JVC AX-R551X PROBLEM

[73's de Edd]

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Sir Constantine . . . . . . .


Is it possible that the PCB does not use R802 ?

I would expect it to be placed to the side, just as the R801 is now located.
Minor issue, since it's JUST being a s l o w drain after power off, for those massive E-caps.

I will check again but i am confident that it is not a soldering issue.

Not soldering, since the transistor goes into PCB holes, BUT possibly you inverted that parts installation, a full 180 degrees.


Looking ahead for the next troubleshooting step:

Referring to ADOBE schematic page 39:
You see that the LEFT channels schematic has all of its parts well marked up but you have to figure out the
companion parts if working on the other RIGHT channel.
ALSO they have the audio flow shown as a grey defined path for the LEFT channel.
What we want to ascertain, is if this HIGH level signal on the RIGHT channel; as is being confirmed by your frequency analyzer display . . . .by its FULL bars UP on the extreme right bar display.
Now . . .Is that signal being generated within the final power output stage . . . .or is it just coming into that stage.

To determine if it is an incoming signal:

Look at schema connector P-701 coming into the Power stage.
Its pin 2 would serve as a good shared common ground connection and the RIGHT audio coming into the
stage would be on pin 7.
Take a 0.1 through 1 ufd capacitor and connect between pin 2 and 7 and see if the unwanted signal at the display either disappears or diminishes in amplitude, if using the 0.1 value.
That then should show if an incoming signal . . . .which I can't imagine the origin of THAT freq of signal . . .or is it being created within the output stage circuitry ?
And you do have some SPECIAL little devices, in the form of those IC751 and 752's.
But we could inter swap them, if it comes down to that .

That's enough for now, until seeing the testing results.



73's de Edd

 

[HellasTechn]

Referring to ADOBE schematic page 39:
You see that the LEFT channels schematic has all of its parts well marked up but you have to figure out the
companion parts if working on the other RIGHT channel.

I thought they are just the same. Arent the two channels symmetric ?

 

[HellasTechn]

I used an 0.1 poly cap. across p701 pin 2 and pin 7. That eliminated the presence of signal on the bar graph.

now when i removed the capacitor and put all the way they where the speakers relay will not click on.

i measured the protector (IC401) pin 2 to ground and got 0.75 Volts.

I have triple checked everything to make sure i havent shorted or forgotten anything and came up empty.

I will just call it a "night" because it is 2am here and get back to it tomorrow or on monday. I got tired and i may have done something wrong and just can not see it now,

 

[HellasTechn]

I did noticed the Q705, Q706, Q707 and Q708 getting hot while i had the capacitor on. I am not sure if the same was also happening before i mess with it.

 

[73's de Edd]

Sir Constantine . . . .

I never did see this below, being confirmed


I will check again but i am confident that it is not a soldering issue.

Not soldering, since the transistor installs into PCB holes, BUT possibly you inverted that parts installation, a full 180 degrees.

Can you get still audio from the headphones ?

You mentioned Q705-6-7-8 as potentially getting hot.
Yes, the schematics right and left channels are symmetrical / the same .
Look at the bottom right channels data and you will see that they have placed the expected voltages.
Compare the specified voltages against what your unit is experiencing on those transistors for both channels.





73's de Edd

 

[HellasTechn]

Not soldering, since the transistor installs into PCB holes, BUT possibly you inverted that parts installation, a full 180 degrees.

I have checked and all are placed correctly.

Can you get still audio from the headphones ?

No. there is no audio.

In addition to post #43 what happens now when i power on the amplifier is that far right bar graph is at max and a few seconds later all bar graphs go max.

i have checked the Q705-6-7-8 transistors (removed from the board) and are ok but have not checked the voltages.

I have no clue what went wrong there...

 

[73's de Edd]

What is the present audio signal sourced from ?

After the initial high freq end of the spectrum analyzer maxes the display and then the lower frequencies show up on the display . . . . . .will adjusting the volume level bring their display down and to a minimum ?

73's de Edd

 

[HellasTechn]

What is the present audio signal sourced from ?

No idea. I have nothing connected on the inputs.

After the initial high freq end of the spectrum analyzer maxes the display and then the lower frequencies show up on the display . . . . . .will adjusting the volume level bring their display down and to a minimum ?

No. turning the volume knob changes nothing.

 

[73's de Edd]

.

Sir Constantine . . . .

What is the present audio signal sourced from ?

No idea. I have nothing connected on the inputs.

Ohhhhhh . . . . then I guess that I had better go back to my very first suspicion.
That some loss of, or deterioration of power supply filtering, has let that
mystery high level 53 KHZ appear.

Referring to Adobe page 39 of the schema:

Top left corner find:
P354 - - - - - -P301 - - - - - - P405

Scope out, using 1X probe--- vert sens initially set for 1V---- use AC coupling mode on vert input

Check P354 center pin for ripple present . . . .scope ground referencing is available on either side pin.
Check P301 pins 2 and 3 for their ripple content . . . .ground referencing is available on pin 1.
Check P405 pin 3 for its ripple content.

Find your big D801-804 Full Wave Bridge rectifier unit at the very top of the page and drop down about four of its size dimensions and see C 910 filter, being used for a NEGATIVE supply.
Use its left + terminal as your scope ground reference and see what the ripple content is on its NEGATIVE terminal.

Waiting to see what shows up . . . . .


73's de Edd

 

[HellasTechn]

I will get back to you with the readings on monday. THANK YOU !

 

[HellasTechn]

Here are the scopings. Every measurement was taken twice, second measurement was taken with the Oscope's Autoset function.

Look at C910 (1uF 50V)... I replaced it just in case but nothing changed

 

[73's de Edd]

.


Sir Constantine . . .

Look at C910 (1uF 50V)... I replaced it just in case but nothing changed
That's EXACTLY what I would have done also.
In seeing that ripple value, which is being 1/3 of the supply's DC voltage output.

Still referencing Adobe page 39.

Overall you see them them going up to one AC leg of the secondary of the power transformer.
They transport AC down through R 937 and then it gets loaded a bit with R 936, then it passes through
D 904 to create the DC of a negative supply, which is further loaded a bit with R 935 and then filtered a bit with that small filter capacitor C 910.
That supply then goes down to the IC901 protection circuitry.
How about taking a scope readings of the other side of that R916 to see what the ripple level is being on the other side.

Also go to the RY 901 relay and see if it has ~ 62 VDC on its supply side and ~38 VDC on its other side,
Also scope across C909 to see if it is pure DC.




73's de Edd

 

[HellasTechn]

Working on it...

 

[73's de Edd]

..

Sir Constantine . . .

If that unit has been well "cooked" thru the years of use, check out these particular areas of power devices.
They are being pointed out with YELLOW MARKINGS . . .particularly . . .C . . .area.
If any crystallized joints . . . .optimum procedure would be to pull components scrape leads and retin leads.
For its companion foil land , use solder wick to absorb and get free of old solder, retin and then install parts leads and use fresh solder for the joints.

Illustration:

73's de Edd



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[HellasTechn]

I forgot to mention that the coil of RY901 was measured with probe set to X10 so true reading is 56.4 Volts

 

[73's de Edd]

I see that there is just but a trace of ripple carrying on to the other side of R916.
The idea on the testing across Ry901 was to use a DMM across it for the measurements.
To see if there was being any voltage change across it, from initial power up, on until a couple of minutes.
If you happen to have an analog meter, it might be better, since there is no settling time, such as a DMM requires.

73's de Edd

 

[HellasTechn]

I will test some time on friday and get back with resaults. THANK YOU !!!!