Stairlift weird relay circuit

[throbscottle]

Patient is a 10yo Handicare 950 stairlift. Foot rest doesn't operate, auto-turn (of the passenger) doesn't operate.

Both things have controllers, which are connected by a single combined data/power wire to the main control board. The data part is found to be OK, but the power is not - there's a relay that's supposed to operate to connect it directly to the 24v supply. Relay itself checks out OK, removed from board (to trace circuit) and tested. Catch diode is also ok, polarity discovered after I'd removed the relay (it's a SOT23 packaged diode).

The coil is getting power, which goes off as appropriate after a delay. What seems to be missing is the return path. It doesn't just go to ground like a sensible circuit. My best guess is there's a sensor for the coil current. Or maybe the 12v it's getting is supposed to be some higher voltage, and something drops it on the return side. I have no clue.

Relay is just a relay, not latching or anything fancy. afaict.

It seems to be a 3 layer board, with a lot of tracks hidden, also very dark resist so it's hard to see even the ones on the surface.

So, I'm guesing it's feasible to just connect a wire from the return side of the relay to 0x, but I'm reluctant to try it without more info. Replacment board is very expensive so I don't want to risk doing more damage.

Any suggestions, or known weird relay-coil circuits?

Thanks in advance

 

[Diver300]

I would suspect that there is something else that is supposed to connect the -ve of the coil to ground at an appropriated time. The connection of the +ve to the +ve supply could be enabled when the chair is running so it could be that you mustn't run the relay whenever the +ve is powered.

Stair lifts are designed to be as difficult to repair as possible, because repairs are only ever needed when the user has no alternative, and will pay whatever it takes, so the design will capitalise on that.

 

[camerart]

Patient is a 10yo Handicare 950 stairlift. Foot rest doesn't operate, auto-turn (of the passenger) doesn't operate.

Both things have controllers, which are connected by a single combined data/power wire to the main control board. The data part is found to be OK, but the power is not - there's a relay that's supposed to operate to connect it directly to the 24v supply. Relay itself checks out OK, removed from board (to trace circuit) and tested. Catch diode is also ok, polarity discovered after I'd removed the relay (it's a SOT23 packaged diode).

The coil is getting power, which goes off as appropriate after a delay. What seems to be missing is the return path. It doesn't just go to ground like a sensible circuit. My best guess is there's a sensor for the coil current. Or maybe the 12v it's getting is supposed to be some higher voltage, and something drops it on the return side. I have no clue.

Relay is just a relay, not latching or anything fancy. afaict.

It seems to be a 3 layer board, with a lot of tracks hidden, also very dark resist so it's hard to see even the ones on the surface.

So, I'm guesing it's feasible to just connect a wire from the return side of the relay to 0x, but I'm reluctant to try it without more info. Replacment board is very expensive so I don't want to risk doing more damage.

Any suggestions, or known weird relay-coil circuits?

Thanks in advance

Hi T,
Have you tried a search?
I found this:

What’s showing on the digital display? – Handicare TechTool

user.handicaretechtool.com

Which may be interesting?
C

 

[throbscottle]

Hi T,
Have you tried a search?
I found this:

What’s showing on the digital display? – Handicare TechTool

user.handicaretechtool.com

Which may be interesting?
C

Yeah, I've got the the installer's manual and the service tech's fault finding manual (no board schematics in there, just general wiring and some flow charts), so I've looked at all the codes. It doesn't give a code for this particular fault - actually I'm not sure it gives a code for when the footrest/swivel are operated either.
Nice try though, thanks

 

[throbscottle]

I would suspect that there is something else that is supposed to connect the -ve of the coil to ground at an appropriated time. The connection of the +ve to the +ve supply could be enabled when the chair is running so it could be that you mustn't run the relay whenever the +ve is powered.

Stair lifts are designed to be as difficult to repair as possible, because repairs are only ever needed when the user has no alternative, and will pay whatever it takes, so the design will capitalise on that.

Yes, my first thought was that could be another switch in there. But then I decided that's just too crazy... But the whole thing's crazy anyway so who knows.
I had a similar thought, which was, they make make it so expensive to repair (this particular board being over £100) that people decide to just get a new stairlift.

Anyway, I'm going to try to rig a little magnetic sniffer and feed a signal into the o/c side, see if I can pick up where it goes. Probably prove to be way more complicated than it sounds...

 

[throbscottle]

Well ok, RF sniffer since it's o/c. That was an interesting experiment...