EV Wallbox repair, Struggling with this one. Please help

[Perrin21]

Hi, i have been trying to repair my Chargemaster wallbox as it has recently started exhibiting a strange fault.  When i plug it into the car the relays engage and it tries to charge the car but after a second or two it disconnects and tries again, this process repeats until the power to the charger is turned off or the car is disconnected.   The charger displays no fault code on its main display when its powered up and disconnected and displays the orange light as normal. 

I have had it suggested that it could be the relays at fault so i have replaced all 3 relays with new ones, however the charger still has the exact same fault.  Can anyone think of anything else i should be checking?  I have checked continuity all around the relays and all seems as it should be.  I have also checked the electrolytic capacitors and their ESR is good.  Do you have any suggestions?  All help gratefully received.  I am unable to locate a service manual so if anyone recognises the board as a clone of another, please let me know.

I also get continuity in both directions on Q7 Triac but im starting to wonder if this is normal behaviour for a Triac anyway.

Here are some pics of the front and back of the main board. 

[Perrin21]

really strangely i have just tried it again and i managed to get it to charge for 30 seconds before it turned itself back off.  Once it turns itself off it keeps trying and you hear the relay switching back and forth as it tries but only the first time lasts upto 30 seconds. 

[fzabkar]

www.completepowerelectronics.com/how-to-test-triac-with-multimeter/

[cozza]

U28, the Power Integrations simple switcher TNY27(6?) - I can't quite make it out.

I've seen these fail in power supplies with the symptoms you describe. They run for a bit and stop.

This could be cause if the all the low voltage supplies disappear when it drops out (no LEDS etc)

Check ESR of the 47uF Cap as well.

[Perrin21]

excellent suggestion, i will take a look and feed back.