Robotron video flashes/oddities

JDGJr

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Reassembled my robotron (after stripping paint and getting the base color applied), using rebuilt PS and reworked IO card (i had powered machine with fixed parts briefly before disassembling, but had not run it for long).

First day after re-assemble, i could play for about 30 minutes until it would reboot or halt - pressing the reset button would show LED code for bad ROM 6. Today i pulled the ROM and reseated the chip (didn't clean) and the problem has not come back.

However, after about 2 hours of powered on, with random plays, it started to display oddities, while allowing normal game play. Sometimes the screen is loaded with vertical stripes, sometimes the area that should be black is an odd green color. Typically the display is flashing between normal and messed up. When in attact mode, it sometimes displays only the green logo circles and the rest of the screen flashes the green color. Resets show 0 on the LED.

Turning the machine off for 10-30 minutes is not allowing normal operation.

any ideas what i can try?
 
Replace the defective 4116 chip on the main pcb. These damn 4116 chips seem to blow out all the time. You can replace them all with 4164 chips but you will then need an adapter.
 
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Although the 4116 RAM does indeed control screen graphics,
the problem would seem to be more video related
(... RAM would cause random color/pixel problems ),
the presence of all green would lead me to think
the problem might be with the Decoder proms. ( on the main CPU ).

Or...,
something as trivial as a bad monitor connection
(...I had problems once because the molex connector
was not properly seated on the header pins ... )

Good Luck.

Steph
 
I see the CPU board has a mix of 4116 chips.

The machine is now a bit more useful, and i was able to adjust the pots on the neck board to get a really crisp display of the 8 colors on test 7.

Guess i just have to keep playing to see if i can figure out the pattern of the display going bad.

thanks for the great suggestions!
 
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Typically when the video goes wonky it can be traced back to the +12V. You may need to reflow the power header on MPU board to make sure that you are getting consistant power.

The other thing to check is to check all of the transistors in the video section. They are frequently smashed down and can have the legs bent near each other. As the board warms up the legs may be making contact. Take a magnifying glass and a dental pick and carefully spread the transistor legs apart.

ken
 
Or...,
something as trivial as a bad monitor connection
(...I had problems once because the molex connector
was not properly seated on the header pins ... )

Looks like this was the root cause - video oddities went away when i reseated 1J1. Has been running for hours, hope it continues.
 
Looks like this was the root cause - video oddities went away when i reseated 1J1. Has been running for hours, hope it continues.

That will be $600 for trouble-shooting fees please !

;-)

Just kidding, ... glad you found the problem.

Cheers,
Steph
 
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