Testing ti99/4a without powersupply?

[Seob]

I have a ti99/4a, but i do not have a powersuplly for it. Any change of testing it without the original power supply? Can i hack into the circuit on some spots, since it uses 19v ac, i assume it converts the power somewhere to dc for the mainboard.

[Ed in SoDak]

Juice is juice if it meets the power input specs. TI supplies should still be plentiful; most of us with even minor TI collections should have several on hand. The outboard supplies were also sold as surplus for years after TI stopped, besides those that came with every console sold by TI. Thus, no lack of genuine TI AC supplies. It's actually a dual voltage supply, with pins 1 & 2 supplying 18VAC and pins 2 & 4 carrying 8.5 VAC, so 19 VAC alone won't cut it.

 

Hack-wise, I'd simply tap onto the connector on the rear or solder directly to the power port on the inside of the case and bring out your own wires. Specs for the power port are widely published, plus full schematics of everything, so it should be quite easy to find the pinout. And yes, the console did carry it's own supply board with regulators to convert the incoming AC. The only place in the TI99 to tack in "raw" AC would be on that board, and its AC input comes straight from the rear connector.

 

Which would all be laid bare once you open up your console, with no need to open the clamshell covering the main board, just aim for the power board located beneath the cartridge port and its connector to the rear of the console and all will be pretty self-explanatory.

 

-Ed

Edited March 22, 2018 by Ed in SoDak

[Opry99er]

If you need a power supply (and youre in the US) just send me your address.

 

If youre abroad, there are users all over the world who might be able to help you.

[Seob]

Had a bit of difficulty trying to figure out the power output of the power board since nothing is labeled. According to http://www.mainbyte.com/ti99/hardware/power_supply.htmlthe board I have is the top one, the ti99 one. If you would then convert the pin out using the second psu board and the connector pin out down the page, I would have wired the psu wrong and had blown out the ram chips.

Using the scematics on the page and trying to trace back the leads I was finally able to wire my ti to a pc power supply.

And it works. Next I need to modify the rf modulator so I can use component video instead of rf.

[Tursi]

Good work! Fair warning to anyone else trying this though -- I've had at least one TI motherboard that does have power labelled - and the labels are wrong. So work slow and careful if you're trying to run without the power supply board.

[Ed in SoDak]

Glad you got juice and not smoke! The RF modulator is easy to figure out. I traced the wires from the console and soldered on a couple RCA cables and modified the cover a bit so they would pass. One cable is line level output for sound and other is composite video. I didn't need a new cable and still have RF output if needed. To derive component-level Y/Pb/Pr would probably require a converter of some kind.

-Ed