KW-AVX720 Head Unit Repair - diyAudio
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Old 15th December 2012, 08:40 PM   #1
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Default KW-AVX720 Head Unit Repair

I have a head unit that is not powering up, i cant get a image on the screen. it apears to very very similar to a florecent tube backlit tv. at first i thought it was a bad bulb so i soldered some wires onto the HV transformer to check for voltage but there is no voltage at either end.

almost all of the op amps have no voltage on any of the legs except for one of them

M 847
1228
has 3v on the bottom right corner leg in picture 2651. its the op amp almost right in the center of the board.

the power button on the front of the face. when i press it, the radio will beep, and when i had the dvd drive it was spinning.

i have checked he transistors on the board for shorts and have found nothing, and i checked all the caps and they all seem to be good. i dont have any diagrams and i cant find anything silk screened on the board for ribbon connectors nameing which voltage should be where.

any ideas anyone?
Attached Images
File Type: jpg 000_2653.jpg (811.1 KB, 65 views)
File Type: jpg 000_2641.jpg (496.1 KB, 61 views)
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File Type: jpg 000_2651.jpg (679.3 KB, 13 views)
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Old 15th December 2012, 09:06 PM   #2
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I have the service manual. If you want it, email me. Your email will have to be able to accept 10MB files.

babin_perry@yahoo.com
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Old 16th December 2012, 09:55 PM   #3
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I think i have chased down something. I have enclosed pictures and schematics for where I think I need to be. my video driver circuit was all 0v so I chased it back to cable 11 on the ribbon out from the mainboard to the panel board. here is my measurments.....

A 14.6V
B 15V
C 0
D 14.4V
E 0
F 0
G 14.6V
H 0
I 0
J 14.6V
K 0
L 0
M 13.9V
N 0
O 0
P 14.4V
Q 14.4V
R 14.5V
S 14.5V
T 0
U 14.5V
V 14.8V
W 14V
X 14.6V
Y 14V
Z 14V
1 13.1V
2 13.2V

I am not sure if im even in the right part of the board but these resistors look burnt and there are meausing 0 ohms across the 2.

I cant put it into diagnostic mode because the screen wont light up so i cant verify for sure its on the radio, and I cant have the dvd drive attached when stabbing with my multimeter because I dont have a cable long enough, but everything else is hooked up. I can make an extesion cord if i really need one.
Attached Images
File Type: png Driver.png (359.9 KB, 28 views)
File Type: png Powerr.png (276.6 KB, 25 views)
File Type: jpg 000_2667.jpg (518.8 KB, 23 views)
File Type: jpg 000_2676.jpg (585.3 KB, 22 views)
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Old 17th December 2012, 06:44 PM   #4
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If you shine a very bright light onto the display and look at the display from different angles, can you tell if there is anything displayed?

You stated that it beeps when you push the power button. Do you see a slight increase in current draw after it beeps?
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Old 17th December 2012, 08:31 PM   #5
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no there is no display at all with a bright light.

I assume there is a amp spike because the dvd in the drive is spinning. I blew the fuse for the amp circuit in my meter, i will get a new one asap.

It beeps on then the dvd spins then it shuts down, I can repeat that all day. what I cant do is eject the disc or shut it off.
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Old 17th December 2012, 09:48 PM   #6
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Are the various toggle/control pins of IC721 toggling from 0-3.3v when you press the power button?

When you check for an increase in current draw, you'll have to wait for the CD to stop spinning.

It's better to use a current shunt resistor to measure current if you don't know for a fact that the current will be less than the current rating of the meter.
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Old 17th December 2012, 10:30 PM   #7
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pin 61 "power-on" 3.00v
pin 29 "back-lamp" is 0v
pin 88 "illumi" 0v

Im not sure what any of the other pins are doing. i am best guessing at these ones.

I wont be able to check for current draw until tmrw at the earliest
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Old 21st December 2012, 08:06 PM   #8
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im not sure what is really considered increase current draw but i am at about 1300mA at startup for just a second then when the disc is spinning it drops to around 950mA then 1300mA for a second after the disc stops then it shuts off.
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Old 22nd December 2012, 03:26 AM   #9
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Pull the drive and check current draw again.
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Old 22nd December 2012, 03:58 PM   #10
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now i am at about 650mA for about the same time duration

is there anything else i should check for voltage on the IC721?
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File Type: pdf IC721.pdf (68.0 KB, 18 views)
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