| Description |
When fading the fader of St1 or St2 the output level didn't change!
1.
We press the grey button on the master module and switch on the sine generator.
We need a continuous sine signal so that we can more easily see what is happening with the sine signal.
the sine signal.
-> See Photo 1
-> See Photo 2
2.
Consideration:
Where is the audio signal St1 regulated up and down? See at 3.
3.
When you move the St1 fader, digital data signals are sent.
These "digital signals" end up in the masterboard section on the "right side".
These "digital signals" then go via H4 to the "right side (analogue side)" of the masterboard.
Then these signals go to H5,H6,H7 and from there go directly to the Quad-DCA boards.
On the Quad-DCA boards there is a DCA, this controls the volume of St1.
We measure an audio signal at H1:5 (In1L-) and H1:2 (In1L+),
but there is simply no up/down control at the output.
-> See Pdf1
So, where is the audio signal St1 regulated up and down?
At the Quad-DCA-Board 1 !
-> See Pdf2
The Quad-DCA-Board has two sides: "left side" and "right side".
- St1 is on the "left side",
- St2 is on the "right side
We go to "left side" tap the following audio signal: H1:5 (In1L-) and H1:2 (In1L+).
The St1 signal is present there.
4.
Is U8 possibly defective?
No. Reason: The sine audio signal does not move when ST1 is moved, if U8 OP270 were broken,
you would see an 18V DC voltage instead of a sine wave!
5.
Is U7 possibly defective?
No. Reason: The sine audio signal does not move when ST1 is moved, if U8 OP270 were broken,
then you would see an 18V DC voltage instead of a sine wave!
6.
We look at this audio signal on the oscilloscope.
Settings for oscilloscope:
-> 2V
-> xx
-> See Photo 3
We see the following: If we move the fader slowly from 10 to 0, the following happens:
Normally, the volume would get quieter and quieter. In our case: The volume is turned down, e.g. at 9, for about 200ms, i.e. very briefly,
and then falls back to the maximum original value.
In fact, you can't see anything, it's as if the volume didn't change at all.
Even if you fade down from 9 to 8 or from 8 to 7, the same thing happens.
The volume goes down very briefly for 200ms and then returns to maximum.
The volume still does not change.
7.
Are the digital data signals possibly broken?
8.
The data signals come from the master module in the mix controller and enter Tower 1 via the black cable.
From there, they enter the master module on the "left side". We now go to Masterboard_01.pdf.
H4:13 It says "Data In". This is where the 32-bit signal comes in.
The data signal goes into U83, then U84, then U85.
U85 is a shift register and grabs the first 8 bits and then passes the remaining
then passes the remaining 24-bit on to pin 9 and from there it goes into
into U86, U87, U88.
9.
We now check U85, we want to know if St1 is opened at all,
so that the data signals can arrive there.
Either the so-called low signal (i.e. 0V) or the high signal (i.e. 5V) is present at U92 pin 15 (YO).
When St1 is moved, low signal must be present there.
10.
When ST1 is moved, this controller data must go out at U92 at Y0.
U92 is a 74HC138 is a 3-to-8 line decoder/demultiplexer. I.e. a 3 bit signal arrives at input A,B,C,
which then causes one of the following pins to be opened: Y0,Y1,Y2,...Y7
I.e. Y0 must go low!
Low means = data streams flow through YO
High means = there are no data currents flowing, instead 5V is present.
Initially, all Y0 to Y7 are high. But in order for the data to be allowed to pass through U92 at all,
U92 must first receive a short command from U91 Y5.
And for U91,Y5 to execute the command again, it needs a command from U85 from Pin3, Pin4, Pin5.
The U91 must receive the following 3-bit: "101" i.e.: U91-Pin1=1 U91-Pin2=0 U91-Pin3=1
We measure at U91, Pin1=1 when we move ST1.
We measure at U91, Pin2=0 when we move ST1.
We measure at U91, Pin3=1 when we move ST1, so this condition is fulfilled!
The U92 must receive the following 3-bit: "000" i.e.: U92-Pin1=0 U92-Pin2=0 U92-Pin3=0
Why 000?
Y0 means = 0
Y1 means = 1
Y2 means = 2
Y3 means = 3
etc...
-> See pdf 3, the binary system is explained there.
0 in the binary system = 000
1 is in the binary system = 100
2 is in the binary system = 010
3 is in the binary system = 110
4 is in the binary system = 001
5 is in binary system = 101
6 is in binary system = 011
7 is in the binary system = 111
We measure at U92,Pin1=0 when we move ST1
We measure at U92,Pin2=0 when we move ST1.
We measure at U92,Pin3=0 when we move ST1, so this condition is fulfilled!
-> All conditions are fulfilled, we now measure at U92, pin 15, where 0 volts must be present when we move ST1.
-> Result: No, 5 volts are still present (high), i.e. U92 is defective!
-> We replace U92, signal now goes low!
-> But the volume is still not controlled, i.e. the error is still there.
-> So what could be the problem?
11.
We now check:
U85, pin 11, ok
U85, pin 10 V, ok
U86, pin 11, ok
U86, pin 10 V, ok
U87, pin 11, ok
U87, pin 10 V, ok
U88, pin 11, ok
U88, pin 10 V, ok
12.
Is the 32-bit possibly defective?
The 32-bit signal arrives at U83 H4:13, where it enters U85. From there
the remaining 24-bit signal reaches U86, U87, U88 one after the other.
U86 grabs the first 8-bit and removes it. (16-bit remain)
U87 also grabs the first incoming 8-bit and removes them. (8-bit remain)
U88 then grabs the remaining 8-bit and removes them (leaving 0-bit).
This 8-bit shift register finally converts this serial data into parallel data.
We now want to check this data.
13.
For this purpose we go to H5 "right side", because all data signals arrive there anyway.
We will check all pins there.
The oscilloscope is set as follows:
- 2V
- 100us
- The black wire from the oscilloscope is connected to digital ground.
- the red wire comes to the respective pins
-> See Video 1
-> this is what a healthy bit signal looks like. The bit signal is at 5V!
Pin 01: 5 volts are present, everything is OK.
Pin 02: 5 Volt are there, everything ok
Pin 03: Ground is there, everything ok
Pin 04: Ground is there, everything ok
Pin 05: Ground is there, everything ok
Pin 06: -
Pin 07: St1, signal goes from high to low, ok!
Pin 08: St2, signal goes from high to low, ok!
Pin 09:
Pin 10:
Pin 11: ok
Pin 12: ok
Pin 13: ok
Pin 14: ok
Pin 15: ok
Pin 16: ok
Pin 17: ok
Pin 18: ok
Pin 19: ok
Pin 20: ok
Pin 21: ok
Pin 22: ok
Pin 23: ok
Pin 24: ok
Pin 25: ok
Pin 26: ok
Pin 27: not ok, 2.4 volts are present, not ok!
Pin 28: not ok, 2.4 volts are present, not ok!
Pin 29: not ok, 2.4 volts are present there, not ok!
Pin 30: not ok, 2.4 volts are applied there, not ok!
Pin 31: not ok, 2.4 volts are applied there, not ok!
Pin 32: not ok, 2.4 volts are applied there, not ok!
Pin 33: not ok, 2.4 volts are applied there, not ok!
Pin 34: not ok, 2.4 volts are present there, not ok!
The remaining 8-bits are processed at U88, which is where the problem arises.
The 8-bits all have 2.4 volts present there. U88 must be replaced!
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