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TI-99/4A does not boot up

PostPosted: April 26th, 2013, 2:00 pm
by Flywheel
My newly acquired TI99 does not work.
Please help, I am sure you guys have all the experience I lack with this system. My expertise is somewhat with ZX81 and ZX Spectrums.

I have tested the power supply: all the correct voltages are there.

I have removed and re-seated (not really cleaned yet) the GROM and video chips but I get the same effect:
- Black screen (at the correct channel 35/36 it is)
- Continous high beep sound (loud) starts after a second delay when switched on
- No boot, nothing, when switched off the sound and black screen are gone

The situation has not changed by removing the GROMs and Vid chip and re-inserting into the sockets.

I checked temperature of the chips:
- Processor gets warm
- Video chip gets warm but less warm than processor (from Internet docs I'd get this chip should be very hot he4nce the cooler)
- The chip next to the video chip gets warm (little bit warmer than video chip actually)
- Sound chip gets warm
- Middle two 4116 RAMs a little bit warmer than the rest
- GROM chips all a little bit warm
Nothing else warm, and nothing gets really hot.

Regards and thanks,


Re: TI-99/4A does not boot up

PostPosted: November 22nd, 2013, 11:01 pm
by ksarul
Definitely sounds like a video problem--and this is a pretty common problem with the /4A. You might want to change out the 9918A first, as it is socketed, but if that doesn't work, you might have to replace the VRAM chips. The VRAM dies more often than the VDP. . .