On Saturday, July 2, 2022 at 01:01:41 PM EDT, John Kolb <jlkolb@...> wrote:

In my younger days, I've turned on a long unused scope, and after a
couple of minutes, heard a loud bang as a cap exploded.

The electrolytic cap anode is a metal with a thin insulating oxide
layer.  After long idle periods, the oxide layer disappears. When
voltage is applied without the insulating oxide layer, large current
flows, causing heat, pressure, and eventually BANG.

I power up unknown equipment by turning power on for 10 sconds, then off
again, Wait awhile so that if heating occurred, the cap can cool off
again. Another power on, 15 seconds, this time; another cooldown. The
process continues with increasing on time periods until I run out of
patience. The applied voltage causes the oxide layer to form again

I don't know if this theory is correct or not, but I haven had any
explosions while using it.

John


On 7/2/2022 8:17 AM, David C. Partridge wrote:

Bring it up slowly on a Variac. This has the advantage of giving alum electrolytic capacitors time to reform before they get full voltage

Just don't do this if the 'scope has a switching Power Supply (like most 7000 series and later 'scopes).

Just plug in an turn on (after checking the voltage selector is set correctly).

Dim bulb approach is fine.
D.