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MPI 360k won't read/write

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    MPI 360k won't read/write

    Just dragged out my 5150 for a check. One of the two drives, an MPI unit, has some issues. When you try and read or write anything, it lights up and spins, but there's no sound of heads moving or anything attempting to do anything. It just gives you a failure message. I don't *think* it's alignment, I think even out of alignment it would try to format at least? Wondering if there's anything simple I can check first... I did do the obligatory head cleaning.

    Sure; to see if the positioner is working, manually move the heads toward the head before powering up. You should see the heads move to track 0 when the system boots.

    Failing that, there are ways of checking without a computer attached--you only need a power supply.


      Yeah, I did move the heads towards the front of the drive and it does drag them back. I've watched when I engage the drive to do something.. it just spins but there's no movement of the heads at all apart from that.
      Last edited by falter; August 5, 2019, 10:55 AM.


        Well, that tells you a lot--that the basic driver and positioner work--that's a huge part.

        Have you tried stepping the drive manually using IMD? I'm wondering if this might be a cable issue.


          The ImageDisk program will let you manually attempt to move the heads forwards or backwards in "alignment mode". It will also show you the track id of whatever track is under the head, if it can read anything, regardless if it is the right track or not.

          Yes, usually an out of alignment drive will still format a floppy fine, but can't read other disks, and the formatted floppy will not read in other drives.

          It's probably some problem just reading anything at all. (Have you cleaned the heads?) But ImageDisk might help narrow down the problem. As always, quadruple check the cables.


            I assume you actually opened it up and cleaned the heads?


              Yeah I took the PCB off and cleaned right in there.

              Here's a few shots of it (it's the drive to the right). I think the cables are right.. it responds as Drive B, there's no weirdness with Drive A..



                I can see one thing that is wrong but I don't think that is the issue. Both drives have terminator resistors. Only the last drive on the string should have a terminator.


                  It is possible that the track 00 sensor is not working. You should be able to trace the optical transistor to a comparitor. You can move the head out some and then reset the machine. the output of the sensor should change as the head moves to the end. As mentioned before, it is not likely an alignment issue as it would still be able to write and read it self. Still, it can't read the disk if there is no track 00 indication.
                  Although, the disk on the right doesn't look like a MPI92, it will still be similar. Look at the PDF on bitsavers. It looks like it matches the drive on the left but like I say, it will still need a comparitor to drive the logic so that is a good place to start.


                    I'm not sure if this suggestion could help, but it might be worth checking. Just looking at the pcb, in the photo of the drive on the right, I think the cylindrical black objects are possibly inductors (should have a low DC resistance), one looks like it has 68UH written on it. Also there are a couple of parts there that look like a resistor, but just with a central black band, probably a 0 Ohm resistor used as a link or a small chance of a fusible resistor. Check these all these parts for continuity with a meter with the drive not powered. If those objects are inductors I have seen some of these small axial ones go open circuit with age. Then with the meter you could easily check the diodes there as a start. But it is always a shot in the dark testing random components and the fault might not definitely reside on the pcb, though its likely.

                    Also, there may be other inductors on the board to check, the two pale green devices (with stripes) that look like resistors on the left of the white preset potentiometer may possibly be inductors, check them too.
                    Last edited by Hugo Holden; August 5, 2019, 07:33 PM.


                      Looking closer at the board, the device at the right, MC3470, is the preamp for the data read. With a disk having valid data on it and the head is loaded, you should see signals there with a scope. It will have a similar circuit to the pdf I pointed you to.
                      Actually, you might start at the Read Data pin of the connector ( pin 30 ). Do this with a disk that has data. You should be able to follow the data path back to the preamp. You can use the pdf I posted as a rough guide, even though this implementation is different. It has to do similar things.


                        I think I've found the main part of my problem. While looking over the drive for broken wires, etc.. I noticed that the upper head was 'floating' above the disk, the little arm sitting above the 'shelf' it appears it would normally rest on. There is a tension spring and it seems to be not letting the head go down all the way. Anyway, when I used a wood dowel to get between the PCB and top of the head, and pushed it down gently.. suddenly it was reading the disk that was inserted!!

                        I don't know what this portends for alignment... but that is the most I've gotten out of it in eons. Just gotta figure put how to adjust the spring.






                            It's the head with the triangular cover there. If I gently push it down until the plastic arm on the left is resting on the 'track's under it, it reads. But if I release the head moves up and reading ceases.


                              It sounds like the head load isn't working. I doubt it is the springs fault. There should be a solenoid that is holding the head up.
                              Do not remove the two screws holding things together or you'll lose the head alignment!!!!!!!!!!
                              Can you get a better picture of the back where the two screws are?
                              Also can you upload the pictures to the MB. Your pictures on the cloud can be lost, we want to show things for future reference. You can remove the two head connectors to fold the board back for a better picture.
                              Last edited by Dwight Elvey; August 9, 2019, 08:10 AM.