Problem with older 31" Mits CRT
Sadly, our 1996 vintage Mitsubishi 31” TV has been showing its age of late. When you turn it on, the picture collapses to a thin white horizontal line across the middle of the screen. When the picture finally kicks in a couple of hours later, it has horizontal lines on the screen that are progressively larger and more numerous towards the bottom of the screen. I’m sure it’s just a minor repair – the picture tube is still nice and bright. Any ideas? Is it something I could do? About the only relevant tools I have are a Greenlee VOM and a soldering iron.
Regards,
Wayne
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What's the trick to getting the back half of the case to separate from the front? It's the underneath side that seems to be hanging up.
Regards,
Wayne
Okay - got it separated - thanks for the tip Tony. Wow, all that dust! I'll have to give it a good vacuuming, or I'll catch my death of sneezing - maybe with the aid of a toothbrush? No black goo jumping at me at this point, though...
Regards,
Wayne
Okay, got everything cleaned up in there, but I’m having some problems here...
Don’t see anything wet looking, or any black spots on the bottom of the board. There does seem to be some brown spots on the bottom of the IC board, but as noted, nothing black. Much of the brown stuff does seem to be in the vicinity of some heat sinks.Look for wet looking circles around electrolytic caps and black goo on the legs (mostly the negative) of the polar electrolytic caps. Also, look for black spots on the traces on the bottom of the board. This is a good indication that electolyte has been doing its work on your board and lots of cleaning is needed.
Seems to be precious few ICs in this thing. Most are located on a vertical board, but none of them are 400-numbers. Only one IC is on the vertical board (motherboard?); it’s not a 400 number either.The short term fix is likely to resolder the vertical output IC, usually numbered in the 400s, often IC401 in mitsubishis of this vintage.
Sorry, but I have no idea what a deflection yoke looks like, and I can’t find any ICs with heat sinks (or maybe I just am not able to recognize it).Look for solder void around the vertical scan IC(usually LAxxxx), and also connector to the vertical deflection yoke. Check if there is any electrolytic capacitor close to the vertical scan IC heatsink.
Much of the brown stuff mentioned does seem to be in the vicinity of some heat sinks.The CS-31305 definitely is one that tends to have leaky caps. They do not "dry out" but actually leak electrolyte because of faulty seals, likely made worse by high ESR and temperature, bu caps even far away from heat sinks do the same thing. It usually occurs on the negative side. There are often several leaky caps in the area near the low voltage regulators (5v & 12v). Scan the board for spots below the caps, black goo on the legs, and use the trick of heating the leads and smell for the ones where you cannot see the legs. Clean the board very carefully to prevent future problems.
I did find a few orange looking things, kinda shaped like a mailbox. Are those capacitors? (Sorry, the only capacitors I know anything about are round like a barrel...) Some of them are near heat sinks, and there is some of that brown stuff there.There is also a tantalum cap that causes problems in this set. IIRC it is orange and 2.2uF.
So - if the **** I'm looking for is brown instead of black, I guess I'm on the right track. Except that I can't find that vertical output IC...
Regards,
Wayne
Okay, I located and re-soldered the IC. No luck. It's no longer going to the thin vertical line like it was, but what I get now is a light gray screen with a number of white horizontal lines. I hooked up a DVD player and the image is barely visible "behind" the light gray.
I didn't replace the caps in the vicinity. They are not leaking as far as I can tell. Besides, they are down in a "valley" between a big vertical circuit board and the heat sink for the IC401. The big vertical board is right next to a smaller vertical board, and I see no easy way to get either out to access the caps.
I think I've probably reached the limits of my skill level here...
Regards,
Wayne
When I turned the knob the TV turned itself off. Now, it won't stay on more than 15-20 seconds before shutting off. :huh:
And it didn't help the picture - still grayed out with white horizontal lines that obscure the signal from a DVD player.
Regards,
Wayne
Yeah, I forgot to plug a connector back in. :duh:
Okay it's staying on now, but turning that knob didn't help the gray-out problem.
Regards,
Wayne
I guess the CRT board is the one hanging on the back of the CRT? No switches there. Plus I didn't do any dust clean-up on that one, so I was never messing with it. Don't see any bad solder joints on it, and the solder joints on the flyback transformer all look good.
Regards,
Wayne
Hmm. Well, I'm pretty sure I haven't damaged any connections (at least not the kind with a cable and plug attached.
). The one I mentioned before that I forgot to plug in, I determined was for the two speakers.Guess it's going out to the curb...
Regards,
Wayne
1 - 10 of 23 Posts
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