Stone
10k Member
Once it's been correctly discharged there's nothing left to ZAP you. Or, you could just leave the ground strap connected to the anode.
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IBM CGA 5153 - red tint on right side of screen
- Thread starter offensive_Jerk
- Start date
offensive_Jerk
Veteran Member
Do it. Be careful. It's no big deal.
Just don't get nervous. You'll think you got shocked and jerk your arm back and get shocked, then jerk again and break the neck.
I'd say you could bring it here but I can't even make time to work on my own projects.
Just don't get nervous. You'll think you got shocked and jerk your arm back and get shocked, then jerk again and break the neck.
I'd say you could bring it here but I can't even make time to work on my own projects.
Hugo Holden
Veteran Member
I would be cautious, initially at least, when it came to making any physical adjustments to the purity rings or yoke position. These items would already have had the correct relationship with the electron gun structures and beam positions in the tube and set at the factory. This does not change unless the monitor has been dropped (decelerated) and even then the crt has to be on the verge of breaking for the gun electrode structures to change position. What can & does change though is the magnetic field the beam experiences due to external magnetization or exposure to magnetic fields (typically near speaker magnets etc). The internal degaussing coil or an external coil of similar design does not have enough intensity to correct this. So before any adjustment is touched, like the purity rings or yoke, it must be fully degaussed with a proper wand first. If that is not done you will end up chasing your tail with the purity ring and yoke adjustments and never quite be able to average out the errors because of the residual magnetism in the shadow mask and structures around the crt that has not been eliminated.
I can also see why there was the suggestion that it could have been an electronic fault, in that the apparent purity error (from looking at the photos) is slightly atypical for a purity error in that it looks like a fairly uniform tilting of the color balance on each horizontal scanning line toward the right hand side of the screen. Usual purity errors due to magnetization are a bit more blotchy and affect one corner more than the other. This could be checked by putting a scope (synchronized at H rate) on the CRT's cathodes R,G & B guns looking for any tilt in the voltage across a horizontal line. The only way the crt beam intensity can change is by the relative voltage of the crt's grid and cathodes. (the grid is common to all guns so a tilt voltage there would not change the apparent color).
If you do not have a scope, you could check this (with the set turned off) connect a 4.7uF say 300 V or more rated electrolytic capacitor from the crt cathode to ground (+ of the capacitor to the cathode), turn it back on and see any change. You'd have to do this for the red, green and blue gun cathodes as separate trials. If there was a voltage there on one of the CRT's cathodes changing over the H scan time interval, and causing a change in one of the gun intensities, this added capacitor would clamp it out. So if a capacitor changed it or cured it, it would indicate a fault in the gun drive circuits. Though overall it is more likely that it is a magnetization/purity type of error and not an electronic fault, so I still think the first move is to get a proper degaussing wand, something like this works well, and not expensive:
http://www.ebay.com/itm/DEGAUSS-DEG...hash=item257e85a293:m:m3Dx462BmWOiA4_LceIhFog
I can also see why there was the suggestion that it could have been an electronic fault, in that the apparent purity error (from looking at the photos) is slightly atypical for a purity error in that it looks like a fairly uniform tilting of the color balance on each horizontal scanning line toward the right hand side of the screen. Usual purity errors due to magnetization are a bit more blotchy and affect one corner more than the other. This could be checked by putting a scope (synchronized at H rate) on the CRT's cathodes R,G & B guns looking for any tilt in the voltage across a horizontal line. The only way the crt beam intensity can change is by the relative voltage of the crt's grid and cathodes. (the grid is common to all guns so a tilt voltage there would not change the apparent color).
If you do not have a scope, you could check this (with the set turned off) connect a 4.7uF say 300 V or more rated electrolytic capacitor from the crt cathode to ground (+ of the capacitor to the cathode), turn it back on and see any change. You'd have to do this for the red, green and blue gun cathodes as separate trials. If there was a voltage there on one of the CRT's cathodes changing over the H scan time interval, and causing a change in one of the gun intensities, this added capacitor would clamp it out. So if a capacitor changed it or cured it, it would indicate a fault in the gun drive circuits. Though overall it is more likely that it is a magnetization/purity type of error and not an electronic fault, so I still think the first move is to get a proper degaussing wand, something like this works well, and not expensive:
http://www.ebay.com/itm/DEGAUSS-DEG...hash=item257e85a293:m:m3Dx462BmWOiA4_LceIhFog
offensive_Jerk
Veteran Member
Perhaps it got banged around when it was shipped, I don't know. Maybe I'll try the wand first. Seems cheap enough. That little wand has more power than my ring?
Hugo Holden
Veteran Member
Because the coil is wound as a solenoid, the magnetic field intensity is very strong (concentrated) at each end, so when you put the wand tip close to the metalwork you will feel a vibrating force and hear a few buzzing sounds too. Also, as mentioned, only do this around the front and side areas of the crt within a few inches of the front (face) of it, keep the wand away from the tube neck and purity/convergence magnet assembly as you don't want to demagnetize that. Also keep the wand well away from things like hard drives and floppy diskettes. If you are wearing an electronic wrist watch on the wrist of the hand holding the wand, take it off first or it might end up showing the correct time only twice per day.
Hugo Holden
Veteran Member
I also agree with a remark in a related thread, I think the PTC resistors in these 5153 monitor have a limited life. I have two 5153's and neither of them behave as though there is any activity in their own internal degaussing coil. I will look into this and see if there is a suitable easy to get replacement part.
Common 2 terminal ones ones (available on ebay) appear to be the M272 series, for example the M272-9RM is a 9 Ohm version and the M272-18RM is the 18 Ohm version, these are the cold resistances. Looking inside a spare 5153 psu, the unit is labelled PTHBG 180M290, it tests 20 Ohms cold. Presumably it is an 18 Ohm unit.
Common 2 terminal ones ones (available on ebay) appear to be the M272 series, for example the M272-9RM is a 9 Ohm version and the M272-18RM is the 18 Ohm version, these are the cold resistances. Looking inside a spare 5153 psu, the unit is labelled PTHBG 180M290, it tests 20 Ohms cold. Presumably it is an 18 Ohm unit.
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I also went chasing a degaussing issue on my 5153, but it turned out that the PTC and coil was working fine. These monitors degauss immediately upon powerup and don't make the typical degauss noise. Because they degauss on powerup, the cathode hasn't heated enough to produce a picture so you won't see a wobble either.
OP - I had pretty much the exact same symptoms as you and to fix it I replaced C567 & C569, C507 & C509, C537 & C539. That's 3x 2.2uF @ 250V and 3x 4.7uF @ 250V.
I saw you got the 4.7uFs in your list but not the 2.2uFs - which are the ones in series with the colour signal path.
OP - I had pretty much the exact same symptoms as you and to fix it I replaced C567 & C569, C507 & C509, C537 & C539. That's 3x 2.2uF @ 250V and 3x 4.7uF @ 250V.
I saw you got the 4.7uFs in your list but not the 2.2uFs - which are the ones in series with the colour signal path.
offensive_Jerk
Veteran Member
I got the other type of degausser delivered finally. It did not appear to make any difference in the discoloration.
Perhaps I'll try the above post.
Perhaps I'll try the above post.
Yes try the 3 caps C507, C537, C567 since you do have streaking in the video. Then if you still have the shading, there is the possibility of loosening the yoke clamp and nudging the yoke straight ahead or back just a slight distance to fix the discoloration w/o having to do a bunch of adjustments, maybe only 1/8 to 1/4". Don't tilt the yoke or move the rings. Do this as a last resort if caps don't help. I forget if I asked this but the rings on the back of the yoke are usually painted with locktite. Take note if that glue looks broken because that means it has already been adjusted since factory.
Larry G
Larry G
offensive_Jerk
Veteran Member
I broke the glue when I tried adjusting it in a previous post.
Sometimes you can tell where it was when it was glued by the way the glue broke.
Hugo Holden
Veteran Member
Another way to confirm it is an electronic problem causing the the color defect is to simply short together the 3 picture tube cathode connections. Then they all acquire the same potential. This is ok to do even if there is some imbalance at the amplifier outputs as there are current limiting resistors in series. This way the beam intensity for each of the CRT's guns will be the same (even if there is a tilt voltage across the horizontal scan time from one of the R, G or B amplifiers). If you still see the color anomaly on the screen with the three cathodes connected together, then it means the fault is essentially magnetic, and there is a shadow mask magnetism or physical distortion or magnetic misalignment issue with the crt. If the color becomes uniform, then you know there is an electronic fault (possibly the caps) in the R,G or B amplifier channels.
Hugo - have you done this in practice? In all my years of CRT service I never heard that one. I would imagine the brightness would increase because it changes the cathode impedance plus the shade would not be gray but probably green because it has the most luminance. As you say, the cathode resistors would limit the current. I would imagine the shade of color, whatever it ends up being, should be the same from left to right since there is no dynamic color correction. The brightness across the screen could vary but not the color. Sounds practical in theory but I hesitate to condone it, however I don't think it would harm anything to try. If it shows a color aberration please take pictures.
Larry G
Larry G
My words precisely, except that I'm not sure the brightness would increase. If it works, I say it's genius, mostly because I never heard of it.
What I have done is swap cathode connections. Normally only to verify that a cathode has gone soft without having to measure anything. But I suppose it would work for this too.
What I have done is swap cathode connections. Normally only to verify that a cathode has gone soft without having to measure anything. But I suppose it would work for this too.
Hugo Holden
Veteran Member
Well, normally at least the cathode voltages are nearly equal, and the impedance of the circuit that sets the resting cathode voltages (from the 3 setup potentiometers is is fairly high) and the output from the R,G and B amps is AC coupled, so linking the cathodes is of no threat to the circuit components or crt. So if there is a signal coming out of one or two channels of the R,G,B amplifiers that is causing the "color tilt" it would be eliminated on the image, even if there was a small change in brightness of the overall crt raster.
I have never had the need to do this myself, because I would simply put the scope on the output of the amplifiers or on the CRT's cathodes (sync's at H rate) to look for a tilt voltage. I thought this idea up as a way to help diagnose it without the luxury of a scope or familiarity with a scope. Yes and swapping cathode connections would also work as the colors would change if it was due to a changing voltage over the H scan time coming from one or two of the R,G,B amp outputs.This could be done swapping the wires leading from the R,G,B amps on the main board to the pcb on the crt socket assembly.
.....if its not a problem in the amplifiers, and it did not alter or improve after using a de-gaussing wand on it, I would wonder if there is physical damage to the shadow mask in the crt....
I have never had the need to do this myself, because I would simply put the scope on the output of the amplifiers or on the CRT's cathodes (sync's at H rate) to look for a tilt voltage. I thought this idea up as a way to help diagnose it without the luxury of a scope or familiarity with a scope. Yes and swapping cathode connections would also work as the colors would change if it was due to a changing voltage over the H scan time coming from one or two of the R,G,B amp outputs.This could be done swapping the wires leading from the R,G,B amps on the main board to the pcb on the crt socket assembly.
.....if its not a problem in the amplifiers, and it did not alter or improve after using a de-gaussing wand on it, I would wonder if there is physical damage to the shadow mask in the crt....
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I don't know what you guys' experiences are, but I've run into damaged shadow masks quite a few times.
I know of at least one case where one was obviously physically warped by a very strong magnet during a degaussing attempt. Don't ever turn on a degausser for the first time in front of a CRT; try it out on something else first. Shamefully I have to admit I did it. Luckily it was my own prized, freshly rebuilt Curtis Mathes, and not a customer's.
The reason I would swap cathode leads was because I could quickly determine if I was dealing with a tube that needed to be rebuilt, or a weak amplifier, before I dragged in my scope and set it up on site. On older TVs, I found it common to have one or even three individual plugs on the chassis or mainboard that I could pop the pins out of and isolate and/or rearrange. Sometimes the plug can be intentionally mis-mated to rearrange the cathode connections. Later TVs were less likely to have plugs, but rather were typically soldered.
I know of at least one case where one was obviously physically warped by a very strong magnet during a degaussing attempt. Don't ever turn on a degausser for the first time in front of a CRT; try it out on something else first. Shamefully I have to admit I did it. Luckily it was my own prized, freshly rebuilt Curtis Mathes, and not a customer's.
The reason I would swap cathode leads was because I could quickly determine if I was dealing with a tube that needed to be rebuilt, or a weak amplifier, before I dragged in my scope and set it up on site. On older TVs, I found it common to have one or even three individual plugs on the chassis or mainboard that I could pop the pins out of and isolate and/or rearrange. Sometimes the plug can be intentionally mis-mated to rearrange the cathode connections. Later TVs were less likely to have plugs, but rather were typically soldered.
Yes, I saw several CRT's that I concluded were damaged shadow masks because I couldn't achieve purity but no 100% method to prove it. Actually some were new tubes we received in shipping as warranty replacements so pretty sure it was shipping damage mainly because the old tube was just weak and had no purity issues. Seems like the purity was always off in a corner and not a straight vertical bar, though. I do vaguely remember a color display for an IBM PC which likely was a 5153 with purity I couldn't correct and told the customer it needed the tube. Seems like he indicated it could have been jarred in a move. He didn't want to pay for a new tube, though so didn't actually repair it. It was discolored in an angle to a corner. I do remember in training being told the shadow mask was bonded to the glass in the corners so generally a corner would come loose and fold but that could have been just that manufacturer's method. I know in Sony training on the Trinitron, I saw a 2nd mask in the front with a mesh of vertical metal wires and one string that runs horizontally about a 3rd of the way up the tube to keep the wires from "singing" when the beam scanned across them. If you look closely at the lit tube, you can see the wires. They showed a photo of what it looks like if that mask came loose and it was like an LSD trip. It would be interesting for a test on a CRT display to tie the 3 guns together since all guns would be at the same potential and the same signal. Any shadow mask warp (or magnet) would throw the gun beam at another color phosphor and cause a change in color shading on the raster. If I get ambitious, I might try it on an old CRT display of mine and then put a magnet on the side and see what happens.
Since this thread seems to cover a similar problem, I have a 5153 that has been working great since I picked it up about 3 years ago. Recently it started developing a dark purple tint on the right side of the screen. I've taken some pictures of checkit to show the symptoms. I've never attempted CRT repairs before, but I'd love to learn how to fix things like this since I'm a big CRT fan and I have several that I'd like to be able to maintain in the future. I have a few questions. First off, check out the pictures below.
Going by previous discussions in this thread, I'm leaning toward it being a capacitor issue, but what do you guys think? It seems like the green is dark on the right side, which is causing anything other than pure red or blue to be tinted purple. What would be the first thing you'd check\replace to fix this? bjt earlier said "I had pretty much the exact same symptoms as you and to fix it I replaced C567 & C569, C507 & C509, C537 & C539. That's 3x 2.2uF @ 250V and 3x 4.7uF @ 250V." It seems quite common for the capacitors that are part of the the "green" circuit to go bad first, but I'd definitely replace all of them if I had to get in there. Also, since I'm going to be inside this thing anyway, are there any other components that commonly fail in the 5153?
Now, the big question for me: Without a fancy tool or any experience with CRTs, what is the most fool-proof way to be sure that the CRT has discharged before working on one of these? I watched this video and I'm a bit concerned about the fact that he mentioned getting shocked WHILE discharging other CRTs with a screwdriver grounded to the chassis. Along those same lines, any suggestions to make servicing a 5153 easier or simpler beyond what is shown in the video (he also complained that it was a pain to work on) would be much appreciated.
Thanks guys!
Going by previous discussions in this thread, I'm leaning toward it being a capacitor issue, but what do you guys think? It seems like the green is dark on the right side, which is causing anything other than pure red or blue to be tinted purple. What would be the first thing you'd check\replace to fix this? bjt earlier said "I had pretty much the exact same symptoms as you and to fix it I replaced C567 & C569, C507 & C509, C537 & C539. That's 3x 2.2uF @ 250V and 3x 4.7uF @ 250V." It seems quite common for the capacitors that are part of the the "green" circuit to go bad first, but I'd definitely replace all of them if I had to get in there. Also, since I'm going to be inside this thing anyway, are there any other components that commonly fail in the 5153?
Now, the big question for me: Without a fancy tool or any experience with CRTs, what is the most fool-proof way to be sure that the CRT has discharged before working on one of these? I watched this video and I'm a bit concerned about the fact that he mentioned getting shocked WHILE discharging other CRTs with a screwdriver grounded to the chassis. Along those same lines, any suggestions to make servicing a 5153 easier or simpler beyond what is shown in the video (he also complained that it was a pain to work on) would be much appreciated.
Thanks guys!
