Compaq Portable PSU Capacitors Replacement

[willmurray461]

I've been working on fixing my compaq portable's power supply and found that some of the tantalum capacitors were shorted, but don't have any tantalum capacitors on hand. I read in another thread that you can replace them with electrolytic caps with a 0.1uf ceramic cap in parallel (both of which I currently have), but wanted to make sure that this true. Otherwise, I'll just buy some tantalums off eBay.

 

[Chuck(G)]

It's odd, but not unheard of, to see 0.1 µF tantalum caps being used extensively. Are you certain about their value?

 

[willmurray461]

Did you mean 0.1uf tantalum or ceramic caps? I didn't see any 0.1uf tantalums in the PSU. And I'm pretty sure about the values of the capacitors that need replacing: 2.2uf 25v and 15uf 25v.

 

[Chuck(G)]

Your first post was a bit confusing, to wit:

I read in another thread that you can replace them with electrolytic caps with a 0.1uf ceramic cap in parallel (both of which I currently have), but wanted to make sure that this true.

In most cases, you can forget about the parallel 104 ceramic. In a power supply, it shouldn't matter; just go with quality electrolytics.

The exception is when a tant is used in a timing circuit. Tantalums generally exhibit much tighter tolerances and less drift with age. You'll mostly see them in the lower end of the capacitance range. Replace with MLCC or poly film caps. Electrolytics with 20% tolerances are typical and that value is not constant with age.

 

[mcs_5]

In a power supply, it shouldn't matter; just go with quality electrolytics

In some power supplies it most certainly matters. Many voltage regulators are designed to be stable within a range of ESR. Lower or higher will cause instability. Regulators designed for tantalums expect the low ESR. Replacing with ceramic caps sometimes works - unless the ceramic caps have too low ESR... Don't replace power supply capacitors with a different type without studying the circuit first. If there's a standard ESR electrolytic type there, don't replace it with a low ESR type - or the opposite.