Category Archives: TI-99/4A

Hardware/software for the TI-99/4A

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 … Continue reading

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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 … Continue reading

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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 … Continue reading

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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 … Continue reading

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Refurbishing a TI PEB power supply

I’ve seen a number of people recommending replacing the older forty-ish watt TI PEB power supply with AT(X) power supplies. As with most stopgaps/workarounds that the TI community has come up with, I’m not sure that’s a good idea. The … Continue reading

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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 … Continue reading

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Well, it wasn’t the 32k card

I spent an unreasonable amount of time trying to get an in-console expansion working. I’d previously modified my main console with the 16-bit mod, which worked fine, and I thought I’d give Tursi’s scheme a test drive. I wasn’t successful. … Continue reading

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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 … Continue reading

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Refurbishing a Horizon 4000 RAMdisk

Ksarul and IM sent over a Horizon 4000 that wasn’t working right. To wit, it wouldn’t be detected at all by what passes for an OS on the TI-99/4A. got it working, and it didn’t take too long. Along the … Continue reading

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No more AtariAge.

Well, there I was basking in the warmth that was the TI-99/4A AtariAge forum. I felt comfortable, I was among friends (some of whom I wouldn’t like in real life, I think, but at least civil people). However, I forgot … Continue reading

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