I finally got a chance to take a look at this 2247a. At the test point you
mentioned (c2202, before the startup and pre-regulator, marked 14A on the
schematic), I¡¯m only getting 77VDC, but got about the same 77V when I
tested for AC. I measured 120-122VAC up to the diode ring. Does this
suggest that C2202 is bad? Or something else?
Thanks!
Nick
On Thu, Oct 25, 2018 at 12:55 PM nielsentelecom@... <
nielsentelecom@...> wrote:
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
