Tuesday, June 9, 2015

Digging into the Pertec disk drive while sorting out the repair/replacement part for the 1053


No luck finding spare parts to replace the margin rack latch part which I broke by snapping off a tab that ends a carrier return as the carrier reaches the left margin. I do have an acquaintance who has several 1053 printers and has offered the option of getting critical spare parts if I need them. I might need this.

The other option is fixing the part I have. I continue to look at possibilities to repair or replace it. It may be possible to make a 'daughter' part that sits under the existing broken part and provides the vertical tab I need to trip the carrier return unlatch arm.


The documentation is extremely incomplete for this drive. The terminator card does not match any of the documents I have, although the remaining cards seem pretty close. That means I can't figure out the signal assignments of the two 50 conductor flat cables that are used with the drive, nor the method of powering the terminator pull-up resistors.

There is not even a list of the pins on the 100 conductor connector that the terminator boards all plug into - thus I know there are 47 or 48 signals on the interface but no idea which wire corresponds to them. I had to begin reverse engineering the terminator card, but before I could do that I had to know which of the 100 locations on the main connector were each of the interface signals. That information was strewn across dozens of schematics.

Once I had the main connector locations of the input and output connectors, I could begin continuity tracing to find where they are connected on the two 50 conductor IDC connectors on the terminator board. This is quite slow, involving testing 5000 pairs of pins to find the 50 connections.

I traced six of the output signals, found them all to be on the IDC connector J102, then checked a couple of input signals such as the remote start/stop line, which were both on IDC connector J101. I have a working hypothesis that my inputs are on J101 and the outputs are carried on J102. That could reduce the search space in half, if I can eliminate 50 pins on the 'wrong' connector for every search.

I also traced the power to the terminator resistor packs, which pull up with a 133 ohm resistor and pull down to ground with a 266 ohm resistor for each signal line. I found that the power for the pullup comes in pin 1 of J101. The terminator board does receive the +5V power from the main connector, but it only runs to pin 49 of J102, to let the other end of the interface to do termination of the signals we are outputing to that end over J102.

My solution was pretty direct - jumper pin 1 of J101 to pin 49 of J102 which provides the main board +5V to the pullup resistors of the terminator board. That did allow me to initiate a startup sequence when I pushed the Start/Stop button. I am now looking at the next problem to diagnose. I hear a groaning sound but don't see any rotation of the blower/spindle motor. It hums for a few seconds then times out and resets the drives state.

It was time to investigate the mechanical condition of the motor, belts and spindles, to ensure they could turn freely, which they did. I then started to look into why the motor isn't starting. It may be a failure of the starter capacitor, due to age. Time to dig into the schematics and begin collecting data to diagnose and then repair.

I am pleased because this is definite progress. While I am looking mechanically and checkout out the starter capacitor, it would be a good time to clean the fixed disk platter, the platter in my removable cartridge and the four heads. The motor and mechanical items turn easily, so my attention turns to the motor and the control circuitry. Could be starter capacitor, could be starting windings, could be the centrifugal switch in the motor, or could be the logic in the drive malfunctioning. For example, the motor is used as a brake when slowing down to stop, but if the brake logic is active it could stop the motor from starting.

My check of the pair of start capacitors ruled them out. It is dark out now, but tomorrow or the next day, I can check the four windings and the internal thermal switch to see if the motor itself is good.


  1. I have recently restored a couple of these Pertec hard disk drives, as part of Altair "Datakeeper" subsystems. I've written some notes about restoring these drives that may be useful to you. They are Altair-oriented, in that I assume you have an Altair for exercising the drive, but they also contain a lot of general info about disassembly, repair, realignment, reassembly, etc. I also have several versions of schematics for these drives.

    A word of warning right now: if you get your drive to power up successfully, it will attempt to load the heads withing the first 30 seconds or so after the spindle is up to speed. If the disk and heads are all not *perfectly* clean, you will crash the heads, ruining the disk platters (and their data), and possibly ruining the heads too. (They are probably not perfectly clean...) I recommend removing the heads until you get the spindle and voicecoil servo working, even though this will probably force you into a head alignment when you are done.

    Let me know if you are interested in talking - I think you can reply to me via my google account? I'd rather not post my email address here.

    1. I am definitely interested, however the profile for your post only contains a (presumably) first name and no way to respond. I understand that you would prefer not to post email addresses, so we will have to be a bit clever in making the connection.

      Are you by chance Martin E......?

      I have met some members of the MARCH retro enthusiasts and we might be able to pass contact information through people we jointly communicate with.

  2. I am Martin E. I took a guess at your email address at your employer. Maybe I got it right :-)