my pioneer DJM-500 has a problem with the left master

Thread Starter

Shaneperry

Joined Mar 19, 2020
12
output doesn't seem to work. i can get a very faint, distorted signal out of the left and the right seems to work fine. the master's left side lighted volume meter isn't showing anything. just the right. left and right are working out of the headphone jack. Checked continuity of ic556 &ic557 also input and output voltages of voltage regulators 7808 7815 7908 7915 all reading ok, where should I start looking to rectify thanks in advance
 

Thread Starter

Shaneperry

Joined Mar 19, 2020
12
Thanks Les
I will try to post a schematic ASAP I’ve been reading though this site where there has been some useful info from members on this site that’s how I knew how and where to check for voltages
 

abrsvc

Joined Jun 16, 2018
34
The most common failure of these types of units is the "output" op amp IC. Typically these are 4558 ICs or something similar (4570). Look for these near the output RCA connector and check the pins using an oscilloscope. You should see signal at the inputs and outputs of these. If the final one is OK, trace back to an earlier one although it is usually the final one that is the problem.

Dan
 

Thread Starter

Shaneperry

Joined Mar 19, 2020
12
Thanks abrsvc
can these only be tested with a oscilloscope or could I possibly use a multimeter thank you for all the replies so far
 

JoeJester

Joined Apr 26, 2005
4,259
IC804 has four sections. Once section could be bad. Did you measure the output of the IC to determine it being bad?

The transistor that mutes the left channel on that particular output could be bad.

on edit ...

You know the input is good because the head phones received the same signal.

Output.png
 
Last edited:

abrsvc

Joined Jun 16, 2018
34
Thanks abrsvc
can these only be tested with a oscilloscope or could I possibly use a multimeter thank you for all the replies so far
Using a scope will clearly show the distortion or small signal. A multimeter won't help in this case. But... These are cheap enough (usually less than $1 each), that I would just change it. These do go bad on occasion for no apparent reason. If you have one available, swap it out and try it. You can check the voltages on the pins as a pre-check, but unless you see a shorted op-amp, I doubt that the meter will show much.
 

MrChips

Joined Oct 2, 2009
21,074
There are alternatives to having an oscilloscope.

Before being able to afford an oscilloscope, repair shops (and I) used a signal injector and tracer combination in order to trace the signal through a circuit.

Since your input front end is working you only need the tracer part. What is this? Any audio amplifier will do such as a PC amplifier or a simple LM386 or similar audio amplifier IC with speaker or headphones as output. This will allow you to find the presence or absence of your audio signal.

In fact, since one channel of your mixer is working, you can use this as your tracer.
 

Thread Starter

Shaneperry

Joined Mar 19, 2020
12
Using a scope will clearly show the distortion or small signal. A multimeter won't help in this case. But... These are cheap enough (usually less than $1 each), that I would just change it. These do go bad on occasion for no apparent reason. If you have one available, swap it out and try it. You can check the voltages on the pins as a pre-check, but unless you see a shorted op-amp, I doubt that the meter will show much.

Thanks was just going to Test the op amp with testing between pins and gnd but wasn’t sure didn’t want to blow anything on board I’ll look at ordering a new op amp
Thank you for your replies
Been appreciated
 

Thread Starter

Shaneperry

Joined Mar 19, 2020
12
Just to let everybody know I not up on my electronics but I am a electrician, so confused and excited at the same time learning new stuff
thanks too all you technicians
 

LesJones

Joined Jan 8, 2017
2,638
I was going to say that checking the DC conditions on the op amp should give a good idea if it is working correctly but looking at the voltage readings in the schematic in post #13 the output voltage does not agree with what I calculate it to be. For both channels the DC gain (And AC gain except for the effect of the 27 pF capacitor at high frequencies.) should be 5.4
((33K + 7.5K)/7.5K) So for the top half I would expect the output to be at + 19.44 mV (3.6mV x 5.4) and for the bottom half 21.06 mV (3.9 mV x 5.4) I can't see the reason for this difference but if the DC voltage on the output of the suspect channel is very different then the op amp is probably faulty. (But if they are about what is expected then it doesn't prove the op amp is good.)
I like MrChips suggestion in post #15.

Les.
 

JoeJester

Joined Apr 26, 2005
4,259
MrChips certainly reminded us of the Signal Injection and Signal Tracing. Signal Tracing would definately aid. You can get an oscilloscope APP to use because all you are looking for is a go/no go condition of the amplifier right now. Of course, I wouldn't attest to the calibration of such a device, but as a signal tracer or the signal generator app for signal injection, can be helpful.


Those would not be wise, without external attenuation, for anything higher than line level.
 
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