Hello all, i am a newbie when it comes to electronics (i have a basic knowledge of soldering, some basics about capacitors, resistors and that´s mostly it) and i am trying to repair an old Motor control unit for an adjustable desk.

It was working normally untill a couple days ago when it displayed an error and there was the dreaded smoke and smell and so i just unplugged it.
I was able to open it up and confirmed that was burned was a VCR 04D4 70k varistor (i think). (i had the change to open up a working identical unit as this was old stock purchased from the company i work at).



I was wondering if someone knows if it is possible to replace this with a MOV-04D470k or 04D471k as these seem to be more easy to obtain, and additionally, if there is some other component worth investigating in the board itself, that might have caused this varistor to burn (maybe some capacitor needs to be replaced or something?) or if replacing the burned varistor should be enough to get it working again.

It seems this control unit is quite old (produced 2008) and as such it's really difficult to find datasheet and/or additional info on it.

hopefully i can get this working again as it was a really useful feature for my back to be able to raise and lower the desk ;D

Thanks in advance!

 

Hi,
Are you talking about varistor on the righthand side of your photo?
Or by the bridge rectifier?
Good luck...........

 

Hi!
In between the bridge rectifier and the capacitor in the middle photo there used to be a varistor just like the one on the last photo.
Used to be, because that's what popped!

 

Where on the pcb tracks does it connect to, it may be in series with something that has been damaged as well.?

 

The traces put it between the big capacitor and the bridge rectifier

 

So check the capacitor and bridge rectifier for shorts, and any transistors and diodes after the fuse, you need to follow the tracks and eliminate anything else.

 

Thanks for the help! i'm not very experienced so i'll take a look at how to check for shorts. I did notice that the positive lead on the capacitor does seem to have some weird corrosion on it that seems unrelated to the varistor burning, don't know if that can be an indication of something