Asteroids Deluxe Vector problem..

mcandrewsoun

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I dont think this is the monitor.. I repaired the 4016 and TL082 in the X output section of the board.. The screen looks completely out of whack, both on the monitor and on the scope in xy mode. The images appear in a smaller scale..but fill the screen. I was thinking that there may be some bits missing on the DAC..but both DACs? Anyway, I put the game in test mode, and Im getting two small crosshatch grids.. Looking at the x and y outputs on the scope, theres a wierd shift from pos to neg at the sametime on x and y.. Anyone ever seen this before?
 

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Fixed

After going through the tech manual, Since everything was in the correct spot (well mostly), just the wrong size...let me to the vector timing circuit. I was thinking the scaling lines were messed up, but they were all active.. finally checked the vector counters, and found the 161 was outputting all high. Couple of interesting notes.. I read somewhere to first check for "cool" chips. This one was noticeably cooler then the other 2 timers. Also it had been replaced fairly recently.. So I installed a socket..;-)

Andrew
 
After going through the tech manual, Since everything was in the correct spot (well mostly), just the wrong size...let me to the vector timing circuit. I was thinking the scaling lines were messed up, but they were all active.. finally checked the vector counters, and found the 161 was outputting all high. Couple of interesting notes.. I read somewhere to first check for "cool" chips. This one was noticeably cooler then the other 2 timers. Also it had been replaced fairly recently.. So I installed a socket..;-)

Andrew

Great tip and I will file it in my troubleshooting list. The opposite is also true - <carefully> check for very hot chips. I bought an infrared thermometer cheap on clearance at Radio Shack and it has been helpful, especially if there are multiples of the same chip I can compare the temps. Quick and dirty yes but still no substitute for an oscilloscope or logic probe.


Bill
 
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