Reusing caps

[PCBONEZ]

Re: Reusing caps

not a matter of your time or money. for most of us, we (more specifically customer) wants something NOW. Can't wait for online orders, and sometimes we try to stock new caps, but in the end, occasionally we run into a cap that we don't have new

I just recapped a lcd monitor that had the 'shut off in 2 seconds' issue (dell, of course). In addition a bad screen image (kind of a faded ghost image, an inch off to the right). I replaced 2 elite 16v 1000 with pannys off a asus board, and the 35v 470 elites with some 16v 270 polys from a asus pegatron board. Monitor works beautifully, no ghost image, and actually goes from black to bright probably faster then it would new (something that almost worries me).

one good thing though is I saw radioshack stocking some 25/35v 470 nichicons lately, more expensive then thier general circut caps but totally easy to come by.

and of course you do have somebody in a country that has NO way to get caps, though even paypal is blocked, theres other ways of paying for caps online with other dealers

What does that have to do with using a bad cap?
.

[Uranium-235]

Re: Reusing caps

well I just took the thing apart and yeah, the cap thats part of the vrm circut poly-exploded

kind of funny I was looking at the screen when it did and didn't see as much of a tiniest change, backlight and screen were both fine, no wierd line for the microsecond it popped, nothing, just working fine, no change in inverter output

I should of asked here, and i'm sure our resident genus and grumpy old fart bonez would of told me the poly halfing rule only applies to cpu vrms, not power supply ones unless the power supply was built for polys, which i'm sure no lcd vrm is

well this is odd, I can't find the memory stick for my camera to give you a pic but basically....

I started taking it apart and lowel and behold, hearing something loose inside. as I figured, it was the outside of the polymer cap itself

looking at the board, there is some mess around the blown polymer, which now looks like a black roll of burnt paper. I heard of polys blowing up like this. I think the other polymers I used were spared cause I bet they're part of the vrm for the video adapter, which is less stress, and closer to being a input/output type vrm you would see on a motherboard

soooo, polymers aren't to be used for the inverter VRMS on lips boards. I bet if I would of asked bonez he would of told me this. I think the monitor will be fine when I change that exploded poly out for a nichi 35v 470, and not a 16v 270 polymer

[Uranium-235]

Re: Reusing caps

What does that have to do with using a bad cap?
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it has to do with the original topic, reusing caps, which I partially jumped into your reply on the original subject

<-that isnt for you, thats for me as you're probalby saying that now considering my last post

[PCBONEZ]

Re: Reusing caps

My point in that post was to say what might happen if one of those used caps was bad.
- Examples of used caps that were good are not relevant to what I said.
.
Using old caps is risky. - Just is.

I buy the idea for temp use [trouble shooting] just to see if something is worth buying caps for but I would never put something in service with used caps.
[And I do keep some odd-ball sizes around for that.]

If you people that are giving your customers used caps aren't making it clear to them that you are using used parts then you are leaving yourself open to Law Suits.
All it would take is the guy at the next shop [after your fix fails and you lost the customer anyway] to read the date code on something you put in.
-
That doesn't even consider the GREATER possibility that the pissed off customer is going to spread around town what shoddy work you do for YEARS.
Pissed off customers have long memories and a habit of doing that....
You won't even know about most of the business you lost from ONE bad cap going out to a customer.
.

[Uranium-235]

Re: Reusing caps

okok. I did't think about that, cause in the end, I don't advertise myself as a guy who exclusively fixes caps, 99% of the time, my work is general/advanced repair/replace and only occasionally run across a cap fix, but when I do, I love it, except for last night and today

off the subject, what did you think about my prevous post bonez? are polys in a lcd power board ok with the 'half rule' for the video vrm, but (obviously) not for the inverter? or should I just go ahead and replace them all with lytics, which I might have to order to find, if radio shack dosen't have any 35v 470 nichis?

yeah its a partial thread hijack, so shoot me

[PCBONEZ]

Re: Reusing caps

off the subject, what did you think about my prevous post bonez? are polys in a lcd power board ok with the 'half rule' for the video vrm, but (obviously) not for the inverter? or should I just go ahead and replace them all with lytics, which I might have to order to find, if radio shack dosen't have any 35v 470 nichis?

yeah its a partial thread hijack, so shoot me.

~BANG~

I would not use the 'half rule' for that situation because it seems to me the uF used for 'bulk capacitance' there is already on the skimpy side.
[Bulk capacitance being the consideration for not for ripple but for slower voltage changes - as in the cap acting like a temp BU battery to smooth out line transients or load changes.]
IOW: If the voltage 'wants to' dip low and you don't have enough bulk uF [stored energy] to prevent it, then it -will- dip low.
If it dips low enough [or overshoots high enough] it can trip off the circuit.
.

[Uranium-235]

Re: Reusing caps

in this case, blow off the poly

smells like burnt popcorn, not sure why

[PCBONEZ]

Re: Reusing caps

Maybe voltage went higher than the cap's rated voltage.
.
[Shhhh,, (whispering),, Is not in backwards is it?]

[momaka]

Re: Reusing caps

Most caps cost well under $1.
Using one bad cap can easily cost an hour (or hours) of your time.
My time is worth more than $1/hr.
.

True.
My time isn't worth shit, though.

I replaced 2 elite 16v 1000 with pannys off a asus board, and the 35v 470 elites with some 16v 270 polys from a asus pegatron board.

Maybe voltage went higher than the cap's rated voltage.

I would say more than likely. Putting lower voltage caps than what was originally in the circuit is asking for trouble. Don't do it unless you've thoroughly checked all of the voltages.
I've done it many times, but I have always checked the voltage in the circuit, both with and without load and under other various stress conditions.
The "half-rule" for capacitance only applies to the CPU VRM in motherboards. For other VRMs, it depends (check the data sheet for the PWM/buck controller of that circuit).

[PCBONEZ]

Re: Reusing caps

I didn't catch that voltage change.

Last I checked a 1 cuft bag of shit was 97 cents.
.

[Uranium-235]

Re: Reusing caps

True.
My time isn't worth shit, though.



I would say more than likely. Putting lower voltage caps than what was originally in the circuit is asking for trouble. Don't do it unless you've thoroughly checked all of the voltages.
I've done it many times, but I have always checked the voltage in the circuit, both with and without load and under other various stress conditions.
The "half-rule" for capacitance only applies to the CPU VRM in motherboards. For other VRMs, it depends (check the data sheet for the PWM/buck controller of that circuit).

yeah i'm pretty sure this is what got me. the crappy inverter circuts I bet are immune from the half rule. the vrm for the video board I bet will be ok, it seem to be at least two-phase, with now two panny input caps. but I will go ahead and replace the 16v 270s with 16v 330's I found. I was only able to get two nichis from radio shack, and they're VX series, not as low ESR as HM, but gotta be better then the shit elites that were in there to begin with. only sucky thing is they're-not sure what the exact term is, but the leads are on each side, but no biggies cause you just bend one around

[PCBONEZ]

Re: Reusing caps

Axial lead.

The first problem is the 16v, not the uF.
The old caps were 35v.
.

[Uranium-235]

Re: Reusing caps

well just great then. I gotta wait for radioshack to get two more in. Even used I can't find any that high, unless I look in a PSU, and most of the caps they use in PSU's are so shitty anyways, it would be going from one crappy brand to another, and to a crappy used cap, which is out of the question. I could always try to get a new Lelon cap from radioshack, they had plenty of those (joking)

My dad used to be big into electronics, more back then, than now. I asked him last year about caps in parallel, and he consulted a basic electronics book and told me it would double the capacitance, and half the voltage

[PCBONEZ]

Re: Reusing caps

It won't half the voltage.
The voltage written on a cap is a limit for the cap, not an affect on the circuit.
.

[stevo1210]

Re: Reusing caps

What does that have to do with using a bad cap?
.

Oops, must have mis read it. My bad . I thought you were referring to me re-using those panny FJ's from the dead Asus board.

[larrymoencurly]

Re: Reusing caps

How good are Toshiba caps? I mean the ones that go back to the 1970s or 1980s, when the Toshiba logo had the long cursive "T".

About 3 years ago, I fixed the switching supplies in some of dot matrix impact printers with them.

[ratdude747]

Re: Reusing caps

the old style t in toshiba isn't that old... I have an ATA dvr-rw drive made by them with the old logo, and it is from, eh, 2003ish.

[PCBONEZ]

Re: Reusing caps

How good are Toshiba caps?

That's one I don't know.
I've seen rare few of those.
.