Wima 5/35 capacitor

[deliverance]

I am checking around the AF/IF board on a Redifon R550A and come across a Wima 5/35 capacitor leaking it is marked plus and minus what are the values?

Thanks, Chris.

[Maarten]

Most likely 5uF 35V. Where is it in the circuit?

[deliverance]

Hi Martin. I can't find a service manual for it so I am looking at a manual for an R551 which states C168. So it's a 5uf 35 volt electrolytic it's only small.

[Station X]

How about a picture of the cap?

[HamishBoxer]

4.7uF 35 V DC will replace , 105 C if possible.

[deliverance]

Also a 10uf leaking.

[Radio Wrangler]

Straight forward aluminium electrolytics. Go for one of the reputable Japanese makes. Panasonic, Nichicon, Nippon Chemi-con or Rubycon. Be wary of fakes trying to look like those names.

David

[deliverance]

Got it thanks for your help guys.

[deliverance]

Hi all, What type of capacitor is this.

[G6Tanuki]

Looks like a Tantalum to me.

They were used extensively in the 70s and 80s in places where you needed high capacitance and low ESR in a small space [e.g. for decoupling].

They have a high failure-rate when old, going POP! and emitting some impressive smoke/orange flames!

These days conventional low-ESR aluminium electrolytics are the recommended replacement.

[deliverance]

Yes this one has gone pop ! Its off the 1.4 mhz oscillator board the service manual only shows the top of the board not the bottom it has brown red brown stripes on it so I am stumped as to the value .

[Uncle Bulgaria]

I thought they were highly reliable, which was why NASA used them extensively in space, as they don't leak or degrade and have a lot in a small package. I thought they went POP when overloaded, which is apparently common, expense meant lots of equipment didn't have suitably derated specifications - a 10V capacitor decoupling a 9.5V rail, for example.

[G6Tanuki]

The supposedly-reliable ones were 'wet' Tantalum always encased in a metal tube. They have turned-out to have a less-than-spectacular extended-service life [1970s-1990s 'Clansman' military radios use loads of them - and they fail!]

As to the particular value of the failed one, I can't help alas: the ones I've come across either have the value printed on them, or they have two different colours to the resin encapsulation along with a spot at the junction of the 2 colours (shades of the old tip-body-spot resistor colour code?).

[MotorBikeLes]

G6T, sorry, Body-Tip-Spot, not tip-body-spot.
I think they were ALL like that when I first played about!
Les.

[Craig Sawyers]

Originally Posted by Uncle Bulgaria

I thought they were highly reliable, which was why NASA used them extensively in space, as they don't leak or degrade and have a lot in a small package. I thought they went POP when overloaded, which is apparently common, expense meant lots of equipment didn't have suitably derated specifications - a 10V capacitor decoupling a 9.5V rail, for example.

They never used solid tantalum bead capacitors. Hermetically sealed wet tantalums were used, and the ESA guidance is that the voltage rating has to be at least 1.5x the operating voltage in the circuit. And space grade ones are hundreds of quid each.

Going back to terrestrial matters, tantalum beads only go pop when used in power supply decoupling. The data sheet guidance was to use a 6V capacitor on a 5V line and a 16V one on a 15V line. And 6V/16V rated tants were the ones available for that reason. And I used them in my first job in the early 1980's in exactly that way.

The mechanism for failure seems to be their lack of ability to absorb ripple current. They last for maybe three or four decades and then pow. If connected to a supply with no crowbar, they can explode leaving just the leads sticking up, or ignite and burn clear through the board.

When used in signal circuits, in coupling or decoupling applications, tant beads seem to be entirely reliable.

Craig

[peter_scott]

Originally Posted by G6Tanuki

The supposedly-reliable ones were 'wet' Tantalum always encased in a metal tube.

The nice thing about wet tantalums was very low leakage current but the down side was that they would not tolerate even the slightest reverse polarity.

Peter

[deliverance]

So how do you determine the value they are more like golf balls than beads .

[vidjoman]

You’ll have to work out what it’s connected to and then find those parts on the circuit diagram.

[Julesomega]

The maximum value doesn't matter, just needs to be large enough to decouple or remove hum. This photo is 47µ 25V. Replace with a modern electrolytic, as suggested above

What guarantees an explosion was a high inrush current, as anyone connecting one straight across a supply line soon found out

[Julesomega]

Your Tant looks like 1µ, as in 1,000 nF
If anyone wants a few bags of NOS tantalums, just let me know...