Re: 2247A PSU Troubleshooting

nielsentelecom@sbcglobal.net
 

Nick,

I have a 2246A that I had to overhaul, which most likely has the identical power supply for your 2247A. I would do a search for the 2246A power supply also here. So I will refer to the component number in your schematic if there is a difference. I wouldn't be concerned with the diodes and caps mentioned in Alex's post until you verify the following.

I also blew up U2201 when I accidentally shorted my scope probe shield against a heatsink while probing. That caused a no power on the main 44VDC bus measured at C2203. even if that is good, I would get a spare replacement. they are not expensive and still available as of a couple years ago.

Get the service manual, refer to page 97, or 3-59, the power supply block diagram, and verify the voltage indicated prior to the preregulator and startup circuit at c2202. that is the main DC bus that feeds the Switching power supply pre-regulator. If you are plugged into 120VAC, it should be at about 160-170VDC. then switch meter to AC, and see if there is any ripple there. That's 120 hz so any meter will work. If that is good then check the previous paragraph for the 44VDC check.

I also was able to test my power supply out of the cabinet. It was risky, but necessary. I used a 10KV AC rated linemans glove and placed the CRT lead inside of it. I also have the resistor values that were close loads for the power supply to operate at a typical load.

NielsenTelecom

Join TekScopes@groups.io to automatically receive all group messages.