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Finished and verified: SMD replacement boards for Horizon HRD+

As previously mentioned, I’ve been working on an old Horizon HRD+ RAMdisk card for the TI-99/4A. Three of the chips (a 74LS138, a 74LS154, and a 74LS259) had other chips stacked and soldered on top of them, with leads bent out and wires connecting to various places on the board. One chip (the 154) is […]

Real instructions on getting a Lantronix UDS-10 serial-to-Ethernet bridge working

The Lantronix UDS-10 is rather popular among the AtariAge TI-99/4A crowd. It’s basically one port of a Cisco 2511; it’s a bidirectional telnet-to-serial bridge. The TI folks use it to connect to the outside world, because it is extraordinarily unlikely that the TI will ever get even a ten-megabit PEB card, due to the screwed-up […]

The HRD+ upgrade design is validated

The final piggyback board arrived today; this one eliminates the open-collector 74xx156 with a 74xx155 and a 74xx08 to handle what the pullup resistor used to do. Everything works well, with one caveat: I never could get reliable operation out of the low-power CMOS 6264 handling the DSR. The old [HN]MOS 6264 that came with […]

Notes on building a 32k RAM expansion for the TI PEB

I finally gave up on the OEM TI 32k RAM PEB card. It just wasn’t reliable … it passed all diagnostics that I could find, but it wouldn’t pass the acid test — function-6 GROM verification in Gazoo’s excellent Extended BASIC Suite v2.7. I’ve previously detailed attempts to build a working in-console 32k expansion. The […]

Replace your #$%& console power switch!

If “the solder joints are always bad” is rule #1 when repairing old gear, “the power switch is worn out and must be replaced” is rule #2. The TI-99/4A in-console power supply has a DPDT switch that handles +5VDC and +12VDC. The switch internals will wear grooves in the contacts over time. After nearly forty […]

Notes on reworking a low-serial-number HRD into a HRD+

Along with the Horizon 4000 (that I repaired and documented in the previous entry), IM also sent an original HRD. It uses the same board as the HRD+, but had a bit of extra glue logic and was missing the ‘259 and ‘138 stacks. It was populated with a number of stacked 6264s, and had […]