Tantalum capacitor value & replacement for old Luggable Computer

[maxrecording]

Greetings all. Am finishing up a Compaq Portable 2 power supply. All tantalums & electrolytics have been replaced, save for 1 lot of smaller yellow tantalums.

They show "K5M" on one side and "224" on the other side. This leads me to believe they could be replaced with 22uF. However an older diagram done by a member of Vogons shows 68uF replacements, which is confusing.

Questions:

1. Which value could they safely be replaced with?

2. Is there a difference between the smaller yellow rectangular tantalums, and the larger orange "tag" or "teardrop" tantalums with regards to need of replacement?

3. There are many of these on the motherboard and the video card, which I'd like to replace.

How to determine the value & voltage if they simply have 3 numbers?

The ones that seem to explode in videos are labelled on mine as follows - K2R 104M and K2K 151, along with 106 15K and K1Z 473

Many thanks in advance

[Benta]

I suspect they might be ceramic, not tantalum, and in that case the correct value is 220 nF or 0.22 uF (same thing).
But without photos it's hard to say.

[TimFox]

If they are tantalum, there should be a polarity indication on them.
I have seen both tantalum and ceramic capacitors in rectangular yellow TH cases, but the tantalums are usually taller.
The ceramic capacitors in those cases are almost always square (e.g., CC05  https://datasheets.kyocera-avx.com/CCR05-09.pdf  )

[maxrecording]

Thank you all. Please find below, photos of the capacitors that I am trying to find the values for.









Anecdotally, on videos of these machines, it appears to be the taller, rounded ones that burst. Is it preferable to replace both Tantalum and ceramics?

[TimFox]

The ones with a "+" sign on them are tantalum, which can fail.
On all such capacitors, the numerical code is in pF:
224 = 22 x 10⁴ pF = 220 nF (ceramic)
151 = 15 x 10¹ pF = 150 pF (ceramic)
106 = 10 x 10⁶ pF = 10 uF (tantalum);  the "15" indicate 15 V rating.
Ceramic capacitors of this sort rarely fail, at least compared to polarized Ta and Al electrolytics.
When you said "rectangular", I thought you were being literal, as in the CCR05 ceramics I linked to above.

[Benta]

From your photos:
K5M 224: 22 plus four zeroes = 220000 pf = 220 nF ceramic
?5M 102: 10 plus two zeroes = 1000 pF = 1 nF ceramic
K2K 151: 15 plus one zero = 150 pF ceramic
K2R 104M: 10 plus four zeroes = 100000 pF = 100 nF ceramic. The "M" is open to discussion, I'd quess higher voltage due to its size.
K1Z 473: 47 plus three zeroes = 47000 pF = 47 nF ceramic
106 15K: 10 plus six zeroes = 10000000 pF = 10 uF tantalum, 15 V

[maxrecording]

Fantastic! It seems as if it would be prudent to simply replace the tantalums due to their propensity for failure, and retain the knowledge of the values of ceramics in case they require replacement in the future. When replacing ceramics with electrolytics, is there a specific voltage that works best?

With many thanks for your help - looking forward to getting this machine up & running.

[gnuarm]

Fantastic! It seems as if it would be prudent to simply replace the tantalums due to their propensity for failure, and retain the knowledge of the values of ceramics in case they require replacement in the future. When replacing ceramics with electrolytics, is there a specific voltage that works best?

With many thanks for your help - looking forward to getting this machine up & running.

I use tantalums in a product I've built for 15 years.  After shipping 10s of thousands of units, I've never had a unit returned for the tantalum cap failure. 

I did have trouble with them on initial power application.  We shipped a few thousand of them before I learned from the assembly house that when they had any problem with a unit working, the first thing they would do is replace this part (clearly reactionary, but they are techs, not engineers).  I investigated and found lots of manufacturer's info on the nature of the problem and how to mitigate it.

Seems that in the factory, the oxide coating (both an insulator and dielectric) will have tiny flaws which result in shorts.  In testing, the current is initially limited, which allows the shorts to be isolated and removed from the circuit.  However, the same thing happens when being soldered.  So on first power application, the current again needs to be limited, so the shorts can be isolated.   I added this step to the test procedure and we have not had an initial power application failure since. 

In researching this issue, I don't recall anyone talking about problems with reliability in use.  In fact, the manufacturers all reported the parts as being rather robust.  Did I miss some documentation?  Or am I remembering this wrong?

[helius]

You remember correctly: tantalum capacitors don't wear out.
However, they are often used on power rails where the primary smoothing on the PSU side is done by aluminum electrolytics. So the PSU caps do wear out, increasing power rail ripple, and now the tantalums get exposed to higher voltages than before. Since the dielectric is voltage sensitive, some of the tantalums go short or burn up as a result. But they were not the cause of failure.

[maxrecording]

Many thanks to all who contributed.

The machine is running perfectly now.