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#1
04-15-2017, 01:40 PM
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Here are pictures of the pattern composite wave forms. Vertical scope input is .5 volts per division.
    
Last edited by Kevin Kuehn; 10-21-2017 at 08:52 PM. 
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#2
04-15-2017, 05:52 PM
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I was staring at my scope screen pictures and it finally dawned on me that the vertical sync pulse was about 1500 uS long. Duh! So I tried adjusting the vertical blanking pot and it has zero effect on the width of the sync pulse.
Last edited by Kevin Kuehn; 10-21-2017 at 08:53 PM.
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#3
04-15-2017, 08:05 PM
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That was it. The vertical sync pulse was so long it was blanking too far into the beginning of next frame. All it needed was a 1.5k resistor from ground to the vert sync input of the sync mixer gate, so now the vertical blanking width control works as expected. The way it was, the gate input couldn't recognize the change in pulse width(RC differentiator) because it had no DC reference. Apparently that was an inherent design flaw. Now I have to wonder if Heathkit at some point implemented a fix for that small oversight.
  
Last edited by Kevin Kuehn; 10-21-2017 at 08:55 PM.
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#4
04-15-2017, 11:56 PM
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Before you fixed the problem I was going to say that the horizontal sync pulses look a little too wide. Maybe your fix changed that also.
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#5
04-16-2017, 12:32 AM
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Quote:
Last edited by Kevin Kuehn; 10-21-2017 at 08:57 PM.
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#6
05-11-2017, 12:56 PM
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I've had one of these for a long time. If I remember correctly, mine does the same thing. I replaced all the IC's and IC sockets. I'll pull it out. Maybe you just got the answer on fixing these critters!
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#7
05-12-2017, 09:56 AM
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I've got mine open here. Digital IC's are not my forte', I admit. Could you tell me from what junction of two parts you put the resistor to ground.
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