Old Sunbeam 6900 staying hot when turned off.
New member of the forum here. I have a question if I may ask please...
I was given a Sunbeam 6900 that had a worn out and leaky collar. Original owner didn't want to fix. It's a well used but well loved machine. Apart from the collar leak it made decent coffee. Previous owner was not really a 'coffee snob' or a 'pro user' and to be honest neither am I (although this website may change that). turned out the collar threads were corroded and destroyed.
Not being able to find a replacement 6900 collar to suit, I decided to buy a newer 6910 thermoblock/collar/thermostat and change out the old ones. All wiring was the same and it was a simple, though time-consuming, procedure to complete. For the last 4 or so months since then the machine has made decent coffee.
It recently became apparent that the machine keeps the thermoblock hot even when machine is switched off (all lights go out).
Machine will only cool down if it is turned off at the powerpoint.
Am 99.9% certain this wasn't always the case. The machine usually makes a familiar 'tick' noise as the thermostat cuts in and out keeping the thermoblock heated and this sound would have been noticeable in my apartment.
Searching old posts uncovered mention of cockroaches and moisture causing machine to short some circuits. Or a dead variac causing the the pump to run if not turned off at the powerpoint. But nothing about the thermoblock staying hot unless switched off at the powerpoint.
Disassembly shows no moisture or cockroaches etc.
I know it's an old machine, but i'm happy to tinker (mechanical engineer) and kind of like saving otherwise good machinery from landfill.
Any help most appreciated. Thank you in advance.
Most likely one of the relays on the sub-PCB on the control board will be failed closed, most likely the coffee thermoblock relay. When the steam relay fails, it usually blows the thermal fuse and stops heating.
The machine powers the thermoblocks with the relays using thermocouples as the sensors. Each thermoblock has two safeties, a thermal fuse on the neutral and a thermostat on the active. When the relay fails closed for the coffee thermoblock, the thermostat opens and closes rather than the relay opening and closing. This is why the thermoblock stays hot.
Due to the age of the machine it's probably best to replace both relays. If you remove the control board, there's a smaller board on it that's connected to a silicone mount with three wires coming from it. They are labelled neutral, steam and coffee so it's easy to see which relay powers which thermoblock.
I haven't been able to find direct replacement relays as they are 6V. 12V relays (used in the EM7000 and up) to suit the form factor are available and are part number 719-6341 on RS Components. I've never personally used one in a 6900/6910 but I think I recall reading another member here had used one to no apparent ill-effect.
Thank you. Possibly the most comprehensive and helpful answer I could have hope for. Awesome.
Your ability to discern that it's the steam thermoblock and that the obtrusive ticking of the thermostat is awesome.
I really appreciate your high level of knowledge and diagnostic thinking. You make this forum valuable.
I'll run the part number past a mate who is an electrical engineer, procure the part and report back once the job is complete.