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WG K7000 dead... flyback? (SOLVED)
Sarver Systems:
I'm at the point now where I am 100% certain there are no solder bridges or cold solder joints. I also verified that all of the caps are placed in the proper positions, and in the correct orientation. I even went as far as reinstalling the old bipolar cap, since it was much bigger (but the same value) as the replacement.
I am able to keep the monitor powered up for anywhere from 1 minute to 10 minutes before it shuts off.
Sometimes I can even get through the calibaration screens, and even play a game or 2 before it shuts off. Other times, as soon as the memcheck is done, it shuts off.
I reflowed every solder joint on the neckboard, just to be sure.
My B+ is 119VDC until it shuts down, at which point it goes to 190VDC (if I recall correctly).
Sarver Systems:
PS, if you want me to start my own thread (damn hijackers!), please let me know, and I apologize.
lilshawn:
--- Quote from: MKFan4Life on December 05, 2013, 12:49:41 am ---I checked for B+ at the large resistor (180 Ohm 25 Watt resistor) on the bracket the voltage regulator is mounted against (on the opposite side). I have read that you can read each side of that resistor for input and output (B+). It's reading 179.5 VDC on one side and 177.7 VDC on the other. (ARGH!)
I know it's best to check on IC4 Pin 4 (positive lead) Pin 3 (negative lead) right? Just so darned hard to cram my hand there and make good contact with the chassis mounted in place at the moment.
What do you think? :-\
--- End quote ---
6 to one 1/2 dozen to another. yes, you should have 2 different voltages on the resistor (the resistor blops down the voltage for the rest of the system that's why it's so honking huge)
that said, the B+ sounds a little off (should be somewhere around +120VDC on one side of the resistor and +145VDC @ the other side) try unsoldering one end of D10, this will disable the shutdown circuit...crank up the contrast and brightness (or black level or whatever they call it) and see if the monitor powers up then. (don't leave it too long like this, just verify it comes on.) if it does power on, quickly see if you are getting just a line on the screen. (this is why we crank the brightness) this means something else is wrong. if not the regulator is probably going bad and will need to be replaced. but you can try replacing C57 first...if it's still wonky replace the regulator.
--- Quote from: Sarver Systems on December 05, 2013, 09:13:21 am ---My B+ is 119VDC until it shuts down, at which point it goes to 190VDC (if I recall correctly).
--- End quote ---
if that's the case, you could probably follow the same steps, but you likely have something going open and your B+ spikes up and the high voltage protection is kicking in. you may still have broken solder joint someplace. They can be super hard to see. the voltage looks good until it shuts down.
check the temperature of your horizontal output transistor and your vertical IC after it cuts off... something is conking out. there has to be a tell someplace.
Sarver Systems:
Can you describe some steps on determining where those components are located? And how do I measure the temperature? Just touch them or with an IR thermometer? Am I expecting to find hot components or cold components?
lilshawn:
--- Quote from: Sarver Systems on December 05, 2013, 11:41:35 pm ---Can you describe some steps on determining where those components are located? And how do I measure the temperature? Just touch them or with an IR thermometer? Am I expecting to find hot components or cold components?
--- End quote ---
all the components have an ID designation next to them. :dunno i dunno what more i could tell you. search the board until you find the one you are looking for. the k7000 is pretty disorganized. so it's tough to find some of them.
temperature can be measured any way you like. if you decide the "touch" method, i would recommend powering down first before touching. some of those caps have aluminium cases that are open on the top. they can carry hundreds of volts while it's operating. if you have an IR or thermocuple thermometer, take a reading sitting idle to get a base and then power it on and take your readings after it's failed..
failed components with either be hot or dead cold (depending on the mode of failure. Shorted components will be hot and failed open components will be cold.) yours still works, so i suspect your problem part will be hot.
parts will get warm, but failed parts will be OBVIOUSLY way hotter.