No signal into DJ mixer - Need help locating PCB with problem

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mynamesalex

Joined Oct 4, 2012
53
If you look at CN903 on page 59, you'll see the voltages that I tested. I found a way to test them without single stranded hookup but I will also do that later tonight. Each connector has small metal pins on the top which I can retrieve the voltages from so I'm relatively sure they're accurate. I did find a weird voltage on this also, though. I got the following:

1. +15.09V
2. +5.06V
3. -4.0V(GND)
4. -14.72V
5. -0V (GND)

Now I'm pretty sure I shouldn't be getting a negative charge for a ground haha. Keep in mind this connector goes directly to the PSU so it is direct voltage. This may be a good find, yes?
 

sheldons

Joined Oct 26, 2011
613
your ground lead is where your positive and negative supplies are referenced from-do not connect you negative lead from your multimeter anywhere else other than the case which should be at ground potential or the ground on the pcb-also here is the part of the manual which refers to the fuse i mentioned-if they arent present and replaced with links etc then it may well be a simple case of find the board break....a double sided plated thro pcb only needs 1 thro hole connection to be missing-or its simply a wire break in which case feed your 15v supply to the point where it is missing via a 1 ohm fusible and power up.
If the resistor goes oc on power up then you know the possible reason why the relevant thro hole connection/track etc has failed-you will have to play hunt the sc with your meter .....

edit--now according to your last measurements its your 12v supply missing (post 39) ? its important your properly using your meter when taking measurements -you can try the same trick with a 1 ohm fusible and if it goes oc then you have a definite starting point for then taking resistance checks to help localize where the sc (if it does read sc) is
 

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MrChips

Joined Oct 2, 2009
24,226
Trouble shooting electronic systems is like solving a Sudoku puzzle. If you get one piece of information wrong you have to start all over again.

The last time we did something like this on AAC the tester failed to tell us that the meter was indicating mV and not V. Then the tester failed to tell us that the meter was showing a negative sign.

I know that this is not happening here but you can see how the diagnostic process would be completely on the wrong track.

We have already gotten off track with the +15V supply line.

So let us confirm the readings at the two connectors:

CN903
1 +15V
2 + 5V
3 GND
4 -15V
5 GND

CN904
1 + 5V
2 GND
3 + 15V
4 GND
5 -15V
6 +12V

At this stage of testing, we are not too concerned with precision. ±0.1V is good enough.

As Sheldons has pointed out, all voltage measurements are taken with the BLACK lead connected to GROUND somewhere. Look for a metallic shield or the GND of a jack somewhere.
 

Thread Starter

mynamesalex

Joined Oct 4, 2012
53
testconnections.jpg
Trouble shooting electronic systems is like solving a Sudoku puzzle. If you get one piece of information wrong you have to start all over again.

The last time we did something like this on AAC the tester failed to tell us that the meter was indicating mV and not V. Then the tester failed to tell us that the meter was showing a negative sign.

I know that this is not happening here but you can see how the diagnostic process would be completely on the wrong track.

We have already gotten off track with the +15V supply line.

So let us confirm the readings at the two connectors:

CN903
1 +15V
2 + 5V
3 GND
4 -15V
5 GND

CN904
1 + 5V
2 GND
3 + 15V
4 GND
5 -15V
6 +12V

At this stage of testing, we are not too concerned with precision. ±0.1V is good enough.

As Sheldons has pointed out, all voltage measurements are taken with the BLACK lead connected to GROUND somewhere. Look for a metallic shield or the GND of a jack somewhere.
I may be relatively new at this but I do understand the basic principles so rest assured I understand where the black lead goes hahaha. I'll attach a picture of the ground I've been using to this post. It's the overall ground lead from the AC plug that is a big screw on the bottom of the unit. It has the earth ground symbol on it. Now, I have re-tested the voltages and results were as follows:

CN903
1 +15V = +15.10V
2 + 5V = +5.06V
3 GND = -4.0MV
4 -15V = -14.72
5 GND = -0V

CN904
1 + 5V = +5.05V
2 GND = 0V
3 + 15V = +15.09V
4 GND = 0V
5 -15V = -14.71V
6 +12V = 4.6MV

I'm assuming that the 6th connector on the CN904 connector should probably not be 4.6MV.. Other than that all voltages seem to be normal.

Edit: Note that when I test the +15V and +12V TEST LOCATIONS on the board I get incorrect readings as stated earlier. (about -.897V for the +15V and .354 or something for the +12V) There is a picture called testconnections attached to this post where you can see the small areas that I'm able to test voltages on the board at. One is labeled V+15 and the 12V tester is on the right but the 12 is covered by black cloth by the screw hole. The readings posted above where I labeled the pins are when just testing pins, not test connections on the board. The test connections are tested when I actually plug the CN904 cable into the board. I don't know if that helps anything but I just wanted to clarify. Thanks!
 

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MrChips

Joined Oct 2, 2009
24,226
Delete: [There is a board labeled HPAMP shown on page 114.
Can you take a clear well focused photograph of the lower half of the board?]

[There is a board labeled INPUT on page 84.
Please take a clear, well focused photograph of the upper left corner of the board where CN455 appears.]

Edit : I see you have already posted that photo in post #45

btw 4MV is 4 million volts.

You mean 4mV, i.e. 0.004V

Also, I need to know the brand and model of your test meter or you can post a photo.
You will have to make a current measurement soon.
 
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sheldons

Joined Oct 26, 2011
613
you need to connect your negative lead from your meter to the relevant ground for the supply you are measuring on the secondary of the power supply to avoid the chance of getting incorrect readings-are all the supplies correct at the source?....if they are then all you need to do is trace the relevant supply around the unit until you find the exact point where its missing leaving your ground lead on the relevant point on the power supply secondary-also bear in mind that not only could it be a missing 12v supply etc but is your ground good board to board?
 

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MrChips

Joined Oct 2, 2009
24,226
On the INPUT board as shown on page 84 (your last photo)
please measure the voltages at the two points shown as 1 and 2 each with respect to GROUND.

 

Thread Starter

mynamesalex

Joined Oct 4, 2012
53
Hey guys. Sorry for the delay in posting as I was away at a wedding in Seattle. I've measured the voltages at the two points and they are as follows:

1) 15.09V
2) -.887V

Chips, do you still need a photo of any of the board areas? Also the meter I'm using is a Micronta 22-171A. If you need a picture of it I can provide it. Thanks!
 

MrChips

Joined Oct 2, 2009
24,226
You have found the problem. Now comes the difficult part.
That device labeled IC810 is a fuse and it is blown.
Before replacing the fuse we have to figure out what caused it to blow.

Your meter does not measure current. Do you have access to an ammeter?
 

Thread Starter

mynamesalex

Joined Oct 4, 2012
53
You have found the problem. Now comes the difficult part.
That device labeled IC810 is a fuse and it is blown.
Before replacing the fuse we have to figure out what caused it to blow.

Your meter does not measure current. Do you have access to an ammeter?

Ah success! I can pick one up tomorrow. Do you suggest I just get a new multimeter that measures current or just an ammeter?
 

MrChips

Joined Oct 2, 2009
24,226
Get a multimeter that has current measurement capability.
Many handheld DMM have two separate ranges, 0-200mA and 0-10A or 0-20A.
The fuse in question is listed as part number DEK1096 and rated at 0.75A.
Hence an ammeter with a range of 0-200mA will not do. You need a meter that can measure 0-10A or 0-20A.

You will have to replace that fuse with a similar 0.75A SMD fuse.

In order to remove the bad fuse you will need access to two soldering irons.

Before we do that. Unplug the AC POWER cord.
Measure the resistance between the point I labelled 2 and GROUND.
Reverse the meter leads and measure again.
 

MrChips

Joined Oct 2, 2009
24,226
That's good. Hopefully you will get the chance to use it a few more times in the near future.

We need to measure the current through the blown fuse to see if it is excessive.
Switch the DMM to the 10A range
Connect the RED lead in the upper jack that is labeled 10ADC.
Connect the BLACK lead to the bottom jack labeled COM.

With the DJ mixer plugged in and power on, connect the two leads at the points labeled 1 and 2.
Measure the current.

You will need a new fuse.

Here is an example of an SMD fuse:

http://www.digikey.com/product-detail/en/ERB-RD0R75X/P15121CT-ND/2796800

If you cannot get an SMD fuse an axial thru-hole fuse will do if you bend the leads to fit the SMD footprint:

http://www.digikey.com/product-detail/en/0251.750MAT1L/F5522CT-ND/3306912

Let's find out if there's anything wrong with the circuit first.
 

Thread Starter

mynamesalex

Joined Oct 4, 2012
53
That's good. Hopefully you will get the chance to use it a few more times in the near future.

We need to measure the current through the blown fuse to see if it is excessive.
Switch the DMM to the 10A range
Connect the RED lead in the upper jack that is labeled 10ADC.
Connect the BLACK lead to the bottom jack labeled COM.

With the DJ mixer plugged in and power on, connect the two leads at the points labeled 1 and 2.
Measure the current.

You will need a new fuse.

Here is an example of an SMD fuse:

http://www.digikey.com/product-detail/en/ERB-RD0R75X/P15121CT-ND/2796800

If you cannot get an SMD fuse an axial thru-hole fuse will do if you bend the leads to fit the SMD footprint:

http://www.digikey.com/product-detail/en/0251.750MAT1L/F5522CT-ND/3306912

Let's find out if there's anything wrong with the circuit first.
Do I put the black lead on one side and the red on the other? Or does the black still go to ground?

Edit: That was a stupid question. Which side does the black lead go to?
 

Thread Starter

mynamesalex

Joined Oct 4, 2012
53
I'm getting a 0.23 reading. I don't know if I'm doing something wrong but the fuse seemed to spark. No smoke or anything. Maybe one of the leads was touching something else but I was very careful.

Edit: Also, any clue to where I could pick up a SMD fuse or do I have to order it online?
 
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MrChips

Joined Oct 2, 2009
24,226
You might get an initial current surge as the filter capacitors charge up.

You might have to order the fuse online if you cannot find it locally.
 
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