IBM 3745 Series, Hardware Maintenance Reference

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Disk and Diskette Drive ON/OFF Control
DC vo5V and +12V are supplied by the PS1 to the disk (HDD) and diskette (FDD) drives, when
the PS1 receives a 'HDD ON' or 'FDD ON' command from the MOSS through the PCC card.
If the disk and diskette drives have not been used within 15 minutes, the PS1 receives from the MOSS the
'HDD OFF' and 'FDD OFF' commands, and DC voltages are no longer applied to the drives.
Disk and diskette can be also controlled manually (DIF function 7).
HDD ON/OFF command FDD ON/OFF command
─────────────────┐ ┌─────────────────
│ │
To:ð1H-J1 ┌┐ ┌────┴───┴────┐ +5V and +12V DC ┌────────────┐
│├──────┤ PS1 J3i==================iJ2 Diskette │
└┘ │ (F) │ = │ (B) │
│ │ = └────────────┘
│ │ = ┌────────────┐
│ │ ========iJ3 Disk │
└─────────────┘ │ (D) │
└────────────┘
┌─ │ │
│ ┌───────────────────────┐
│ HDD ON/OFF │ │
│ command ────┘ └───────
│ 5│──│% 4ð ms max │
│ ┌─────────────────────────┐
Disk │+ 5 V Level 7 │ │ │ │
│ ───────┘ └──────
│ │ │
│ ┌─────────────────────────┐
│+ 12 V Level 1 │ │ │ │
└─ ───────┘ └──────
│ │
┌─ │ │
│ ┌───────────────────────┐
│ FDD ON/OFF │ │
│ command ────┘ └───────
│ 5│──│% 4ð ms max │
│ ┌─────────────────────────┐
Di 5 V Level 7 │ │ │ │
│ ───────┘ └──────
│ │ │
│ ┌─────────────────────────┐
│+ 12 V Level 2 │ │ │ │
└─ ───────┘ └──────
│ │
Disk Voltages and Tolerances (From PS1)
For DC test points, see pages YZ.
Table 10-7. Disk Voltages and Tolerances (From PS1)
VDC Level Vmin Vmax Ripple
+ 12.00 1 + 10.80 + 13.00 0.10 p-p
+ 12.00 2 + 11.40 + 12.60 0.10 p-p
+ 5.00 7 + 4.75 + 5.25 0.10 p-p
10-14
IBM 3745 Models 130, 150, 160, 170, and 17A: Hardware Maintenance Reference