repair JVC indash unit no power up

[fuzzysig]

I'm somewhat of a noob at advanced repair.
but I do know how to check for pulse and breathing etc
visual check, burned trace, fuse etc. I fixed few items like that

and I have a voltmeter and know how to use it lol

besides that I have a general idea of how things work but no more than that
end of intro.
-----------------------

bought this unit for 80 bucks on ebay seller says dead no power at all
its more of a project for me since it was damn cheap.
model JVC kw-nt800hdt

I only found 2 videos on where to start troubleshooting car stereos and there wasnt much there
just checking for blown caps and blown amp and input diode.

I haven't got the stereo yet but I was wondering if anyone here knows how to test a dead car stereo
I'm assuming its something with power supply or blown amp.
I know the notorious pioneer surface mount fuse but I don't think jvc uses it.
JVC is now merged with kenwood btw for few years so I would assume their circuitry would be very similar

anyone have a link for me or something to read on the topic would be great.

 

[Martaine2005]

but I do know how to check for pulse and breathing etc

You and @73's de Edd will get on just fine!!

My advice would be to wait for the unit and then start by checking voltages.
It could be anything!!

Martin

 

[Martaine2005]

Here is the installation instructions.. It gives the wiring colour code, which is very useful.
JVC pdf.

Martin

 

[fuzzysig]

does anyone have any good links to articles that maybe give some basics to troubleshooting and repairing car stereos?
like how the circuit boards usually arranged, common problems to check for etc. I couldn't find much at all on repairing and troubleshooting car head units most of the articles cover the very basics and are about home theater. but almost everything related to car audio is just about installation issues and not about actual unit repair..

I'm very familiar with the installation part ive been doing it for over 10 years just never tried repairing anything beyond basic trace repair or replace burned component after visual inspection

 

[Martaine2005]

just never tried repairing anything beyond basic trace repair or replace burned component after visual inspection

Well, I would guess that you need to know what all the components are and DO.
Also, a burned component might be caused by an underlying fault.

What tools do you have for troubleshooting / repairing?

The link I gave you has the wiring diagram for the connection pins. That can be a valuable resource by itself!
You really need the service manual for most electronic items today, as they are complex.
So try and get that and learn to read it.
Google is your best friend..

Martin

 

[fuzzysig]

wow this was a good bet. I feel like I'm in the casino when bying things on ebay.

this unit only powers on when I ground it to the unit chasis but not through the ground wire.

does it mean theres an internal fuse in it? or a diode of some kind?
I haven't taken it apart I just got the package and tested it real quick and got too damn excited lol
got it for 80 bucks shipped and usually its like 400-500 dollars for a used one.

 

[Martaine2005]

 

[fuzzysig]

theres no service manual for that model
or anything similar that I could find

 

[fuzzysig]

finally took it apart and found a burned ground trace right off the terminal on circuit board.
maybe someone can answer what would be the most likely cause of this?

like I said before I'm a certified installer I know what I'm doing outside the box. I never repaired circuits besides simple stuff

I just want some ideas on what to look for when I'm in there

links to books or any kind of tutorials would be great.

 

[fuzzysig]

so after repairing the trace I put it together. and everything works except theres no sound from the speakers....
I felt like...

and then indash was like: you almost had me?...

and now I have to take it back apart again...

I'm assuming no sound means the amp is blow too?
I haven't tested rcas yet I didn't have anything to test it with.

theres no sound at all not even at full volume no noises or crackle or anything
I reset the unit also.

 

[73's de Edd]

Sir fuzzysignals . . . . . . . ( due to floating ground shells )

so after repairing the trace I put it together. and everything works except theres(sic) no sound from the speakers....

Meaning that the NAV system and its display is, at the least, now showing minimal info ?

Were any fuses blown and are you currently testing through an ~ 15 A fuse?,( IF power is fed in thru an inline fuse holder.).

How many amps is the system pulling ?

Where you had reworked those heat crazed "gray" solder connections , what two components wire leads, were those two involved wires being connected into ?.
(Your pic didn't go far enough back in between those TWO Potted Power IC's *** to show the component side view of those connections. )

Pass us all the numbers from those big *** modules so that they can be function identified.

I am vaguely seeing the left one as providing multiple power supplies and the right one, as one that provides 1 or more POWERFUL supplies .

The NAV system, its display and uP is needing power requirements as sophisticated as a laptop.

I am expecting your audio power amp to also be using one of those *** like type of units, look around and see if you find one more similar unit on a heat sink, near your audio speaker output connections.

Overall . . . analytically . . . . looks like you has done "gots" yourself, one "Dell of a Heal" . . . .. . . OR ELSE . . . . . one elegant PILE of electronic scrap.

Standing by . . . . .

73's de Edd.

 

[fuzzysig]

I bought it for 60 plus shipping so even if nothing else works out I think it still worth about 150 if I sell it back on ebay or craigslist. im sure someone has one of these with a busted screen or some other issues
every single feature works on it I tested every menu and option

I fixed the burned trace as soon as I got it apart. I know how to do that lol.
and I spent about 30 minutes today going through every circuit board with a flashlight and a magnifying lens to look for any more physical damage. everything looks clean as a whistle and not even a discolored mark anywhere from overheating.

I checked all the surface mount fuses they all clean as well on every circuit board

also tested rca output today. also dead. and the option to switch off internal amp is also not accessible for whatever reason. it stays "on" and wont let me select "off" option like my other unit.
I snapped some more pictures of the boards today
and will take more tomorrow at work
this is more of a project to learn how to fix these things I do like fixing things just not very experienced at anything past basic troubleshooting.

the amplifier chip is Toshiba TB2926CHQ
the smaller chip next to is LV5680
theres also what im guessing a preamp chip (BA3131FS) on the cirguit board attached to cd player mechanism which also has all the input/output RCAs on it.

LVL3 this is what I guessed is preamp board( or at least has preamp on it?) the ba3131fs chip in the center
the 3 capacitors in the center vertical from the pointing finger are the only ones slightly bulging out on top. cant say if they are damaged or not. others are completely flat.


LVL1 this is the bottom board that has the power plug with speaker outputs and the above mentioned chips Toshiba and lv5680


LVL2 this is the middle board that has the memory module and sd card slot along with the USB connector and the ribbon cable that goes to the touch screen
and the tuner board on the other side of it


this one goes on the front behind touch screen and connects all 3 other circuit boards together

 

[73's de Edd]

Sir fuzzypants . . . . . . . .whooooooooooooops, my disdainful and abysmally poor retentive memory . . . .make that fuzzysignals . . . . . (Check your grounds !)

That doesn't even look like the same board, with your now, par excellance top shot.
As per your two-three, bulged electrolytics, they are being the filters that belong to the three nearby BD7981 , switch mode power supply in a chip devices, along
with their ancillary , blue sealed , pot core inductors ( spel chek sez "instructors" but WE 'soitanly knoes diferntly !) over to their right.

Can't hurt to change out all 3 caps now, to head off their full / highly inconvenient, failure tomorrow.

Take note of their hi 105 deg temp range rating , as well as being LOW ESR units.
Also be VEWY-VEWY carefwull , and use your BEST soldering expertise.

The LV5680 is providing four sections of LINEAR voltage regulation and output switching control.

And now . . .the magic bullet . . . .is being that larger TB2926CHQ potted module , which is SUPPOSED ? to be providing you with 4 channels of hefty audio.

It produces four times 50 watts per channel . . . . . . . . .babycakes !

Here is the TB2926CHQ Da-Da Sheet:

http://www.datasheet4u.com/download_new.php?id=897124

That unit is being of a 2009 developmental design time frame . . . . and would you believe it . . . . .already is being designated as OBSOLETE for new design

Since we still don't have a schema, find its pins 6 and / or 20 and have the set disconnected from 12 VDC power, and then, take ohmmeter in hand, and trace down
their foil paths to see how close you come to finding them connecting into the 12 VDC supply or possibly into that LV5680, if they are using one of its sections for
DC power switching, to the power amp.
Most likely its pin 15, since its other outputs are related to much lower power ancillary functions,like CD Player, audio preamp, ant,ILM and accessory enabling..

Here is the LV5680's Da DA Sheet:

http://html.alldatasheet.com/html-pdf/440330/SANYO/LV5680P/150/1/LV5680P.html

Go see what you can confirm now, in a no power connected mode.

Step two on that TB2926CHQ would be to get in low ohms mode and check:
(With no speakers connected)

The resistance between Pin 8 to 7 and 9 and then just between 7 and 9
The resistance between Pin 2 to 5 and 3 and then just between 5 and 3
The resistance between Pin 18 to 17 and 1 9 and then just between 17 and 19
The resistance between Pin 24 to 21 and 23 and then just between 21 and 23

Of course it could be less of a failure, than having a dead shorted CMOS output power device condition.
It could also be some DC voltage leakage into the speaker output line, with that then triggering the audio output section into a protective shutdown mode.

BCNU

73's de Edd.

 

[fuzzysig]

Dam im gonna have to buy a decent multimeter for this lol. My crapsman shows .2+- everything but its enough for car stereo installation.

So i was wrong about thinking that preamp is on a separate board?
The toahiba chip is a preamp and the high power amp all in one?

Im gonna need a week or so to get a better multimeter got bills to pay this week so il be back in a few days with some results

 

[fuzzysig]

Protection mode would show a warning on the screen.
And if it was a voltage leak wouldnt it at least pop during power-up?
The output is dead silent at full volume rca or spkr out.
Ive been looking for a service manual for this about a week now cant find anything remotely similar to this model
Heres few pictures

 

[fuzzysig]

 

[73's de Edd]

.



Sir Fuzzzzzzzzysig . . . . . . . . . .


Submitted herewith . . . . . is all of the info that I think will be needed in the troubleshooting / analysis of this units audio power problem(s)

CIRCUIT AND COMPONENT FAMILIARIZATION . . . . .

All of the units audio magic and hocus pocus initiates at the far left TDA4416 chip, where the audio input selections , volume control, tone control functions, Stereo balance Front to Back sound distribution, etc are shifted by control menu input.

Four separate audio sources, leave out of the TDA4416 chip's Pins 24-25-22-21, and route over to the right as being the units RIGHT FRONT--- LEFT FRONT --- RIGHT REAR and LEFT REAR audio outputs, they are flagged at occasional points, as they pass across the page to the right, using BLACK / YELLOW BOXES.

INITIAL ANALYSIS AND TROUBLESHOOTING . . . . .

I had already given you info as to the initial troubleshooting of the 12 VDC main power path into the power module via an ohmmic testing path, but looks like you need to put a fresh battery into your meter.

This time, by the use of voltage measurements, the 12 VDC input starts at the red arrow and flows across the mini "RED arrow path" until it reaches the large toroidal donut and then the large electrolytic and finally passes up the foil path to IC371's two power sector inputs of pins 20 and 6.

In real time operation, that 12VDC supply line ALSO branches to the right to activate digital transistors Q3071 and Q3072 that slams pin 22 of the AF POWER IC into MUTE mode, via the GREEN ARROW path, passing thru the C-E path of Q3071 to ground.
By use of that procedure, the receiver will not exhibit speaker "pops /or / plops" on initial turn on .
Upon the GREEN STAR designated C3075 having accumulated its initial charge, the system then rapidly reverts from being in mute mode and is then ready to make music.
CONSIDERING that there is being no further MUTE / audio over ride demand made via the BLUE ARROW path that feeds down and back to the units Line out and Phone circuitry,
(IF . . . . . those functions even have anything plugged into them.)

( FIO . . .the PINK / BLACK markups are for a line output path, IF ever being needing referencing later on.)

Looks like our testing will be on the sets LEVEL 1 PCB.

The first thing to test is if the 12 VDC power is being present at pins 6 and 20 of the AF power module IC371.

If testing proper, the next test will be to use pin 1 of the CN901 battery and speaker connector, as DC metering ground referencing.
Then, probe pins 5-12 to see if each is having approx 7 VDC presence.

Standing by for feedback . . . . .

Mon Dieu . . . . un schématique ! ! ! . . . . .

73's de Edd



.

 

[fuzzysig]

damn how where did you find that diagram?
i will get new meter soon. mine is not dead is just blown out and old its 10 years old and been shorted and burned few times working on car electrical stuff...
so its slightly crosseyed
thanks for all your help btw this is more than i hoped for.

 

[fuzzysig]

still working on gettingthat multimeter had to pay some bills

but funny thing happened
I brought another model in the whop to take it apart and see if I could swap the boards around to see which one has the probems on it.
they are same unit seems like they both use same firmware (kw-nt500hdt)

but having to use some ghetto test bench the 12 volt fell on the ground and shorted the other unit.
exactly same spot as the other one. well I thought it was dead as well
but after soldering it togetherit seems to be working like it should.
so I'm suspecting the problem Is elsewhere
I haven't tested the other unit. just thought I would update this.

 

[fuzzysig]

Was bored and tested power and ground to the amp with my old meter
All the ground and 12 volt terminals have continuity from power plug.

The only thing odd is the capacitor right under thae terminal 15 its the only one that has continuity to ground on both sides.
C2353. Last picture of the bottom of main board.


Thanks again for that diagram