This FAQ will show you how to test your cable using a multimeter.
This is NOT for ad2cp cables. Only midlife.
Do NOT connect to your instrument using a bad cable.
Here we have tested a standard 8 pin inline RS232 cable, but the principle is the exact same regarding the 8pin RS422; except that you have two lines of Rx and Tx to test.
If you need to test other cables and/or connectors/harnesses please contact us for schematics.
However, the principle is the same:
- Power is supposed to be applied to ONE line (PWR)
- All lines should be continuous and not shorted in any way.
Making sure power is at the correct pin:
It is important to make sure that the:
- Power is sent through the correct pins
- There is no short circuit anywhere resulting in broken protective circuits.
- The right voltage is being applied to the instrument.
How to perform the test:
- Disconnect the USB-contact from the PC.
- Disconnect the converter from the cable (do not perform this test with the converter connected)
- Connect the power at the dry end of the cable.
- Set the multimeter to measure voltage.
- Connect one pin of the multimeter to ground (pin 1) of the instrument, now use the other pin of the multimeter to test each pin in the cable while having the other pin still connected to ground.
See picture 1 where pin 2 (PWR+) is tested on the 8pin (15V).
A result of 0V confirming that power is not connected at a specific pin, is just as important as confirming that power is at the correct pin.
If power is connected to multiple pins, or at the wrong pin, this could result in the destruction of the protective circuit and no communication with the instrument.
When measuring the pin for power (PWR+), it’s measuring the supplied voltage from the power supply, this should show a stable voltage close to 15V (depending on the supply). If the measurement shows less than 14V, something is wrong and should be investigated. A good starting point is to measure the voltage directly from your powersupply.
The instrument’s operating voltage can be found in the technical specifications, but is usually between 9-18V.
Lower than 9V (midlife) is not sufficient to send out sound waves and voltage above 18V can fry the instrument without an internal converter that lowers the voltage.
Showing a voltmeter set to measure continuity/voltage, measuring between pins 1 and 2 on the wet end of the cable.
Testing the cable for continuity:
- Disconnect the power supply and converter, to isolate the cable alone for this test (D-sub to 8 pin).
- Test the cable for continuity (meaning the line is continuous) and make sure the pinning on each side corresponds to eachother.
- Refer to picture 1 (8pin end), picture 2 (D-sub) and picture 3 for the pinout of the cable.
- Use a multimeter at each side of the cable.
We only want to test the continuity of the lines used: Rx, Tx and Ground.
From picture 3 it can be seen that this is pin number 3, 4 and 5 at the 8 pin and pin 2, 3 and 5 at the D-sub respectively.
See picture 2 of a continuity test between pin 3 and 2, (the Rx line).
Showing continuity (no resistance) using continuity mode, between pin 3 (8pin) and 2 (D-sub).
Showing the cable diagram/pinout for the standard RS232 w/ analogue in options.
Do not be alarmed if you have a different version, as this document only addresses the RS232-Tx, RS232-Rx, Power, and GND lines.
These pins should be the same for all RS232 versions.
Use a multimeter to test for continuity using the continuity mode (usually a picture of a diode with soundwaves) if available, or by testing the resistance between the pins.
If the multimeter has a continuity-test, then the multimeter will make a sound if there is contact (continuity) between the pins. If the multimeter does not have a continuity mode then set the multimeter to the lowest resistance mode (measured in Ohms, check for the symbol Ω.) and test.
If there is no resistance (0 Ω or very close to 0) then there is continuity, if there is resistance (might show infinite resistance or open loop / OL when set to the lowest setting) there is no continuity and the line is discontinued somewhere inside the cable.
The cable might also have intermittent continuity, meaning a line is discontinued only when under stress or movement. If this error is suspected, try to wiggle and bend the cable while performing the continuity test.
To ensure no pins are connected wrongly to eachother within the cable, perform the opposite test:
Test all the pins only at the wet end against eachother and make sure there is NO continuity between any of them.
See picture 4, below, of testing pin 1 to pin 2, showing no continuity /OL (open loop).
Showing OL/Open Loop between pin 1 and pin 2 at the 8 pin
The above tests were performed with RS232 as an example.
However, as mentioned previously, the same tests can easily be performed for the RS422 cables as well.
Showing the cable diagram/pinout for the standard RS422 cable.
There are several tutorials on the Internet for how to use a multimeter if needed and also describing continuity testing and other cable tests.
If, after performing these tests, there appears to be any damage to the cable; then there is a chance that this has damaged the instrument.
And as always; if you need further help please send us an email to firstname.lastname@example.org with a detailed explanation and we will help you as quickly as possible.