TECHNICAL BULLETIN COPYRIGHT 1992 _______________________ TANDY COMPUTER PRODUCTS ______________________ DATE: April 25, 1979 REVISION DATE: March 7, 1983 BULLETIN NO: I:12 PRODUCT: 26-1140 Expansion Interface 26-1141 16K RAM Expansion Interface 26-1142 32K RAM Expansion Interface SUBASSEMBLY: AXX-0100 Expansion Interface AXX-0008 Model I main logic board SUBASSEMBLY REVISION: All Revisions ______________________________________________________________________________ PURPOSE: Buffer cable and Twisted-Pair cable installation instructions. ______________________________________________________________________________ DISCUSSION: The following are the procedures for installing the Buffered cable and the Twisted-pair cable. These modifications are to correct system noise on the CAS, RAS, and MUX lines which could cause random reboots or memory crashes. These instructions incorporate some fixes for problems that have shown up after other installations. This Technical Bulletin covers installation of both modifications. If you install the buffered cable, you MUST install the Twisted-Pair. If you have a Buffered cable already installed, go to the Twisted-Pair modification. PROCEDURE: BUFFERED CABLE INSTALLATION Procedures for the Component Side of Board (see figure 1). 1. Cut the MUX etch at points (1) and (2), above pin 23 of the Edge Connector and below pin 1 of Z17 respectively. 2. Cut the etch at point (7) between 37 and 39 of the Edge Connector. 3. Cut the etch at point (8) between pin 37 and point (G). 4. Connect pin 39 to point (G) with a 3/16" bare wire. 5. Connect pin 37 to point (H) with a 2 1/2" jumper wire. _____________________________________________________________________________ Proprietary Information TB I:12 Tandy Corporation PAGE 1 OF 7 TECHNICAL BULLETIN COPYRIGHT 1992 _______________________ TANDY COMPUTER PRODUCTS ______________________ Procedures for Copper side of board (see figure 2). 1. Cut the CAS etch at points (3) and (4), near pin 2 of the Edge Connector and below pin 4 of Z24. 2. Cut the RAS etch at points (5) and (6), above pin 2 of the Edge Connector and below pin 1 of Z43. 3. Prepare three pairs of 220 ohm resistors. Cut one lead of each of the six resistors to 1/4". Allow 1/8" and bend the lead into a right angle, then solder them together into pairs (see detail A). 4. Solder the common lead of the resistor pairs to: Point (B), pin 1 of Z17 (MUX) Point (D), pin 4 of Z24 (CAS) Point (F), pin 12 of Z22 (RAS) 5. Of the remaining leads of each resistor pair, solder one lead each to the nearest +5V and the other to ground. TWISTED-PAIRS INSTALLATION Procedure for the Expansion Interface board (see figure 2). 1. If the Buffer Cable modification above has just been installed proceed to step 3. If the Buffer Cable was already in unit proceed to step 2. 2. Cut the White-Black, Blue-Black, and Red-Black twisted wires where they connect to the resistors pairs. Then cut the same wires at points (A), (C), (E), and the common ground. Discard these wires when finished. 3. Select the cable with the male DIN connector and connect the twisted wire pairs as described below. 4. Connect the Red-Black wire pair to: Red wire to point (B) Black wire to ground _____________________________________________________________________________ Proprietary Information TB I:12 Tandy Corporation PAGE 2 OF 7 TECHNICAL BULLETIN COPYRIGHT 1992 _______________________ TANDY COMPUTER PRODUCTS ______________________ 5. Connect the White-Black wire pair to: White wire to point (F) Black wire to ground 6. Connect the Green-Black wire pair to: Green wire to point (D) Black wire to ground 7. Route the cable along the board so that it comes out beside the Edge Connector to the computer. 8. To prevent possible shorts from IC pins pressing through the cable's shield, cut the pins in the area of the cable flush with the PCB and if available, tape a thin but stiff piece of cardboard under the cable. 9. Installation on the Expansion Interface is complete. Remount the PCB in the case, being careful not to short the exposed wires of the cable, so the DIN plug connector is alongside the CPU to EI edge connector. Procedure for the CPU board (see figure 3). 1. Select the cable with the female DIN connector and connect the twisted wire pairs as described below. 2. Solder the common leads (Black) of twisted wire pairs Green-Black and White-Black to point (1). 3. Solder the Green wire (CAS) to point (2). 4. Solder the White wire (RAS) to point (3). 5. Solder the common wire (Black) of the twisted pair Red/Black to point (5). 6. Solder the Red wire (MUX) to point (4). 7. Position the CPU board back into the lower case. Route the cable towards the CPU to EI edge connector. With a wire tie, tie the cable to the nearest case standoff, this will prevent the cable from being pulled loose at a later date. 8. Position the top case so that you can route the DIN connector through the card edge cutout (you may have to work the connector through the cutout because of the close tolerance). _____________________________________________________________________________ Proprietary Information TB I:12 Tandy Corporation PAGE 3 OF 7 TECHNICAL BULLETIN COPYRIGHT 1992 _______________________ TANDY COMPUTER PRODUCTS ______________________ SYSTEM CHECKOUT 1. Position the TRS-80 and the Expansion Interface in their normal operational locations. 2. Connect the Buffered cable to the TRS-80 and Expansion Interface. 3. The system should be tested with a full 48K of RAM. If needed, install some RAM temporarily for the testing procedures. 4. Connect the CPU and EI DIN plugs and run the following programs for checkout: a. MEM4 b. DMT c. FORMAT d. BACKUP _____________________________________________________________________________ Proprietary Information TB I:12 Tandy Corporation PAGE 4 OF 7