27K7391 blowing fuse

SilverDuck

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I just received a 27K7391 monitor today that I bought on eBay. When I power it up, it blows the fuse on the monitor chassis.

Where do I start?
 
Pull the chassis, check the flyback for cracks, check the HOT, check the critical safety cap, check all the fuses for popped tops, look it over for burnt parts, check the VR, make sure it has an iso...
 
Put your meter on diode or beep test and check between the different leg combinations. beeps all around mean a bad HOT...
 
Where is the HOT on my chassis? W/G website does not think my monitor exists.
 
It's probably the same as the K7000 - attached to the metal bracket that goes up and over the flyback?
 
I can't get a continuity beep between any of the 4 legs of my HOT.

Good or bad?
 
Your HOT will only have three legs, so if you are seeing 4 legs, then it's not the HOT.

After looking at the blurry schematics for the K7300, the HOT should be...
 
Found a better schematic. The HOT is Q402 and is a 2SC4789 (it might just say C4789)...
 
You may get a false "short reading" through T401, so you may to pull it to test it properly...
 
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The part I think is the HOT is Q11? and it is marked D1398 and 2J4. It has 3 legs, and is on the metal hump over the flyback. Is this the HOT? The spec sheet shows it as:

Q 11 086X0190-001 T RSTR 2S D 1398

I guess that is the HOT?
 
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Ok, it has 3 legs. I get continuity between the outer legs, but nothing with the middle leg and either of the outer legs.

What next?
 
It's probably ok. Take out the screw, unsolder it and take it out. Then test it again. There is a low value resistor there that is across the two outside legs that a lot of people read and mistake for a short.
 
Before I go unsoldring things, will this thing pop the fuse if I do not use an iso? The reason I ask this is because of my other project I have going, my KI2 machine with a 25" K7000 that requires and ISO, but has never had one, and I am pretty sure, no KI2 has ever had one.

That K7000 worked with no ISO, so...shouldn't this one?
 
Neither the K7000 or this one should be run without an iso. If you have and are blowing fuses, then you probably have a bad voltage regulator or bad rectifying diodes in the power input section...
 
I have been trying to power this thing up on my test bench, does it still need an iso?

Why did they build this game with this monitor, but never use an iso, when the monitor has a huge sticker that says MUST USE ISOLATION TRANSFORMER?
 
As Ken mentioned in another thread here, It most likely shipped with a different type monitor (like the U2000) and that does not require an iso. Whoever put that monitor in knew even less than you about why isolation is required.

And yes, you should have it isolated on your test bench.

My personal test bench has an iso permanently wired into the monitor power, regardless of whether the monitor requires one or not. An iso won't hurt a monitor that doesn't need one, but no iso will hurt a monitor that does...
 
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