Towel warmer repair and reverse engineering  - Page 1
Forum section: electronics / repair

author: edy
author_rank: Super Contributor
timestamp: February 02, 2025, 07:41:03 am
content: Hi everyone,I have a towel warmer that blew a cap. It has a zener across the terminals of the blown cap and I’m trying to understand the circuit so I have provided lots of photos as well as my rudimentary schematic trying to reverse-engineer it (photo and PDF attached). Can you please review the attached photos and let me know if I have my wiring diagram/PCB schematic accurate?I would like to replace the cap but not sure if anything else on the circuit could have failed as well. I noticed several instances where 2 components are used in series or parallel configuration (resistors, caps) and wondering if they could have just gone with 1 component of the correct value or if they did this to handle the current to reduce heat/stress.I will have to post several replies to include all the photos. Thanks for all your help in helping me understand the circuit. Note that CN1 is the connector to another board with a couple of buttons to turn on/off the unit and change length of time it’s on. I believe the 3-wire connector to this other button controller timer board is just power and a third to switch on the relay.

author: edy
author_rank: Super Contributor
timestamp: February 02, 2025, 07:50:11 am
content: This is the second posting for most remaining photos.

author: edy
author_rank: Super Contributor
timestamp: February 02, 2025, 07:59:01 am
content: This is the last post of photos, and a PDF of my schematic (please let me know if it looks correct as I would like to figure out what is going on in this circuit, especially the low-power side). I colored the AC side with green wire and then tried to color code the low-voltage side with red/black but I’m confused about some of the control elements and the need for all of the cap/resistor from + to - as well as various diodes after the bridge rectifier.The large tub is covered with silver tape and underneath must be some nichrome wire heating element. The white wire that comes off the board (which connects to the relay output) is going first through a thermal resettable fuse like you see on microwaves, and then what looks like a non-resettable fuse (with orange see-through tape) also connected to the metal tub lining. Then is goes under the silver tape to the heating element, looping up and down around the tub and after a complete revolution it exits out of the silver wrap and goes back straight to the neutral terminal on the board.

author: edy
author_rank: Super Contributor
timestamp: February 04, 2025, 07:10:11 pm
content: Interestingly about the same time as mine crapped out, AvE posted the exact same model having the same issue on his YouTube Channel. He opened his up in a more brutal way (missing some top-side screws so you can avoid ripping the white shell apart) but basically found the same cap blown (EC3). He didn't seem to think much of it, and wasn't entirely sure if that was a Zener across the cap leads. I tried to share a link to this thread here on EEVBLOG on his video comments but YouTube automatically deleted it, as I was hoping more people could chime in and help analyze the schematic I put together and see if there are any mistakes and explain what is going on.Here is the video dated January 31, 2025... I started opening up mine January 24, then went on a vacation a few days and came back and posted my first photos here on Feb 2. Strange coincidence?

author: Poroit
author_rank: Frequent Contributor
timestamp: February 05, 2025, 04:50:16 am
content: G'day edy,Based on the video it looks like the capacitor failure is a common fault.How old is the towel warmer?I suggest you replace the capacitor and start measuring a few voltages with the unit powered up.(Bridge Rectifier Output, Voltage Regulator Output)Add more component part numbers ,cap values etc to your drawing to help members better understand the circuit.

author: edy
author_rank: Super Contributor
timestamp: February 10, 2025, 03:38:46 am
content: This towel warmer was only a couple years old, we barely used it (maybe 10-12 times)? We didn't purchase it... it was a gift so we have no idea what store it was bought from. Also, because it was a gift (we didn't really think ever about getting one) we also did not use it often. So the bottom line is, other than me trying to learn about the circuit and trying a simple fix, I didn't want to go down the rabbit hole and waste too much time on it. My wife has a number of other more important projects already lined up for me to get done around the house!So the only thing I did was replace the faulty capacitor that blew and poked a bit more around the circuit to check voltages, continuity, etc. The fuse was fine, all of the thermal fuses were fine on the tub, so I think the main issue was with the controlling circuit that turned on that master relay. Aside from that blown cap there must be other issues... either the cap failed first and then other components failed, or something else happened which ultimately led the cap to fail. Either way I'd be spending more time on it which I don't have given my numerous other priorities. So sadly I don't think I learned as much from this fix except it was beyond my skill level and time commitment needed. I have the photos and can still try to work out what happened and I kept all the electronics so if I can one day still manage to figure out why that relay is not turning on.

author: Poroit
author_rank: Frequent Contributor
timestamp: February 10, 2025, 04:34:59 am
content: hahaha....get those other jobs done and keep the wife happy.One thing...you know more about towel warmers now than you did 3 weeks ago