TI994/A Power Supply

[wrcooke at wrcooke.net]

> On November 4, 2019 at 5:12 AM Liam Proven via cctalk <cctalk at classiccmp.org> wrote:
> 
> On Mon, 4 Nov 2019 at 06:59, Kevin Parker via cctalk<cctalk at classiccmp.org> wrote:>>> These voltages appear to neatly align with most PC power supplies so Ishould be able to tap into an old AT power supply of which I have quite afew.The PSU apparently outputs AC, not DC, which is unusual... but a PCPSU can do it, and Molex connectors can be bodged into fitting.
> Does this help?
> http://oldcomputer.info/8bit/ti99/index.htm
> Schematic:http://www.mainbyte.com/ti99/hardware/power_supply.html

A couple of notes.  First, I'm not all too familiar with the TI, but I was always under the impression the PS provided +5 and +12 DC.  For a while in the 80s the power supply module was available separate (even from Radio Shack!) and I bought one.
I did a quick search and found the same site Liam linked above.  It shows a schematic of a transformer providing 8 and 16 VAC, but then also mentions that there are various schematics floating around and that the author has been told his is non-standard.  It does also mention, however, that the machine uses 4116 RAM which requires -5V as well.  The summary is that I would make real sure what it takes before connecting anything.  If it does indeed need AC, it may use the AC internally to regulate -5V and providing DC could damage the RAM.
Another note is that many PC power supplies will have a minimum required load that the TI may not meet.  Some will simply not power on if the load isn't met, but I have seen a few that will provide unregulated voltage.  Been a while since I saw one of those, though.  but do be careful.

Will



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