Scoping UD 2.7 GDT outputs, does this look normal? / Tesla Coils / Forums

Forums

4hv.org :: Forums :: Tesla Coils

« Previous topic | Next topic »

Scoping UD 2.7 GDT outputs, does this look normal?

Move Thread

LAN_403

nzoomed

Wed Apr 27 2016, 09:20AM

Registered Member #54503 Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288

Im running my initial tests and am doing what loneoceans instructions say and am injecting a signal into the CT input on the driver board at 5VAC at 50KHz, my signal generator only goes up to this so i hope 50KHZ is OK. I would have liked to go higher.

Anyway, it does not look like a clean square wave when scoping the GDT outputs when the midi interrupter is turned on.
Below is my screenshot. Its at 10v per division and 2m/sec on the time base.

Loneoceans also says that all four pins on the UD board should put out a clean square wave.
I only get what you see in the image below on the two outer pins (the left pin on the first GDT output and the right pin on the second GDT output)

TIA for any help.

nzoomed

Wed Apr 27 2016, 09:22AM

Registered Member #54503 Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288

here is the photo

1461748966 54503 FT176577 20160426 224849

Blackcurrant

Wed Apr 27 2016, 10:35AM

Registered Member #2989 Joined: Sun Jul 11 2010, 12:01AM
Location: UK
Posts: 94

What sort of load do you have on the GDT output?
You could use a resister and capacitor to give a sort of dummy load if needed for testing.

nzoomed

Wed Apr 27 2016, 11:25AM

Registered Member #54503 Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288

Blackcurrant wrote ...

What sort of load do you have on the GDT output?
You could use a resister and capacitor to give a sort of dummy load if needed for testing.

Well i guess i should try hooking my GDT up to the outputs, im just following the instructions for initial testing.
Do you know if its normal to get only a signal on one pin on each GDT output?

From what i read, all four pins should give a signal on the scope with the earth lead grounded to the board.

Blackcurrant

Wed Apr 27 2016, 01:15PM

Registered Member #2989 Joined: Sun Jul 11 2010, 12:01AM
Location: UK
Posts: 94

Probe the tabs of the FDD8424H?

As all the parts are very small I would go over it with an eye-glass and look for solder splots/blobs etc
Is any part getting a bit hot, supply current a bit high etc.

loneoceans

Wed Apr 27 2016, 03:18PM

Registered Member #4098 Joined: Fri Sept 16 2011, 09:26PM
Location:
Posts: 236

If you have 2ms/div, you will not be able to see the 50kHz driving signal.

From the scope shot it looks like your signals are interrupted at ~5ms intervals (BPS at ~200). You need to zoom in -much- more to see the driving waves. At 50kHz, the square wave should have a 20us period so zoom in closer to something like 20us/div and you'll see it, just make sure your pulse widths are long enough (a few cycles of 20us at least). What you're seeing is just each burst at ~200Hz.

You should be seeing this on both outputs, failing which try probing the gates of each fet pair and see if they are being driven correctly. Likewise check the voltages going to the D and S of the fets. Did you replace the blown fets previously, and are they working correctly?

By the way may I recommend creating one single thread on your coil build on 4HV? You've created something like 15+ threads just on the same project asking one question each thread. Many possible issues may be inter-related and it would be more useful as well as much more tidy to have all the build details and questions in a single thread.

nzoomed

Wed Apr 27 2016, 09:30PM

Registered Member #54503 Joined: Sun Feb 22 2015, 10:35PM
Location: New Zealand
Posts: 288

Ive carefully scanned the board for blobs of solder and bridges etc, i gave it a good scrub with flux cleaner to get rid of any blobs that may have been stuck.

No components appear to be getting hot that i can see.

Loneoceans, yes i did zoom in all the way with my scope and it just widened the gap, thats all.
Im going to try and see if i have better results on my friends Rigol scope.

There was only one fet that i saw smoke come from and that was the top one (I think U1?) At the time i quickly switched it off and that one was the only one that felt hot. They are a complementary pair in the same package from what i can see.

Ive just managed to find another source so have some more spares ordered, so i may end up replacing the lot, but i figured that the other pair should be working OK.

I dont think its possible to test them properly on the board with other components in place, but ill check the voltages as you mention.

Anyway it looks like things are getting close for me now which is good.

Sorry for creating several threads, but ive found i dont get any replys if i change the subject on a thread ive already started, but i will have a thread on the coil soon when i start putting it all together.

Moderator(s): Chris Russell, Noelle, Alex, Tesladownunder, Dave Marshall, Dave Billington, Bjørn, Steve Conner, Wolfram, Kizmo, Mads Barnkob