BBC Micro Power supply fix
8 May 2021
In search of the fault .. Commodore 64 black screen
9 June 2021
A brief history
The TI99 family of home computers was the first to have a 16bit processor and has been on sale since 1979 with the 99/4 and the successor 99 / 4A came out in '81. The computer was not totally 16bit but only in the communication between the processor with the RAM and ROM, the RAM to be precise is dedicated to the processor and therefore very limited, we are talking about a memory of only 256 Bytes, for the other functions 16K were used with 4116 DRAMs.
Production ended in 1983 when Texas Instrument left the home computer market due to the trade war with Commodore. This was Commodore's revenge for being ousted from the calculator market years earlier, when TI lowered prices so much that Commodore pulled out of this market. Now with MOS Technology in their hands and having all the components for its computers available, Commodore significantly lowered prices and made TI withdraw and allowed many people to have a computer at home at the expense of theirs. financial health which then made itself felt.
Enough chatter!
Now let's start putting some meat on the fire.
I took this computer also for the story it tells and also because I found it at an acceptable price, to be cleaned yes, but it works!
The version is PAL and unlike the NTSC one, this one does not have a composite output but a YPbPr, has an external RF modulator to allow connection to a TV and this is what we will modify to have the composite output.
Here you can see the inside of the modulator and the input pins on the RF block: starting from the right we find video followed by GND, and these 2 wires are all we need for our signal. Audio can be found on the yellow wire, but rather than cutting it, it’s better to solder a wire directly to the resistor shown in the picture.
The video connector has to be removed and the 2 AV RCA sockets can be fitted in its place. If you need a bracket to hold them, I’ve 3D-printed a holder for the 2 RCAs; you can download it from the page download or here:
ti99a_composite_rca.zip
To have a signal free from disturbances, I advise you to unsolder all 4 wires of the modulator.
This is the end result with RCA support.
As usual, the modification is non-destructive and it is possible to return to the original signal with very few steps.
Enjoy the component !.
It's not over yet!...
There is another modification to obtain the composite video and it consists in taking the signal on pin 13 of the LM1889 chip and amplifying it with a transistor, the scheme can be found on the side.
I also tried this mod to see if it was better than the other one but for me it wasn't like that. The signal obtained with this modification was less amplified, maybe I was wrong.
If you want to try, otherwise do the simple modification seen above.
if you are satisfied with a B / W signal just take the Y (luminance) output from the DIN connector of the computer.
The pinout can always be found below.
Check out the guys who created this mod:
https://www.ti99iuc.it/web/index.php?pageid=119&pagina=mod_proj1&sezione=4&data=Mod_and_Tuneed
Watch the video
3 Comments
ciao, bel tutorial, molto chiaro. sto modificando il mio ma il link al supporto RCA non funziona è 404… puoi sistemarlo o mandarlo via email? Grazie
Corretto grazie, avevo tolto l’account da Thingiverse
Bellissimo Tutorial…mi è arrivato un bel Ti99 e questo era quello che mi ci voleva. Chissà per la multicard se si trova qualcosa in rete…