CRT vertical deflection -- bad solder joints?

If the solder joints look bad -- they probably are. It would be a good idea to clean them up, simply to reduce the chance of future problems.

Look for a non-polar capacitor in the vertical deflection area somewhere around 10 uF. Try replacing it.

tm

Bad cap.

Though, while you've got your head in there, you could reflow any joints that look disgusting (taking care, of course, not to

*add* to your problems!)

You should really remove & replace the solder, not just reflow it.

Electrolytic capacitors will often "warm up" and work well enough to satisfy the circuit until they fail completely. If you can map out the vertical signal and amp section(s) you might want to first hit some suspect solder joints. After that is still no deflection you'll need to scope out where your signal is lost.

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Live Fast Die Young, Leave A Pretty Corpse

Yes. The first place to look is the big fat pins that the deflection yoke connector plugs into. Unplug the yoke connector from the main board before reflowing the solder, it can get stuck permanently if you don't.

Usually, the hint of bad solder joints is in sensitivity to vibration (give it a whack, it works for a while). Overheated switch transistors and bad coupling capacitors can also kill vertical sweep, and if the screen only has half the vertical sweep range, it could be a push-pull amplifier is now only a push. Or only a pull.

A visual inspection is not enough here. resolder all the pins on the IC, change the associated caps, they're cheap enough and often there is no reliable way to test them.

Also check for an open circuit feed resistor in its b+ line (probably from the line output transformer). Using the tv with poor regulation of the supply to the frame chip probably ended up damaging it, so you might have to change that too. they're not usually dear though.

-B

Yup, my first suspect too. This cap is normally found attached to the vertical deflection transistor electrically closest to B+. They are not always non-polarized. On our Sanyo video game monitors they were regular

10ufd/250V. Find one that has a good ripple current rating if you want the replacement to last...

John :-#)#

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It turns out I live a few blocks from to you. If I brought in just the board, would you be able to take a look at it? You seem to be far better equipped to deal with this -- I don't even have an oscilloscope. I assume it would take less than an hour, since I already did the boring part of getting it out of the cabinet. How much would you charge for this? Reply by email if you wish.

Thanks,

In article , Sean Hamilton writes

Yes, but it's more likely to be a bad cap.

Yes.

Visual inspection is not enough. You need an ESR meter.

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Mike Tomlinson

Maybe not; the ESR issues crop up mainly in high-performance low voltage power supplies (like computers); the vertical sweep circuit doesn't need a low-ESR capacitor. It will take (and work well with) just about any capacitor with adequate voltage rating and capacity.

The capacitor is inexpensive; just replace it with a new one, don't bother with testing the old unit.

I think you are missing the point of what he was saying regarding ESR. This parameter is a valid test of the 'goodness' of any electrolytic capacitor, regardless of its ESR pedigree. Even 'normal' electrolytics have a relatively low ESR when they are properly functional. As they fail, that figure will increase, and that is readily spotted with an ESR meter. As to the OP's actual problem, whilst bad joints in vertical output stages in CRT televisions were common, this more often lead to initially intermittent, and finally permanent frame collapse, than geometry problems like foldover, which the OP said was the problem he had. My money would be 100% on it being a bad cap, or possibly the feed resistor to the output IC having gone high. This was also a relatively common problem on many chassis, and could cause a severe foldover, usually at the bottom of the screen where the deflection drive current needed to be at its highest.

Arfa

In article , whit3rd writes

*whoosh*

And how is he supposed to locate the offending capacitor without some form of test equipment?

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Mike Tomlinson

In article , Arfa Daily writes

I think so too :o)

+1

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Mike Tomlinson

Just look for the 100uF at 35v cap next to the output IC. :-)

Mark Z.

Hello? Instead of fussing over it, why not replace all the electrolytics "in the vicinity" while the bad-looking solder joints are being re-done?

This is a common problem in servicing. As an EE, I want to know exactly why something isn't working correctly. But I learned a long time ago that it's more important to simply get the damned thing fixed. If that means shotgunning likely components, so be it.

In article , William Sommerwerck writes

If you're fixing stuff regularly, particularly many of the same item, it's worth diagnosing the problem so that in future you can say, "oh, that model, that fault, it's C35", and replace that - saving time and the cost of replacing components unnecessarily.

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Mike Tomlinson

A test, yes; but not a complete test. The ESR of a 10uF capacitor can be good, but it won't do the work of a 100 uF capacitor. A combination of ESR and capacitor-meter testing is better, and a test at the frequency of interest for ripple reduction is better still.

I wouldn't bother with any of that parameter testing, though. If you suspect the 10-year-old capacitor, replace it. You'd possibly have to desolder to test it anyhow, spend the eighty-five cents to put in a new one.

Shotgunning is, IMHO, very bad practice, and often leads to the creation of more problems than it fixes. I am actually quite surprised that you would advocate doing this, William.

Arfa