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gary wrote:Oh and Harry please, please, PLEASE try and change only ONE thing at once per test I beg you - for instance when you change your pulse width have only one pulse width per test not various widths through the wave form which makes the wave form just a big mess and I can't show you the detail like I have in the first test.
gary wrote:Harry, I just want to make it perfectly clear that it is NOT becoming more sensitive to light, it is just that widening the pulse is making the average of the signal more positive.
gary wrote:aaaaah! That's better Harry (although really you should have a diagram showing us how you are tying the top circuit into the mixer - a couple of strokes of a pencil would do it). I presume the sync pulse from the is being fed into the top of the voltage divider at the base of Q1?
In any case you can't have blown up Q1 otherwise you would be generating no syncs at all (I assume it IS still producing syncs?)
Q1 is acting as a switch for the strobe input of IC2 effectively tying it to ground - when this happens the output pin 6 swings to the voltage at pin 4 (which is tied to ground.
SO, the fact that your sync pulses are so deep must be that black clamp level (top of R2) is NOT .8v (please check with a volt meter) OR the gain of IC2 is too high (set by R4 - please check it's value).
Harry, I should have asked this before but I have assumed that when you record your tests that the output of mixer is being fed directly into your sound card? That is, there isn't another gain stage between the mixer and the sound card?
Anyway if you could check those 2 values (black clamp - .8V, and R4 we might get somewhere.
[/quote]I have no explanation of why you are getting distortion when you supply rail is 12V - then again you haven't stated what kind of distortion it is.
The problem is at the moment the line sync pulse from pin 7 adding it to Q1 sync mixer with out over riding the video ...just looking into this again if a cap or a resistor or both might be a better way to connect the two circuits and as you said i also have an amplitude problem of the sync pulse might be again the 12 volt supply dropping that to the 4528 monostable should shrink the pulse it works from 3 to 18 volts ,another thing i didn't take into account.
gary wrote:Harry it should just go into the top of divider that's already in the circuit )between the pd1 and R6. (It's all on the same 12V power supply right?). The level of the input is not that important unless it burns Q1 out as Q! is only acting as a switch that is, on or off.
Harry first test - tie your video input to ground (VR1 full down will do that so it's easy).
[/quote]Record a few seconds of that and post please.
Note there should be NO ac content at all at "black level clamp" just .8V (approx).
gary wrote:Harry you just use the voltage divider part - it will look like the video input but it will be the voltage divider R6 and R7 instead of RV1 - you do understand that RV1 is just a "variable" voltage divider right? Just think of R6 and R7 being the same as RV1 with the slider fixed in one place.
Yes I know you have done it before but I want to make sure that the input is grounded - once I have confirmed that and had a look at the wave file then I can tell you what to test next.
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