TEK 221 O-Scope Power Supply Problems

I have an earlier Tek 213 scope that had a similar problem when I bought it: The problem was that some of the "D" size NiCd batteries were shorted. With the batteries shorted, dead, or missing, the AC power supply would not run. I suspect that the 221 might have a similar design and problem:

I got my manual from here

The miniscope series has weird power supply configurations. This one shuts down if the battery voltage is below 10.3V. Don't try to run it with the battery disconnected...it's a critical part of the regulator. It's 10 NiCd A-cells, but they're only 600 mAH. Should run fine on more modern AA NiCd's. Should also run on NiMH, but the charger will probably kill them with overcharge if you leave it connected to AC.

Be careful probing around in there. There are connections between the line side and the isolated side that you'd not expect without a schematic. And some things that you might think were ground referenced aren't.

Don't want to smoke your scope probe or yourself.

If I am not mistaken, those supplies work like some UPS supplies and if the battery is no good or missing, it won't start.

Normally there is some sort of slow charge and once the batteries get up to snuff, the inverter will start.

Not sure if using an external supply is going to allow you to test for this? Some charging circuits and supplies are smart and test the condition of the batteries. You may need to put a resistor in series to fake it if you attempt an external supply test in place of the batteries.

Jamie

I have a 212 on my bench and it definitely will not work without a good battery pack. I rebuilt the battery pack and still had a problem. Some diode in the power supply area had also failed but I can't remember which one. Chuck