Newbie Question -why foil peels from PCB

[DTLMG]

I am new and very obsessed with recapping. I got started a month or so ago when a friend of mine that owned an electronics recycling center called me and told me that he had several Dell 745 and GX520 computers dropped off that I may be interested in. (I like to rebuild PC's)

I quickly learned that the Caps were bad and recapped my first MOBO. Well I should say that I practiced and practiced removing caps from some old PCB's and MOBO I got my hands on.

I did my first recap and WALA...it works... so since then I have done several including LCD monitors and even a couple HDTV.

I have a couple of questions...When recapping on two occassions the foil on the PCB has "peeled away" from the PCB. I realize that the board is shot at this point right? What causes this? Too much heat from the solder iron? Poor board? what?

the second and most confusing to me is how to identify the caps that are on a board and what to replace them with...For example.. Today I was working on a board from an LG LCD monitor-I identified several bad caps, but there were a couple of (examples), There were 2- 25V1000uF caps that were 10mm x20mm When I look at the Rubycon list how do i know if I want a ZLG, ZLJ, etc? Are the caps that are sold on this site for MOBO sufficient for LCD monitors and HDTV too?

How do I identify which manufacturer of cap I have if there are no company markings on it?

Thanks...I look forward to learning lots from this forum!

[severach]

Re: Newbie Question -why foil peels from PCB

The copper is glued to the board. The glue is made to be heat resistant but if you heat too much the glue lets go and the trace comes loose. The board may not be shot but lifting the trace makes the repair much more difficult. If you're already struggling at desoldering without using too much heat then making the job even more difficult might well make the board unrepairable.

As you get better you'll be able to desolder with much less heat and the trace lifting problem will largely disappear.

[Koda]

Re: Newbie Question -why foil peels from PCB

If a copper trace peels of the PCB most of the time it will still work if you manage to connect the legs of the component and the copper trace with a blob of solder. If a piece of the trace peels of and then breaks off you need to place a jumper wire somewhere on the trace and the component leg and make sure it stays in a stable position.

[Agent24]

Re: Newbie Question -why foil peels from PCB

Crappier boards probably fail sooner, but ultimately it's caused by too much heat.

The smaller the trace\pad you are working on, the easier it is to overheat.

If your soldering iron is not temperature controlled it will be easier to cause damage (but with practice it's OK)

[Bager2700]

Re: Newbie Question -why foil peels from PCB

the main cause circuits lift off the board is PRESSURE while soldering or De-soldering.

Try this take a old circuit board, and heat a trace with a pool/blob of solder, without touching the circuit trace it's self, you will find you can heat it let it cool, heat, let it cool as many time as you like. The trace will not lift unless you are using way to hot of a solder Iron..

Now try this heat the trace with the same pool/blob of solder and press down on the trace at the same time... presto, the trace will lift..... it's the pressure downward on the trace more than the heat.


So when solder, always try to float the tip of the iron in a pool of solder, the solder and the flux will do all the work.... pressure is NOT required...

[ben7]

Re: Newbie Question -why foil peels from PCB

Also, traces tend to lift up on old, or cheap boards too. From poor glue quality


-Ben

[PlainBill]

Re: Newbie Question -why foil peels from PCB

I am new and very obsessed with recapping. I got started a month or so ago when a friend of mine that owned an electronics recycling center called me and told me that he had several Dell 745 and GX520 computers dropped off that I may be interested in. (I like to rebuild PC's)

I quickly learned that the Caps were bad and recapped my first MOBO. Well I should say that I practiced and practiced removing caps from some old PCB's and MOBO I got my hands on.

I did my first recap and WALA...it works... so since then I have done several including LCD monitors and even a couple HDTV.

I have a couple of questions...
the second and most confusing to me is how to identify the caps that are on a board and what to replace them with...For example.. Today I was working on a board from an LG LCD monitor-I identified several bad caps, but there were a couple of (examples), There were 2- 25V1000uF caps that were 10mm x20mm When I look at the Rubycon list how do i know if I want a ZLG, ZLJ, etc? Are the caps that are sold on this site for MOBO sufficient for LCD monitors and HDTV too?

How do I identify which manufacturer of cap I have if there are no company markings on it?

Thanks...I look forward to learning lots from this forum!

First of all, it's voila!, not 'walla' Voila! is Italian for 'there!', and expression of triumph; Walla is half of the name of a town in Washington.

The answers to your second question can be found in the FAQ with a little digging. First you must identify the brand and series of the original cap. For example, CapXon labels their caps with their name. Others use symbols - United Chemicon uses a heavily stylized crown, Panasonic uses the letter M in a box. The series is represented by two or three letters. With these you can often identify the ESR specs of the cap.

As an example, I just pulled a Teapo cap out of the bag on my desk (don't ask). On one side it says Teapo 2200uF 16V On the other side, SC 105°C, 05/03, A3. The cap is 25mm high, 13mm in diameter. Googling Teapo SC, I find the first hit is a datasheet. Looking down the chart, I find that the original caps were rated for 2000 mA ripple current, .028 ohms ESR.

Going to my favorite supplier of caps (Digi-Key), I enter 2200uf 16V and hit search. A few clicks to select the proper component - capacitors, the proper capacitance, in stock, temperature range, etc I am left with a single page of candidates, with the unspecified parameters arranged in columns. Each column can be used to sort the candidates. Sorting by impedance I find that United Chemi-Con KY and Nichicon HE have slightly lower impedance and slightly higher ripple current. Both will fit in the same space. Panasonic FR is my preferred replacement, but has somewhat higher ripple current (higher is good), but significantly lower impedance. Lower is better, too low MIGHT cause problems.

Now, what do I do if I can't find a datasheet? For the power supply in a monitor or a TV, I will use Panasonic FR, FM, or FC (in that order), knowing that the precise parameters aren't super critical. For a motherboard, I'd be a little more critical. If I were rebuilding the control panel for a fusion reactor, I'd be super careful to match the design specs.

PlainBill

[severach]

Re: Newbie Question -why foil peels from PCB

http://wiki.answers.com/Q/What_does_voila_mean

Voilà is French. There's an Italian word voilà but it doesn't have typical meaning.

[thesloc]

Re: Newbie Question -why foil peels from PCB

Lifting pads? You need to use a good soldering flux everything you put your 300C+ soldering iron to your PCB.

[999999999]

Re: Newbie Question -why foil peels from PCB

If a pad lifts, what I do is super-glue it back down, solder the cap in, clean off any remaining flux residue, and put a blob of clear epoxy over the area.

If it instead tears off, get a suitably sized bare piece of solid core wire, put the cap on the board, make a loop in the end of the wire and compress it tight around the cap lead with pliers. Solder that point, then find the nearest area on the trace that has not lifted, cut off the loose area after that, scrape off the enamel on trace so solder will stick, and solder the other end of your jumper wire to that. If it is a very long term repair, consider tinning the entire wire and putting epoxy over at least both ends you soldered.

The typical monitor caps that fail are in the switching power supply section. Pick very low ESR japanese brand capacitors. They need not be exotic solid polymer type. Pick the tallest that will physically fit in the available space, same capacitance or as close as possible (some generics have unattainably high capacitance for their form factor when replacing with good quality caps), largest diameter and lead spacing that will fit in the available space without touching anything hot, and use a little higher voltage IF it will fit, or if you can't even achieve the same capacitance as the original, see whether the circuit is actually operating at a voltage that would require the rating the cap has.

For example sometimes a manufacturer will use a 10V rated cap in a 5V circuit to increase lifespan and lower ESR, instead of a 6.3V rated cap, but when you try to replace it you find you cannot fit a good 10V cap with the same capacitance in the same available space, it's too big, so knowing it was a 5V circuit allows you to use a 6.3V cap. The same sometimes applies for when they use 25V caps in circuits under 16V.

Generally speaking yes caps sufficient for motherboard switching supply circuits are suitable for monitor supply repair, except that often in monitors they use fairly short capacitors, height is the biggest problem as there is usually a metal shield that needs to go back on after the cap is replace. Sometimes I have even cut a hole in the shield to make a cap fit for a quick 'n dirty cheap fix and it worked fine, but it's better not to have to bother.