alan8086
Experienced Member
These updates are drifting - the endpoint elusive!
I've recapped my one working vdu driver board. It now does not work. At least I have nothing on the screen now. I managed to work out that I'd blown an NPN power transistor - the one on a heatsink. Also didn't realize that the cap that smoked was a bipolar type, so I've swapped that cap and transistor from spare boards. I've now got 15v back at the 4th pin on the connector plug - before I replaced the transistor, it was down to 6.5v, so it must have been pulling the supply voltage down.
The issue could also be the cheapness of the electrolytics I bought - off ebay. Too cheap to be true! I'll stick with Didgikey in future!
It's possible my driver board is ok but maybe ive damaged something on the psu/logic board. Ran out if time to test for Hor / vert / vid signals with my scope - I spent most of the afternoon removing and socketing the RAM chips on a friends TI-99 motherboard.
Try again tomorrow!
I've recapped my one working vdu driver board. It now does not work. At least I have nothing on the screen now. I managed to work out that I'd blown an NPN power transistor - the one on a heatsink. Also didn't realize that the cap that smoked was a bipolar type, so I've swapped that cap and transistor from spare boards. I've now got 15v back at the 4th pin on the connector plug - before I replaced the transistor, it was down to 6.5v, so it must have been pulling the supply voltage down.
The issue could also be the cheapness of the electrolytics I bought - off ebay. Too cheap to be true! I'll stick with Didgikey in future!
It's possible my driver board is ok but maybe ive damaged something on the psu/logic board. Ran out if time to test for Hor / vert / vid signals with my scope - I spent most of the afternoon removing and socketing the RAM chips on a friends TI-99 motherboard.
Try again tomorrow!
