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#31
08-02-2015, 01:27 PM
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STR
X6737 I'll get some more readings soon as i can. 
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#32
08-02-2015, 04:11 PM
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Ok. I took a look at this chip. I have a "typical application" diagram to go by. Yours MAY be a bit different...BUT the functions WILL be the same.
pin 1==should have full hot B+ on it--as it is the drain pin--the one going to the transformer. Measure to HOT gorund. Pin 4--the chip B+ line.If it is Near 0--measured to HOT ground (as are ALL voltages on this IC.). either the chip or something erxternal is loading it--likely that optocoupler. It should measure at least a few volts to hot ground--when the chip is running. There does appear to be a "start up" resistor on it. if it was OPEN...NO start and no power up. The strat resistor will be a high-value one--100K or higher--and come off of the HOT B+ from that cap in some way--to pin 4. If it DOES show 0..unsloder that pin and re-check. If it THEN shows a decent voltage...the chip IS VERY likely bad. If it does NOT come up when unloaded...a diode or that optocouplwr is loading the line down. After the chip is up and running...a diode form the feedback line THEN supplies the chip with this voltage and the "start voltage" is bypassed. Pin 2.. Source... goes to hot ground through a current sense resistor. if the chip was in over current mode..it will mute oscillation to prevent damage. But since you have nO power or squealing or chirping noise..likely NOT the issue. Just measure it to hot ground with an ohm meter and see if it is very close to zero ohom to ground. Pin 3--Ground. Should also be zero ohms to hot ground. Pin 7--over current protection. Shares part of feedback ckt and voltage developed from pin 2. . Likely will NOT show any voltage--since the chip is not running. Pin 5..feedback pin. This is used by the chip to know if it is producing enbough output. it will be connectoed ot the HOT side of that optocoupler. WHen running...there should be a few volts on it--but with it dead...likely NONE Pin 6..soft start.. Likely will not show anything with the chip not running. It goes through a cap to ground to allow the SMPS to start "gently". THIS should give you an idea. I would bet..either your chip is bad..or that optocupller is bad (amybe BOTH of them), or a zener diode in the ckt is shorted. Check around the optocoupler and feedback pins for any diodes there and see if any are bad. CHip is NOT overly expensive on Ebay--new. $16 INCLUDING ship..from FL. Last edited by rca2000; 08-02-2015 at 04:30 PM. Reason: more info.
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#33
08-03-2015, 07:23 AM
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Sounds good. I'll try and get on this later today and see whats there.
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#34
08-05-2015, 07:38 AM
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Looking on the board, im having trouble identifying these "pins" you refer to. If i had a pic marking what i need and where to test, it would be easier for me. I can barely even get in there so i had to unhook everything and bring out that board. Labeled "POWER & LF PWB LCB90284 -001C. would another pic of this area help especially now that its out where it can be seen better? maybe you can circle or mar where to check. placement of the red lead and black.
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#35
08-05-2015, 07:54 AM
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here's some new ones:
Last edited by pac.attack76; 07-14-2016 at 02:47 PM.
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#36
08-08-2015, 07:44 AM
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Should i just go ahead and change both the chip and the optocoupler?
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#37
08-09-2015, 08:17 AM
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Where did everybody go? I really need to get this thing running since its sitting in the middle of my living room. I'll make it a point to get those numbers today and see whats going on. Anyone know the part number of the optocoupler?
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#39
08-09-2015, 02:42 PM
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Sorry--I have been busy for the last few days--with the 127 corridor sale and such.
ANYWAY...before you order ANY parts... what did you measure on the STR IC--to hot ground ? :Pins 1, 4 and 5...in particular. If 4 or 5 is off by much...that optocoupler is likiely loading things down.
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#40
08-09-2015, 06:05 PM
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Thanks Andy for the service manual. Very handy. I'm having trouble fiuring out which pins are which and if the board needs to be installed in the set when i test. Where is "hot ground"?
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#41
08-09-2015, 06:38 PM
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Hot ground is ther negative lead of that big capacitor you measured 171 volts on. This is the reference point for ALL voltages on that IC.
Looking at the IC from the front...see where the pins all go into it. From left to tight--pin 1 should be on the left and in order from there. I KNOW they are "staggered" in the way they end up on the PC board..But if you look at how they enter the IC--you should be able to figure out which pin is which. I tried to dowlaod that manual myself...but was NOT able to do so for some reason.
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#43
08-10-2015, 08:12 AM
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Ok, guys, looking at the board where the words "live" and "isolated" read upright, the pins are like this:
. . . . . With the cap out to the left. Now, going from left to right, left to right, i got: -.033, -14.06, -.003, -1.26, .000 Not sure if i did this right. Red on right side of cap since the other side has a plus mark. Set to VDC.
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#44
08-13-2015, 07:46 AM
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Did i do this right. If not, i can hit it again.
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#45
08-13-2015, 09:55 AM
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You did it BACKWARDS. Put the black probe lea don the hot ground. Use ther red or positive one---for all of the other readings.
BUT...i did NOT see any 171 volts on ANY pins of that chip. Are you SURE_-you got all of the pins? 2 of them are scattered from the otherrs--remember. if you did NOT...then check those 2 large resistoirs beside of that chip...and see if they are OPEN. They likely read LESS than one ohm. If OPEN--that ahip IS shorted.
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Linear Mode
