Hello all,
I'm attempting to fix a dental chair lift at a low resource hospital in Guatemala.
The chair had been functioning fine for some time but one day stopped working. A previous technician removed the circuit board and made some attempts to fix it, however, no one could tell me what the technician did or what changes were made. Eitherway, the chair still does not work.
Photos of the circuit board are included below - VR1 has exploded and you can see the soot all over the heat sync.
I know this is a long shot, but if anyone has any suggestion on how to find out what part VR1 was and/or other ways to troubleshoot this circuit, please let me know. I've searched online for a manual or schematic with no luck, However, the internet is a big place so it's very possible someone else knows where to find more information on it.
Thanks

 

VR1 appears to be a VDR (Voltage Dependent Resistor) often used to suppress power surge etc.
In some cases the device suffers in order to protect the circuit.

 

VR1 appears to be a VDR (Voltage Dependent Resistor) often used to suppress power surge etc.
In some cases the device suffers in order to protect the circuit.

Thank you! This is helpful insight and makes sense. Much of the equipment I've seen here have blown fuses related to power fluctuations.
Before I go looking for VDRs in electronics shops throughout Xela, is there a more modern approach that I could take to replacing this component? I'm not terribly familiar with VDRs.

 

It is a little difficult to re-engineer the circuit without knowing the design details.
D1 & R16 looks a little black, unless fall out from VR1 ??!

 

It is a little difficult to re-engineer the circuit without knowing the design details.
D1 & R16 looks a little black, unless fall out from VR1 ??!

Yeah I think its the fall out from VR1. I probed D1 and R16 in circuit and they seemed fine.
I'm not sure the best way to go about finding the original value for VR1 without a schematic.

 

If it is in fact a VDR then you would need the normal and peak operating voltage seen across it .

 

It looks like a PTC as it's in series with the input AC supply, again we don't know what value it could be,,
the previous engineering repair could be to replace the copper coil as it's in a different colour.