View Full Version : TI 99/4a black screen

September 22nd, 2018, 08:48 AM
just got a used TI 99/4A that suppos to work. I only get a black screen thorugh the modulator. Although the machine seems in nice condition and the modulator is in good shape (tested). Any ideas how to start looking for possible problems?

September 23rd, 2018, 11:29 AM
An quick guess would be the VDP (TMS-9918A) which is socketed and big.

September 27th, 2018, 11:16 PM
Do you hear any beeps or other sounds when you turn it on? If you press a key right after it boots, do you hear a beep? You should hear a beep on startup and the first time you press a key (and you can get a third beep if you press the "1" key after that). If there are no beeps at all, your machine isn't making it through the initial boot process. There are several possible problems there, so knowing what the machine is doing will help. There is a troubleshooting guide for the 99/4 on the WHT FTP (https://ftp.whtech.com/datasheets%20and%20manuals/99-4%20Computer/) site. Look through the flow charts to see where the problems may lie. One note, the manual is for the 99/4, not the 99/4A, but about 95% of it is applicable.