I've got a Manrose SCF200TC inline extractor fan whose timer overrun facility has recently started only running for 5 minutes or so compared with the 20 minutes it used to.
I've not had chance to open the cover and see if there are any obvious telltale signs on the board, however I was wondering if anyone can advise on what would likely be the cause? I am assuming that the control circuit will be fairly crude in design.
Mathew
Maybe it uses a simple charging capacitor that has dried out via some kind of timer and a relay.
Brian
Mine had a pot inside you could adjust.
Possibly that's failed. Or got corrosion across it lowering its (electrical) value,.
has recently started only running for 5 minutes or so compared with the 20 minutes it used to.
telltale signs on the board, however I was wondering if anyone can advise on what would likely be the cause? I am assuming that the control circuit will be fairly crude in design.
Most likely culprits are a deteriorating electrolytic timing cap or a pot thats got dirty. You have a multimeter? You'll likely need one.
NT
has recently started only running for 5 minutes or so compared with the 20 minutes it used to.
telltale signs on the board, however I was wondering if anyone can advise on what would likely be the cause? I am assuming that the control circuit will be fairly crude in design.
Many lowcost timers needing 10s of seconds to 10's of minutes use cmos chip 4020/4040/4060 variants with cheap ceramic capacitors and high value resistors in the timing circuit which then count down by factors of 2^n to give the required duration. Often the capacitor fails or the high value resistor gets affected by damp causing the oscillator to run too fast and the time shorten.
hth
Bob
cility has recently started only running for 5 minutes or so compared with = the 20 minutes it used to.
telltale signs on the board, however I was wondering if anyone can advise o= n what would likely be the cause? I am assuming that the control circuit wi= ll be fairly crude in design.
Another component that is a weakness is the resistor that drops the mains voltage. I don't know how that would have an impact on the timing, but I've had several cheap electronic items where heat from this resistor has damaged nearby parts.
Rob
I took the board out and all the components seemed fine, with the exception of a capacitor that had a definite pronounced bulge on the top (no apparent leakage or anything). Will try replacing that and see how I get on.
Thanks for all the help,
Mathew
Just to follow-up on this; I replaced the suspect capacitor and all is now well.
Mathew
replying to Mathew Newton, dazseaton wrote: Im having same trouble. removed my board and as you can see the large grey resistor is red hot even though fan is off (except permanent live) and has burnt the board. I'm assuming this is the one you changed?
No, he changed one of the capacitors.
Chances are the design simply runs that resistor hot. It does not look damaged on your board even if it has "cooked" the cheap and nasty SRBP PCB a bit.
See if you can tweak the timing with the pot on the board. If that does not allow enough adjustment, then replace both the capacitors (the black cylindrical things standing on end with silver tops). Use similar values and make sure the working voltage is the same as (or higher than) the ones already there.
what are the ring colours on the resistor?
NT
replying to tabbypurr, Badger wrote: Mine was marked red brown brown but measured at 21k ohms so guess it had discoloured.
replying to dazseaton, Badger wrote: I stumbled on this thread and thought I'd add my observations on fixing one of these boards which was either cycling on and off every few seconds or buzzing and refusing to run the fan. The large resistor on mine also looks like it runs hot but measured fine (23 k ohms), I tested and replaced the larger capacitor (tested 370 uf instead of 470 uf, 8.4v esr) but this made no difference. The solution was to replace the smaller capacitor next to the potentiometer (even though the esr value etc tested better, the capacitance had dropped to 24 uf instead of 47 uf), and this did the trick. Hope this information helps someone.
sounds like you need a doctor
NT
Probably used for hysteresis so the fan does not go on and off all the time as it would if their was a simple detector. Brian
it's a hysterical fan controller
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