I would initially test replacing the thyristor with a momentary switch
from anode to cathode. Be careful! 

If you can trigger the tube by activating the switch the t1, r21 and c15 are ok.

If you can not, expect a problem with the capacitor. try a different one. You could
try raising its value to 220 nf or so.

If you are able to trigger put the thyristor back in , pull the optocoupler out.
put the  momentary switch in the spot where the opto's transistor is.

If you can still trigger the circuit the thyristor is ok and the problem must be
with the opto or the quality of the pulse to the led of the opto.

If you can not trigger the flash with the switch the current into the gate may
be insufficient for the thyristor, check diode polarity, double check r20's value and
check the thyristors gate to cathode diode.

Peter


----- Original Message ----
> From: Jinx <joecolquitt@clear.net.nz>
> To: Microcontroller discussion list - Public. <piclist@mit.edu>
> Sent: Thursday, July 16, 2009 10:49:31 PM
> Subject: Re: [EE] High voltage opto-coupler
> 
> Picked up my H11D1 optos for Figure 3 at
> 
> http://www.rory.co.nz/projects/lighting/beat_strobe.html
> 
> and been trying, unsuccessfully so far, to get a flash out of it
> 
> The problem appears to be that the SCR gate rises to only 200mV
> when the opto is activated. Looking on the scope there don't seem
> to be any gate pulses higher than 200mV and no activity at all on the
> cathode. Voltage on the cold side of the 2k2 (opto collector) also
> drops to near-zero
> 
> With the transformer out however, the gate sees 65V (V+ = 310V).
> Using a 470R resistor as a light load instead of the transformer the
> gate voltage again drops to 200mV
> 
> Transformer datasheet
> 
> http://www.jaycar.co.nz/products_uploaded/MM2520.pdf
> 
> It measures OK. Something under 1R on the primary and 17R on
> the secondary. I've tried a couple of BT151 800R SCRs, rated at
> 100A peak. It seems a bit unlikely that a-k is broken, given the
> energy available from C15
> 
> Any ideas ? The author's pdfs show no extra, omitted or changed
> components so of course I wonder why his works and mine doesn't.
> My only thought would be a separate 65V supply for the opto/gate
> that won't drain C15 (if that's what's happening now)
> 
> TIA
> 
> 
> -- 
> http://www.piclist.com PIC/SX FAQ & list archive
> View/change your membership options at
> http://mailman.mit.edu/mailman/listinfo/piclist



      
-- 
http://www.piclist.com PIC/SX FAQ & list archive
View/change your membership options at
http://mailman.mit.edu/mailman/listinfo/piclist