GDT doesn't output signal

[LoOdaK]

Hi all, I recently got a chance to test my logic board for my first sstc and I have one problem.

First of all, I must say I'm constrained in terms of test equipment, I only have a digital multimeter.

Schematic:

What I tried to do is to simulate the interrupter signal using a 555 timer set to a very low frequency, maybe about 1Hz.

I measured inputs to the UCC27425 enable pins and I have voltage when the interrupter signal goes high.
I measured between pin 7 and pin 5 of the UCC27425 and the same thing was observed.

The problem occurs when I try to measure between the UCC27425 output pins, which are after 1uF capacitor (schematic), I don't read any voltage.

My question is, am I doing my measurements incorrectly, or have I messed up my circuit somewhere ? I know a multimeter is not ideal for this situation but that is what I have now.

Note: GDT is connected to the circuit, I tried to measure GDT outputs but there is no voltage present also.

[Magneticitist]

You will probably read little to no voltage feeding the interrupter pins with this signal especially at such a low frequency.
You need to put the signal into the feedback pins and just have the interrupter pins tied high if needed. Use a higher frequency so the GDT doesn't just get ringing pulses. Do something in the hundreds of khz or something. Assuming a 50% duty cycle you can use the DMM to measure the gate driver output voltages and expect a DC reading of half the pk voltage at the time.

[Rafft]

a dmm is wayy slower than an analog vom. maybe get a  logic probe of some sorts(or diy it) if you dont have access to a proper oscilloscope. a dmm is not meant for probing GDT outputs

[Mike]

So far everything sounds like it's working properly.

You can see a signal between pins 5 & 7 of the UCC27425 which means that the output is working. .You won't see much after the capacitor because the signal there is AC coupled, so it returns to zero very quickly when there's a transition. If you had an oscilloscope you'd see a spike up to 12V followed by a rapid decay down to zero volts, on an analogue meter you might see a little twitch of the needle. How long this spike is would depend on the GDT and the load on the output but is probably only a few tens of micro seconds, this is fine because when you have actual feedback from your antenna the output would switch again causing another spike in the opposite polarity.

I'd continue adding the rest of the sstc and see what happens. From this point on you will be running a little blind without an oscilloscope. If something like a siglent or rigol is outside of your budget at the moment, even those cheap "kit set" or similar scopes are handy for having some idea of what's going on. Most of those really cheap scopes can't live up to their specifications and often claim sample rate as bandwidth, but if the sample rate is ~10x your oscillation frequency it will at least let you know that things are working correctly. Something like this https://www.aliexpress.com/item/32973233356.html has plenty of limitations, but is a lot better than nothing.

[LoOdaK]

I forgot to mention, that I have an LED placed in the circuit to know when the signal of the interrupter goes high.
I have adjusted the timer to output signal in couple of khz and I was reading about 2.5 volts after the capacitor, and I have about 3.8 volts on the output of the GDT which seems ok, my transformation ratio is about 1.5.

Thanks Mike, I will definitely look into buying this little scope, I hope it will be okay for now, until I save for something better.

I will continue with my build and post If I come across another problem. Thanks a lot guys.