IBM Thinkpad 850

[Compgeke]

This here is one of those computers that I would trade my 20th Anniversary Mac Prototype for, which may seem odd, but the Thinkpad 820\850 are one of my dream computers.

[aberco]

ThinkPad 8500 teardown

Very excited to receive today my very own ThinkPad 850!

Got it from the UK, in very good condition. There's just some minor pumps and scratches on the external cover, the inside of the laptop looks almost new. Keyboard and trackpoint show almost no wear from use. It is just missing the rear connector covering door as well as the battery cover. I did not had any information on the configuration, turns out it is maxed out with 1.2GB hard drive and 96MB of RAM. Rear sticker reads Type 7249-851, made 08/96, so this would be a ThinkPad 851 (would the difference between 850 and 851 the built in options?). Unit is rated 20V @ 2.5A, a whopping 50W, quite large for laptops of its days. The original owner told me the display was working a few weeks ago, and then turned black, so it needs to be fixed. I managed to get the screen back twice, and it also displays on an external monitor, powers on fine and boots AIX 4.

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Since it needs to be fixed it was also a perfect excuse to do an entire teardown and document the hardware of the machine, so there it is! I will try to include as much info as I can, as well as IBM part numbers (PN) and FRUs.

The keyboard lifts vey easily to reveal the hard drive and CD-ROM drive. They can be removed by lifting on the blue tab and un-securing the metallic retaining lock. The keyboard is made by Keytronic for IBM (PN 45H8729 - FRU 29H8110).

My hard disk model is 1.2GB, 2.5" SCSI packaged in a cradle with a custom 60pin mating connector directly on the motherboard. I did not disassemble it, but it seems to be a 17mm height model, likely from IBM (PN 30H1471 - FRU 30H1465).

CD-ROM drive is also SCSI, also attached using a custom 100pin mating connector directly on the motherboard. I do not know the manufacturer or model (likely a 2x unit, PN 84G4538 - FRU 84G6357).

The battery is NiMH 9.6V 3.3AH (PN 84AG4603 - FRU 85G2677).

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Once removed are the memory upgrade slots, which are in the form of DRAM cards that must be installed by pair. They are like Type I PCMCIA cards but with a different mating connector for DRAM cards. Since the unit also has internal DRAM slots the computer can operate without these cards. I have 2x 32MB DRAM cards, rated
32MB 70ns (8Mx36) 5V (PN 07H4019 - FRU 92G7282).

Also visible are the speakers, and the two batteries. The green one is rechargeable and used for standby mode, a custom made Varta NiMH, rated 3.6V 110mAh (PN 39H1265 - FRU 39H1266). It has apparently a tendency to leak, and mine did. The computer gives an error boot message likely because of it, but it does not prevent it to boot. The other battery is visible as a round yellow shrink-wrap unit, and is used for backing up NVRAM and clock. It is a regular Panasonic CR2032 3V lithium cell (PN 84G4434 - FRU 84G4535).

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Getting past this point is tricky, the unit is not be easiest to disassemble. The upper plastic cover is held by 2 screws hidden under adhesive plastic covers. Removal reveals screws holding the covers of the left and right screen hinges, and of the central LED status indicator. The microphone is also visible on the left. The keyboard is also held by 2 screws with plastic articulation for the hinges that can be removed.

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[aberco]

The entire electronic assembly is located on the upper side of the unit below the metallic shields. The keyboard, trackpoint and LED indicators can be removed by disengaging the flat ribbon cables from the connectors. Visible on the very far right is the microswitch for detecting screen in closed position.

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Those 4 connectors are located on a small vertical riser board that connects to the motherboard. Visible on the right is the microswitch for detecting closed position of the keyboard topcase.

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Removal of all shielding shows the graphic card on the left, and the power supply on the right. The LCD is attached to the graphic card by 4 connectors. Video data is carried by a flat-flex PCB going in the left hinge, with two black connectors, while power for the CCFL inverter is supplied by a 4 wire cable going in the right hinge. The camera terminals are also routed on the flat-flex PCB and is connected using a 6 pin connector. Both graphic card and power supply board are connected to the logic board by a single large board to board connector.

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The power supply board is manufactured by Matsushita/Panasonic for IBM (PN 29H8037 - FRU 29H8106), and sports the charging battery circuitry and DC/DC converters that step down the 20V input to 5V and various voltages needed by the computer. The upper side of the power board shows the main DC/DC transformer and filtering capacitor (which are high quality polymer type). The white square is a power resistor likely used as a shunt for monitoring power consumption and calculating battery usage.

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The bottom side shows most of the discrete switching MOSFETs and analog circuitry. The converter is driven by a MAX782, a triple-output power-supply controller for notebook computers according to the datasheet. The MAX782 is a 95% efficiency converter with 5.5V to 30V input range, supplying +3.3V and +5V using dual PWM buck controllers, and 0V/5V/12V dual outputs for the PCMCIA slots. It is available in 3 fixed voltage versions (3.3V standard CBX, 3.45V High-Speed Pentium RCBX and 3.6V PowerPC SCBX). Here the standard (CBX) version is used. The board to board that connect the converter to the logic board is visible on the right. At the top, a surface mount 3 wire connector link the 3.5 jack directly to the audio board.

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[aberco]

The top side of the graphic card (PN 91G055 shows the various video memories and a custom IBM controller (85G7815) manufactured by Seiko/Epson.

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The bottom side of the graphic card reveal 3 large QFP208 and 160 chips, two of which are thermally connected to an aluminum heatsink by thermal pads. The left package is a Western Digital WD90C24A SVGA LCD controller addressing a pair of Hitachi HM51S4260 262144 x 16bit DRAM, providing 1MB of video display memory. At the top is the large board to board connecter that connects to the motherboard.

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Under the heatpads is the analog composite digitization subsystem, cosseting of a Brooktree BT812 NTSC/PAL to RGB/YCrCb Decoder associated to a pair of Hitachi HM530281 high speed 331776 x 8bit Frame buffer DRAM providing about 650kB of buffer. it is supported by an ASCII V7310AS (アスキー, asukii) Video Capture Device. The role of the custom Seiko/Epson chip is unknown, but as Seiko/Epson manufacture display solutions, it could be linked to the conversion of the digital stream from the WD90C24A into analog SVGA for the external mirroring output.

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The audio subsystem is mounted on a separate board (PN 91G0574) featuring a Crystal CS4231 16bit stereo codec with various op-amps for buffering analog audio inputs and outputs.

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[aberco]

I have not removed the motherboard but several chips are visible on the top side. Three are covered with heat transfer pads. A connector is provided for two stacked DRAM DIMMs

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Both DIMM slots are populated with 2x 16MB DRAM 72pins modules (PN 59G3997 - FRU 40G4530).

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The main board supervision is provided by a Hitachi H8/338 (HD647338 8bit microcontroller in a QFP64 package. Very unusual is its placement on a ZIF socket (these are ROM based microcontrollers). There's also a PLCC32 flash memory (unknown capacity, I did not remove the label).

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The chips covered by the heatpads are part of the PowerPC L2 cache system. It consists of a pair of 32k x 36bits IBM043614 burst SRAM (256k L2 cache total) and a IDT71216 240K (16K x 15bit) cache-tag RAM for PowerPC and RISC Processors. The IDT part is also used on L2 cache DIMMs for PowerMacintosh.

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Most of the chipset and glue-logic between, the CPU and peripherals are likely located on the bottom side of the motherboard which I have not taken out. They are likely custom IBM chips. The processor module is however accessed from the bottom of the unit, by removing a large adhesive plastic sheet. Removing the sheet ultimately destroys it.

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[aberco]

The bottom cover removed. A square cutout is made in the board under the CPU to connect the ceramic substrate to the metallic cover for heat-spreading.

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The CPU board with its two connectors. 33.33MHz frequency from oscillator is tripled for 100MHz system clock. A metallic bar connects to the top of the CPU to transfer heat away.

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Here's what everyone wants to see!
The PowerPC 603e CPU @ 100Mhz. It comes in a flip chip QFP208 package potted with a blue compound. This package was used for the PowerPC 601, on some early IBM versions of the PowerPC 604, but rarely on the 603e which also came in a full ceramic QFP208 package.

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Disassembling the display does not require to take the frame out of the unit. 6 screws covered by adhesive pads holds the cover. The two upper screws are made of white plastic.
The LCD is an active matrix 800x600 24bit color module (PN 84G6835). Very interestingly, the inverter and CCFL lamp (PN 85G0531 - FRU 85G1031) are mounted on a removable plastic frame meant to be replaced in case of failure. It is the very first time I see a LCD made to be serviced without taking everything apart.

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My unit also came with a PCMCIA ethernet card, without the dongle. I am wondering if this is a regular unit or one specifically designed for RS/6000 systems.

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Now will be the time to do more troubleshooting in order to repair the backlight, since I doubt the display assembly was used in another IBM laptop. The replaceable CCFL seems to be specifically designed for the ThinkPad 850.

[NeXT]

I have one of those ethernet adapters too but with the dongle. They have support built into Warp 4 and Windows 95. I see no reason why it wouldn't work in the 850. I have a Token Ring card which is also detected and supported. Got anything cool on the hard drive that you noticed?

[aberco]

Cool! Yeah the PCMCIA Ethernet II adapter came with it, it seems to be a fairly generic card, AIX has drivers built in for both the IBM Ethernet I and II cards.
It boots to login, then I have no idea of any account or root password. I also lack any installation CDs (AIX 4.1.5 is what I would need for this machine, last OS to be supported officially). So, can't really check what's on it yet.

Went further on the backlight, the connector of the CCFL module got desoldered probably because of the heat. However resoldering it in place did not bring it back to life. I have to get my meter to do more troubleshooting, but I also found a replacement display that I brought... just in case I can't save the one I have.

First step in RS/6000 systems for me, so I have to look for documentation!

[NeXT]

Can't help you there. Mine came with no documentation either but received a fresh reinstall form a friend.

[billdeg]

Nice writeup. I have a 2603-17N.