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Hello all

I just picked up a 2246 scope that won't power up.
Although I'm a very experienced tech, thought I would ask for any common SMPS faults before digging in further.

The +44VDC on primary side is OK.
Nothing on secondary side, except for short "blip" of voltages on outputs as it attempts to start up, then
of course, drops to zero.

The unit is absolutely spotless inside, doesn't look like its ever been used. (Cabinet exterior is also excellent)

Thanks in advance,
Mike

UPDATE: Fixed. Shorted rectifier, -15V supply.

Feel like I got a real bargain. $99, included shipping.

That didn’t take you very long. You get an A+.

It is a well known issue in the 224x series scopes power supply that any original rectifier diodes marked ZM or ZS tend to get leaky or fail over time. There is a total of 17 diodes that should be replaced and MUR160 600V 1Amp 50nS diodes (Mouser PN 863-MUR160G) is a good choice, although any fast 1-amp rated diode will also do. Just don't try to use common 1N400x diodes.

Before you close up your scope, I suggest you check for any additional suspect diodes (probably they all will need to be replaced) and get it done now to be on the safe side, otherwise there is a good chance that over time you might have yet another shorted diode causing problems.

And while you have access to the big main board, check the voltage on the Lithium battery and see if it might need replacement. Anything under 3.0V is suspect and should be replaced. Fortunately in this scope series there is no calibration data at risk, the battery just holds any settings information so the scope can power up in the same configuration used before powering it down.