JVC AX-R551X PROBLEM

[73's de Edd]

.


Sir Constantine . . . . . . .

Yes headphones work fine.
That makes me feel even more that the power amplifier section is not working correctly.

The headphones get their drive from the SAME speaker drive line.
With only a variance of inserting some series resistors in their feed line line for attenuation.
Also if you are hearing audio through the headphones, that means that the protective Rly901
has NOT tried to disengage the speakers and headphones, due to a fault.


JVC Manual page 10 or ADOBE page 7 explains the units specific speaker switching action.


Well in looking at the power supply scopings, I see no abnormalities, ripple wise .
HOWEVER you do have one bodacious level of 52khz signal, present at the shared Q770 and Q772 emitters, as the power output for that channel.

You are certainly not going to be hearing that POST- ultrasonic and -SUB RF frequency !

Flip the input off the present CD position in an attempt to see where ? that high frequency signal is coming from ?, while you are scoping that channels output.

You might go back to the audio source input that was previously letting you hear a feeble audio through the speakers.



73's de Edd




.

 

[HellasTechn]

The headphones get their drive from the SAME speaker drive line.
With only a variance of inserting some series resistors in their feed line line for attenuation.

Ok but still why do i hear audio from the headphones correctly and from the speakers at very low volume .
Speakers volume will change accordingly to the volume control knob but still the maximum level on the knob gives low volume at the speakers.

Also if you are hearing audio through the headphones, that means that the protective Rly901
has tried to disengage the speakers and headphones, due to a fault.

I am a little confused.
Speakers and headphones ? But in my case the relay takes no action.
When i power up the amplifier i hear one relay click (PSU relay) and a few seconds later i hear the speakers relay click. After that i get no other relay action.

Flip the input off the present CD position in an attempt to see where ?

I was not playing with the inputs i just use CD input But also all other inputs give me the same low volume as the CD input.

You might go back to the audio source input that was previously letting you hear a feeble audio through the speakers.

like i sayd before all inputs give me the same levels of audio volume.
In all inputs i can control volume with the knob but all are giving very low output volume.

 

[HellasTechn]

Do you want me to take snapshots while i have audio input connected ?

 

[73's de Edd]

.


Sir Constantine. . . . . . .

OK lets go this testing route, IF you are able to hear your audio good through both channels with the headphones, but the audio from the speakers is being weak.

Note that the ground connection of the J901 headphone is a good common ground point for both
the headphone or the speakers.
Or you could ohm out and find several other points that it also connects to, just in case that connection is physically hard to get to.
Then if you consult your manual on its ADOBE page 38 you will see that they have grey shadow lined from the R787 pair of emitter resistors all of the way to the speaker.

Can you get the RIGHT speakers working feebly and take the LEFT speakers lead and confirm that it is connected to our previously mentioned ground.
Then you take the other lead of the speaker and you just might also need a double clip jumper wire, to make it reach everywhere.
Initially touch it to the origin of the left channels power audio output, which is at the R787 dual emitter resistor. If you get STRONG sound decrease your volume control a bit.
Then move that connection down the grey path to the input of R901's relay contacts and then over to the other side past the relay.
Then you see the next input would be to the bottom left contacts of that S 902 4PDT System 2---System 1 switch and it ends up at the + connection of Left channel System 1.
You can see that S901 --- DPDT switch is switching ground connections.
Only a bad switch connection should stop the audio before you reach that final test that is made at the final speaker connection.
Or you don't realize that you can have either System 1 or System 2, but not BOTH, with this systems switching arrangement.




73's de Edd




.

 

[HellasTechn]

Then you take the other lead of the speaker and you just might also need a double clip jumper wire, to make it reach everywhere.
Initially touch it to the origin of the left channels power audio output, which is at the R787 dual emitter resistor. If you get STRONG sound decrease your volume control a bit.

So i put speakers black wire to the ground and the red one to R787 right ? then move all the way to relay ?

Is relay switching the ground on and off the speakers ? Am i getting something wrong here?

Or you don't realize that you can have either System 1 or System 2, but not BOTH, with this systems switching arrangement.

That i dont understand.

One last thing to clarify is that both speakers have low audio volume, it is just that one of them (left i think) is even lower.

I have a little trouble understanding what you are suggesting me to do here.

I will read your post again and again and try what you suggest and then get back to you with resaults.

I will be away today so i will do that tommorow.

Thank you very very much !!!

 

[73's de Edd]

.


Sir Constantine. . . . . . .
Most Honnable apologies . . .as I initially didn't know the connector situation on those speakers of yours.
Now I am knowing you have loose wires OR either loose wires with terminal lugs.

Starting over again, and having a test audio signal into the unit, and working with the grey shadow marked up schematic of the channel which uses the Q769 and Q771.
Place the "negative" speaker wire to any of the many ground connections which connect into the R801 and R802 bleeder resistors shared junction, which you are already familiar with.

THEN you have test audio input coming into that channel and touch your "positive" speaker wire to the center of the shared Q769 and Q771 emitter resistor R787 ***.
If your power amp on that channel is functioning normal, you will have normal audio coming from the test speaker , and can be run UP to its power limit .

Considering that power level is found, its then a matter of moving that test speaker down that grey shadow marked up path to EACH junction until you reach the final speaker terminal. . . . . . OR you loose the audio.

Standing by . . . . as you are either going to have normal audio level and control initially at *** or not.

73's de Edd




.

 

[HellasTechn]

Most Honnable apologies

Please, it is me that i have to thank you not you to apologise to me

I will get to work right now...

 

[HellasTechn]

Ok. So from the emitters of Q769 and Q771 and the resistor R787 i get the same audio as from the speakers output (only from resistor R787 Pin B it is a little lower).

Same thing with the emitters of Q770 and Q772.

I checked audio going out from the relay to board ENH III-4 (headphone and system selectors) and before the attenuator resistors i also get the same audio as in the speakers output.

That is weird. why is then headphones volume correct ?

Here i have to say that i have noticed that whenever i have both systems on there is no audio on any of the speakers output while when only one of the two is selected, either only system 1 or system 2 it gives the audio output as described in all the above posts.

From what i can tell based on the schematic this is normal because when s901 is on then ground is not transfered to system 2 and when s902 is also on audio is not transfered to system1. Only when one switch is on at a time then the coresponding system gets both audio line and ground.

 

[HellasTechn]

Ok something i just noticed and strikes me as surprise. the schematic says that:

Q769= 2SD1718 and Q770= does not say. Same i guess ?
Q771=2SB1163 and Q772= does not say. Same i guess ?

While when i got the amplifier i found mounted and damaged the following:

Q771, Q722 = 2SA1264
Q769, Q770 = 2SC3181

I replaced them with exactly as i found them mounted:

Q771, Q722 = 2SA1264
Q769, Q770 = 2SC3181

I am more confused now....

 

[HellasTechn]

One other thing that i beleave is of no importance but i should have probably mentioned in post#1 is that the A933 transistors i have replaced are not exactly the same package as the old ones.

The original where TO-92 bu the new are a bit smaller and flat both sides.

 

[73's de Edd]

.


Sir Constantine. . . . . . .

That is weird. why is then headphones volume correct ?
It doesn't take much power at all to drive headphones.


Clarify:

The audio that is now coming from the speaker (s).
Since I am being ~24,794 . . 7/8 ths kilos away from being able to HEAR it, is the sound from the speaker (s) at least as strong as low radio listening volume or is it very feeble?
And does it seem to be clear and distinct audio, and not distorted ?
Also on the headphones , is it clear audio and probably capable of being louder than you need?




I am more confused now....(on the output pair transistors)


On different manufacturers, for their choice of the power output transistors that they used .
(And there are being MANY-MANY different options out there, made over a long time period. )

Refer to these three possibilities of selected complementary power pair / sets below.

RELATIVE MATCHED SET COMPARISONS:
(Being designated as NPN / PNP Stars 1, 2 and 3)

You can see that Set 1 transistors are being 120 Watt @ 12 Amps units
You can see that Set 2 transistors are being 150 Watt @ 15 Amps units ***
You can see that Set 3 transistors are being 80 Watt @ 8 Amps units
*** Note their potential disparity in Beta matching of 40/90

The 845/755 set were the ones specified on the schematic
The 3181/1264 set was your "prior persons" replacement choice being found.
So you are down in the 80 watt category from the original parts spec.
BUT . . .BUT . . . . Who is going to be constantly using that obscene of a POWER level,
OR unless one has some brand of hellishly inefficient speakers .
I can shake the walls and move adjunct furniture with 35/35 watts of power into my speakers.

While I am at it , which ADOBE page is like your unit, and the one which I should be consulting, for its power supply and amp.

Since you are WELL covered in the scope department, do you also have / or / can borrow an audio / or / function generator to do some progressive signal injection in frontal AF stages ?
Or, will we just have to improvise ?


Aside:
No problem on that small signal transistors replacement . . . its just using a different manufacturers casing profile . . .which I think is neat, but just don't see them much anymore..

73's de Edd




.

 

[HellasTechn]

It doesn't take much power at all to drive headphones.

Makes perfect sense.

is the sound from the speaker (s) at least as strong as low radio listening volume or is it very feeble?

Yes it has the volume of a small radio. You can hear it within a small room.

And does it seem to be clear and distinct audio, and not distorted ?

Left channel gives nice audio output but less volume while Right channel gives a little distorted audio but louder.
If i turn input audio signal low then i hear almost no audio from the Left while from the right i hear low volume but not distorted audio. As if the Right channel has a higher "amplification factor"

Since you are WELL covered in the scope department, do you also have / or / can borrow an audio / or / function generator to do some progressive signal injection in frontal AF stages ?
Or, will we just have to improvise ?

I may be able to do something.

While I am at it , which ADOBE page is like your unit, and the one which I should be consulting, for its power supply and amp.

hmm i will have to check. not sure.
We do know for sure it is the 80 watt version though. the european version.

 

[HellasTechn]

Or, will we just have to improvise ?

I think for the time being this is the case.

 

[HellasTechn]

Two other things.
1. While i see the r801 bleeder resistor on the PCB, i can not find the R802 anywhere on the pcb.

2. when i power up the amp. the display bar graph is showing no audio but when speaker's relay click on then the far right bar graph goes up to max and stays like that even with no audio input connected !

 

[73's de Edd]

.


Sir Constantine . . . . . . .

Two topics being of interest this time:

Remember when you mentioned your new 933's transistors being in the rectangular cases. Can you test them to see if that new casing profile might reverse the ECB-- CBE pinout layout on them, from the former TO-92 units.
You can do the standard ohmmeter test on them to confirm the base, or you MIGHT? just have one of those SMART testers which identifies the leads also.
I am initially leery of that being a possibility.
The other possibility is that you misconnected one / two of that 933's leads on the RIGHT channel, and inadvertently, have NOW made yourself a post sonic - sub RF power oscillator; with that being confirmed in post # 34's photo.

Do you know that new 933 transistors brand, as I thought that the very few that I have seen in ages past were being of the Matsushita / Panasonic family.

Update:
Sanyo . . . . . Rohm
Referencing, being of . . . pooooor . . . . . quality.

http://www.datasheetbank.com/2SA933S-Datasheet-PDF-ROHM

Nope, the E-C-B lead configurations are being the same.
I'm now just thinking that you made a lead install error on the Right channels 933.



73's de Edd




.

 

[HellasTechn]

Remember when you mentioned your new 933's transistors being in the rectangular cases. Can you test them to see if that new casing profile might reverse the ECB-- CBE pinout layout on them, from the former TO-92 units.

Nope, the E-C-B lead configurations are being the same.

Yes they are the same.

Do you know that new 933 transistors brand, as I thought that the very few that I have seen in ages past were being of the Matsushita / Panasonic family.

I have no idea the brand. it is not printed on them.

The other possibility is that you misconnected one / two of that 933's leads on the RIGHT channel, and inadvertently, have NOW made yourself a post sonic - sub RF power oscillator; with that being confirmed in post # 34's photo.

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

 

[HellasTechn]

By the way i do have a ~ sinwave signal generator left at my parents house but i do not remember if it is an RF or LF signal Generator. I will have to go pick it up ans see.

 

[HellasTechn]

While i see the r801 bleeder resistor on the PCB, i can not find the R802 anywhere on the pcb.

Is it possible that the PCB does not use R802 ?

 

[HellasTechn]

So i got the signal generator today but unfortunately it is an RF generator ranging from 115Khz to 130Mhz
(TECH TE-20D)
A pice of technology back from the 60's

I am thinking to download AF generator software and use the PC sound card as AF signal gen.

 

[HellasTechn]

And so i found this site
http://onlinetonegenerator.com/

and checked the output of the sound card and it looks OK.