Substitutions

[CudaDave70]

Hello: Just really needing a little input Guys possibly Gals ,I believe I saw it in a post somewhere,not able to remember ,about uaing a higher voltage cap in place of a lower one I can't seem to find them anywhere.Is this OK as long as the difference is not so great. Can I do this?
Dave

[Harvey]

Re: Substitutions

Yes. There's no problem using higher voltage rated capacitors provided they will fit.

It used to be generally recommended not to go too high with electrolytic though as they [used to] need about 5%-10% of their working maximum voltage through them to keep them working. I've not seen any up to date data sheets specify that though so maybe its no longer an issue.

[CudaDave70]

Re: Substitutions

Thanks Harvey,your input is greatly appreciated.
Say I was to sub a 35 volt in place of 25 ,this is not a big deal ? But is it not advisable to go lower than what was being replaced ,say like using a 16volt in the place of a 25 volt?I don't mean to keep asking but this is for a video board for a HDTV flat panel and I don't want to let the smoke out of it ,I hear they stop working when the smoke escapes.They must need that inside to keep working.
Thanks
Dave

[severach]

Re: Substitutions

Going a little above like 25 to 35 is fine. Some claim that if you go way above the cap won't last as long as it should because the voltage is too low to keep it in good condition.

Going down is only ok if you know that the actual circuit voltage is lower. Power supply companies often use 10v caps on 5v circuits where 6.3v caps function just fine.

[Krankshaft]

Re: Substitutions

Going down is only ok if you know that the actual circuit voltage is lower. Power supply companies often use 10v caps on 5v circuits where 6.3v caps function just fine.

They use 10 volt caps just for a bit more elbow room and who knows maybe the caps will have a longer life because of it.

I don't believe in running caps that close to their "red line".

I usually like to stay at least 5 volts away from whatever the voltage on the cap is.

[severach]

Re: Substitutions

If you have a power supply outputting 6.4 volts on the 5 volt rail, the output caps would not be my first worry. Besides, during one of my GX270 recaps I put 10v caps onto the 12v circuit where 16v caps belonged. They were not damaged when I pulled them after a month of service. I think there's some leeway above the printed voltage though it is a good policy to not exceed it.

Other posts indicate that they use 10v caps because higher voltage caps have lower ESR.

[CudaDave70]

Re: Substitutions

Thanks guys for the input ,I think I made a good choice joining these forums. I think I am going to learn plenty from some real pros.I already feel my IQ going up a bunch,I don't take alot though when it isn't very high to start with ,though.
Not only do you get your questions answered, you learn why and some examples are given,where to get the stuff and how to hook it all up.
I did learn on my own that 125 degree caps are almost impossible to get.
Now I cannot locate a IC Chip that I suspect that may be bad . I purchased an unworking 15MF605T/17 Magnavox (Phillips) LCD TV that I am attempting to troubleshoot ,this one chip gets really hot , immediately after turning on the power switch (I could smell something cooking) and I burnt my test probe (right index finger) when I checked around the board. Is it a possibility the chip is getting too much voltage?
I don't have a schematic or enough brain power to know what it does for a living. I do know this though, parts for this thing are harder than woodpecker lips to locateAnd I know these chips get pretty hot ,but if I left it on more than 20 seconds it would make the wierdest cigar lighter anybody would ever have in their posession. The name and number on this chip is Novatek NT68F632ALG .I wanted to just go ahead and replace the whole board but after looking everywhere 0 0 0 0 0 0 nada.
Any help would be greatly appreciated,or it is going to end up stored the black plastic parts bin in the garage with the coffee grounds and egg shells.I need to add that:No evidence of bad caps, nothing seems shorted out ,fuses not blown ,I will attempt to send a picture of the board .
Thanks
Dave

[Krankshaft]

Re: Substitutions

I think there's some leeway above the printed voltage though it is a good policy to not exceed it.

Agreed if you install an air hose with a max rated pressure of 200 psi and pass 210 psi through it.

It will not magically explode the instant you exceed its maximum pressure however as you said its not a good idea to exceed the rating.

Other posts indicate that they use 10v caps because higher voltage caps have lower ESR.

Yeah I noticed that when I was checking some lower WV caps out of the bag with my ESR meter the little lower voltage caps had higher ESR. I forgot about it until you refreshed my memory .

[Krankshaft]

Re: Substitutions

I will attempt to send a picture of the board.

A picture would be nice. I did some searching a datasheet for that IC would be difficult with a pic we may be able to tell you what the IC is for.

This is why I hate Phillips, RCA, and a few other select brands the lack of servicing information and parts for some models is frightening.

I guess its the price that we pay for living in a throwaway society.

Go ahead keep throwing away I'll be at the curb with my van .

[arneson]

Re: Substitutions

I understand your trying to save the set.
They are on ebay, here is one going for almost nothing.
http://cgi.ebay.com/Magnavox-15in-LC...QQcmdZViewItem

[CudaDave70]

Re: Substitutions

Yea I have been bitten on Ebay a few times already, that is where I got this little jewel,you know it has evidence of somebody's uncle that can fix stuff gets his chubby little fingers in it ,they always have big ole pry marks on the case where he jammed a screw driver in it ,so that way you know you are hosed before you even open it up. I am sure the one Jim showed me will go fairly high by the time the auction is over, being it is a working version ,especially if I try to bid on it . About the picture of the board with the IC Chip- heating element,I tried to up load a few being I have a dial up connection that is incredibly slow. They booted me out of trying to edit my post and I had to write an Email explaining why I am too dumb to post a photo,quickly enough. I don't know what goes on next,maybe they will send me more Magnavox LCD to try and fix for punishment.I am going to try again so please bear with me. Thanks Krank and Arn for your intrest and input. Maybe some day I will be able to help someone out,it could be awhile though.
THANX
Dave Notice this transistor underside that lookks kinda like someone used a Bernzomatic on ,I am suspicious of this.

[Paul S]

Re: Substitutions

It looks to be this:
Novatek NT68F632ALG [PLCC44]

The PLCC44 must be the style of chip or mounting style:


I can't find any info on it. Even the Novatek web site doesn't list the products.
http://www.novatek.com.tw/index.asp

[arneson]

Re: Substitutions

Still at a buck fifty,
but if I find they do go high
I keep an eye out for one with broken screen.
Usually no one bids.

[CudaDave70]

Re: Substitutions

I guess I jumped the gun bidding on this Magnavox- Phillips without doing any research because at one time ,that name was a good reliable unit.I am learning but just like school,you got to pay for that education. Already found out what it feels like to get nailed with the 6-9 hundred volts from a backlight inverter. The info on the chip is appreciated Paul. Just at a w.a.g it looks similar too the chip on video boards. Like this one. I'll supply a pic.

[CudaDave70]

Re: Substitutions

I guess I am the only one with a Magnavox or Phillips piece of s--t on here,see I told you I was green,but that is my way,learn it the hard way. I spent alot oftime today searching. NFG.

[CudaDave70]

Re: Substitutions

I finally got another with a broken screen ,now I hope I can finish this one up ,it got lots of dust on it from setting and waiting for the right price.