Kenwood DNX7100 navigation receiver blowing SMD fuse

georgeNCSUee · Joined: 12 Jul 2005 Posts: 16 Location: Garner, NC USA

I have a Kenwood DNX7100 car navigation receiver and it keeps blowing a fuse on the video board, on the +5V line, so the LCD doesn't work. I'll link up the service manual (http://www.mediafire.com/?avx9ehrzbukquch) if anyone can take a quick look (not sure what would be a better way of doing this). The schematic of the video board is on pages 46-47.

So far I disconnected the LCD, backlight, touchscreen, and buttons form the board, and removed IC100, IC102, and IC303 which are powered by this 5V line. I also checked all the inductors and resistors on the line and the bypass caps, and all seem fine. I checked the resistance from each side of the fuse to the input and output connectors and I get a couple of ohms. Checked form each side of the fuse to ground and got open circuit. Yet the fuse (F100) still blows when I power it up.

I'm stuck now. If anyone can make any suggestion, I'd really appreciate it.

vtech · Joined: 08 May 2006 Posts: 1264 Location: USA

Looks like you have already isolated most everything on the 5V line. Unless there is more than what's shown on the schematic, there should not be any reason for f100 to blow? Obviously ther is more than .6amps pulling thru the line. I have never worked on the specific unit but, I have had situations where the 5v line may not actually be shorted to GND and instead to another line indirectly or there may be something spilled on the pcb that may not be apparent. In looking at the diagram you can isolate it further by removing L106 and instead of using another (F100) fuse, use an amp meter in place of it and monitor the current draw. I'd use an external adjustable 5V supply and slowly bring it up.

Guest · Posted: Wed Jul 28, 2010 10:08 pm Post subject:

I don't have an adjustable power supply (I know I should, but never got around to getting one) so I'll just have to power the board from the unit. I thought about connecting the ammeter in place of the fuse but I'm scared I'm going to fry something else by letting all that current through, and I'll never figure it out after that. I'll try to see if the 5V line is shorted to another line. If anyone has any other suggestions, feel free to chime in.