Still no reply from Trevor, but here’s the progress report:
The charger is fixed.
After changing the capacitors, the charger board still booted to a red light. There is evidence that the board had been running very hot. After more investigation, I discovered that the output contactors are shorted, which means that they are constantly live. It looks like excessive current has been drawn at some point. I also found that the energising relay for the contactors has variable contact resistance, so I’m wondering if this has meant that the contactors were not pulling in properly, and maybe chattering. This could cause the contacts to overheat and eventually weld themselves shut. Both contactors make a loud buzzing noise when energised; I tested a good one, and there’s just a quiet hum.
I removed the contactors to confirm where the short is, and they are both definitely short circuit (the board is OK). For some strange reason, the 2 contactors are connected in series, both driven by the same relay, so that they switch together. I can see no reason for this, so I replaced just one of the contactors, and wired the other across. I also replaced the energising relay.
I have tested it by charging may car for about 30 mins and all is well.