Why am I getting all these crazy assed boards!
Whew!
Doing a repair/renew kit on a Bosconian (Same CPU board as Galaga but with an extra chip & ROM)... Replaced all the sockets... resistor packs were the good kind and didn't need replacing.
The board would boot but would come up with flickering on the text and the graphics would get all kinds of glitches and turn blocky. If you tapped on the board it would come and go (which makes the repair all that much stranger!!!) so I redid the solder joints, checked for bad traces/gouges, cleaned the board interconnect socket, and looked it over and over and over until I was sure it was all perfect.
Started probing things to see if I could hear the glitches on the screen with the audio on the logic probe. Found if I put it on pin 13 of one of the LS367 chips that the text would go crazy. Checked the schematics and it went to pin 1 of a 74LS138 and pin 13 on 2 more LS367 chips. Replaced all 4 of those chips.
Now instead of a perfect screen, the text was flickering and flashing all kinds of colors and every other character would flip upside down then right side up repeatedly. If you pressed start the game would crash... but there was no more flickering out to the blocky screen.
If the logic probe hit pin 1/15 on the upper 3 LS367s then the game would crash. These are the select lines to enable the outputs from the address bus to the video board through the LS367s. Replaced the other 2 LS367 on the main CPU's address bus and the game played perfect.
Replaced the other 3 LS367s for good measure.
Yes... the failed ones were Fujitsu chips. And they must've had failed bond wires because I've never seen a chip that failed to where if you tapped the board the symptoms would come & go.
What a strange freakin' repair!
Now to redo the sockets on the video board tomorrow.
RJ
Whew!
Doing a repair/renew kit on a Bosconian (Same CPU board as Galaga but with an extra chip & ROM)... Replaced all the sockets... resistor packs were the good kind and didn't need replacing.
The board would boot but would come up with flickering on the text and the graphics would get all kinds of glitches and turn blocky. If you tapped on the board it would come and go (which makes the repair all that much stranger!!!) so I redid the solder joints, checked for bad traces/gouges, cleaned the board interconnect socket, and looked it over and over and over until I was sure it was all perfect.
Started probing things to see if I could hear the glitches on the screen with the audio on the logic probe. Found if I put it on pin 13 of one of the LS367 chips that the text would go crazy. Checked the schematics and it went to pin 1 of a 74LS138 and pin 13 on 2 more LS367 chips. Replaced all 4 of those chips.
Now instead of a perfect screen, the text was flickering and flashing all kinds of colors and every other character would flip upside down then right side up repeatedly. If you pressed start the game would crash... but there was no more flickering out to the blocky screen.
If the logic probe hit pin 1/15 on the upper 3 LS367s then the game would crash. These are the select lines to enable the outputs from the address bus to the video board through the LS367s. Replaced the other 2 LS367 on the main CPU's address bus and the game played perfect.
Replaced the other 3 LS367s for good measure.
Yes... the failed ones were Fujitsu chips. And they must've had failed bond wires because I've never seen a chip that failed to where if you tapped the board the symptoms would come & go.
What a strange freakin' repair!
Now to redo the sockets on the video board tomorrow.
RJ

