Casio TV-8500 Green Screen

[PortableTV]

I have been picking up more and more of these Casio TV's and a bunch have the dead green screen.

This one I watched happen. I put batteries in it and it held the picture I had broadcast to it from my Blonder Tongue for about 30 seconds and then slowly went green.

Is this a capacitor issue? Any guidance would be helpful!

[zeno]

Heat related problems are often easiest to find with freeze mist.
Pick up a can.
1) Spray a very small area at a time lightly. If no change let things warm up again. Then move on to another area.
2) If you find an area thats sensitive spray some on a Q-Tip & touch the individual parts with it. Wait a minute for results.
NOTE that chilling something to way below 0 F can cause oscillators
especially to go nuts. Tuners, hoz & vert. They straiten out when things
warm up again.

Beyond that I cant help. In the day we wouldnt touch these things with a
ten foot probe. We gave the customer the info on the MFG to send it
to them.

73 Zeno
LFOD !

[Electronic M]

Are you sure your batteries are good? I've seen sets do that when the batteries die and come back when the batteries are replaced with good new ones.

[JohnCT]

Originally Posted by PortableTV

I have been picking up more and more of these Casio TV's and a bunch have the dead green screen.

This one I watched happen. I put batteries in it and it held the picture I had broadcast to it from my Blonder Tongue for about 30 seconds and then slowly went green.

Is this a capacitor issue? Any guidance would be helpful!

Generally, electrolytic capacitor symptoms dictate that the problem improves with running, not get worse. The exception are what we in the camcorder repair business used to call "fish" caps, because they stunk like low tide when they were powered up. They ooze their electrolyte out of the bottom and become conductive as they rehydrate any crap that was under or near the cap.

Open it up, exhale, and take a deep breath. If the board smells like your cat after it eats, you will need a wholesale swap of every cap on the board most likely.

We used to do tons of 8mm and mini DV (mostly Sony) that needed dozens of these changed on a board the size of a deck of cards.

John

[PortableTV]

Originally Posted by Electronic M

Are you sure your batteries are good? I've seen sets do that when the batteries die and come back when the batteries are replaced with good new ones.

Yeah, freshly charged. Same with A/C adapter as well. Multiple different Casio TV's from the era.

[PortableTV]

Originally Posted by JohnCT

Open it up, exhale, and take a deep breath. If the board smells like your cat after it eats, you will need a wholesale swap of every cap on the board most likely.

We used to do tons of 8mm and mini DV (mostly Sony) that needed dozens of these changed on a board the size of a deck of cards.

John

I opened it up. No discernable smell.

There's only 4 caps on the back of the screen, 2 are larger SMD's so at least I can change them. Fingers crossed that that's the fix. The main board has a bunch of regular caps but almost a dozen tiny SMD's that I would have zero idea how to go about changing.

I guess we'll see...

[JohnCT]

Originally Posted by PortableTV

I opened it up. No discernable smell.

There's only 4 caps on the back of the screen, 2 are larger SMD's so at least I can change them. Fingers crossed that that's the fix. The main board has a bunch of regular caps but almost a dozen tiny SMD's that I would have zero idea how to go about changing.

I guess we'll see...

If there's no smell, it might respond to heat. *Gently* warm the boards with a hair dryer and try again. If it produces a picture, the easiest way to find the offending cap(s) is with a scope. Most of those caps are bypass, so there will be no signal on the neg side (assuming common ground) and very little signal on the pos side. Most caps should have about the same amount of "hash" on them. If you find a cap with a double or more the amount of noise on the pos side that the others do, the cap is prob bad.

Before you change it, make sure it's not a coupling cap where the same signal would be on both sides of the cap, so move the scope to the neg side. If there's no signal there, it's a bypass and prob bad.

John