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In Reply to: RE: a breakthrough at last...... posted by vinnie2 on December 05, 2016 at 18:18:38
Thanks, 32.5 kHz makes more sense, although I'm still curious why the scope display showed about 140 kHz. That's worth revisiting, because you now have two instruments telling you different things. The scope won't lie, and that's the reason you need to repeat the previous measurement (I also posted on this below). Anyway, if 32.5 kHz is correct, it's too close to the audio band. That might be the reason it sounded harsh. So, you might still need to modify the little oscillator transformer to raise the frequency. I can walk you through that with photos if it will help (I'll need to do it to an unmodified unit and photograph the sequence). We should look at the scope display again before I do that.
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Buy Chinese. Bury freedom.
Follow Ups:
32.5khz is correct prior to removing some coils off the oscillator transformer. I have this same exact supply, removing a couple coils should net you around 65KHZ. That needs to be your next step and your done!
Is the oscillator transformer the little blue dude just to the left of the cap in the photo? that's going to take some careful surgery if it is.
Just unsolder, rewind and resolder
I tried this this morning and got a surprise I wasn't expecting. The Khz reading dropped to 18.5 from 32.5 when I unwound one loop of the blue wire and reconnected it. Thinking maybe I needed to unwind a loop of each color I did one of the red wire too. It dropped even further. What exactly did you do when you did yours to raise the khz? Which wire and how many loops? Did I do something wrong?
Also puzzled by the fact that the voltage goes down when you take a loop of the bigger toroidial, but the Khz is supposed to go up when you take loops off the smaller one. Seems counter intuitive.
My process is to...
1. Remove it form the board (solder wick works OK for this)
2. Cut the two primary leads at the terminals
3. Remove the bit of remaining wire soldered to each terminal
4. Resolder the windings after removing all but one turn on each side of the primary
Vinnie, I can photograph this process if you want. I'm home from work today, so I have time to do this if it would be helpful.
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Buy Chinese. Bury freedom.
Yes please! I am having a hard time understanding the process, and I really want to try this so I give it a fair trial. Thanks!
The center winding does not have any wraps.
The outside windings are just one wrap, not sure if direction makes a difference but I would think so, keep each winding identical just in case...
Edits: 12/07/16
Thanks, I will try that in the morning.
.
Thanks deaf, that will help a lot in the morning. I will let you know how it turns out.
"The scope won't lie, and that's the reason you need to repeat the previous measurement (I also posted on this below)."
One thought occurs to me: I have an old Tektronix analogue scope which has a potentiometer with a knob that is concentric with the horizontal sweep speed knob, and which, if turned anticlockwise from its default (clicked) position, allows a continuous downward adjustment of the sweep speed by a factor of up to about 4. If vinnie's scope is similar (and judging by the screen shot it might well be), then if by chance he had the sweep-speed potentiometer turned fully anticlockwise, the ostensible 1 microsecond per division would in actuality be more like 4 microseconds per division, which would mean a 32.5 kHz input would give the impression of being more like 130 kHz.
Vinnie, is there a potentiometer concentric with the rotary switch that sets the sweep speed on your scope? If so, can you check that it is rotated fully clockwise until it clicks? And then redo the previous measurement you showed in the screen shot?
Chris
I will check it before I run it again as TK has asked. I think it is locked full clock wise because I remember that from the initial set up procedure and I don't think I ever moved it. Will check it to be sure.
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