BK Precision 1627A DC Power Supply - Relays not firing

[epakai]

I bought this 1627A as a "powers on untested" unit. It is a single output 30V 3A DC supply with constant current/voltage controls.

I started out checking the bridge rectifier, but this was cut off from the transformer by some relays. Pulling this main board (pictured below) I checked the voltages on the main taps seeing 8V and 18V.


Connectors counter-clockwise from bottom left:
4 main taps / Main bridge Rectifier / 20V tap going to diode bridge on board / Slave/Master switch / Front Panel connector / Large capacitor / Main transistor sense lines

Since the transformer was working and I saw no other apparent damage I tested the relays with the board disconnected and they clacked normally. I reconnected the board and powered the supply. Fired one relay manually using a second supply and the power supply was working.
I didn't do any testing under load, but the full voltage range was available.

Since then the relay firing has been intermittent. It seems to work for a while even if the supply has been unplugged, but once it fails I haven't been able to get it working without using a second supply to manually close a relay.

I understood enough about the linear supply to follow that path, but I feel mostly at a loss when it comes to troubleshooting any logic controlling these relays. I have no schematic.

[singapol]

If the power supply is intermitant, it could be pcb track/contact problem.Check the solder side for lead
wire cold solder joints or cracks ( use of magnifying glass is helpful and bright lighting) . Trace the relay solenoid wiring trace, that will give you some idea what it is using to trigger them.Could be logic signal and amplification to energise solenoid.
                                                              Good luck.