Hi David,

So am I correct in saying as per the manual that if you hold the Bypass and the Auto plus the Tune together it tests all of the relays? ??

- Yes, it wil vhech the DC path

?in other words I could quickly test with a volt meter across all of the coils of the relays that they are switched on proving all of the transistors.

- Yes you could. But it wont show if the relay contacts are really closure or opening

When you press the three buttons, on power up, it enables the Fast Test Mode: it simply test the DC path from transistors to relays coils, positive voltage and ground.

What was trying to say, is: the Fast Test mode doesn't assure you that the relays contacts are properly allowing the increments (or decrements) of inductance and capacitance, and also the L C (L first and C after) or C L ( C first and L later) configuration, that is what the “search for best tuning” algorithm, could still fail due to bad closure or opening relay contact.

I had a failure on my unit, three months ago, the Fast Test Mode Went ok, but the unit was runing an infinite loop, never finishing the search algorithm.

The cause: a leaking drain to source current on a 2N7002.

Latter I’ve also found a leaking diode (emf protection diode).

A simple multi-meter didn’t show the failure, I’ve used a 9V battery to check the reverse current on the diode and the drain to source current leak on the MOSFET.

A better way to properly test the unit is to set the unit to the simple Test Mode ( see bellow the text from the manual):

"When power is applied to the device with the Bypass and Auto buttons pressed,

the device enters the simple Test Mode. In this mode, you can manually, step by

step, use the Bypass and Auto buttons to change the value of capacitance or

inductance. A long press on the Tune button allows you to select which elements will

be moved at the moment, and a short press changes the point of connection of the

capacitor. In this mode, it is possible to measure input power and SWR in line. The

whole process is accompanied by a clear indication."

On this mode you can test, not only the coils but, also the relays contacts.

If you connect the output to a 50 ohms load and the input to a nanoVNA, you would be able to measure the capacitor values every step. And similarly, every inductance values.

I’ve found the failure on my ATU100 using the Simple test Mode and the nanoVNA changes of impedance values.

An alternative method would be to manually adjust C values, L values and relay S8 contacts, to get the lowest SWR reading for different bands and different antennas or load values.

Best regards,