Troubleshooting the camera electronic: Simple measurements with the oscilloscope

[Andreas Thaler]

Troubleshooting instructions in camera repair manuals make it possible to find and fix problems without detailed knowledge of a circuit or mechanism.

To do this, you work through decision diagrams with yes and no and carry out the instructions, e.g. in the form of voltage measurements or checking mechanical settings.

This gives even laypeople a chance of successfully carrying out a repair.

LCD issues: Troubleshooting the Nikon F3 circuitry


Multimeter: Measuring fixed values

For measuring of fixed voltage and resistance values, which is often carried out in electronics, an inexpensive multimeter with adequate accurate readings is sufficient.

It is usually just a matter of determining whether a value is plausible or not, but not of measurements accurate to the millivolt or milliohm.

Oscilloscope: Messuring voltage changes over time

In order to be able to measure voltage curves, you need an oscilloscope.

The measurement curve determined with this shows how a voltage changes over a certain period of time, e.g. a microsecond.

Such periodically changing voltages occur, for example, in digital camera circuits with an oscillator that is responsible for clocking signals.

Here, too, it is only a matter of displaying a voltage curve with sufficient accuracy, i.e. whether it is a regular rectangle, for example, or deviates from this shape.


Simple and inexpensive

Oscilloscopes offer a variety of setting options that are usually not necessary for working through camera troubleshooting instructions. Therefore, it is sufficient to invest in a simple and inexpensive device.

I work with a small digital oscilloscope that costs around EUR 30/USD 32. After a short training period, it is easy to use and sufficient for the intended purpose.

DSO-138 Oscilloscope | Joy-IT

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In order to record measuring points precisely, a probe is useful as an accessory, which is connected to the oscilloscope instead of the terminals (see picture above).


Measuring signals against ground

When connected to a measuring point, an oscilloscope measures the signal against ground, which in cameras is the metal chassis.

The oscilloscope display then shows the voltage curve, which can be compared with the specification in the repair manual.

This provides an easy way to find errors in a complex circuit, provided they are listed in the repair manual.

Maybe a small and simple oscilloscope is still missing in the DIY workshop


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All information provided without guarantee and use at your own risk.

 

[Andreas Thaler]

Limitations and peculiarities when troubleshooting camera circuits

Of course, you can use a multimeter and oscilloscope to measure the circuit as you wish, even without troubleshooting instructions.

Whether this is successful will depend on the circuit diagrams in the repair manual, which in my experience are not particularly informative. Voltage specifications and component values are usually not given, nor are integrated circuits, which contain the main part of the camera electronics, documented.

Also, circuit descriptions and functional explanations are not always available or are not sufficient.

A particular handicap when electronic troubleshooting cameras is the need to dismantle the camera more or less deeply in order to get to the - usually flexible - circuit board. Parts of the camera are then no longer connected to the circuit, which can affect the measured values. Any repairs or adjustments made to the circuit cannot be checked immediately, but only after the camera has been reassembled.

Cameras from around the end of the 1980s also often require manufacturer software or devices for settings and adjustments which are no longer available.

So you are left to rely on your own knowledge and experience to make any progress here.

 

[koraks]

These little digital scopes are so accessible these days! For those who desire something more functional, very decent 2-channel scopes now already start at around €125 or thereabouts for a standalone model with its own display. Such devices have a vastly higher sample rate than the device presented in the OP, which can be convenient or even crucial in tracking more fast-paced signals.

Cameras from around the end of the 1980s also often require manufacturer software or devices for settings and adjustments which are no longer available.

This reminds me - there's a bit of a special case with the Canon EOS system, where it's in principle possible to use a logic analyzer (these are also very affordable these days) to monitor communication between the lens and the body, because the EF-mount employs a standard SPI protocol. It's kind of a special case and with limited utility. Most digital communications inside a camera will be in proprietary formats and difficult/impossible to decode unless in-depth documentation is available. To the best of my knowledge, repair and maintenance manuals do not contain such information.

In any case, for anyone who regularly works on electronics, a scope is indispensable.

 

[Andreas Thaler]

You can also summarize it:

The more advanced the electronics of a camera are, the lower the chances of finding and correcting a fault as a DIY.

But you should leave no stone unturned