I have two PDP-11/53 in my collection.
The first one came with an RD53 drive, a 71 MB drive, wich was defective. luckily I could reformat it as RD52 with 31 MB capacity.
I’d like to get the 11/53 on the net, so I installed Ultrix11 onto the RD52. But too bad, despite Ultrix-11 has a TCP/IP stack, it is so buggy that it does not work. The newsgroups discuss this every year.
For the second 11/53 I bought an Seagate ST251 (40MB). This is DECs RD32. Ultrix-11 runs also OK here.
But the operating system of choice is 2.11 BSD, with TCP/IP. I installed this on my PDP-11/44 with great success.
But it does not fit onto the RD32 or RD52 disk. It needs a 70MB disk, a RD53.
So I went shopping at ebay.
I could get an RD53 quite fast and quite cheap (it was announced without type designation, on request the seller told me it was a Micropolis 1325: bingo!).
When it arrive, I connected it and tested it with XXDP, the MSCP disk exerciser.
It was 100% OK! I put it aside, and wanted to install 2.11BSd later. (Lets call this drive “B”).
This deals was so easy, I decided to buy a second Micropolis 1325. I found another one, also not with type designation. The seller anounced an “ST504” drive from Micropolis. I made some statistics on the web and found, that almost all ST504 drives from Micropolis must be 1325 or 1335. So it was a blind buy. When the disk arrived, it was no ST504 disk: it was an ESDI drive /150 MB). The cable sets look the same, and the seller was not too exerienec, so he made wrong desription.
I tried to cancel the buy. The seller was quite friendly, but I agreed to a complicated deal: I had to ship the drive back, he would sell it again, and we would share old and new money 50:50. All this took 6 weeks to complete!
The RD53 error: spin up, spin down
After that I bought a 3rd (or “2nd”) drive on ebay. Lets call it “A”. As it arrived, it had an error:
It did spin up, but the sound became not steady. I heard the heads moving, but after 1 minute or so, the drive spun down again.
I got the good drive “B” from its shelf and connected it to my 11/53. But gues what? It had almost the same behaviour now! Spin up, some sounds, spin down. So it was OK, and after a few months it broke too.
I googled a lot after “repair micropolis 1325” and the like. There seem to be a lot of broken 1325’s out there, and all have this spin up, spin down behaviour. One guy wrote, he had 20 RD53 with this error in his basement!
There are tips about a stick rubber, wich glues the heads to its idle positions. Other people recommend putting the RD53 in a freezer and let them cool down, then power them up and never power them down.
Later I opened both RD53 to see whats real working on. Because it was winter and a rainy week, I vaccuumed my room frist and then let lot of dust-free december air into it. By the way, those 1980’s heads do not flight so low over the surface as on modern terabyte disks.
I found “A” and “B” have not the same error.
“A” seems not to get rotating fast enough: the spinning sound is modulating as the heads move from the inner to the outer track. So tracks are likely flying at all, and the motor seems to weak to get hte spindle up to speed .
I changed motor electronics with the other drive, notinh changed.
Drive “B” seems to get on correct speed. But here the heads are not moving, they are permanently set against the inner track.
Quick diagnostics: on drive “A”, the spindle bearings or the motor are weared out,on “B”, the head actuator had some problem.
Maybe in another live, I'd disassemble both drivers and mount the head+ actuator from “A” into the frame with the working spindle subsystem. Let’s save some money for a clean room!
So after all, I deald with four Micropolis drives, and got just one working for a few days.
A year later, while simplifying my live (again), I simply throw those both RD53 onto the local recycling yard. I never will buy them blind again!