K4900 vertical collapse after tube swap

curtislv426

curtislv426

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Hi guys. I did a cap kit and replaced the filter cap on a k4900 that badly needed it awhile ago. The tube was badly burned and I wasn't real happy with the clarity so I did a tube swap today. I also transferred the yoke from the original tube to the new tube and now I have vertical collapse for some reason. I felt like everything went pretty well. Do you think that I should replace those 2 vertical transistors or do ya think most likely it's related to the tube swap since it was fine before the swap?

Thanks
Curt
 
Hi Curtis. I'm going through a vertical collapse issue on my k4900 also. Did you check the ohm readings on the yoke to make sure the coil wire wasn't damaged in the transfer?

yokeplug.jpg
 
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Jaydon said:
Hi Curtis. I'm going through a vertical collapse issue on my k4900 also. Did you check the ohm readings on the yoke to make sure the coil wire was damaged in the transfer?

View attachment 467667
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That would be mega awesome if that's the problem. I sure hope that's it. Thanks for your input. I'll check when I get home from work tonight about 11p.m.
 
mecha said:
why did you tube swap a 4900 this time?
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Because the original tube looked like trash and had some nasty screen burn. And the last time I did it because the image was muddy and awful and had a strange smokey object floating around the tube. And the time before that I had to do it because the inside of the neck arced for some reason and blew a hole in the neck. This is the first time I tube swapped a 4900 and I also transferred the yoke. Why? What's up?
 
Found hairline cracks going across several traces breaking continuity between a few leads. I added my jumper wires to achieve continuity. I checked the vertical transistors. Those were good. I haven't hooked it up yet but my optimism is high.
IMG_20200928_002424716~2.jpg
 
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you know there are better ways to fix those cracks then all the wire which your striped ends look like they are hanging over near other traces. if you clean off the solder mask on both sides of the crack and i flux/tin it, then remove all the solder and put a zero ohm jumper wire or a heavier capacitor lead and resolder it with the wire across the crack and this way its clean and less chance of any touching where it shouldn't touch.
 
security0001 said:
you know there are better ways to fix those cracks then all the wire which your striped ends look like they are hanging over near other traces. if you clean off the solder mask on both sides of the crack and i flux/tin it, then remove all the solder and put a zero ohm jumper wire or a heavier capacitor lead and resolder it with the wire across the crack and this way its clean and less chance of any touching where it shouldn't touch.
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Thanks peter. I always appreciate your tips. You've been very helpful to me.
 
Check the pads and traces around those 2 white ceramic caps in the back corner, especially the one vertically oriented. They get really hot and a connection issue there will cause vertical collapse.
 
Dang! I still got vertical collapse after the jumpers. The fly back makes a high pitch noise as well. Should I replace the fly back? Should I also replace the ic3 and those 2 vertical transistors? 302 and 303? They tested good in my tester though
Yep I also reflowed the 2 white ceramic resistors in the corner.
 

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You can reflow but still have a lifted pad or crack in the trace that causes a connection issue. I think it most likely a connection issue as opposed to a failed IC or component. Buzz out everything with the meter while flexing the board a little. Use a magnifying glass to check for cracks. Wiggle a component on the top side while watching the pads on the bottom. You shouldn't see any movement on the bottom pad, if you do it's likely a lifted pad.
 
TimePiloteer said:
You can reflow but still have a lifted pad or crack in the trace that causes a connection issue. I think it most likely a connection issue as opposed to a failed IC or component. Buzz out everything with the meter while flexing the board a little. Use a magnifying glass to check for cracks. Wiggle a component on the top side while watching the pads on the bottom. You shouldn't see any movement on the bottom pad, if you do it's likely a lifted pad.
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Pretty sure I know how I got those cracks. that tube that I put in the frame had a slightly different angle than the original one and I didn't realize that obviously at the time but so when I was tightening the new tube into the frame it was slowly putting a lot of force up against those shields that those vertical transistors secure to and as a result the board flexed and it cracked. Because when I worked on the board today and then tried to remount it into the frame, it was impossible because those shields were pressing up against the tube. Lesson learned LOL at least I know how it happened. Hopefully I can find all the spots where I'm not getting continuity
 
just sand all the traces open, lay down solder in the exposed traces, bridge using cap legs.

that corner of the board is delicate due to the amount of heat those ceramic resistors produce. apparently these boards are made of fiberglass I'm told, which is why they crack pretty easily. (you can identify this variety by being like a brown or orange color or it's relative shiny surface!) but the heat weakens the board in that corner until it eventually breaks off.

then you start breaking out the school of KenLayton and Bob Roberts to fix it. LOL I actually have one of those sitting in a box at my old job, I should reclaim it and try fixing it someday.
 
security0001 said:
you know there are better ways to fix those cracks then all the wire which your striped ends look like they are hanging over near other traces. if you clean off the solder mask on both sides of the crack and i flux/tin it, then remove all the solder and put a zero ohm jumper wire or a heavier capacitor lead and resolder it with the wire across the crack and this way its clean and less chance of any touching where it shouldn't touch.
Click to expand...

That's a great tip!
 
YeastLord said:
That's a great tip!
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security0001 said:
you know there are better ways to fix those cracks then all the wire which your striped ends look like they are hanging over near other traces. if you clean off the solder mask on both sides of the crack and i flux/tin it, then remove all the solder and put a zero ohm jumper wire or a heavier capacitor lead and resolder it with the wire across the crack and this way its clean and less chance of any touching where it shouldn't touch.
Click to expand...

What would be a good tool for removing just that mask layer and not damage the traces? I was just watching arcade Jason he was using a flathead screwdriver. Is that a bit crude for the job or does that sound about right?
 
curtislv426 said:
What would be a good tool for removing just that mask layer and not damage the traces? I was just watching arcade Jason he was using a flathead screwdriver. Is that a bit crude for the job or does that sound about right?
Click to expand...
I use a X-acto knife...

X-Acto X2000 No-Roll Rubber Barrel Knife with #11 Replaceable Blade and Safety Cap (X3724) - Xacto - Amazon.com

X-Acto X2000 No-Roll Rubber Barrel Knife with #11 Replaceable Blade and Safety Cap (X3724) - Xacto - Amazon.com
www.amazon.com
I just did this on "this" g07 ;)
20200930_200519.jpg
 
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