Minilab 604 capacitors

[viorel]

Hi everybody.

I have a BWD Minilab 604 V2 and it has this power source (see attached diagram). Many of those caps are tantalum and while I agree there's precious little room on the PCB to work with, I think at these low values it would be easy to swap them for electrolytics. The reason I am considering this is that one of the caps in the picture is blown already (that is how I bought the instrument). I have not yet powered it up so don't know if this affects anything or how. I know that one is blown because it has exploded. Still hanging on to the PCB but it is in a sorry state.

The blown cap is BP9 in the diagram. BP10, C6,9, 69 and 70 are also Tantalum. You can find these at the right side halfway up the page.

Not sure why some caps are labelled "BP" - bypass maybe?

Can someone with a better understanding of electronics please advise if I can use electrolytics here?

[ledtester]

Well, the TI datasheet recommends a ceramic or tantalum capacitor for BP9 and BP10. See section 9.2.1 of:

https://www.ti.com/lit/ds/symlink/lm317.pdf

However, the suggested value of that capacitor is quite small -- 0.1u to 1.0u. Not sure why they are using 10u there.

This stackexchange question suggests that the recommendation of ceramic and tantalum caps at the input have to do with ESR concerns:

https://electronics.stackexchange.com/questions/64063/how-do-i-decide-what-capacitor-to-use-in-a-circuit

As for the output capacitors C69 and C70, I'm sure you could replace those with electrolytics.

[viorel]

Thank you very much.

Now I realise I should have checked the datasheet.

Seems you're right. And it seems my guess as to why they label some of these capacitors "BP" instead of just "C" was right too.

Not sure about why they use a higher capacitance than recommended, maybe shooting for a lower ESR? In which case why not use ceramics?

Anyway. Looking for some higher voltage Tantalums I see they get very expensive very quickly. Just trying to cover the possibility that this one blew up due to some higher than allowed transient voltage.