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Old 21st November 2012, 02:54 AM   #31
Zaapp is offline Zaapp  United States
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like a sawtooth wave? ramping up then almost immediately falling toward 0v
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Old 21st November 2012, 03:01 AM   #32
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In the attached image, the top waveform is better than the bottom waveform.
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File Type: jpg psP1010089bx.jpg (70.9 KB, 37 views)
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Old 22nd November 2012, 12:08 AM   #33
Zaapp is offline Zaapp  United States
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Alright, I got the irf3205s in the mail today, 2 days early. I placed the bds in and soldered them in, put the board back in the heat sink and clamped the remainder of the FETs down, used a regular automotive 10 amp fuse in line with the B+ wire, and wired it to a big dry cell battery.
when powered with remote I still get a quick flash of the protect LED and a few seconds later the internal relay clicks on. Just like before.

I used my scope on the gate pads for the FETs and I see a decent looking signal (scope does not have great resolution at all) but as far as I can tell it might only be 180-210Hz according to the scope, but it says 25kHz flat with my DMM... (I think I'll only trust the waveform on my scope)
Shall I install the FETs now? I'm also guessing that the circuit doesn't completely power until the missing FETs turn on and supply power elsewhere to the circuit, and that's why I'm only seeing the boot procedure I'm seeing without a power LED lit?
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Old 22nd November 2012, 02:08 AM   #34
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Post a photo of the drive signal.

Do you have any 1k ohm resistors on hand?
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Old 22nd November 2012, 02:42 AM   #35
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The power led doesn't have power until the one transformer is getting power from the 3205's. (the one closest to the speaker leads in your pictures). I wouldn't worry about this until you have some of the 3205's populated. If your gate signals coming from your new bd139/140 pairs looks good, you can get away with putting only two 3205's in on that left transformer as a test. Put the middle two in as this will probably get you one on each side of the gate drive signal. This way when you power it up and *if* something else is shorted you don't risk wiping out so many 3205's in the process, only 2.
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Old 22nd November 2012, 05:22 AM   #36
Zaapp is offline Zaapp  United States
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Click the image to open in full size.Click the image to open in full size.

that's the best that I can do with this scope, but like i said it says 25kHz on my DMM

I think I probably have some 1k resistors about somewhere... what shall I be needing them for Perry?
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Old 22nd November 2012, 10:48 AM   #37
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The 1k resistors would be used to load the drive signal to confirm that it's as it should be. With no FETs in the circuit, it's not always possible to see if there is a problem.

Neither of those signals displayed would be anything that I'd expect to see on the gate pads. Try it again but this time place the black probe (or ground for the scope probe) on pad 3 for the FET and the red probe on pad 1 for the FET.
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Old 22nd November 2012, 01:28 PM   #38
Zaapp is offline Zaapp  United States
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I don't exactly trust the scope waveform, since it's designed to pick up high voltage ignition events.
I'll take a crack at it right now, I'm still unsure of what to do with the 1k resistors... I load the circuit from where? pad 3 of the FETs to ground?
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Old 22nd November 2012, 01:42 PM   #39
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Post the waveform first.
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Old 22nd November 2012, 01:48 PM   #40
Zaapp is offline Zaapp  United States
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from pads 1 to 3 of the FETs

Click the image to open in full size.Click the image to open in full size.
when I feed the scope a 1k square wave with a wave generator, it just looks like a sine wave with squared off tops, like the first pic, and I see the same spike show up like in the second pic (which is what I believe is for only ignition/spark events)

Last edited by Zaapp; 22nd November 2012 at 01:50 PM.
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