I've breadboarded a circuit that is basically working but could use a tune-up. It isn't as fast as it could be, and more importantly I'd like opinions on whether it will work as intended.
I need to test a TV flyback transformer. There's a commercial ($50) tool for this, but after reading how it worked, I realized my breadboard from a previous project already had the ICs on it I could use to create a similar circuit. The schematics and explanation for the commercial device are given in these pdfs.
First gen View attachment 43636
Second gen View attachment 43635
My circuit:
Note: I haven't drawn in all of the LEDs, but they're there.
One advantage of my device is that by using the 4017 counter, it lights only one LED at a time, saving power and reducing the parts count, since all LEDs can share a single resistor.
Here are the issues:
1) The Blue device runs at 10Hz, producing a 2ms low pulse every 100ms. My circuit runs well up to 10 Hz (set by timer R1, R2 and C2), but fails to give the same results when the low time, the discharge, is reduced below about 15ms. This may not really matter to actually using the tester, but it annoys me that it can't seem to go as fast as the Blue device.
2) The RC (C3 and R5) of the reset pulse sent to the 4017 counter is 47µS versus just 4.7µS for the Blue device. I've been able to get a proper reset of the 4017 with a 18µS pulse but never less than that. This could be due to the LM358 being a bit slow to hit the reset threshold of the 4017, but using a faster op-amp (MC33178) didn't change things. The 4017 counter should be able to reset more quickly, shouldn't it? As with (1), I don't think a slower reset is fatal to the useful operation of the tester, but I don't see why my circuit should be slower than the Blue device.
3) My biggest problem is I don't have any "good" flyback transformers to test versus "bad" ones. I've tried my tester with some transformers from the junk box and can get up to 8 "rings" indicated. (Yay!!) But plenty of other inductors I have give little to no response. The Blue documentation says you can get some result just by wrapping the test leads around each other. Not me. I knew going in this would be the biggest problem: I'm concerned I'll use my tester and not know how to interpret the results.
Any ideas?
I need to test a TV flyback transformer. There's a commercial ($50) tool for this, but after reading how it worked, I realized my breadboard from a previous project already had the ICs on it I could use to create a similar circuit. The schematics and explanation for the commercial device are given in these pdfs.
First gen View attachment 43636
Second gen View attachment 43635
My circuit:
Note: I haven't drawn in all of the LEDs, but they're there.
One advantage of my device is that by using the 4017 counter, it lights only one LED at a time, saving power and reducing the parts count, since all LEDs can share a single resistor.
Here are the issues:
1) The Blue device runs at 10Hz, producing a 2ms low pulse every 100ms. My circuit runs well up to 10 Hz (set by timer R1, R2 and C2), but fails to give the same results when the low time, the discharge, is reduced below about 15ms. This may not really matter to actually using the tester, but it annoys me that it can't seem to go as fast as the Blue device.
2) The RC (C3 and R5) of the reset pulse sent to the 4017 counter is 47µS versus just 4.7µS for the Blue device. I've been able to get a proper reset of the 4017 with a 18µS pulse but never less than that. This could be due to the LM358 being a bit slow to hit the reset threshold of the 4017, but using a faster op-amp (MC33178) didn't change things. The 4017 counter should be able to reset more quickly, shouldn't it? As with (1), I don't think a slower reset is fatal to the useful operation of the tester, but I don't see why my circuit should be slower than the Blue device.
3) My biggest problem is I don't have any "good" flyback transformers to test versus "bad" ones. I've tried my tester with some transformers from the junk box and can get up to 8 "rings" indicated. (Yay!!) But plenty of other inductors I have give little to no response. The Blue documentation says you can get some result just by wrapping the test leads around each other. Not me. I knew going in this would be the biggest problem: I'm concerned I'll use my tester and not know how to interpret the results.
Any ideas?
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