Bathroom timer fan repair faulty Vent-axia VASF100T pulses or runs slow  - Page 1
Forum section: electronics / repair

author: rh100605
author_rank: Regular Contributor
timestamp: January 13, 2021, 11:38:26 am
content: I have two of these that have suffered the same fault so it must be very common. The fan slows down or starts only sometimes or even pulses.The circuit uses ten 8.2K 1206 smd resistors in series/parallel to form a 20K 2.5w resistor to drop the 230V live to a 3v3 zener with a 220uf 10v electrolytic capacitor across it.This forms the 3.3 volt supply for a Sonix microcontroller that is clocked by the line input and drives a 1amp triac in series with the motor.As the capacitor (EC1 next to the corner fixing screw hole) is live all the time and kept warm by the dropper resistors it eventually fails. The 3V3 supply then develops significant pulsing.When triggered by the switched live, the SN8P2501D 8-Bit Micro-Controller keeps thinking that 3.3 volt DC power has been lost and restored.Replacing the electrolytic with a 105 deg C, FR range 220uf 16V from Panasonic restored working.I have a suspicion that many other makes of fan with a run on timer will suffer a similar fate.There is even a video on You Tube "Trying to FIX a Bathroom Extractor Fan that doesn't run on" which swaps out a 330 uF 16Volt electrolytic kept warm by a large 22K wire-wound resistor!Happy fixing

author: ringzer
author_rank: Newbie
timestamp: December 29, 2021, 12:21:47 pm
content: You mentioned that the existing capacitor was 220uf 10V but you replaced it with 220uf 16V. Is that correct? And if so, why did you do that?Thanks

author: Gyro
author_rank: Super Contributor
timestamp: December 29, 2021, 12:34:30 pm
content: 16V electrolytics tend to be more common than 10V ones, certainly in peoples' parts bins. There is no issue with replacing an electrolytic capacitor with a higher voltage rated one, as long as the package will still physically fit. Doing this can even improve reliability if the manufacturer has 'cheaped out' and hasn't left enough margin between the capacitor rating and the voltage it is actually experiencing (doesn't appear to be the case in this example).

author: ringzer
author_rank: Newbie
timestamp: December 29, 2021, 04:46:04 pm
content: Ok, thanks for the prompt reply. I'll take apart the fan and see what's inside before ordering a replacement. But good to know 16V would work just as well

author: floobydust
author_rank: Super Contributor
timestamp: December 30, 2021, 01:33:20 am
content: The electronics is powered up 24/7 and the parts don't last so long.The 220uF 10V electrolytic fails and the dropper-capacitor can also. This is the grey boxed one at the end? Test them both for low value.edit: it was the grey capacitor on another Vent-Axia, but this model has three other film caps which I think are for the fan motor.I don't think resistive-dropper has enough power for the triac but maybe.

author: ringzer
author_rank: Newbie
timestamp: December 30, 2021, 09:53:52 am
content: Quote from: floobydust on December 30, 2021, 01:33:20 amThanks for the reply, although I didn't understand from 220uF 10V onwards I'm afraid...My fan has the same problem so will swap out the 220uF 10V capacitor and see if that does the trick. If not, I'll ljust replace the unit - don't have enough electrics experience to do any more.

author: floobydust
author_rank: Super Contributor
timestamp: December 31, 2021, 12:15:53 am
content: ok then, I would change the 100uF electrolytic capacitor, note the part has polarity so don't install it backwards. You can always take a before pic.I can't find the post, but another Vent-axia fan also had a second bad capacitor. It's best to just measure the caps if you can. Thought it was the grey one at the end.

author: rh100605
author_rank: Regular Contributor
timestamp: January 01, 2022, 10:59:01 am
content: Hi,The choice of capacitor is quite important for long life and to ensure it fits in the space available. I mentioned the Panasonic 16 Volt 220 mfd FR seriesEbay link ishttps://www.ebay.co.uk/itm/111720427091?hash=item1a030e6e53:g:OI8AAOSwu4BVqR-XThese are high temperature long life electrolytic capacitors . As mentioned in other posts take a picture before removing the old one so that you put the stripe with negative signs on the correct side. This is importantLet me know how this goes.

author: Kav1187
author_rank: Newbie
timestamp: February 10, 2023, 03:32:11 pm
content: Hello. Thank you for the info in this post. I had the pulsing issue with my fan and replaced the capacitor to an equivalent one (I've now ordered a 16v one as suggested above). I now have the opposite problem where it runs continuously as soon as the isolator switch is turned to on.Any help would be much appreciated.Cheers,Kav

author: floobydust
author_rank: Super Contributor
timestamp: February 11, 2023, 06:11:52 am
content: What voltage do you measure across the new capacitor? It powers the MCU etc.Fan stuck on - check for a shorted triac TR1 or the on/off switch and its wiring.

author: Kav1187
author_rank: Newbie
timestamp: February 11, 2023, 10:32:06 pm
content: Thank you for your reply.I assume measuring voltage across the new capacitor is done by having the probes on each leg of the capacitor while it's running. If so, then it reads 5.9v.Doing the same reading on my working fan in the other bathroom reads 4.8vI checked the triac on the diode setting when the power was off. I got 0.66 between gate and t1.On the working fan, I got a reading of 0.64.I've noticed a slight browning on the plastic behind the motherboard, roughly where the triac sits. There are 4 resistors on the back of the board there. Please see the pictures attached.

author: floobydust
author_rank: Super Contributor
timestamp: February 12, 2023, 05:38:05 am
content: For the triac TR1, STZ0103it's between MT1 and MT2 to look for a short which would keep the fan stuck on.I don't know the ZD1 zener diode's part number or voltage. Post #1 says it's 3.3V but it needs to be in line with what IC1 the microcontroller needs... which is 2.2-5.5V so 5.9V seems high?That 220uF 10V capacitor Chong_X is not a long life part. I thought you'd already replaced it?The resistors normally sit there and run hot, as part of the power supply.

author: Kav1187
author_rank: Newbie
timestamp: February 13, 2023, 08:14:50 pm
content: Hi. Thanks for your reply.The 10v capacitor was a cheap part I got off amazon to try and get the fan working. I've just soldered on the 16v one that arrived today.Checking continuity between t1 and t2 on the triac doesn't show a short. I get the same result as I do with my working fan.I'm seeing the same 5.9v across the new capacitor. Could it be that one of the resistors is faulty?

author: 4262mikeb
author_rank: Newbie
timestamp: October 13, 2024, 05:43:11 pm
content: I've a fan with part # F100TS1 with the pulsing problem. I've changed the 220microF cap but after working fine the first time the fan was repowered the pulsing has returned. With the fan powered I put a meter (set AC V) accross the big yellow rectangule 0.33microF cap .. measured mains voltage .. but surprisingly the pulsing stopped. I can 100% consistently turn the pulsing on and off by touching the yellow cap legs with my meter.. is the cap my problem ?ThanksMike

author: Gyro
author_rank: Super Contributor
timestamp: October 13, 2024, 06:34:57 pm
content: Almost certainly. Capacitive droppers (the Yellow cap) are subject to losing value due to self-healing as a result of the inevitable spikes on the mains.Strictly speaking, the replacement doesn't need to be an Class X capacitor as it isn't in a direct-across-the-mains application. A 630V DC rated one would do, but to stay as close to the original design as possible, it would best to fit one. If space permits, fit an X1 cap rather than an X2 as it will give more voltage headroom and hopefully last longer before replacement is required again. [Edit: I see the capacitor is inserted in a cutout in the PCB so specific dimensions and space are probably tighter than they look]

author: 4262mikeb
author_rank: Newbie
timestamp: October 13, 2024, 07:28:20 pm
content: Thanks Chris, as you say space very restrictive due to cutout, X2 is on order .. thanks again Mike