cookerhood PCB Powerpoint ch581

[tom66]

Re: cookerhood PCB Powerpoint ch581

I think the switch on the hood is a low voltage so if I replace the power supply to the lights I'll need a 230v mains switch.

Also I can't see a bridge rectifier so I assume this circuit is AC????

You could just switch the bulbs off using the low voltage switch... the wall plug would probably only use a watt in standby.

The four diodes form a bridge rectifier.

[budm]

Re: cookerhood PCB Powerpoint ch581

From looking at the pictures of the board, the lamps are connected to the output winding of the transformer large gauge winding of the transformer, I am surprised that it shows open circuits sinc the wire is so big to go open, you may want to rempve the tape and see where the open winding is at. The output is AC, it is just SMPS power supply without rectifier at the output for the lamps, the large cap is more likely for the fan motor since this board is also for controlling the FAN speed. The output voltage will be high frequency AC, it can be in the 50~80Khz range (that is how they can get a lot of power using small transformer, driven by the two MOSFET's next to it), so if you use your AC meter to read the output, it may read nothing since your AC meter does not have high enough frequency response to measure high frequency AC.
By the way, the contacts inside the white lamp connector may need to be inspect and cleaned real well since it shows the sign of over heat due to contacts resistance.

[caspermccormack]

Re: cookerhood PCB Powerpoint ch581

cheers lads!

[momaka]

Re: cookerhood PCB Powerpoint ch581

The lamp power supply is a typical 2-transistor resonant choke crapola. Looks like it's controlled (fed power) by that relay next to the blue transformer. Also looks like there is a hidden fuse (or perhaps it's only a jumper wire) under that blue transformer. It picks up from the lamp control relay and continues to the lamp PSU.

You can either wire a new 12V switching adapter (stay away from the cheap ones online) or fix the original lamp PSU by rewinding the transformer.
- If wiring a new adapter, remove D101, D102, D103, and D104, and connect the AC wires of the new adapter there accordingly. Then connect its output to where the output pins used to be of the transformer you removed. Make sure your adapter is rated for at least 1.2 times the total wattage required to run the bulbs.
- If you want to fix the old power supply, open the transformer (there's videos on YouTube on how to disassemble one) and unwind it, making note of how many turns there are on each winding. Then rewind the transformer with new wire.

[budm]

Re: cookerhood PCB Powerpoint ch581

Here is the diagram of the lamp driver section as far as I can see from the board layout, you should check the fusible resistor R102 and the MOSFETS, and as mention above, not sure if there is a fuse at that location or not.

[momaka]

Re: cookerhood PCB Powerpoint ch581

Looks about right. Good job budm. I think this circuit uses NPN BJTs, though, and not MOSFETs.

[budm]

Re: cookerhood PCB Powerpoint ch581

It is still hard to believe that the wire gauge that big will be open on the secondary side, he needs to look real close at the winding.

[caspermccormack]

Re: cookerhood PCB Powerpoint ch581

Here is the diagram of the lamp driver section as far as I can see from the board layout, you should check the fusible resistor R102 and the MOSFETS, and as mention above, not sure if there is a fuse at that location or not.

Checked the fuse/resistor and the MOSFETS at first and they checked out fine. Thanks for the diagrams!!! very helpfull on this forum!

[caspermccormack]

Re: cookerhood PCB Powerpoint ch581

And then there was light!!!


Rewound the transformer, bingo!!

Thanks again!!!

[momaka]

Re: cookerhood PCB Powerpoint ch581

Nice work!
I'm surprised you decided to rewind the transformer. Very few people choose to go that route. Glad you got it fixed, though.

[budm]

Re: cookerhood PCB Powerpoint ch581

Great! Did you find the wire was broken on the transformer with any burning sign?

[caspermccormack]

Re: cookerhood PCB Powerpoint ch581

Great! Did you find the wire was broken on the transformer with any burning sign?

The middle part was very brittle snapped off as i was removing the old copper, must of got lots of heat?

[JonathanAnon]

Re: cookerhood PCB Powerpoint ch581

Hey Casper, I'm only up the N7 from you, and I have a very similar problem with the same model of CH581 extractor - Fan works perfectly but the bulbs just wont work at all... I took the lamp connection from the power board and connected a car battery (12.4V DC) to the 12v bulbs and the connection and bulbs are all fine.

I've checked all the components on the board, and they all seem fine. Tested both lamp transformers off the board and they seem fine too. No opens or shorts. disclaimer: I only have multimeter and no blue ring tester. Resoldered them back on to the board to make sure there were no bad joints... The little round black transformer has a stable frequency of 1.7kHz, and the toroidal (I think) transformer has a frequency that varies rapidly between 1KHz and 1.1KHz..

Below is an image of my board. You will notice that this is version two of the board that is on Casper McCormack... Did you see which component they changed

http://omg.wthax.org/56MaHE.jpg

When I check the output pins for the lamps, I am getting two distinct readings.. I get either ~30V A/C or ~0.9V A/C randomly when I hold the probes to either the transformer output or the lamp output pins... Just wondering what the voltage is meant to be here.. The bulbs are 12V so I assume that they will work with both A/C and DC.

Any advice would be helpful... thanks..

[budm]

Re: cookerhood PCB Powerpoint ch581

The reading may be not right due to the frequency bandwidth of your meter, it may not be capable to read AC in the KHz range?

[kaboom]

Re: cookerhood PCB Powerpoint ch581

These are sort of a "mutated" CFL ballast/power supply:

http://sound.westhost.com/lamps/elect-trans.html

[JonathanAnon]

Re: cookerhood PCB Powerpoint ch581

Thanks Kaboom, I'll have a read of that.. I'm trying to work learning more about lighting circuits and motor circuits at the moment..

The reading may be not right due to the frequency bandwidth of your meter, it may not be capable to read AC in the KHz range?

Yeah I thought about that as well Bud. I think we were through this before on another thread about a switch mode power supply. I cant find out what the frequency range of the multimeter is, it doesnt say so in the manual. Maybe I should disregard the results. Unfortunately I dont have access to a scope.

I cant think of any other test I can carry out with the tools I have. The primary side of that transformer read 0.6 ohms and the secondary side reads 0 ohms, so it is (ostensibly) working fine. But something just doesnt seem right.

[JonathanAnon]

Re: cookerhood PCB Powerpoint ch581

Took out the transformer and unwound it... It seemed like a good idea at the time.. I'm not so sure now...:-(

The primary winding is top left. A few small bits broke off (bottom left), which are most likely due to my unwinding rather than actually having been damaged by overheating. Core is top right and secondary winding is bottom right.
I measured the resistance of both windings "off the core" and they measure the same..

My current plan is to rewind it, obviously without the broken windings and put it back in the circuit.

[JonathanAnon]

Re: cookerhood PCB Powerpoint ch581

I've rewound the transformer.. two and a half hours it took me... Do I need to be worried about the few windings that broke off? I assume that this will mean slightly lower voltage and higher current on the primary side winding?

[ben7]

Re: cookerhood PCB Powerpoint ch581

I've rewound the transformer.. two and a half hours it took me... Do I need to be worried about the few windings that broke off? I assume that this will mean slightly lower voltage and higher current on the primary side winding?

How many turns of the wire broke off? Seeing the number of turns on the primary winding there, I would say that maybe 1-3 less turns might be OK. You could always get some wire and put those turns back on. Use the same or thicker, enameled wire, and wind it in the correct direction too!

[JonathanAnon]

Re: cookerhood PCB Powerpoint ch581

Hey Ben, I put the transformer back in and the lighting circuit still doesnt work. I lost about 5/6 turns when I rewound it. I never even thought about the direction of the turns, but it didnt blow up anyway! Unfortunately I have nothing to check the high frequency part of the circuit, so I'm dont think I can troubleshoot the lighting circuit any further.

So given that the lighting circuit relay turns on with the existing panels button, I'm thinking of wiring one of those 240AC > low voltage 12V transformer (105W) across the lighting relay. I could wire a 10 amp fuse in series with it for protection and connect it straight to the four (20W max) 12v bulbs. I can disable the existing lighting circuit (i.e. so that it isnt also turned on by the relay) by pulling the fuse on it.