Some progress with my PDP-11/73 system - test-drb@ccmp.vtda.org

10 Apr 2007

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Subject: Re: Some progress with my PDP-11/73 system
   From: David Betz <dbetz at xlisper.com>
   Date: Tue, 10 Apr 2007 08:17:49 -0400
     To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at
classiccmp.org>

  RD53s are notoriously unreliable, but I'm
surprised that four out  
 of five simply aren't detected.  Are they genuine DEC RD53s?  You  
 need to add a PCB link to an ordinary Micropolis 1325 or 1335 drive  
 to make it an RD53.  Look on the PCB for the location marked R7  
 (remove two screws and carefully hinge it up) -- if there's nothing  
 there, solder a link in that position.  Oh, and don't use a skid  
 plate with bare metal with an RD53, as it can short things out. 
Three of the four failing drives were official DEC RD53 drives as  
indicated by a sticker on the top. Interestingly, when Iooked at R7  
on the PCB, two of them had the resistor present but one end had been  
cut. I soldered it back together but both drives still fail. At least  
one of the drives spins up but then back down again. I'm reluctant to  
try swapping the PCB between my only working drive and one of the bad  
ones so I think I'll just count them as a loss. 
The one that pinsup and then spins down has the head bumper sticking
problem.  That is repairable and likely the HDA and logic is good.  
Me I'd repair that drive and use it.

Allison