Hi all. I have a Pioneer DJM-500 mixer that is putting out distortion when the volume is up. If I turn the mixer volume down, and the amplifier volume up, it sounds ok. Also the bass seems to get very low when the mixer volume is up. I have tried different amplifiers, different cables, different inputs, with no better results. Any help would be appreciated. Attached is the link to the service manual.

https://www.manualslib.com/manual/701333/Pioneer-Djm-500.html#manual

Thanks,

Mike

 

Welcome to AAC!

The approach you take in order to diagnose this problem will depend on your level of expertise and the test equipment you have on hand. Do you have a DMM, signal generator and an oscilloscope?

I assume that you have a clean audio source and you have tried inputting to all channels.

The first thing you should do is measure the supply voltages using a DMM.
There are four supply voltages to measure with respect to GNDA.

Look at connector CN121.

1 - V-8A
2 - V+8A
3 - V-BB
4 - GNDA
5 - V+BB

 

Thank you for the reply. I have a DMM - a Fluke 287. I had an oscilloscope, but not sure if I gave it back to my friend or if it's in my garage, I'll have to look and see if I still have it. Either way, I don't know how to use it. It's just something I never learned to use. I do not have a signal generator.

I would consider myself a hobbyist, not a technician. I am very comfortable with soldering and using a DMM (use it for work every day).

I will measure voltage tomorrow. Once again, thank you for the reply.

 

V-8A is -7.23 VDC
V+8A is +7.92 VDC
V-BB is -22.62 VDC
V+BB is -16.05 VDC

 

Your V-BB power rail is bad.
See if you can find the circuit schematics for the power supply board.

 

Hi all. I have a Pioneer DJM-500 mixer that is putting out distortion when the volume is up. If I turn the mixer volume down, and the amplifier volume up, it sounds ok. Also the bass seems to get very low when the mixer volume is up. I have tried different amplifiers, different cables, different inputs, with no better results. Any help would be appreciated. Attached is the link to the service manual.

https://www.manualslib.com/manual/701333/Pioneer-Djm-500.html#manual

Thanks,

Mike

Have you checked the level of the signal on the input? It sounds as though you are over driving it.
Here is the spec sheet showing what the different input levels should be:
https://www.djresource.eu/Topics/story/12/Pioneer-DJM-500/

 

Look at the power supply assembly.
You will find transistor looking devices with three terminals mounted on the heat sink.
Find the one that has markings NJM7915FA. Replace this.
You can find replacements from the usual suppliers Digikey, Mouser, Newark.

You may want to replace the NJM7815FA as well.
Make sure you get devices with insulated tabs and apply heat sink compound before mounting on the heat sink.

https://www.digikey.com/product-detail/en/njr-corporation-njrc/NJM7915FA/NJM7915FA-ND/805807

https://www.mouser.com/ProductDetail/NJR/NJM7915FA?qs=YkwXVBeUzeg1Sl1cPb/adg==

https://www.newark.com/stmicroelectronics/l7915cp/ldo-voltage-regulator-fixed-15v/dp/26M0593

 

Thanks . I see them. I will order and replace.

 

Still getting similar readings, and the v8a polarity is reversed .

V-8a 7.05
V+8a -7.93
V-bb. -23.10
V+bb -16.05

 

Which regulators did you replace?
Double check all installations, polarities and meter connections.

 

I replaced both the 7815a and the 7915a. It was a direct swap . Removed regulators and replaced, 3 legs each.

 

Double checked my meter leads. They're correct.

 

Ok.

I only just noticed the wrong polarity in post #4
I will need some time to look at this.

Can you post a photo or model number of your test meter?

 

I have a fluke 287.

Thank you for taking time to look at this.

 

Something is obviously amiss with the readings indicated in both posts #4 and #9.
Can you confirm that the meter is measuring voltage and polarity correctly by testing a good PP3 9V battery, for example?
After doing that, we will focus on the actual test points you are using for measuring the four supply voltages.

 

Something is obviously amiss with the readings indicated in both posts #4 and #9.
Can you confirm that the meter is measuring voltage and polarity correctly by testing a good PP3 9V battery, for example?
After doing that, we will focus on the actual test points you are using for measuring the four supply voltages.

I checked the meter polarity and voltage with a new AA battery yesterday.

 

I know it seems off that the 7 volt polarity swapped with the regulator change.

 

Please measure the voltages directly at the 7808 and 7815 3-pin voltage regulators.

Input wrt (with respect to) Ground pin
Output wrt Ground pin

Pinouts for 7908 and 7915 are different.

Note that in your case the metal tabs are insulated and make no electrical contact with the heat sink.

 

The diagnostic info we are getting is not consistent with the symptoms. A reversed polarity on one of the rails would certainly have caused complete failure, not distortion when turned up.

The symptoms are consistent with over-driving the input as suggested in post #6, which you seem to have ignored. Have you verified that the input signal is at the correct level for the input?

Bob

 

The diagnostic info we are getting is not consistent with the symptoms. A reversed polarity on one of the rails would certainly have caused complete failure, not distortion when turned up.

The symptoms are consistent with over-driving the input as suggested in post #6, which you seem to have ignored. Have you verified that the input signal is at the correct level for the input?

Bob

I tried 2 different turntables, using different phono inputs on the mixer, and a bluetooth device into a line input on the mixer and it was the same - distorted. I know bluetooth isn't the best for clarity, but for all intents and purposes I used the same bluetooth device in my downstairs stereo and it's clear. I also have used the turntables directly into the denon receiver that the mixer was hooked up to, and it is clear. I also changed from the Denon receiver to a crown xls1000 amplifier and a Pyramid PA800x amplifier, same result, distorted. The mixer seems to be the common denominator.