Thanks for the tips. The transformer that drives the bricks is a real beast. Did you find an alternative more convenient way to power them on the bench?
I don't see the Kunkin unit for sale except for a couple of items on ebay from China. I am really reluctant to buy anything at all from China. I couldn't find a manufacturer site for them, and I was wondering if there are alternatives since they don't seem to be particularly available. I did find this which is a bit more expensive (I know Rigol is Chinese, but it seems to be decent quality kit) https://www.rigol-uk.co.uk/product/rigol-dl3021-programmable-dc-electronic-load/ Thanks Rob > -----Original Message----- > From: cctalk <cctalk-boun...@classiccmp.org> On Behalf Of Fritz Mueller via > cctalk > Sent: 05 December 2021 01:03 > To: General Discussion: On-Topic and Off-Topic Posts > <cctalk@classiccmp.org> > Subject: Re: PDP-11/70 Boards > > > > > 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.
