> On Dec 4, 2021, at 3:57 PM, Rob Jarratt via cctalk <cctalk@classiccmp.org>
> wrote:
> What kind of load tester are you looking to buy? I have an 11/45 which I need
> to test the power supplies on too.
I picked up a Kunkin KP184 this last year, and it does nicely for testing those
brick regulators and the power control boards in isolation (a bit more
convenient than the old light bulb or power resistor approach.)
Some of the large electrolytics in those bricks will likely have dried out. I
disassemble and “reform" these with a bench supply and current limiting
resistor on any of these bricks I have not yet personally serviced (Yes, I know
the reforming thing is controversial for some. I think its safe to say it at
least doesn’t hurt anything :-)
Check the big bridge rectifiers carefully; I’ve seen a few of those cracked or
toasted.
It’s also been my experience that beyond the bricks that are dead or fail at
the start, some smaller fraction will also let go after the first few hours of
continuous operation. The don’t tend to fail with fireworks — you’ll generally
get a slowly increasing whiff of magic smoke so generally plenty of time to
shut things down.
The operation indicator bulbs on these seem almost always dead. You can sub
CM7381 for the +5V regulators, and OL-6003BP for the -15V.
Last, if you have H742 supplies on your 11/45, be sure to check the small
muffin fan above the power control board. It is quite common for parts of the
internal wiring harness to rub up against these and stall them out, eventually
leading to a fried controller board.
Good luck! Good winter time project :-)
—FritzM.
