Mackie mixer power supply no power

[garrymc123]

Hi, Guys, I got a mixer for repair and the problem was no power on the mixer I have removed the power supply and on checking components I found that D4 is an SB360 diode checking it with a multimeter on diode mode I only get 0.189 on the forward voltage but according to the datasheet it should be 0.74 could this be the problem ..thanks in advance

[stj]

Re: Mackie mixer power supply no power

that's a schottky diode, they always either bounce or read about 160-180 on a meter.
keep looking.

[budm]

Re: Mackie mixer power supply no power

0.74V at If of 30A, your meter only putting out in mA. look at the graph of Vf VS If.

[budm]

Re: Mackie mixer power supply no power

We need good clear straight shot of the WHOLE top and bottom side of the board.
What Voltage testing have you done so far at various points on the board?

[sam_sam_sam]

Re: Mackie mixer power supply no power

Dose this power supply have a IC chip that 4 pins or more on one of the heat sinks if it does what is the part number

I would be looking for a switching regulating IC chip of some sort
Do you have any voltage on the row capacitors on the left hand side of that board
Be careful when measuring the voltage on those capacitors

[budm]

Re: Mackie mixer power supply no power

0.74V at If of 30A, your meter only putting out in mA. look at the graph of Vf VS If.

BTW, it is Vf @ 3.0A

[garrymc123]

Re: Mackie mixer power supply no power

Hi there thanks for all the info I understand now about the diode. I will upload more pics very shortly. I haven't had a chance to do a voltage test as I need to make a cable with clips on it to connect it to the mains I only did a quick check with a multimeter on the diodes I will do it tonight with power applied... Thanks in advance

[stj]

Re: Mackie mixer power supply no power

replace c9

[garrymc123]

Re: Mackie mixer power supply no power

Thanks, stj for your info can I ask why you suggest replacing capacitor c9 ..Thanks

[sam_sam_sam]

Re: Mackie mixer power supply no power

Because that could be the start cap for switching regulator IC chip I was talking about in an earlier post

It might be surface mount IC chip that is on bottom of board

What is the part number for U100

[stj]

Re: Mackie mixer power supply no power

exactly, first suspect in a psu that wont start is the startup cap.

[garrymc123]

Re: Mackie mixer power supply no power

Cheers guys the part number for the ic is ob2269cp I have taken voltage from various test points and none of them match I've got 324vdc at the big filter cap that's ok at d4 its says 7v but I am only getting 1.906vdc at the +15v i am getting 3.62vdc and at the -15v I'm getting -3.59vdc at the last one is the +48v and I'm only getting 10.68vdc will I defo check/Replace c9. Thanks for the info much appreciated

[garrymc123]

Re: Mackie mixer power supply no power

Also, I'm trying to find schematics for this power board but I'm having no luck anyone have such a thing. Thanks

[R_J]

Re: Mackie mixer power supply no power

There is a 2 leg component mounted to the main fet heatsink, is that thermister or could it be a thermal cutout (fuse)

It looks like the power supply is working at a reduced level. You could check and post the voltages on the U100 ic (hot ground) try and probe a component on the same trace rather than on the actual ic pin (probe slipping is not good)
I would also check across the 2 secondary pins of the optocoupler and report the voltage, and measure the voltage across the 2 pins on the primary side of the oprtocoupler
Also check the voltage on U101, that is the voltage reference (one pin will be ground)

[sam_sam_sam]

Re: Mackie mixer power supply no power

Here is the data sheet for this device

[garrymc123]

Re: Mackie mixer power supply no power

Thanks, i will check the voltages when I get back from work I was hopfully wanting a full schmatic for the full power board.

[garrymc123]

Re: Mackie mixer power supply no power

[QUOTE=R_J;835469]There is a 2 leg component mounted to the main fet heatsink, is that thermister or could it be a thermal cutout (fuse)

I have had a quick test of the green thing mounted to the main FET heatsink with a multimeter, it has no continuity either way with probs

[sam_sam_sam]

Re: Mackie mixer power supply no power

Need to post a photo of this

“There is a 2 leg component mounted to the main fet heatsink, is that thermister or could it be a thermal cutout (fuse)”

I would also replace C9 and go from there

[R_J]

Re: Mackie mixer power supply no power

The green device on the heatsink looks like a thermistor it is in series with R133 and seems to be connected to the optocoupler. It may be some sort of temperature regulation.

[garrymc123]

Re: Mackie mixer power supply no power

cheers guys yes I think it is a thermistor it has a k or a x on it I have taken some pics of it. how would I go about testing this... Thanks in advance