UART Chip Replacement on COM4 and COM4A Boards

This procedure provides instructions for the replacement of the UART chip on the COM4 or COM4A board in the APU-102 card cage. It applies to 486-based Comet Electronics APU units, especially those that have been upgraded with the APU Version 5 Pentium Kit. This applies only to units containing either a COM4 board or a COM4A board manufactured before 1999.

Specifics

Compatibility testing has revealed that in rare instances, when a 486-based Comet Electronics  APU is upgraded with the APU Version 5 Pentium Kit, there may be a conflict with the existing quad-channel UART on the COM4, or COM4A board that was manufactured before 1999. The issue is manifested as communications difficulty and may affect any of the ports on the COM4(A), e.g., AI1200, ITC, REDI, etc.

COM4(A) boards manufactured after 1999 have not exhibited this issue.

The issue may be remedied by replacement of the incompatible UART chip on the COM4(A) card or replacement of the COM4(A) card entirely.

Procedure

WARNING!

Observe proper ESD procedures when performing these procedures.

COM4(A) Card Replacement

1)  Power off the APU and remove the COM4(A) card.

2)  Examine the UART chip, U11, on the COM4(A) board. If the chip is manufactured by any manufacturer other than Texas Instruments (TI), the card needs to be replaced with an acceptable spare with the TI UART chip installed. Follow standard RMA procedures to return the suspect board for repair.

Board Identification

Figure 1: COM4 board (older version) with non-TI UART chip	Figure 2: COM4A (current version of board) with non-TI UART chip

UART Chip Replacement

Field replacement of the UART computer chip should be done ONLY qualified technicians. Most readily available PLCC chip extractors (or other methods) can damage the chip or socket if not used properly. If the socket is damaged, the board must be returned to Comet Electronics for repair following our standard RMA procedures. Our flat rate repair charges will apply for damaged boards. If the pins of the replacement chip are damaged, it must be replaced.

Important!

DO NOT perform this rework on the COM4 from an operating site. If the COM4 from an operating site is damaged, the site will be out of service until a spare can be obtained. Perform the rework on a spare or replacement board only.

Caution

Observe proper ESD procedures when performing this procedure.

1)  Lay the board, solder-side down, on a firm, non-conducting surface.

2)  Insert the steel jaws of the PLCC extractor fully into the notches in the socket on the upper-right and lower left corners.

Figure 3: PLCC chip extractor

Figure 4: Notches for PLCC extractor

Figure 5: Inserting steel jaws into notches

3)  Gently squeeze the tool until the plastic part of the jaws is resting on the corners of the socket. Make sure the hooks of the steel jaws are hooked under the chip.

4)  Gently increase pressure on the tool until the chip lifts out of the socket. DO NOT lift on the tool. The squeezing action on the tool pulls the hooks up while holding against the socket. A gentle rocking motion while squeezing (in-line with the jaws) may aid in removing a stubborn chip.

5)  Remove incompatible chip and prepare replacement chip.

WARNING!

Notice upper-left corner of the UART chip is angled. You must align the angled corner of the new chip to the angled corner of the socket when installing. DO NOT rely on labeling on the chip to align the chip to the socket, use the angled corner. Failure to properly align the chip may damage the socket or chip.

6)  Align the angled corner of the UART chip with the angled corner of the socket and make sure that ALL pins are aligned with the correct holes in socket.

Figure 6: Aligning the angled corners on socket and replacement chip

Figure 7: Evenly press the replacement chip into socket

7)  Press firmly and evenly to seat the chip in the socket.