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TI/99 4a clone

Almost everything is available through Mouser, Digi-key, Jameco and Unicorn Electronics.

The TI-99 specific ICs, well you’re going to have to use your best judgement on the source. I suggest only buying within the US (If you’re US based).

Here’s mine so far…
 

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I always order common ICs from Mouser; but for the TI specific ones I've only found Chinese sellers, yours come from China?

Btw, good work, seems that you've mostly finished the building phase!
 
Shared from another forum…I’m in the same situation with my build.

“I decided to power the 99/22 up after triple checking all connections for solder bridges. Having my fingers crossed and nothing. Just a black screen, no tone, nothing.

So, for my first test, I tested all my voltages to make sure they were all reading good on all the chips for their correct voltages. On the 9900, -5v on pin 1, +5v on pins 2 & 59 and +12v on pin 27, all read good. Verified none of the logic chips are getting hot which would indicate a bad or fake IC. Next, I pulled out a logic probe to start testing some things and I have found that pin 6 (reset) of the CPU is being held low. The reset line of the CPU should stay low for a split second then go high when you turn the unit on. This is not the case, it stays low, this will basically cause the processor to halt from my understanding and not allow it to do anything at that point.

I know the processor is good. I have pulled from a working unit the TMS9900, 9901, 9904 and 9918.

Now I'm at a loss. What could be causing the CPU reset line to stay low at power up? According to the troubleshooting guide I need to check U601, which I believe is the 9904 (maybe someone can verify that for me). the 9904 tests good and as I said came from working unit and it was already socketed so it was an easy pull for testing.

suggestions anyone?”
 
It's looking like the 9904 could be the culprit. The TIM9904ANL, which is fitted to my and others boards requires a 12MHz oscillator and different resistors and capacitors. According to those in the know, these 9904ANL was fitted to later 99/4As. The /4 and early /4As used the 9904N and a 48MHz crystal. This should have been changed on this board to use the later common configuration of the 9904ANL with the 12MHz osc and associated components to support the ANL IC.

I will follow up if this is indeed the fix. For now, it's a waiting game while we wait on 9904N chips to arrive.
 
Thanks Steve, I was worried that something was not quite right with the board PCB. I started looking at the pad and through holes, without criticising, I think this board was computer routed, it lacks the fingerprint of hand routing. I would love to reroute this board by hand, so many small details I would change, first I would move U15, U14 and U10 to the left to give more room for the cartridge. I am sure the Crystal choice is the only problem, I know Dan Werner had the board operating and I am grateful he did all the hard work for this project, I am looking forward to building this unit, thanks for your help.
 
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@artoj I can’t take credit for the 9904 issue. I’m just passing it along from what others are discovering. I want my board working as much as everyone else building one of these and anything I can do to make it easier and less stressful, I will.

There’s two options, get a 9904N or swap out the needed components to support the ANL IC.
 
Here's my 99/22 up and running.

I have shift838's 99/22 specific USB keyboard adapter, internal I/O Port Extension, and GROM riser installed. I also have a Pico9918 installed in the VDP socket. I can confirm that the TiPi and speech synthesizer works with the 99/22.
Some things have been discovered:

TI BASIC is unstable. TI Extended BASIC works much better.
It has been confirmed that FinalGROM is a no go.
The sound chip chosen for this board in unobtainable. Cannibalizing one out of a 4A is your only option here.
Making the internal Extended Basic work requires an EPROM and some sorcery with the unicorn board, thus far, we have been unable to make it work.
The internal cartridge port and the GROM port can not be used together, it's one or the other, no exceptions.
 

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The sound chip chosen for this board in unobtainable. Cannibalizing one out of a 4A is your only option here.

You mean U33 - SN76489?. Through eBay sellers it can be easily found, most of them being cheap. Of course usually are chinese supplies; but I'm sure you can find a US seller or at least a trusted chinese one. I think that the 76489 is not commonly faked...
 
I shouldn’t have said unobtainable. We’ve discovered that is doesn’t put out the right sounds that you’d expect from the 4A.

Example: the high pitch beep comes out as the low “donk” sound. Not sure if it’s the sound chip itself or something else in the board.
 
Complete for now. I built up the Shift838 Unicorn Board. There's a new I/O board in the works. Stay Tuned.
 

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