Av123 MFW-15 power supply problem

[atul123]

Re: Av123 MFW-15 power supply problem

Hi Guys, my MFW15 recently died on me. I also had c1 blown up, it apparently very strongly. It also destroyed two of the underlying connections. Does anyone know the circuit layout of the power supply and help my redo the connections?

[Silverado0618]

Re: Av123 MFW-15 power supply problem

I just got one given to me and having similar issues. Everything seems ok except for c1 and it is gone. I am looking for the value and type to replace. I'm new and going thru this forum I'm not sure if I missed it or if someone could help.

Anyone know what c1 disc cap value is?

[Silverado0618]

Re: Av123 MFW-15 power supply problem

I just got one gave up me and having similar issues. Everything seems ok except for c1 and it is gone. I am looking for the value and type to replace. I'm new and going thru this forum I'm not sure if I missed it or if someone could help.

[xXDigitizerXx]

Re: Av123 MFW-15 power supply problem

Bump

[xXDigitizerXx]

Re: Av123 MFW-15 power supply problem

Well, installed the new fets, it turned on than 20 seconds of being on it started to have a high pitch hiss and popped the fuse, replaced the fuse and I'm back to instant popped fuses. Runs fine green light stays on, with fets removed..... Any ideas? :/


EDIT: even with the power switch in off position it blows a fuse when power is applied and the new fets are blown...

[Khron]

Re: Av123 MFW-15 power supply problem

I'm sorry, I'm fairly new to this, do i have to hook up the power supply board back to the amp and power up to do the volt measurement?

No, that's just to make sure the power supply board and the transformer both work as intended.

[Gr33d]

Re: Av123 MFW-15 power supply problem

@ khron. So hook the power supply board back to the amp and power it on to check correct?

[Khron]

Re: Av123 MFW-15 power supply problem

No, that's just to make sure the power supply board and the transformer both work as intended. And yes, for the probing.

[Gr33d]

Re: Av123 MFW-15 power supply problem

OK, R1. R2 resistors are just bleeder resistors to discharge those four filter caps.
C4 and C5 are connected in parallel with the big filter cap for high frequency filtering.
The R1, R2, C4, C5 are not needed for the circuit to function, you can remove the burnt cap for now.
Right now we need to verify if you do have all the Voltages coming out from the power supply board or not.
Please check the DC Voltage with ref. to the GND pin of the connector
CN4B (for running the power amplifier section) and see what you have on:
I expect the +/- VCC to be arund 35 ~50VDC range, depends on how powerful the amplify is.
-VCC pin
+VCC pin
+VCC +15V

CN5B (this is the +/- supplies for running the pre-amp section): with ref to GND pin
+15V
-15V

I'm sorry, I'm fairly new to this, do i have to hook up the power supply board back to the amp and power up to do the volt measurement? Or i just measure without it?

And by measuring it, the black com will be on ground and the red cable will be on the point you going to test?

[xXDigitizerXx]

Re: Av123 MFW-15 power supply problem

The MOSFETs are actually IRFB31N20D, the 807 is just some date-code thing, see page 8 of the datasheet:



To double-check them, use the diode-test mode on your multimeter, black probe on the middle leg (or the metal tab), and red probe on the right-most leg; normally (ie. on a good MOSFET) you should get something around 600mV or so voltage drop across that, and "OL" if you reverse the probes.

MOSFETs usually fail shorted, so that would explain the fuse-blowing.

I called them 807s for short, I tested them in my cheap ebay tester as well as with my multimeter one probe on the metal back than to each leg, getting a beep on all 3 and viceversa. the 2 that were wide open on all legs I tossed the other 2, like I mentioned I put back in 1 in each bank and turned it on and got the green light then pulled them back out and tossed those also, cause all 4 of them were from different batches and I ordered 4 new ones of the same batch. 7.99 for 4 and 7.99 for shipping. Orignally ordered from digikey but got an email saying they didnt have 4 of the same batch for sure.. so went to mouser and got 4 there of the same batch. But I did get all the replacement caps for all the boards from digikey still. Should all be here in a few days, once I get it all installed I'll post the results.

https://www.mouser.com/ProductDetail...jAq5UtOClqM%3d

[Khron]

Re: Av123 MFW-15 power supply problem

The MOSFETs are actually IRFB31N20D, the 807 is just some date-code thing, see page 8 of the datasheet:



To double-check them, use the diode-test mode on your multimeter, black probe on the middle leg (or the metal tab), and red probe on the right-most leg; normally (ie. on a good MOSFET) you should get something around 600mV or so voltage drop across that, and "OL" if you reverse the probes.

MOSFETs usually fail shorted, so that would explain the fuse-blowing.

[xXDigitizerXx]

Re: Av123 MFW-15 power supply problem

The cable that you unhook is for +/-VCC power supply to run the power amplify section.
There are 4 3-pin power devices attached to that black metal plate/chassis, I believe that is where the shorts circuit is.
You will have to remove the two metal clamps that hold the devices against the plate so you can see the P/N.
This is not going to be an easy job because those devices are direct coupled so when one goes bad it causes the chain reaction and takes out other devices with it.

Thank you for your efforts. Replacement IR807P's will be here in2 days, hopefully after installed I don't fall victim to that hiss. I will be recapping all these boads while I wait for the 807s tho. Cheers

[xXDigitizerXx]

Re: Av123 MFW-15 power supply problem

The cable that you unhook is for +/-VCC power supply to run the power amplify section.
There are 4 3-pin power devices attached to that black metal plate/chassis, I believe that is where the shorts circuit is.
You will have to remove the two metal clamps that hold the devices against the plate so you can see the P/N.
This is not going to be an easy job because those devices are direct coupled so when one goes bad it causes the chain reaction and takes out other devices with it.

So I ripped it all off the plate as you mentioned. Seen some browning on the fets so I check them with a multi meter and one on each bank tested OL, so I pulled them and 2 of 4 are completely wide open then I noticed all 4 are from different batches... So question is perhaps thats reason for fuses blowing? P.S. this glue is horrid.. lol since 2 of these are dead, I'll have to replace the driver transitors also? I don't have an oscope to test the driver waves, mine had a fight with a cup of coffee and lost the battle.


EDIT: I put one of the good fets in each bank L@R and powered it up and presto green light. I'll order 4 of these IR807P's from digikey or mouser so I have 4 of the same batch. Going to replace the driver transistors right away too.

[budm]

Re: Av123 MFW-15 power supply problem

The cable that you unhook is for +/-VCC power supply to run the power amplify section.
There are 4 3-pin power devices attached to that black metal plate/chassis, I believe that is where the shorts circuit is.
You will have to remove the two metal clamps that hold the devices against the plate so you can see the P/N.
This is not going to be an easy job because those devices are direct coupled so when one goes bad it causes the chain reaction and takes out other devices with it.

[xXDigitizerXx]

Re: Av123 MFW-15 power supply problem

I am talking about just plain resistance reading using Ohm meter, we are trying to find out if those caps have leakage resistance or not, it is not the same as ESR.
Those ceramic caps tend to fail as shorts circuit and burn up.
See post #9 too.
This power amp looks to Class D amplifier.

2.765k on both when measured on my auto range multi meter on ohms.

On a side it doesn't blow fuses if I leave it unhooked like the pic I'll attach, but soon as I hook up the remaining boards fuse pops instantly.

Thanks for the help on this. Hope I don't make you pull your hair out. I'm kind of a noobie.

[budm]

Re: Av123 MFW-15 power supply problem

I am talking about just plain resistance reading using Ohm meter, we are trying to find out if those caps have leakage resistance or not, it is not the same as ESR.
Those ceramic caps tend to fail as shorts circuit and burn up.
See post #9 too.
This power amp looks to Class D amplifier.

[xXDigitizerXx]

Re: Av123 MFW-15 power supply problem

What resistance do you get when measure the resistance between the two legs of C4, between the two legs of C5?
I am still waiting the straight shot pictures of the bottom side of the board with less glares so i can trace out the circuit.
Your board also has those nasty brown glues that will conduct and eat away copper traces and component's leads.

98nf 15ohm esr on c4 and 96nf 15 ohm on c5

[budm]

Re: Av123 MFW-15 power supply problem

OK, R1. R2 resistors are just bleeder resistors to discharge those four filter caps.
C4 and C5 are connected in parallel with the big filter cap for high frequency filtering.
The R1, R2, C4, C5 are not needed for the circuit to function, you can remove the burnt cap for now.
Right now we need to verify if you do have all the Voltages coming out from the power supply board or not.
Please check the DC Voltage with ref. to the GND pin of the connector
CN4B (for running the power amplifier section) and see what you have on:
I expect the +/- VCC to be arund 35 ~50VDC range, depends on how powerful the amplify is.
-VCC pin
+VCC pin
+VCC +15V

CN5B (this is the +/- supplies for running the pre-amp section): with ref to GND pin
+15V
-15V

[Gr33d]

Re: Av123 MFW-15 power supply problem

Sorry for the late update. Can this power supply be fix or salvage?

[budm]

Re: Av123 MFW-15 power supply problem

I am currently trying to repair this same amp.. mine is blowing fuses. I have r1 and r2 1 leg unsoldered to test, it's reading .692 on both r1 and r2. I removed D1 diode cause it was letting voltage go both ways ( I suspect thats what is popping fuses) the R1 on the other board you can see has a chip in it but reads out at .692 like the other one altho both them have different color bands...

What resistance do you get when measure the resistance between the two legs of C4, between the two legs of C5?
I am still waiting the straight shot pictures of the bottom side of the board with less glares so i can trace out the circuit.
Your board also has those nasty brown glues that will conduct and eat away copper traces and component's leads.