Best caps to keep in stock?

[no1knows]

I fixed my first LCD monitor the other week. I used caps from Radio shack only because I wanted to prove to myself that I could even make the repair before ordering them online. Now I want to buy a good supply of the right caps so I can repair 10 or more screens.

The only rule I was following up until now was using caps of the same voltage or higher and the same uF rating or higher. But now, I started reading some posts about caps rated for "general use" and some that are better for a power supply... and so on. I'm pretty sure my radio shack caps are rated pretty low.

Anyways, on to my question:
I want to use Panasonic caps. It sounds like everyone likes the FC model. Could I just order a good selection of the better Panasonic FC caps and use them even where a FCs aren't called for?

For example, I would order FCs all 25v or 35v. then 10ea 47uF 220uF 470uF 1000uF and maybe some 1500uFs.

I know I could run into problems fitting them onto the board. I can live with that. I just don't want to risk giving someone a "fixed" monitor that blows up or burns their house down.

[c_hegge]

Re: Best caps to keep in stock?

What series to use depends on what your repairing. It's best to find a series with the same ESR as the ones your removing. So, if the ones your removing have the same ESR rating as Panasonic FC, then use FC to replace them. As a general rule, Panasonic FC/FM are good in PSU, CPU VRM in and as the small 1000uF caps scattered on motherboards. They are probably OK in monitors also (although I haven't personally repaired a monitor yet). For VRM out, FJ series is a better option.

As for the voltage and capacitance, try to keep them both the same. Although a bit higher voltage is OK, it will mean that the cap is bigger and may not fit on the PCB (although you did say that you could live with that).

Finally the risk of burning someone's house down is minimal as long as you don't touch the 240v (or 110v if you're in America) side of a power supply. I've asked some electricians and they say replacing caps on the 12v side should be fine.

[Player2]

Re: Best caps to keep in stock?

Don't bother stocking 47 uF, caps that small rarely fail. You may need 220 and 330 uF occasionally, 470 and 1000 uF are very common.

[PlainBill]

Re: Best caps to keep in stock?

Don't bother stocking 47 uF, caps that small rarely fail. You may need 220 and 330 uF occasionally, 470 and 1000 uF are very common.

Unfortunately, that's not true. Most monitor power supplies use one or two of those in the Vcc supply for the SMPS controller. If it fails, you get a variety of symptoms ranging from a totally dead power supply to output voltages pulsing every few seconds. I've seen this problem twice in monitors. Since I've repaired about 20 monitors, that's a 10% failure rate. Of course, they don't show any signs of bulging, leakage, etc. At their low cost I keep a supply on hand and replace them as a matter of routine.

PlainBill

[no1knows]

Re: Best caps to keep in stock?

Thanks for the feedback. So would it be bad to use higher ESR caps? Also, everyone seems to have mixed reviews on using a higher uF and voltage. I'm still wondering if it would be that alright to use 35v caps everywhere and round the uF up to the next size. Like replacing a 330 uF 16v with a 470 uF 35v.

Thanks.

[PCBONEZ]

Re: Best caps to keep in stock?

So would it be bad to use higher ESR caps?

Yes.

Also, everyone seems to have mixed reviews on using a higher uF and voltage.

People used to go higher on uF thinking that was a benefit. - The real benefit was that higher uF caps [of the same or better grade] have lower ESR and higher Ripple ratings and THAT'S what improved things, not the uF.
-
If you go up in uF but change grades on the way to a cap that has a higher ESR or lower Ripple then you may adversely affect the the circuit.
-
The voltage rating on caps is a LIMIT -> on the CAP. Using a higher voltage is fine but as far as the circuit operation goes it won't improve anything.

Like replacing a 330 uF 16v with a 470 uF 35v.

In some circuits changing uF may affect the frequency responce of the circuit. In Noise/Ripple Filtering circuits that much uF change won't matter much.
- BUT:
If the 470uF/35v has higher ESR than the 330uF/16v you will leave more noise/ripple in the ciruit.
-
Worse yet, if the 470uF/35v has a lower Ripple rating than the 330uF/16v then the cap may overheat in the circuit. - That's the road to bloated caps.
.

Given that between LCD monitors and TV's I've only done maybe 18-20 [so I haven't seen everything] my take is:
- With screens probably 80-90% of the time Panasonic FC or Nichicon PW exceed [better than] the original specs for Ripple and ESR.
- For those times they didn't, Panasonic FM have exceed [better than] the original specs.

Panasonic FM are often cheaper than lesser grade caps so if you want a 'universal' cap for screens then FM is probably the one. - But - Once I a while FM are too big [diameter] or too tall so even those won't fit -everything-.

.

[PCBONEZ]

Re: Best caps to keep in stock?

Unfortunately, that's not true. Most monitor power supplies use one or two of those in the Vcc supply for the SMPS controller. If it fails, you get a variety of symptoms ranging from a totally dead power supply to output voltages pulsing every few seconds. I've seen this problem twice in monitors. Since I've repaired about 20 monitors, that's a 10% failure rate. Of course, they don't show any signs of bulging, leakage, etc. At their low cost I keep a supply on hand and replace them as a matter of routine.

PlainBill

Agree.
YES, you need the small caps too for screens.