View Full Version : TI-74 problem, need C70009 datasheet...

March 10th, 2011, 02:04 PM
I have this computer, it have hardware problem, probably in main CPU. There is the 5V VCC and crystal oscillator works, but there is no any impulses on the other pins of the chip. There is contrast regullation only of the half display, probably caused of the un-working CPU, I think there is no problem in the LCD module. I try to unhook the whole reset circuit, but I am not shure that was the reset circuit, so I need datasheet or pinout of the CPU... Also I desoldered all the via connections between the layers of the main PCB, there is no result...

The TI-74 inside:

http://s2.postimage.org/2fgqtcd5w/P1010007.jpg (http://postimage.org/image/2fgqtcd5w/) http://s2.postimage.org/2fgu4f25g/P1010006.jpg (http://postimage.org/image/2fgu4f25g/)

March 12th, 2011, 07:10 PM


Here's what's out there - Good luck.


March 23rd, 2011, 03:12 PM
Thanks for the help, the CPU is already dead...

March 24th, 2011, 06:27 AM
Fortunately, 74's aren't that rare. That's probably the only place you'll find the exact cpu needed.

TI was really bad about putting machine specific ROM sequences in the cpu. That's what differentiates the TMS 7000 in the TI-74 from the one on the TI-95 and CC-40. Heck, the CC-40 even had 2 different cpu's in it, the 70C20 and 70C40! Only difference were a few patches on the OS.

IF I remember correctly...