"Shoot from the hip" Electronic trouble-shooting (Peter Stow, Isomass)

wistfultitleElectronics - Devices

Nov 24, 2013 (3 years and 7 months ago)

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Mass Spectrometry

Fault finding and trouble shooting

Or: Giving the bullet to those pesky
faults

Disclaimer

3000 volts can kill

Protect your eyes

230 Volts can kill

Mass spectrometers can cause pain

Mental pain!

Please beware that any work on the instrument

is carried out at your own risk. Isomass Scientific

cannot be held responsible for injury or damage

caused by following these techniques.

Hot soldering

irons can burn

Salesman’s view of solving instrument
problems

New!

Reality




Budget shortfalls


Not enough money to buy a new instrument


Not enough money to pay for service

What to do


Learn how to look after your own instrument


Go on the manufactures training courses


Ask questions during the installation and any visit
made by an engineer


Regularly attend ASITA


Read the manual and other books


Take an electronics course

Fault Finding


Use the instrument supplier as a resource


The engineers are trained on the instrument


The engineers want to help


The engineers will have access to more
information


Take your time


Fault finding is not a race


More intervention usually leads to more damage


Take notes and pictures

Fault Finding


Beware of dangerous voltages that might be
present in the unit under investigation


The 230 volt supply into most units can be fatal if
touched


Source supplies are usually at high voltage, > 3kv


Be careful when connecting or disconnecting
meter probes


A badly placed probe can cause a short and further
damage


Double check connections and meter setting
before turning on the unit under test

Fault Finding


Check power supplies first


Fuses, check with a meter on resistance not just
visually


If a supply voltage is less than expected it could be
that the supply is damaged or the load is pulling
the supply voltage down


Regulated supplies should have very low
a.c
.
ripple


All electronics can be seen as either a supply or
load

Fault Finding

Think before acting #1

5 minutes thought can save hours of work

Fault Finding

Think before acting #2

Think about the problem before acting

Art is a science


Learn to draw


Draw a block diagram of the fault area


Write down the inputs and outputs of each block


Make a list of possible causes

My block diagram

Power Block Diagram

A few simple techniques


Swap


Exchange the suspected part


Measure


Compared the measured parameter with the
expected value


Observe


Look to see what’s happening


Write


Keep good notes

Swap

Pirani

reads 1e
-
3mbar

Pirani

reads atmosphere

Simplify

Pirani

showing

atmosphere after

10 minutes pumping

Use a blank at point 'A' to

test the sub
-

system within

the instrument as a whole

Voltage Measurement

Voltage Measurement


Multimeter

set to
a.c
. or
d.c
. voltage as required


Black lead in common socket


Red lead in V socket


Voltage measured across one component
measures across all components in parallel


Voltage is measured in parallel


Circuit is powered


Connect red probe to one lead of the component and
the black probe to the second lead


If meter is auto
-
ranging note the displayed multiplier

Current Measurement

Current Measurement


Multimeter

set to
a.c
. or
d.c
. current as required


Black lead in common socket


Red lead in
mA

or A socket as required, if in doubt start in A
socket


Multimeter

must be in series with the component


If necessary unsolder one lead from the board


Circuit is powered


Connect red probe to the lead of the component and the black
probe to the point the lead was previously connected to


If meter is auto
-
ranging note the displayed multiplier


Often easier to measure voltage across a resister and use V=IR

Resistance Measurement

Resistance Measurement


Multimeter

set to resistance


Black lead in common socket


Red lead in
Ω

socket


Component must be measured in isolation


Circuit is not powered


If necessary unsolder one lead from the board


Connect red probe to one lead of the resistor and the
black probe to the other lead


If meter is auto
-
ranging note the displayed multiplier

Start with the obvious

If a light does not work....

Check the light bulb before dismantling the

light switch, changing the fuse in the basement etc.

Start with the obvious

Two bulbs might have blown but it's more likely that there is a
fault common to both e.g. the fuse in the basement

If two light bulbs do not work....

Fault Finding

Take good, clear notes when the instrument is working correctly
and notes during any fault finding procedure

Don't forget, "RTFM" !

Power Control

230 Volts

Switched outlet

Relay

Control

Vacuum control

Vacuum parts

Vacuum Start
-
up

Quick Rotary Pump Test

Penning Gauge

Turbo Pump Faults

Vacuum Service


Rotary pump


Change the pump oil every 6 months







Turbo pump


Change the oil wicks yearly

Ion Source Control

Ion Source Electronics

~4A

~700µA

~800µA

1.5mA

~4.2A

Ion source

Exploded Ion Source

Source Cleaning

Magnet Supply

Magnet Screwdriver Test

Inlets

Dual Inlet Valve Control

GC Combustion

EA

GasBench

GasBench

#140, 5700


1 Street S.W.,

Calgary, Alberta T2H 3A9

isomass@isomass.com

Tel: (403) 255
-
6631
.

Fax: (403) 255
-
6958

Toll Free: 1
-
800
-
363
-
7823