MPI 51 floppy drive repair

[nama]

I thought I'd start a new topic on this rather than wrap it into my previous OSI 4P repair thread, here:
http://osiweb.org/osiforum/viewtopic.php?f=3&t=49

I will start by listing all the things I have done so far:

- Replace main spindle bearings
- Pull main motor (not the stepper motor) apart to see why it's very noisy (screaming at times) and it's speed is inconsistent. No obvious problems found
- Speed inconsistencies found to be in the power supply that regulates the motor speed. This circuit is supposed to ramp up and slow down the motor to keep the disk spinning it at a constant speed. Therefore it is not unusual for the power to fluctuate, however there must be an issue as the drive certainly does not spin consistently, and sometimes even stops completely as the voltages drop off.
- Fixed a severed cable that runs from the read/write head to the main circuit board. Not sure how this was severed, but I initially didn't notice it as it was quite hidden.

I am presently waiting on another motor to arrive, which may fix the speed inconsistency issues.
As the wires were very fine the job was very tricky. afterwards I decided to check the continuity of the reconnected wires. I gently lifted the seal on the back of the read/write head and placed one probe of the continuity meter on the connections within, the other probe I touched to the corresponding pin at the other end of the cable where it connects to the drive circuit board. I tested all the pins and got continuity. However I noticed that there was actually continuity through all the lines as if they were all somehow connected together!!! Very strange. My repair work is usually very neat and although I can imagine a situation where maybe one of the connections I made had broken free, I can't imagine a situation where I could have accidentally soldered everything together. I can only think that this is somehow a function of the read/write head. Maybe someone can confirm this?

Even though the motor is dead is acting funky I decided to see what it can do one connected to the OSI machine. Firstly I loaded the Disk Dump software. Previously when I tried this All I got was a dump of 00's, Now that I believe the read/write cable is fixed I wanted to see what if anything changed. This time I actually got something other than 00's. Track 0 seemed a little different, but at the beginning of each track the floppy dumped data, but after about 20 lines (sometimes after 17 lines sometime 18 or 19 or 20) it consistently dumped 00's. The first track actually had data half the way through it, and much more than subsequent tracks.
I tried this on a couple of disks, one which was unformatted and new, and another which was formatted on an Apple II.

Here is a typical dump of track 0 and 1:

Code: Select all

00 00 18 08 FE FF 00 74 30 61 E0 00 04 94 00 00
F8 00 34 1C 68 C0 D0 38 D6 6C C1 40 08 09 00 00
00 00 10 18 00 08 00 07 00 48 80 24 D0 C0 80 84
60 98 00 20 00 40 08 20 80 00 00 00 00 20 00 10
20 00 00 00 00 00 00 00 00 00 00 00 00 00 00 02
00 00 00 00 00 80 00 00 00 00 00 40 20 0A 80 00
28 9B 22 2D 05 5A 39 20 CD 04 89 58 84 70 92 20
10 E9 FF 61 22 80 00 26 22 00 80 80 80 00 00 02
F0 FF 7F 5E EA 22 E8 91 00 75 61 FC 1A 5A 52 EE
1F 95 20 22 01 0A 00 20 04 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 02 00 00 E0 00 00 26 B0 20 00 00 02 05 00 00
40 00 A0 0C 80 00 00 00 00 40 80 01 0A 02 C2 10
2E 8A 00 A9 08 20 04 00 21 40 42 AC 51 32 40 CA
C7 22 70 92 32 36 34 51 31 92 A1 92 09 42 0B 08
00 00 00 20 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 F0 00 00 00 00 00 00 00
08 00 00 50 01 00 00 00 01 21 38 40 98 80 C1 41
83 03 03 5C 19 08 12 4A 23 8A 7C 34 CC 10 00 4C
C8 07 AD 98 6D 11 68 E0 B7 97 3B 9F 7D 01 00 04
80 00 00 22 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 02 44 15 70 22 08 00 17
40 20 00 80 08 00 80 00 34 64 80 08 C0 80 00 06
04 16 01 8A 14 50 01 9A 00 2D 9E 00 16 66 2A 92
90 45 0B 03 5E 83 00 73 49 02 A4 04 0C 99 C2 2E
40 31 90 04 00 00 00 20 00 00 20 00 01 00 00 40
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 02
40 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 40 04 51 17 00 80 C0 48 00 02 0B 00 20 00
20 10 20 42 12 22 03 AC 62 04 8D A5 A1 C1 9C 23
40 80 AA 02 D0 43 48 22 10 29 1C C0 11 00 C0 C1
02 00 8C 02 08 00 0B E0 81 22 A4 4B 22 07 9D 5F
46 00 00 00 00 00 40 00 00 40 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 20 00 00 00 00 40
00 00 00 00 00 00 00 00 00 00 00 90 A0 61 66 A0
15 00 4C 40 10 95 87 20 30 36 00 10 10 A0 82 00
0D 02 40 00 0C 04 C8 A0 00 00 20 20 08 04 0A 06
78 48 1D 45 04 00 04 00 10 40 00 54 90 03 11 11
12 51 20 61 41 05 06 00 00 03 24 00 00 00 00 00
60 00 00 00 00 00 00 04 00 00 00 00 00 00 00 00
80 00 00 00 00 00 80 08 00 00 00 00 00 00 00 20
00 08 00 10 01 86 9C 05 D0 A8 40 89 27 42 0C 49
04 51 2C 03 12 83 99 28 A2 49 0C B1 00 EB 20 04
04 08 28 24 80 81 9A 00 A0 00 C0 41 C2 40 10 01
F8 01 00 A6 01 00 01 10 20 00 00 10 00 00 44 C0
01 21 00 04 00 00 00 00 00 04 00 00 00 00 00 00
00 02 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 02 00 F0 18 22 20 60 80 40 96 40
57 12 40 80 94 A9 C6 10 C8 20 02 00 FD 30 05 0D
00 00 E0 20 01 00 00 80 00 98 80 00 00 00 30 00
01 00 20 00 00 F0 10 01 02 00 00 00 06 80 00 00
80 FF 00 00 00 00 00 00 00 F8 00 20 00 00 00 00
00 02 00 00 00 00 00 00 00 00 00 00 00 00 00 00
20 00 00 83 80 40 18 C0 04 08 04 20 04 60 20 05
C1 40 80 00 00 00 10 0A 00 00 00 04 00 00 00 01
80 00 40 80 08 62 00 00 00 00 00 00 00 08 00 00
00 10 10 00 00 00 00 90 00 40 00 81 41 00 00 00
10 00 80 10 06 00 00 09 00 00 00 00 10 00 FF 00
40 00 00 00 00 08 00 00 00 00 00 00 00 00 00 00
00 00 20 00 00 00 00 01 04 04 80 40 08 80 00 01
06 00 00 90 10 00 00 20 40 44 A0 00 20 50 F0 00
84 00 00 00 20 00 00 80 00 00 00 00 00 20 00 01
00 04 00 00 08 08 00 00 00 00 00 00 01 04 00 00
00 90 00 80 20 22 00 00 20 52 81 00 00 00 00 00
10 00 40 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

2C A8 D1 A9 04 10 19 03 33 62 0A 0A F8 46 FF 0B
FB FF FF FF FB 95 FF FF FF FF EF 1C 61 39 12 E2
07 06 84 00 90 BE FF 6C F5 C3 51 E1 1A 99 DC 0E
94 B2 6F FD FF FF FF FF 4F BD A3 FF FF AB 75 EB
37 1C 1C A5 16 20 80 31 40 74 20 48 62 B2 74 E8
FF FE 3F BE 91 E5 84 90 22 A1 8A D0 98 68 EA 39
FF F8 E1 5D CC 62 47 25 E1 B8 FF FF E5 FF FF FF
FF 81 53 AE E4 87 C1 37 01 E5 EE FF CF E8 ED FD
FF FF 57 26 44 10 E3 95 46 A3 14 03 00 53 24 A6
82 00 01 91 F0 81 FC E9 F4 FF FD FF 95 04 C0 FF
81 A1 28 80 41 8C 26 6F 84 29 BD 0F 8D 08 2C 0A
06 B4 A1 4D 57 80 04 B8 E6 F2 1D CA FF B4 85 FF
F1 BA FF FF FF FF A0 FF F8 FF FC 0A C6 FF FF FD
60 FF FF FF C4 56 B4 55 CC 0E FF CF FF FF EB 5F
04 E5 11 D2 1A 28 0D 65 F0 24 E9 FD 3A 17 69 8F
A4 3F B0 23 E3 6D 84 8C 34 B8 07 18 E1 87 70 F4
61 FF 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
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00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00

Finally I tried loading through serial the first 4k of OS65D 3.2 (from an image that I found on the internet which I stripped out the track header info). I have also been told before I do this I should press 'D' at the D/W/M prompt so that the PIA is initialized first. I was able to get the following prompt sent back through the serial connection to my terminal software on my Mac:

Error #7
A:

Not sure why the syntax error is there, but I can now see the 'A:' prompt.
Typing INIT or INIT xx (where xx is a track number) results in an track zero is write protected Error #3. It seems that the drive thinks that it's always positioned above track 00. As per the MPI manual, I'm next going to look to see what readings I am getting from J4-12 which is the track zero sensing line.

Well, thats about as far as I have been able to get with this drive. Really hoping with the help of the community that I can repair it.

Cheers again

Phil

[nama]

Quick update.
I tested the track 0 sensing line at J4-12. When the head is at track 0 the line is low, at any other position the line becomes high so it seems that the sensing is indeed working at this point. Trying to take a reading from pin J1-26 which is the floppy cable connector track 00 line, I can't seem to get any reading at all with my logic probe, and the voltage is at about 0.4V regardless of the position of the head. I'm assuming the signal gets messed up elsewhere. I will look into the logic for this. Unfortunately the copy of the schematic I have is not so clear making it a little difficult to read.

Please let me know if you think I'm barking up the wrong tree.

[nama]

I found some much clearer MPI 51 manuals and schematics here:
http://z80cpu.eu/mirrors/oldcomputers.d ... /hardware/

This evening I traced the track_00 signal back from the track_00 LED sensor through the logic and back to the J1 floppy connector pin 26. Seems that the very last IC (3E) in the circuit is a 74LS38 and track_00 input comes in at pin 5, there is another input at pin 4, and the output is pin 6 which connects to J1-26. Both inputs are GND and there is no output shown on my probe at pin 6, so maybe this is an issue that needs fixing?

I do have one question that has me quite confused. When I was probing the track_00 logic with my logic probe, I noticed that when I half inserted a disk, and at the moment the disk covered the index sensor all logic levels disappeared. I couldn't get any reading from various places with my logic probe. If I pulled the disk out the levels would return. If I inserted the disk fully and closed the door allowing the disk to spin, which in turn would trigger the index sensor once every complete rotation of the disk, this causes the index line to pulse. This however also causes nearly all other lines (such as the track_00 line) to pulse at the same frequency. Is this normal? It certainly wasn't what I was expecting.
EDIT: OK, I have a hypothesis as to why it does this. I may be taking the 5V line to power the probe from the wrong location. What I was assuming was 5V may actually be part of the index circuit. I'll check this today.
EDIT 2: Yep, Stupid me. I was taking the 5V from the wrong place. Please ignore the above paragraph
Phil

[nama]

I tested the track_00 line today with it plugged into the C42P and running the disk dump utility. At the 74LS38 (E3) pin 6 (or J1-26, it's the same thing) when the head is over track 0 the pin is low, if the head moved to any other track the output had no reading using the logic probe. The pin seems to just die. So I tested voltage. When the head is at track 0 the voltage is 177millivolts. If the head is at any other place the voltage is 3v. Looking at the MPI manual it seems that a high on this line is rated at 2.5V min, so I can only assume that the track_00 circuit is functioning correctly.

I guess I need to look elsewhere for the reason why the load of OS65D 3.2 (first 4k) gives an error #3 when trying to 'INIT' a disk.

EDIT: Just looking at the 505b schematic. The track_00 input comes into the PIA on pin 3. There also seems to be some pull up resistors which I believe (given my very limited knowledge of electronics) should bring the 3V to 5V before the signal enters the PIA. However taking a voltage reading at pin 3 of the PIA still shows 3V. Maybe this is all that is needed as an input high at the PIA. Can anyone conform this for me... much thanks.

[nama]

The new motor arrived today. This was a motor from a newer MPI drive so Installing it was simple and there was no need to cut wires and solder.
Everything is nice and smooth now, but unfortunately that hasn't changed much in the operation of the unit. Still seems to dump an awful lot of 00's and my load of OS65D 3.2 still won't INIT the disk. I even manually brought the track_00 line high (5v) at the PIA which didn't seem to change anything. I'm beginning to suspect a bad dump of OS65D or that the loading of the first 4k of OS65D might not work as expected.

I think I may try finding another dump of OS65D and see if I can get that work.

Phil

[nama]

Oh dear, I'm running out of ideas in how to get OS65D working and/or confirm wether this disk works. I just feel to be going around in circles now.
One thing I may try is taking the data separator board off the drive and try plugging it into my System 80 (TRS80 clone from Australia and NZ) as this is the only other machine I can presently connect an old 5.25" floppy to. Maybe I'll be able to get a better outcome from this setup, and confirm the operation of this drive or not.

Phil