8550 Z Planar

rf5060a.exe Model 50/60 Reference Disk v1.08 (zipped image)

188-080 IBM PS/2 Model 50 Z Desktop Systems With Improved Hardfile and Memory

Resurrecting 50Z by Mark Baker

8550 Z Planar
System Firmware
   ROM Images
Open a Locked Case
8550z Drive Controller

8550 Z Planar FRU 90X9533

F1 LF 5MF 3A/250V KB/mouse fuse
J1 Floppy riser slot
J2 Battery/Speaker header
J4 16-bit HDD Adapter slot
J5,6 16-bit MCA slot
J7 16-bit MCA slot w/ AVE
J8 Case fan header
J9 HDD15 video connector
J10 Parallel port
J11 DB25 serial port
J12 Keyboard port
J13 Mouse port
? Power supply edge connector
OS1 1.8432 MHz osc
OS2 25.17500 MHz osc
OSC3 28.32200 MHz osc
Q1 TIP120 5A darlington (for bus ctrl.)
Y1 32.768 kHz xtal (RTC)
Y2 14.318 MHz osc
Y3 4.0 MHz osc
ZM1 80287-10
ZM3 90X8134(ESD) DMA Controller
ZM5 15F8365 BIOS Odd
ZM6 15F8366 BIOS Even
ZM8 Motorola MC146818A RTC/CMOS
ZM12 80286-10 CPU
ZM20 90X9228
ZM33 Ceramic module (floppy PLL)
ZM37 90X8723
ZM41 23F9177
ZM42 05F3994
ZM45 72-pin SIMM slot
ZM46,48 68X6143
ZM49 P8042AH Keyboard controller
ZM50 NEC µPD765AC-2 Floppy controller
ZM51 15F6864
SP "SPARE" DIP solder pads

ZM46,48 68X6143 PCBs with four NEC D41464-12

System Firmware (POST & BIOS)

Firmware stored in EPROM.

ROM Images

Unknown P/N - 28 Feb 1988, rev. 2, 2x 27512 (ZM6 / ZM5)
15F8366 / 15F8365 - 18 Apr 1988, rev. 3, 2x 27512 (ZM6 / ZM5)
15F8362 / 15F8361 - same contents as above


Uses 85 ns 1 or 2 MB SIMMs (1 slot on the planar).

Zero wait state.

Open a Locked Case

Turn the unit with the rear facing towards you. Loosen the thumbscrews - then use a *large* flat blade screwdriver to lift up the cover about 3 mm over the lock position.
   The inside lever goes only behind an edge of the case... pry between case and rear wall and lift the case up a bit. Then push the cover from the rear to the front.
   When you have it open pull the retainer bracket from the lock assembly - fumble it out and throw it away...

8550z Drive Controller

The 50-021 uses a proprietary MFM / ST-506 controller along with a CMOS version of a MFM 20 MB harddisk - and that's the only drive supported on that controller. The 50 Z uses the MCA DBA-2 controller... usually they use ESDI-like auto-detection for the drive size and doesn't use any tables (104xx error codes).
   The 50 Z BIOS however has an "AT-style" table for the MFM drives, which ends at Table ID 33 for the 30 MB MFM version of the MCA DBA-2 (17xx error codes).
   This table can be edited for larger MFM drives (up to 500 MB) with correcting the CRC checksum of the entire ROM pair. Did that long time ago for a Model 60 to install a 350 MB MFM drive. Basically you can forget that stuff.

Content created and/or collected by:
Louis F. Ohland, Peter H. Wendt, David L. Beem, William R. Walsh, Tatsuo Sunagawa, Tomáš Slavotínek, Jim Shorney, Tim N. Clarke, Kevin Bowling, and many others.

Ardent Tool of Capitalism is maintained by Tomáš Slavotínek.
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