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Discussion Starter #1

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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It sounds like your flyback transformer is going (very common). It happend to our Yamaha CRT a few years ago. It can be replaced however that depends on availability of the part as our Yamaha had to be repaired with a used one.
 

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The flyback transformer is most certainly NOT the problem. What Wayne is experiencing is a collapse in the vertical sweep. A horizontal line and any picture at all means that there is high voltage and there is horizontal sweep. This cannot happen with a bad flyback, which is actually very RARE in these sets. What is common that will cause loss of vertical are bad solder connections. Also, in some of the Mitsubishi sets, there will be a number of leaky (physically leaking electrolyte, not d.c. leakage) electrolytic capacitors. The electrolyte can cause corrosion that will create bad connections and the caps tend to not perform as they should when they leak. The lines are likely due to poor vertical linearity (the vertical sweep is not consistent for the entire interval) and this is often due to capacitors which are off value or have high ESR.

Post the model number, Wayne. 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.

The short term fix is likely to resolder the vertical output IC, usually numbered in the 400s, often IC401 in mitsubishis of this vintage. Another way to know if you have leaky caps is if you smell rotten fish when you heat the negative legs of the caps in the area.
 

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I agree with lcaillo. This is a very common failure symptom of vertical output circuit. Look for solder void around the vertical scan IC(usually LAxxxx), and also connector to the the vertical deflection yoke. Check if there is any electrolytic capacitor close to the vertical scan IC heatsink. It tends to dry with the heat from heatsink.
 

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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.

There is also a tantalum cap that causes problems in this set. IIRC it is orange and 2.2uF.
 

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if its anything like our old Sony there will be screws holding the A/V input/output connector to the back of the set, those will need to be removed as well (the connectors stay with the inside circuit board) check the spot where the power cord goes in as that may have a screw also.
 

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Remove all of the screws, including the ones that Tony described, and tilt the CRT forward a little. It should slide off, but it can be tight, especially with the weight of the CRT.
 

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Ya, that dust is real nasty if it gets in your lungs, I think is has something to do with it sitting around all that electronics but it gets almost acidic in nature.
 

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Discussion Starter #12

Okay, got everything cleaned up in there, but I’m having some problems here...
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.
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.


The short term fix is likely to resolder the vertical output IC, usually numbered in the 400s, often IC401 in mitsubishis of this vintage.
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.


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.
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).

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.
Much of the brown stuff mentioned does seem to be in the vicinity of some heat sinks.

There is also a tantalum cap that causes problems in this set. IIRC it is orange and 2.2uF.
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.

So - if the gook 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
 

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The vertical output is labelled IC401. Start by reslodering it and replacing the caps in its vicinity numbered in the 400s.
 

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Discussion Starter #14

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
 

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You probably bumped the screen (G2) adjustment on the back of the flyback transformer. It is the big black device with the red anode wire coming out of the top. The screen control is the bottom control on it. Switch to a blank input and adjust so that you have a dark screen and don't see the lines (retrace lines).
 

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Look for a connector that may have been pulled loose. If it changed when you worked on it you probably just have something like that. Generally, that symptom is most common with an open resistor on the CRT board, but it is unlikely that you would coincidentally have that kind of failure with the other. Another possibility is that you missed some leaky caps and moving the board finished off a solder joint that was weakened.
 

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Check to see if there are any little white switches on the CRT board. Some mits sets had them to control the various guns and/or g2 for testing and they would get bumped easily. Also, look for broken solder joints on the CRT board or around the flyback transformer.
 

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Discussion Starter #20

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

 
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