RF burns.

RF cavity fault. The high SWR setup a high voltage node inside the phase monitor that caused an arc to the case (ground). Unfortunately the arc impedance inside the box was close to the normal load impedance so the 3 KW RF amp didn't shutdown until real damage as done.

 

RF testing a repairable burned board.

 

Older model board fault isolation.

RF shorts to board bypassing the normal 5pf RF sample capacitor on E1. RF energy shorts D1 & D2 after pass through voltage limiting resistors.

1N4148(s) fried, system loses phase tuning voltages. A easy fix if the board didn't get burned too badly.

 

Ordered the right diodes for the old unit but needed to get the tool up and running so a SMD mount was made from some header pins for the 1N4148 SMD types I have.

The newer style board has a SOT-23 dual (series I think, one diode is shorted but a series connection matches the old board rectifier circuit for the phase balance signal path) diode part on the board backside for the phase detection rectifiers.

Used two SMD 1N4148 parts to replace that.

Those bare high power RF cable conductors really need some insulation to reduce arcing. A few Kapton tape wraps might help.

 

Surge protection diodes all fried. https://www.mouser.com/datasheet/2/240/Littelfuse_TVS_Diode_1_5KE_Datasheet.pdf-1761343.pdf

That's what caused the magic smoke detection.



Carbonized.

Milling the carbon out

Just need to refill the holes and soldered diode connections with some Loctite 444.
View attachment 199387

Gaps filled with vector board and Loctite 444.

 

This one is a classic.
The EE from another group asks if I could add some protection on the circuit after a trace was burned. Sure, no problem I added a few wire holders for a pico fuse and glued a few stabilizers to keep the long leds from moving. A few hours later the tech asks me to repair the board again because one wire holder melted.

You know the sequence.
1.5A blown
2.0A blown
4.0A melted

The short that caused the original trace burn was never fixed.

Second repair with new terminal for a fuse wire holder.

 

Miracle fix, they finally checked all connections from the board by unplugging and reconnecting. The short magically disappeared and the 1.5A fuse holds.

 

More of a relay burn. HI-voltage inert-gas pressurized power relay failure. The stupid lever roll pin slipped almost all the way out causing a contact gap failure when the relay switched over.

 

 

Long skinny arc from the board across the insulation sheets to the cover to ground. Cleaned the board and cover, then replaced the HV Kapton insulation sheets.

Kapton® Polyimide Film
https://www.mcmaster.com/polyimide-sheets/electrical-grade-kapton-polyimide/

 

Your job seems like a lot of fun, NSA... I almost envy you ... and I say almost because mine is fun as hell too.

 

Another HV board burn.

The magic smoke and the resistor are missing.

 

The magic smoke and the resistor are missing.

The all mighty circuit gods should be appeased by the resistor's sacrifice... at least for a while...

 

Another HV voltage board burn.

The magic smoke and the resistor are missing.

I like this; wish to get one in my hands (duly discharged, of course).

 

I like this; wish to get one in my hands (duly discharged, of course).

View attachment 233359

Don't have extras of those but you can have a 1000lb leaking magnet coil, you pay shipping.

 

Wow! Nothing is small there...

 

Don't have extras of those but you can have a 1000lb leaking magnet coil, you pay shipping.

Probably a fair amount of copper can be salvaged from that thing...

 

Filter cap shorted and burned. Repairable once the cancer is removed.

 

A four layer board but only digital power and ground were fried to the F/V F/V converter. Clean out the burn, insert a plug with LOCTITE® 444 glue for the new filter cap and external rewire with one trace replacement.

Trace repair kit.

The machine is operational.

 

Board burn protection.
Reverse polarity protection and fuse diode.

Protective magic smoke released after connector short-circuit.

New fuse installed.