Power Supply for Quadrafire Pellet Stove

[mike123333]

I am attempting to repair a power supply for a friend that was water damaged.I replaced the components that were damaged or rusted from the circuit which were C11 the blue large capacitor and U2 which is STR W6756. After the replacement of the parts I do not have the 15v DC output from the secondary side of the transformer. The large capacitor is giving voltage of 168-170V DC. I have checked the capacitors and resisters and do not find anything wrong. I am unsure as to what maybe causing the issue. D2 is an E2204. Any advice or input would be greatly appreciated.

[budm]

Re: Power Supply for Quadrafire Pellet Stove

C11 will not be the cause of the problem, it is for EMI,not needed for the circuit to function.
What ESR and capacitance do you get on that small lytics cap c19. next to the STR SMPS IC?
How about R15, R19 which are connected in parallel, what resistance do you get?
R9 resistance?
This is double sided PCB so it is not going to be easy to trace.

[mike123333]

Re: Power Supply for Quadrafire Pellet Stove

C11 will not be the cause of the problem, it is for EMI,not needed for the circuit to function.
What ESR and capacitance do you get on that small lytics cap c19. next to the STR SMPS IC?
How about R15, R19 which are connected in parallel, what resistance do you get?
R9 resistance?
This is double sided PCB so it is not going to be easy to trace.

The ESR on C19 is 7.63 and the capcitance is 2.9 uF.. the cap is a 2.3uf at 50V
R15 and R19 both have a resistance of 130.6K with meter terminals one way and reversing the terminals I get both to measure 141.8K
Based on the online SMD resistor calculator these should be 0.20 ohm and 0.33 ohms is this correct??

R9=1K

[budm]

Re: Power Supply for Quadrafire Pellet Stove

You have indicated that you replaced the STR-W6756, what did you find wrong with it?
Please check the resistance between pin 1 and pin 3 of the old STR W6756 to see if it shows very low resistance (<10 Ohms).
Right now those two resistors for the Source pin (PIN 3) of the STR-W6756 have gone open circuit probably due to shorted MOSFET inside the STR W6756.
What is the marking on R9? I expect that to be around 10 Ohms.

[mike123333]

Re: Power Supply for Quadrafire Pellet Stove

You have indicated that you replaced the STR-W6756, what did you find wrong with it?
Please check the resistance between pin 1 and pin 3 of the old STR W6756 to see if it shows very low resistance (<10 Ohms).
Right now those two resistors for the Source pin (PIN 3) of the STR-W6756 have gone open circuit probably due to shorted MOSFET inside the STR W6756.
What is the marking on R9? I expect that to be around 10 Ohms.

The STR was replaced since one of the legs was broken off. I will get the rest of the information later after work. After looking up the resistance for the SMD I kind of figured that they were open. So is it safe to assume that the resisters are supposed to be 0.2 and 0.33 ohms? I am not used to dealing with SMD resistors and values.

[mike123333]

Re: Power Supply for Quadrafire Pellet Stove

You have indicated that you replaced the STR-W6756, what did you find wrong with it?
Please check the resistance between pin 1 and pin 3 of the old STR W6756 to see if it shows very low resistance (<10 Ohms).
Right now those two resistors for the Source pin (PIN 3) of the STR-W6756 have gone open circuit probably due to shorted MOSFET inside the STR W6756.
What is the marking on R9? I expect that to be around 10 Ohms.

The resistance at pins 1-3 on the STR is 0.8 Ohms. definitely shorted out. R9 is 01B which turns out to be 1k ohms and that is what it measures.

[mike123333]

Re: Power Supply for Quadrafire Pellet Stove

Since the 0.33 and 0.20 are in parallel which would be basically a total of 0.132 ohms , would I be able to just run a straight wire for testing purpose to see if that would get the secondary side of the transformer to work? Pin 3 which is the ground for he STR goes to those resistors which would be that the STR has no ground.

[budm]

Re: Power Supply for Quadrafire Pellet Stove

The resistors are the path for the GND return as you can see in the application notes diagram. The designer of the circuit uses two resistors in parallel to get that odd resistance for reason so you should get something as close as possible. You can try jumper for quick test to see if you will get DC on the cold side, but I would not run it without those two resistors in place for long.

[mike123333]

Re: Power Supply for Quadrafire Pellet Stove

The resistors are the path for the GND return as you can see in the application notes diagram. The designer of the circuit uses two resistors in parallel to get that odd resistance for reason so you should get something as close as possible. You can try jumper for quick test to see if you will get DC on the cold side, but I would not run it without those two resistors in place for long.

I did place a fuse across the resistors, applied power and nothing on the cold side. The fuse did not blow. on pin4 of the STR I am getting a voltage fluctuation of 13.5-15 VDC. Pin 1 is at 170-176 VDC. The rest of the pinouts at around 0 V

[budm]

Re: Power Supply for Quadrafire Pellet Stove

Per spec sheet on PDF page 5, the typical start up Voltage is 18.2VDC so right now that Voltage is not reaching the startup point (once the IC starts running, when the VCC drop down to 9.7V Typ. then the circuit will stop running) so the IC is not running right now.
You need to check all those components connecting to the IC, especially filter cap on t the VCC pin (I would replace it), the diode that rectify the AC to provide VCC onec the IC is running and the resistor on pin 4 as shown in the diagram.
You can use that application notes circuit as a guide, it may be close enough to your board. I will assumed that the diode on the cold side is OK, same for the caps?

[mike123333]

Re: Power Supply for Quadrafire Pellet Stove

Per spec sheet on PDF page 5, the typical start up Voltage is 18.2VDC so right now that Voltage is not reaching the startup point (once the IC starts running, when the VCC drop down to 9.7V Typ. then the circuit will stop running) so the IC is not running right now.
You need to check all those components connecting to the IC, especially filter cap on t the VCC pin (I would replace it), the diode that rectify the AC to provide VCC onec the IC is running and the resistor on pin 4 as shown in the diagram.
You can use that application notes circuit as a guide, it may be close enough to your board. I will assumed that the diode on the cold side is OK, same for the caps?

I am following the diagram schematics for the STR and checking all the components around there, I do agree about swapping the cap at pin 4. The diode on the cold side checks fine, in diode mode checkign it one way I get open, and reversing the leads I get 200 ohms., so that diode assembly is good. Also the transistor is not shorted out. I will see if I have a cap for that c19

[budm]

Re: Power Supply for Quadrafire Pellet Stove

Something is not allowing the VCC to reach the startup Voltage point, so it can be the resistor on pin 4 or the cap on pin 4 has leakage resistance to not allow it to reach the needed Voltage.

[mike123333]

Re: Power Supply for Quadrafire Pellet Stove

Something is not allowing the VCC to reach the startup Voltage point, so it can be the resistor on pin 4 or the cap on pin 4 has leakage resistance to not allow it to reach the needed Voltage.

I think R23 maybe open I am measuring 65K ohms on it but the writing on it is 33? I can't seem to figure out what the third digit is, since it was wiped away. I am assuming it maybe a 33 ohm resistor. I did change out teh capacitors which did not solve anything.

[budm]

Re: Power Supply for Quadrafire Pellet Stove

I do not see R23 in your pictures so I cannot tell what its function is.

[mike123333]

Re: Power Supply for Quadrafire Pellet Stove

I do not see R23 in your pictures so I cannot tell what its function is.

if you go to the third picture and zoom in it is between R19 and D9, one end of the resistor goes to C22 near by it and the other end is to the cathode of diode D9 and the other end of C22. its like being parallel with C22

[budm]

Re: Power Supply for Quadrafire Pellet Stove

OK, I see it now but I still cannot tell how it is connected in the circuits.

[mike123333]

Re: Power Supply for Quadrafire Pellet Stove

OK, I see it now but I still cannot tell how it is connected in the circuits.

it is tied to pin 7 of the STR

[budm]

Re: Power Supply for Quadrafire Pellet Stove

I found this 15VDC power supply circuit, it looks like they copied to cituit to build your board. The part designators may not be the same so you will have to do circuit tracing and then write down the designators of you board into the diagram.
https://www.arrow.com/en/reference-d...ad9377f6828100

[mike123333]

Re: Power Supply for Quadrafire Pellet Stove

Thank you for the schematics definitely looks like it..the resistor in question would be R4 so it is 330 as I thought. I think the resister is open at 65K Ohms measurement.

[budm]

Re: Power Supply for Quadrafire Pellet Stove

You just have to make sure that it is connected the same way as shown in the diagram because in the diagram I see 68K resistor R13 which is also connected to pin 7.
I think you should also repalce those two resistors that were blown open instead of using fuse or jumper just i case it wants to see the Vdrops on those two parallel connected resistors to function.