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IBM 3270 PC (Model 5271)


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  IBM 3270 PC (Model 5271) by Bill Degnan - 02/22/2022 22:11
The IBM 3270 PC, model 5271 after repairs made to the RAM. Click image for larger view.

View of display connector cable attachment to rear of IBM 5271. Note the dual card. Note also the RAM expansion card has been removed for troubleshooting. Click image for larger view.

The display paired with the 3270 PC (part no. 5272)running a color calibration program. Click image for larger view.

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This computer was donated to Kennett Classic. It initially had a RAM fault that prevented it from booting, but the problem was isolated to the expansion RAM card (a Sigma Designs "Maximizer", which for now has been removed.

Next - Repair the Maximizer or replace with a another RAM expansion card. Clean the system. Unfortunately I don't have access to a 3270 :-)

  MAXIMIZER troubleshootung by Bill Degnan - 02/23/2022 23:28
This Sigma Designs MAXIMIZER Multi board was failing to POST at the 384K mark. I removed the board to allow the 3270 PC to boot, but the software installed in the system requires more than the 256K found in the motherboard. So, I need troubleshoot/ fix the board. I tested all AM9064 RAM chips.

I found 5 bad RAM chips. I moved the good chips into banks 0 through 4, and set the SW2 switches to 320K (5x64=320). I set aside the 5 bad chips. Hopefully 576K (256+320) will be enough to run MS Word and the other contemporary software installed on the hard drive. Id like to see the primitive version of Word as most computers of this era used WordPerfect. The OS is IBM DOS 3.3, meaning the system DOS was upgraded in 1987 or 88. Bank 5 is now completely empty of RAM chips. I believe you need a full bank, meaning I cant use the four remaining good chips. The MAXIMIZER reference guide is found here:

  IBM 3270 PC Update by Bill Degnan - 01/23/2024 22:29
IBM 5271 (3270 PC model 6) next to an IBM 5160 (XT)
This image helps demonstrate the difference between the IBM 5271 (3270 PC) and the IBM 5160 (PC / XT) computers. The base systems are the same, but the 5271 has a 3270 emulation controller, dual graphics card (EGA/MGA) and a keyboard controller to complement the 3270 emulation. Click image for larger view.

IBM 5271 Controllers
The IBM 5271 (3270 PC) was an IBM XT with controllers added to allow a person also use the PC to emulate a 3278 display terminal. Click image for larger view.

The controller in the back is the 3278 network connector card. The next controller is a now fully-populated and properly configured Maximizer RAM/serial/parallel card. The cards joined by a top connector is a dual display card, capable of EGA and MGA graphics. The next two cards are stock hard disk and fixed (360K) 5 1/4" disk controllers. The small controler behind the Tandon 100-2A drive is the enhanced keyboard controller used when in 3270 emulation mode.

Tandon 100-2A FD and Seagate 10Mb HD drives
Tandon 100-2A FD and Seagate 10Mb HD drives. The analog controller of the Tandon diskette drive was replaced as was the FD controller installed in the backplane. Click image for larger view.

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