k4900, no horizontal deflection

sfluter

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I've read as many posts as were here on the subject, but any further help would be appreciated.

I just finished swapping a tube and was going to try to work out the convergence issues. However, when I turned it on there was immediately some smoke from the area around the yoke connector and width coil. I shut it down quickly and then went to get a better light so I could see where the smoke was coming from exactly. When I switched it back on no more smoke, but there is only a thin line of video running vertically (monitor is horizontal).

I have:

switched out the width coil
tested B+ (128.8)
visually inspected and reflowed solder around the yoke connectors and width coil
tested resistance across the yoke's, it is normal

Any help appreciated.
 
Update. I swapped the chassis out for a spare and voila, I have a picture, so the problem is in the chassis itself.

Checking around the horizontal section I found a resistor, R383 that was blown. I will replace it tomorrow if I can track a replacement down locally and post the results.
 
when you swapped the tube did you use the original 4900 yoke of the tv yoke??

if you used the tv yoke, ohm it, ohm the 4900 yoke, and post your readings.
 
No, I swapped the yoke from the monitor as well. I am hoping the blown resistor is a good starting point in getting this sorted out. I still can't find any broken traces or cold solder joints in the horizontal section.
 
Check around that section for a shorted diode or transistor. Usually you won't get a line if the HOT is the problem...
 
Will do. R376 is definitely gone, but I measured voltage at that point and got 128.8 VDC . It also appears that this is the last point on the board before the signal goes to the yoke. If I am reading the schematics correctly (that is a big assumption!) this is in the 130 VDC section of the board. I was thinking too much current was frying the resistor, but now I am thinking it was just heating up because it was open already. Is this the correct voltage at this point? I have a replacement, but will test other components in the section for shorts. Thanks for the input!
 
Well, a closer look at the section was probably in order before I posted here. C365 is missing. Not sure why, but it is. So I will replace it.

If it doesn't fix the problem I will get back to you, but thanks for the input to this point.
 
Well, C365 is the horizontal width cap - what determines the width of the picture. It's normally a 334 (.33uf 200v) polypropylene cap. Without it, the load would be unbalance, probably causing too much voltage to drop across that resistor...
 
I pulled a 334 off a spare board and voila, I have a working monitor.

Again, I should have checked the board over more closely before I posted. Its kind of hard to miss that big orange chicklet once you know where it is supposed to be. The only consolation was that it turned out to be a pretty easy fix.

One final question. This cap is rated to 200v. I am assuming it would be okay to use one rated to 400v. I am only asking because the latter seems to be easier to track down.
 
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