Build Your Own Arcade Controls Forum
Main => Monitor/Video Forum => Topic started by: LTC on June 13, 2025, 11:16:42 pm
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I know it's probably a long shot and sorry for the vague description, but it's the best I could come up with. The top of the screen looks like it is folding over itself, is the best way I can describe it. Any idea what may cause this?
If you look at the top, SCORE and HISCORE are upside gown, and during game play, when the enemies approach, you can see the start right where the lines on the screen appear. They go up, before entering the playfield from the top, so it looks like the screen folds over itself at the top.
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It's a cap that's failing in the vertical deflection circuit. I can point it out to you if the schematics are available. If not, I need pictures of the chassis, top and bottom side in the area where the vertical IC is located.
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It's a cap that's failing in the vertical deflection circuit. I can point it out to you if the schematics are available. If not, I need pictures of the chassis, top and bottom side in the area where the vertical IC is located.
Thank you for the reply. I believe this may be the schematics of the chasis.
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What you have there is indeed generally called "vertical foldover" and is an early stage of vertical collapse - the TV is having problems expanding the picture out from the middle. The fact that it has not "collapsed" completely tells us the vertical IC is probably OK, and (as Princess has pointed out) most likely failure points will be supporting electrolytic capacitors (little aluminum cans) as their electrolyte dries out eventually.
Most CRTs are approaching an age (15-20+ years) where capacitor failures are likely. Many people will just recap the entire board, but usually you don't need to change all the caps. Trouble is, sometimes failing capacitors are obvious (e.g. exploded or leaking), but sometimes they look perfectly normal.
You might want to invest in an ESR (equivalent series resistance) meter, with which you can check the health of electrolytic capacitors without removing them from the chassis. Failing caps usually develop high resistance (ESR) which the meter measures. If ESR is too high, replace.
ESR meters to look for include any made to the Bob Parker/Dick Smith/Silicon Chip design (e.g. for a classic look https://www.altronics.com.au/p/k2574-esr-meter-kit/, or the blue Anatek one which looks different but is the same design). There are others out there on the market too. Shouldn't cost you more than about US$110 or so, maybe cheaper.
I used to have about 8 of the original Dick Smith ESR meters (kit form) in my shed, but haven't been able to find them lately. Worried they might have been thrown out accidentally.
Your vertical deflection IC is IC401, 7 pins. Looks like a long rectangle with a corner sliced off. I see a couple of electrolytics there (470uF and 100uF).
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This is the cap I was talking about, C432 100uF 35V (+ to pin 3, - to pin 7). This cap is in that part of the vertical IC called flyback generator (or booster or pump-up). When the scanning period is completed and a frame has been drawn, the beam must be brought back ("fly back") from the bottom to the top where another scan period will start. During the scanning period the IC works with a 24V supply (on pin 6). In the flyback or retrace period it works with a higher voltage, not supplied externally like the other but generated by the IC itself. If the cap connected to the flyback circuit loses its capacitance, the beam doesn't make it to the top and so you have the foldover issue.
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Thank you both for the great information. I don't have a 100uf 35v cap in my stash. If only Radio Shack was still around. I'll have to wait for Amazon order to get here. Hopefully I can get this done without getting electrocuted.
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You can safely use a 100uF with a higher voltage rating (=>35v).
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You can safely use a 100uF with a higher voltage rating (=>35v).
I should have stated that all of the 100uf caps I have are bellow 35v (16v and 25v) :)
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So my google search for the schematics may have been way off. Here are some pictures of the actual chassis.
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The vertical IC is the 7-pin IC401 (screwed to the heat sink near the rear of the tuner), probably an LA78040 or TDA8170 (same package, same pinout). The cap in question is across pin 3 (-) and pin 6 (+). I can't follow the traces in your pic so I can't tell which one it is but you should be able to identify it with this info (capacitance will most likely be 100uF).
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The vertical IC is the 7-pin IC401 (screwed to the heat sink near the rear of the tuner), probably an LA78040 or TDA8170 (same package, same pinout). The cap in question is across pin 3 (-) and pin 6 (+). I can't follow the traces in your pic so I can't tell which one it is but you should be able to identify it with this info (capacitance will most likely be 100uF).
Thank you again. I found the IC. I will trace the pins to the cap.
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There seems to be some thermal stress going on (blackened/carbonisied area, see pic attached). Might be "normal", but might indicate something about to fail. Worth lookin', to see what's cookin'.
Maybe it is something to do with those three transistors?
What is that blue thing right in the middle of the circle? A tantalum capacitor!!?? They are known to fail dramatically (explode).
Not concerned about that nearby big resistor with a little carbonisation near the legs (just outside the yellow circle), as they are expected to radiate a lot of heat.
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There seems to be some thermal stress going on (blackened/carbonisied area, see pic attached). Might be "normal", but might indicate something about to fail. Worth lookin', to see what's cookin'.
Maybe it is something to do with those three transistors?
What is that blue thing right in the middle of the circle? A tantalum capacitor!!?? They are known to fail dramatically (explode).
Not concerned about that nearby big resistor with a little carbonisation near the legs (just outside the yellow circle), as they are expected to radiate a lot of heat.
I see what you mean. I'll see if I can read any markings on that component.
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The vertical IC is the 7-pin IC401 (screwed to the heat sink near the rear of the tuner), probably an LA78040 or TDA8170 (same package, same pinout). The cap in question is across pin 3 (-) and pin 6 (+). I can't follow the traces in your pic so I can't tell which one it is but you should be able to identify it with this info (capacitance will most likely be 100uF).
Thank you so very much. Cap replaced and CRT is fixed and looking great.
(https://forum.arcadecontrols.com/index.php?action=dlattach;topic=164992.0;attach=397749;image)
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There seems to be some thermal stress going on (blackened/carbonisied area, see pic attached). Might be "normal", but might indicate something about to fail. Worth lookin', to see what's cookin'.
Maybe it is something to do with those three transistors?
What is that blue thing right in the middle of the circle? A tantalum capacitor!!?? They are known to fail dramatically (explode).
Not concerned about that nearby big resistor with a little carbonisation near the legs (just outside the yellow circle), as they are expected to radiate a lot of heat.
I took a closer look. The three transistors are labeled:
K-622
C3202
Y
Do you think I should replace those? The blue component with the red dot is unmarked and labeled L001 on the board.
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I'm having trouble aligning all the parts I see on the photos with your schematic. For example, I can't see where those transistors are. Maybe I'm tired, or going blind, or maybe it is not exactly the right one for your TV.
In any case, the prefix "L" indicates that it is an inductor. Blue suggests "high-voltage"? To identify, there should be a three-color coding, 2 dots on top and a stripe.
For example, as described here: https://coil32.net/design/color-marking.html
These inductors would be of simple coiled wire construction inside. It is uncommon for inductors like this to fail, but when they do they can create a lot of heat.
You can test inductor vs capacitor, without removing from PCB, by using multimeter in ohms mode. Inductor should show low resistance, a few ohms, capacitor should show high/infinite resistance (OL). I also use a "Multi-function Tester T7", which can be purchased cheaply from your favourite online retailers. You'll need to remove it from the PCB for this. Here is a video:
here (https://www.youtube.com/watch?v=ltPXyOzabZQ)
Having a second look at your photos, I also see the blackening/carbonisation occuring on the underside of the PCB at the same spot.
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I'm having trouble aligning all the parts I see on the photos with your schematic. For example, I can't see where those transistors are. Maybe I'm tired, or going blind, or maybe it is not exactly the right one for your TV.
In any case, the prefix "L" indicates that it is an inductor. Blue suggests "high-voltage"? To identify, there should be a three-color coding, 2 dots on top and a stripe.
For example, as described here: https://coil32.net/design/color-marking.html
These inductors would be of simple coiled wire construction inside. It is uncommon for inductors like this to fail, but when they do they can create a lot of heat.
You can test inductor vs capacitor, without removing from PCB, by using multimeter in ohms mode. Inductor should show low resistance, a few ohms, capacitor should show high/infinite resistance (OL). I also use a "Multi-function Tester T7", which can be purchased cheaply from your favourite online retailers. You'll need to remove it from the PCB for this. Here is a video:
here (https://www.youtube.com/watch?v=ltPXyOzabZQ)
Having a second look at your photos, I also see the blackening/carbonisation occuring on the underside of the PCB at the same spot.
I don't think the schematic is correct for the chassis. Here's a closer look at the area in question
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I don't think the schematic is correct for the chassis. Here's a closer look at the area in question
Reckon so too, and thanks for the new pic.
Don't want you to break anything, but maybe you could pull it off to get a closer look? There could be markings on side/below we cannot see from above. You could also possibly measure it using one of those meters.
You can confirm if it is an inductor by just using your DMM in ohms mode, as described above.
If it is an inductor, the red dot suggests "2" but without more markers or clues we wouldn't know if it is 22mH or 2200mH, for example.
OTOH, on your latest photo I see there is a dot on the PCB that aligns with the red dot, so possibly just a polarity marker?
You might want to check how hot it gets when TV is powered on. In the ideal world you'd have a thermal camera or a thermal probe for a multimeter, but realistically you probably don't. Failing that, and if you are feeling brave, maybe you could carefully hold a finger nearby.
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I don't think the schematic is correct for the chassis. Here's a closer look at the area in question
Reckon so too, and thanks for the new pic.
Don't want you to break anything, but maybe you could pull it off to get a closer look? There could be markings on side/below we cannot see from above. You could also possibly measure it using one of those meters.
You can confirm if it is an inductor by just using your DMM in ohms mode, as described above.
If it is an inductor, the red dot suggests "2" but without more markers or clues we wouldn't know if it is 22mH or 2200mH, for example.
OTOH, on your latest photo I see there is a dot on the PCB that aligns with the red dot, so possibly just a polarity marker?
You might want to check how hot it gets when TV is powered on. In the ideal world you'd have a thermal camera or a thermal probe for a multimeter, but realistically you probably don't. Failing that, and if you are feeling brave, maybe you could carefully hold a finger nearby.
I do actually have a thermal probe for my multimeter. I'll dig into this issue again sometime this week.
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I am getting an open circuit when measuring across the blue component.
My temperature probe is unfortunately not working. The readout stays on 80*F no matter where I place the probe. I will need to get a replacement.
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Check the underside closely for any cracks, cold solder joins or copper rot in the traces. Eroded traces or poor connections means resistance, creates heat and components can eventually fail.
Maybe clean the underside with isopropyl or methyl alcohol so you can get a better look.