Besides knowing how to read resistors at a glance, a good technician/engineer can do the same with capacitors. I'm betting not many here know that one.
In the 80's I managed a full line repair center for Tandy and a computer repair center as well.
I studied caps again yesterday, and I saw the color code, and I can't do it. I just don't have a need. I know the resistor color code and I find that most times, I can't really distinguish the colors that well when I see them.
I needed a spark arresting capacitor to protect the contacts of the switching relay on a electromagnetic tooth clutch. The vendor's literature suggested a 4 uf cap, and said it MUST NOT BE ELECTROLYTIC.
I have no real idea why exactly. I know most electrolytics are polar, so I suppose the current draw of the inductance of the clutch coil could amount to a reversal.
Previously, since it was a magnetic clutch using DC power, I protected the contacts using free-wheeling diodes. But when I looked, they were all in two. I asked our top guy, and he said maintenance didn't understand their purpose and cut through them with dykes. That seemed odd to me, why not just remove them? But when I inquired again yesterday, I was informed that the diodes "blew up." Hmmm.
One obvious draw back of a diode is that it will be a dead short (nearly) if maintenance reverses polarity accidentally, so I decided that I would like protection against that situation. But I was really rusty on capacitors, so I didn't know what to choose. So I wound up trying to do a quick study on capacitors yesterday and choosing a polypropylene type. I promised maintenance that if it blew up or something, I'd pick something else next time.
The Germans offered a capacitor in the accessories portion of their catalog, but for some odd reason, they were $250 a piece. This was for a 4uF 50V cap. I have no real idea what made that price justified, but that would have put us over our $5000 local P.O. limit, so we would have needed additional approval to add their cap to the clutch order.
