Board burns

Thread Starter

nsaspook

Joined Aug 27, 2009
8,490
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.
 

Thread Starter

nsaspook

Joined Aug 27, 2009
8,490
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.
 
Last edited:

Thread Starter

nsaspook

Joined Aug 27, 2009
8,490
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.
 

Thread Starter

nsaspook

Joined Aug 27, 2009
8,490
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. :eek:

Second repair with new terminal for a fuse wire holder.
 

Thread Starter

nsaspook

Joined Aug 27, 2009
8,490
Miracle fix, they finally checked all connections from the board by unplugging and reconnecting. The short magically disappeared and the 1.5A fuse holds.

 

Thread Starter

nsaspook

Joined Aug 27, 2009
8,490
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.
IMG_20200621_123728.jpgMVIMG_20200621_123820.jpg
 

Thread Starter

nsaspook

Joined Aug 27, 2009
8,490
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.
 

Thread Starter

nsaspook

Joined Aug 27, 2009
8,490
Board burn protection.
Reverse polarity protection and fuse diode.


Protective magic smoke released after connector short-circuit.


New fuse installed.
 
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