Would undersized startup caps keep a unit from shutting off?

[johnboy1313]

I picked up a few older TVs today. One of them, a Magnavox/Phillips 32MF23ID/37, supposedly would eventually turn on if you played with it long enough. I suspected bulged caps in the PSU. When I got it opened up, there were two 1600uf 35V caps that were badly bulged. I didn't have any of the same size so I put in two 1000uf 35V caps just to test. I plan on picking up the correct ones tomorrow. It will now turn on, but will not turn back off all the way. When I hold the power button in, the set turns off but restarts as soon as I let go off the button. Would undersized caps do this or am I probably looking at a faulty power button?

[tom66]

Re: Would undersized startup caps keep a unit from shutting off?

Philips would have chosen those caps for a reason -- no telling what significantly less capacitance would do.
P.S. 1500uF caps are not startup caps but output caps.

[johnboy1313]

Re: Would undersized startup caps keep a unit from shutting off?

Well, I won't power it up anymore until I get the correct caps in. Thanks for the heads up. Just to answer the original question, it was a sticky power button.

[johnboy1313]

Re: Would undersized startup caps keep a unit from shutting off?

I can't find 1600uf 35V caps local but I can find 1500uf 35V caps. Do you think that would be a problem?

[johnboy1313]

Re: Would undersized startup caps keep a unit from shutting off?

Now that I mention it, I've been reading posts regarding this PSU this morning. I've seen one post that said that the poster's PSU had 1200uf caps there. I've seen one post that said 1500uf. I've even got the schematic and it shows 1mf (1000uf). It's looking like they may have just thrown in whatever was available. Is there a way to confirm that the 1000uf 35V caps I have in there now are OK to run?

[tom66]

Re: Would undersized startup caps keep a unit from shutting off?

There is no such thing as a 1600uF capacitor unless you custom order it, which is unusual.
You need to look at the caps you removed, you did keep them right?

[johnboy1313]

Re: Would undersized startup caps keep a unit from shutting off?

Yeah, I've got them on my bench. I'll look again.

I could be reading this wrong but it looks like Digi-key stocks them.
http://www.digikey.com/product-detai...FcdxQgodpWAAwg

[tom66]

Re: Would undersized startup caps keep a unit from shutting off?

They are not low ESR, just standard caps. Odd, never heard of 1600uF -- may be some common industrial application. 1500uF+1800uF would be close enough, as would 1000uF+2200uF.

[johnboy1313]

Re: Would undersized startup caps keep a unit from shutting off?

Now that I mention it, I've been reading posts regarding this PSU this morning. I've seen one post that said that the poster's PSU had 1200uf caps there. I've seen one post that said 1500uf. I've even got the schematic and it shows 1mf (1000uf). It's looking like they may have just thrown in whatever was available. Is there a way to confirm that the 1000uf 35V caps I have in there now are OK to run?

I believe I do have a 2200uf cap in my spare parts bin. I also found two 1500uf locally. I'm going to double check the old caps first. It would be no surprise to me if I read the cases wrong. I don't hava a lot of experience but I have never seen caps with markings like this in any other TV I've opened. What do you make of my question regarding the schematic in post #5?

[tom66]

Re: Would undersized startup caps keep a unit from shutting off?

They would appear to be 1000uF caps, so replace them as such.

[johnboy1313]

Re: Would undersized startup caps keep a unit from shutting off?

Right on.

[johnboy1313]

Re: Would undersized startup caps keep a unit from shutting off?

Original caps were 1200uf, not 1600uf.

[tom66]

Re: Would undersized startup caps keep a unit from shutting off?

I'd advise 1200uF replacements then.

[johnboy1313]

Re: Would undersized startup caps keep a unit from shutting off?

Too late, TV is in Southern Wisconsin now.