DC Ceiling Fan Motor Controller / receiver

[265chemic]

Hi All,

I'm having a problem with a DC ceiling fan controller (from a Mercator Trinidad fan). This operates via a remote. The light works fine, as does re-pairing the remote (an audible beep is emitted). The fan function itself however does not. This leads me to believe the issue is more than likely with the DC power control part of the circuit. I have another known good controller for comparison.

When it first started having issues - and this might be key to forming a theory from someone more experienced than I - it initially wouldn't work until after the AC isolator wall switch was on for some time - sometimes even taking a few hours from pressing a fan speed button on the remote until the fan actually started turning.

I suspected capacitor issues originally, due to it having some lag time before it would work. Here are some pics - visually all seems okay.






Electrolytic caps;

- The big 68uf 450v cap tested ok. Had .29ohm esr and .7% vloss.
- 100uf 16v tested ok, .49ohm esr and 4.1% vloss
- 100uf 35v tested ok, .07ohm esr and 1.4% vloss
- 47uf 35v tested ok

Film caps;
- cx2 - .1uf film cap tested at 70.3nf .40 esr
- cx1 - same as above, 89.1nf .29 esr

Interestingly, I swapped these over and the fan had not worked even being on for hours like it did before, even after swapping them back.

*The whole input bank (inductors(?)+film caps) in circuit from the AC input wires (brown/blue) to the bridge rectifier measures 164uf (vs 154uf on the good fan control )) - 8.4/7.4 esr respectively, so I'm not sure that even though the film caps are >10% outside spec that this would fix it, particularly as the bad one has a higher capacitance reading.

Diodes;
- Tested all surface mount diodes okay, however. D7 was open both ways.
- D7 is S1J. removed from circuit - tested ok - reinstalled.

Bridge Rectifier;
- bridge rectifier is KBP08. Tested 240vac in, 318vdc out.

Test Points;

Tp0+tp1 = 15vdc (correct supply voltage for PCM as per PDF below)
Tp0+tp2 = 3.5vdc
Tp0+tp3 = 320vdc (correct DC bus voltage)
Tp0+tp4 = continuity, GND(?)
Tp0+tp5 = .5vdc ***Noted that this on the good controller is 3.5vdc - this is the only difference I've measured.
Tp0+tp6 = .5vdc
Tp0+tp7= 15vdc (when light is 'off' only, activates light relay)

Has irsm836-025ma dc power control module http://www.irf.com/product-info/datasheets/data/irsm836-025ma.pdf

Tp5 and Tp6 correspond to pins 5 and 6 on the dc power control module, and the description from the datasheet is;

5 | /FLT | Fault Output Pin
6 | Itrip | Over-Current Protection Pin

Focussing on pin 5, and the description for fault in the datasheet "Once the fault condition occurs, the FAULT pin is internally pulled to VSS and the fault clear timer is activated. "

VSS is described as " 9, 39 | VSS, COM | Ground for Gate Drive IC and Low Side Gate Drive Return "

Should I be interpreting that as it's been pulled to ground (hence the .5v reading vs the 3v on the good controller) therefore it's detecting a fault?

I've hit a bit of a wall here - any suggestions that may help me out?


Also - for the DC motor feed wires (U/V/W) I get 2v out of U/V/W +gnd and 26v from tp3(dc bus voltage)+U/V/W.

 

[rjenkinsgb]

Should I be interpreting that as it's been pulled to ground (hence the .5v reading vs the 3v on the good controller) therefore it's detecting a fault?

That does seem to be a reasonable assumption.

The implication is that either the fan motor is taking excess current, one of the power devices in the power IC is faulty, or the input drive circuits are switching wrongly.
Any of those could cause an overcurrent and the current sense pin ITRIP to go higher than it's threshold voltage, assuming that is wired something like in the data sheet.

A blown or partly burned out current sense resistor could also cause a false overcurrent trip?
Look for a resistor connecting the VRU/VRV/VRW pins to VSS and check that against the good unit - eg. the one across the bottom connection in the diagram on page 12 of the datasheet?

Check the capacitor and resistor on the RCIN pin as well. If that's leaky or the resistor is open, it could cause the start delay you mention.

 

[265chemic]

That does seem to be a reasonable assumption.

The implication is that either the fan motor is taking excess current, one of the power devices in the power IC is faulty, or the input drive circuits are switching wrongly.
Any of those could cause an overcurrent and the current sense pin ITRIP to go higher than it's threshold voltage, assuming that is wired something like in the data sheet.

A blown or partly burned out current sense resistor could also cause a false overcurrent trip?
Look for a resistor connecting the VRU/VRV/VRW pins to VSS and check that against the good unit - eg. the one across the bottom connection in the diagram on page 12 of the datasheet?

Check the capacitor and resistor on the RCIN pin as well. If that's leaky or the resistor is open, it could cause the start delay you mention.

Thankyou - Testing was done without the fan motor attached, so I imagine that rules that out. The unit is actually working again after being switched on overnight (back in the fan) so next time I pull it down I'll inspect resistors between pins you mention, as well as the RCIN cap/resistor.

 

[265chemic]

That does seem to be a reasonable assumption.

The implication is that either the fan motor is taking excess current, one of the power devices in the power IC is faulty, or the input drive circuits are switching wrongly.
Any of those could cause an overcurrent and the current sense pin ITRIP to go higher than it's threshold voltage, assuming that is wired something like in the data sheet.

A blown or partly burned out current sense resistor could also cause a false overcurrent trip?
Look for a resistor connecting the VRU/VRV/VRW pins to VSS and check that against the good unit - eg. the one across the bottom connection in the diagram on page 12 of the datasheet?

Check the capacitor and resistor on the RCIN pin as well. If that's leaky or the resistor is open, it could cause the start delay you mention.

So my next steps were;

- Check between VR1/2/3 pins 12,13/14,15/20,21 to VSS - there should be a .5ohm resistor(s). Make sure this/these test okay. (Marked R500.) Tested - all ok. Are R22/R23/R24.

- Check between pin 8 and VSS for a 1nF cap. Test. (possibly the biggest brown SMD cap near the bridge rectifier.) Is actually C17. Measures approx 1×2mm measured w. calipers. Removed from board and tested, seemed to get 85uf/.15esr initially, then stable @ 42.4uf/.15esr. This seems way too high.

- Check between pin 8(RCin) and 34(VCC) for a 2M resistor. Test. (Expect Marked 205) is actually marked 684, is 680k and measures ok. Pin 8 goes to 34(VCC) via resistor and diode D2 upstream, and also after resistor branches off into into pin 1,3 of U3, which is st electronics 393 60413 - approx 5x4mm in size. Can't find exact data sheet but likely this - SO8 package (https://www.st.com/resource/en/datasheet/lm393.pdf)

Extra notes;

- Pin 1,3 measure 15v, which is VCC supply.
- Voltage across R25 measured 14.2v closest to R25 marking, 15.4 other side
- Voltage across D2 Diode neg side 14.7v, 15.4 pos side
- Also measured 14.7@ pin 34

 

[265chemic]

After testing the cap I attempted to resolder it back - it escaped my tweezers, shooting off somewhere into the ether.

That said, out of interest I reinstalled the controller and it worked after sitting switched on for 48 hours or so. Does this give any more certainty the cap was at fault? Is there a way I can find a replacement without having to measure one off the good board? From some research it sounds like the size plus voltage may be indicative of capacitance in general, is that right? It's from a 15v part of the circuit.