On 2023-05-11 18:01, n4buq wrote:
Hi Jerry,
In case you're not aware of it, the 2400-series power supplies have
line-filtering RIFA caps between line and ground as well as neutral to
ground.
*** Now aware. One exploded cap on the board. Luckily,
I have the big service manual that was in the bag on top of the scope. Do these caps need to be anything special other than
rated for 250V?
There's also a popped resistor next to the popped cap. Broken
in half - probably from the physical force of the cap exploding.
This resistor is in series with the little transformer that produces the "line sync" voltage.
But the popped cap doesn't explain the 60VAC on the chassis.
Especially since it persists with the power switch off. The power
switch disconnects BOTH legs of the AC input. Or it's supposed to :). With the power switch off, the only things left in the circuit
are the EMI module and the fuse holder.
My ohmmeter says that the EMI module is OK; but the ohmmeter doesn't output 125VAC. Actually, I have an old Heathkit capacitor checker that can output a lot of volts; maybe I'll drag that in from the shed.
When I turn on the scope, it gives a failed self test - something about inadequate positive voltage. But then you cancel the self test, and it works normally.
- Jerry, KF6VB
