and now it's back. Gonna give it a shot at fixin it myself this time and save myself 400 bucks ! I've ordered the parts already from Andrews and downloaded a schematic. My problem is that I'm not the most experianced person in the world when it comes to electronics. Fixin a car I can do but I'm a stranger to circuit boards and such. I know where the two STK 392-110's are but how do I know which resistors are the ones that are associated with them to replace ?
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convergence , dcam , resistors , service menu , shutdown , stk , stk392-110 , stk392-120 , stk392-570 , stk394-160

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