No high voltage ! - need your help

[martin martin]

Hey guys,

I found this unfinished Nixie clock project from a guy on the Bay.  After sitting around too long in a box I finished the assembly.  The 12 VDC is fine and the color LEDs do cycle.

However, the 200 VDC D1 is only 12. I did replace UF4007.  I see 12 V at the 100 uH choke too.  I am getting a a small square wave at the OUT of U2

Any ideas why I can't get 200?

thanks!

martin

[Kevin A.]

Sounds like this 555 based boost converter isn't actually switching.

Check the gate of mosfet Q5 to see if the square wave is reaching it. Either the switching tranny is bad or it's not actually being getting any signal at the gate. 

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