I thought I'd start a topic on my Space Duel upright, which developed a problem a while back -- The screen would "collapse" in the Y axis partially, with bands of the display working and at the edges of the properly-displaying bands, you'd see a bunch of vectors overwriting themselves on one horizontal line (IIRC). Sound familiar to anyone? (I'm kind of thinking DAC issue, with one or more bits feeding into the DAC getting dropped, or something like that).
So, it was doing this to me one day and I already had the back off, so I looked around the back just in time to see one of the discrete transistors (I believe it was Q12 -- at least that's the one I have marked) start smoking. I killed the power, ordered up some replacement transistors and promptly got busy with other things in life and haven't gotten back into there until now.
I took the board out last night and started looking at it, and noticed that in addition to that transistor having smoked, C107 (associated with -15V supply circuit) is totally toasted:
C107 is a 2.2uF, 35V tantalum cap. Just for grins, I'm also going to replace the 7915 voltage regulator and the other electrolytic filter cap.
I'd appreciate any input you all might have on this -- any reason this cap would fail like that which would indicate a problem elsewhere? Might it have hosed something else? I ask because the -15V is used in the DACs, and Q12 is part of the DAC reference and bipolar current reference circuit. And the Y output looked questionable with what looked to me like a DAC issue before things went really bad. Coincidence? Or might there be a bigger issue?
This is an -02 version PCB, BTW.
So, it was doing this to me one day and I already had the back off, so I looked around the back just in time to see one of the discrete transistors (I believe it was Q12 -- at least that's the one I have marked) start smoking. I killed the power, ordered up some replacement transistors and promptly got busy with other things in life and haven't gotten back into there until now.
I took the board out last night and started looking at it, and noticed that in addition to that transistor having smoked, C107 (associated with -15V supply circuit) is totally toasted:
C107 is a 2.2uF, 35V tantalum cap. Just for grins, I'm also going to replace the 7915 voltage regulator and the other electrolytic filter cap.
I'd appreciate any input you all might have on this -- any reason this cap would fail like that which would indicate a problem elsewhere? Might it have hosed something else? I ask because the -15V is used in the DACs, and Q12 is part of the DAC reference and bipolar current reference circuit. And the Y output looked questionable with what looked to me like a DAC issue before things went really bad. Coincidence? Or might there be a bigger issue?
This is an -02 version PCB, BTW.

