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<title>fritzm.github.io - PDP-11/45: RK05</title>
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<h1>PDP-11/45: RK05</h1>
Sun 19 March 2017
by <a class="url fn" href="https://fritzm.github.io/author/fritz-mueller.html">Fritz Mueller</a>
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<div><p>Started going through the two RK05 drives. Lots of work to remove and clean up all the decaying foam.
Replaced the emergency head retract NiCd battery packs on both units. They were both slightly leaky, but
luckily neither had made a big mess.</p>
<p>Air filter elbows are intact on both units, and still slightly flexible, though they do have a white
powdery coating where the material is degenerating. Cleaned up okay with some warm soapy water and a
toothbrush. I'm sure these will continue to decompose/decay, however, and in the long term having loose
particulates develop inside the elbow seems a certain recipe for a head crash. I may explore the possibility
of 3D printing some sort of modern replacement for these.</p>
<p>Heads on the first unit look to be in decent shape, but some oxide buildup. In the second unit, the
carriage was not parked, so the heads were in contact with each other. They don't look damaged from a
preliminary inspection, but this head pair has considerably more oxide. Before and after cleaning shots of
the upper and lower heads on the first unit below.</p>
<p>Pulled the H743 power supplies and reformed the larger electrolytics. After this, both power supplies
powered up fine, though the -15V regulator on the first unit was trimmed very hot (-23 or so). Trimmed this
down, put the supply back in the first unit and powered up. Under load, the -15V regulator drooped to -8,
and a pico fuse on the +15V supply blew immediately.</p>
<p>Swapped in the -15V regulator from the second supply, which was not trimmed hot, and replaced the blown
pico fuse. Now under load the supply held without drooping, and the +15V pico did not reblow. So looks
like a bad -15V regulator. Put a few 723 regulator ICs on order in advance of debugging this.</p>
<p>After getting the power supply in the first unit up and going, blower powers on, power indicator lights, and
after about three seconds the door safety relay clunks and load indicator lights. Write protect indicator
toggles with panel switch presses per expectation. If the cartridge-on switch is depressed manually and the
load toggle is hit, the spindle motor spins up and runs smoothly.</p>
<p>There are some significant abrasions on the lower panel of the first unit under both the spindle and spindle
motor axles. It looks like a spacer button which is intended to hold off the lower panel has decayed; will
need to improvise some sort of replacement.</p>
<p><img src='/images/pdp11/rk05_thumbnail_tall.jpg' title='RK05 drive internals' onclick='pswipe("pdp11",47);'/>
<img src='/images/pdp11/h743_thumbnail_tall.jpg' title='H743 power supply pulled and on bench' onclick='pswipe("pdp11",48);'/>
<img src='/images/pdp11/rk05-lower-before_thumbnail_tall.jpg' title='First RK05 lower head before cleaning' onclick='pswipe("pdp11",49);'/>
<img src='/images/pdp11/rk05-lower-after_thumbnail_tall.jpg' title='First RK05 lower head after cleaning' onclick='pswipe("pdp11",50);'/>
<img src='/images/pdp11/rk05-upper-before_thumbnail_tall.jpg' title='First RK05 upper head before cleaning' onclick='pswipe("pdp11",51);'/>
<img src='/images/pdp11/rk05-upper-after_thumbnail_tall.jpg' title='First RK05 upder head after cleaning' onclick='pswipe("pdp11",52);'/>
<img src='/images/pdp11/lower-cover-abrasions_thumbnail_tall.jpg' title='Abrasions on first RK05 lower cover, from contact with spindle motor shafts' onclick='pswipe("pdp11",53);'/></p></div>
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