{"product_id":"156569","title":"443-720","description":"\u003cp\u003eHeathkit and Zenith Data Systems tech documentation, 443-720 is the proprietary engineering part number for a widely used logic integrated circuit (IC).Specifically, 443-720 maps directly to a 74LS203 (or in some layouts, standard 74LS20 Series variants), which is a Dual 4-Input NAND Gate or specialized digital buffer chip. You will find it populated on everything from memory maps to terminal logic loops.If you are restoring or troubleshooting an old rig, it acts as a critical component in the following classic service manuals and circuit footprints:1. Mainframe Terminal \u0026amp; CPU BoardsZenith Z-89 \/ Z-90 Microcomputers: It serves as a glue logic gate on the main system logic board. It controls peripheral interfaces and addresses decoding boundaries alongside part numbers like the 443-792 and 443-730.Zenith Z-100 Series: Used extensively across early S-100 bus motherboard variations for data-bus stabilization and control routing.2. High-End Transceiver LayoutsHeathkit SS-9000 HF Synthesized Transceiver: If you look directly at the Terminal Interface \/ ROM subsystem schematic (specifically Part 10 of 12 on the original factory schematics), 443-720 is explicitly labeled on the chip pinout layout driving the logic gates for the peripheral control bus (U803A).\u003c\/p\u003e","brand":"ZENITH","offers":[{"title":"Default Title","offer_id":67588501504053,"sku":null,"price":16.95,"currency_code":"USD","in_stock":true}],"thumbnail_url":"\/\/cdn.shopify.com\/s\/files\/1\/0219\/7936\/5440\/files\/AP1GczMCXO008qp_K_VXunEu61QWnXtd3NkGOWdDz0peLYOg4Xv4cYFMW7itqIwl9cd0KhO7cKrg1WWt-UYJp4Zf6iqYS-tDHaexsMLRzhbnwFQ-4y6hN3rDcy9wgpit2AtcG0rulfDUGNSry57Y5nDdAw9BrQ_w1794-h1794-s-no-gm.jpg?v=1790724607","url":"https:\/\/greenbrookonline.com\/products\/156569","provider":"Green Brook Online","version":"1.0","type":"link"}