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Faxitron MX-20 Reverse engineering (with some good results)

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KaneTW:
Here's the set of links:
Gun board: https://i.kane.cx/dFTeBu https://i.kane.cx/8JmAtu https://i.kane.cx/xvgpbQ
Controller board: https://i.kane.cx/H7T6TI https://i.kane.cx/GmY9hV https://i.kane.cx/VGPG0v https://i.kane.cx/TGXgZR

Gun board annotated with measurements:


Thermal cam shot:
 

The component getting hot is the reed relay K1. The temperature did not noticeably change whether it was on or off.

Some scope shots of the mA current output:
10kV: https://i.kane.cx/Mh6Z1i https://i.kane.cx/qQl6TF
20kV: https://i.kane.cx/FQfNOj https://i.kane.cx/3cXARo
35kV: https://i.kane.cx/s8l59J https://i.kane.cx/gcR71o

The high frequency content is always present and I'm pretty sure it's just EMI/bad probing (the current output port only fits a multimeter lead). The ~25kHz content however is increasing with increased kV, so something's weird there. Note that the average remains roughly constant at -250mV.

KaneTW:
After some debugging I noticed that L2Q was set to a way higher value than the manual specified, around -280V. It does claim that you need to follow the tube test sheet but I adjusted it to -200 or so and got closer to the 0.3mA of current that it should have. Still can't go above it (so really bad SNR at lower voltages) but that's good enough for me since I image at max voltage.


Some images of a 10-layer board attached.

rickells:


New thread on newer  BiOptics Bio Vision BioVision Faxitron units  ca. ~ 2009 - 2015

See:
https://www.eevblog.com/forum/reviews/faxitron-biovisionbioptics-win7-(pci-resource-issue)/new/#new

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