Not Getting around 100V In Step 4

Hi guys thought i would try build Baracuda rev A but i think something is wrong i have Populated Board to Step 5 Conclusive thought everything was oK till step 4 i am only getting around 51 Volts. Documentation 100V says this is the breakdown voltage of Q1 in the text
Completed step 5 thinking this would help and got 0V in this step.
Do You think Q1 is at fault or something else as i fear only half the voltage probably half the detection ability , so what are your thoughts as to where the fault could lie. Would appreciate some help as i am not so good at diagnosing faults. Graham

[kt315]

hi do you measure the HV by o-scope? what control pulse width on the GATE pin is?

[Graham]

Yes i measured the voltage with an oscilloscope today i will get some parts for step 6 and adjust r14 for 20uS but first i will get parts for step 6 from Jacar Electronics then i will go through step by step and try to discover lack of voltage fault will take some pics with a tablet and some screen shots as well and post them as soon as i can because i don't know whats causing this fault. appreciate any help but first will get pics and screen shots for you. Don't know what you mean by pulse width on GATE pin but will get TX pulse width, Main Sample and Secondary sample on U4 pins 4, 8,10 after i do step 6 will also show pic of oscilloscope voltage. have a good day all you guys . Graham

[Graham]

step 1 to 3 Ok step 4 ennomely hound using the Hantek 6022 Be with 10 By probe i was getteing max11.3V , min -51.5V point to point 62.7V but when i tried a 100 by probe different results got 12.5V max -110V min point to point 122V can't understand why maybe the 6022be dosen't like high voltages with the 10 by probes. these were using 20Us 20V.
Anyway step 5 adjusted to 0V with R6 . step 6i think was 500Us 5V.
Anyway here's some pics.

step 3 U4 pin 4

step 3 u4 pin 4 and u5 pin 7

step 6 u4 pin 6





step 6 u4 pin and pin 6

[Graham]

I was wondering for step 7 baracuda detector as i don't have a LF412A IC would i be able to use a Lt1057 i think i have one of those somewhere it's pin compatible but would i need to make other changes to circuit if it would be ok to use the Lt1057 that's great if not i will have top order an LF412A from overseas that's going to take a while though. Graham

[kt315]

sorry, but your 'Attachments' do not open. certainly you have to use modern opamps, if can. LF412 is good but
obsolete. but in this world of china fakes original USA made LF412 is better than china one LF412. they do not do
something better, they procreate just low performance chip in all housings. chinese world of industry is parasitic.
sorry, my english is low to tell you more.

[Koala]

does Q1 get hot after a minute or so ?

[Graham]

Try srend Pics again















will test heat tomorow after 1 minute Graham

[Graham]

Checked Q1 IRF9530 ran for several minutes only seemed to get a little warm but then it is pretty cool in Ipswich Queensland Australia at the moment being winter. but think it will be Ok but still have the last 3 steps to install yet if the heat changes after the next 3 steps may have to use a heat sink but seems ok for now.Graham