Author Topic: Electronic repair  (Read 2681 times)

markm6164

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Electronic repair
« on: November 07, 2012, 03:59:24 PM »
Hi guys

Wanted to ask before i post. If i post an electronic repair problem i am having with a car audio unit will you help and give your opinions on it? Its quite indepth and i have almost solved it but i have hit a brick wall and need some help. Wasn't sure if this was ok here in this forum.

Mark

Fennec

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Re: Electronic repair
« Reply #1 on: November 07, 2012, 04:13:10 PM »
??

What you think the "Electronic repair" forum is made for ? So let's go.

markm6164

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Re: Electronic repair
« Reply #2 on: November 07, 2012, 04:41:08 PM »
Well ok, I have a Pioneer AVIC-D3 with a problem. The unit works fine except the LCD backlight doesn't work, well i would come on for a second the straight back off. The backlight is a Cold Cathode fluorescent lamp.

I have attached the inverter circuit for the CCFL.

The whole manual can be downloaded from http://elektrotanya.com/?q=showresult for free by searching AVIC-d3.

Anyway, there is a dedicated ccfl driver chip marked OZ961ISN. Searching the datasheet for this chip doesn't show much but searching a OZ960 brings up this datasheet http://monitor.espec.ws//files/oz960_applicationsschema_189.pdf
Which is identical to the driver chip on the board and has the same pinout.

So the main problem i found was on pin 10 of the driver chip labelled CMP i was getting 4 volts which is too much. So because i couldn't isolate the cause of why it was so high i connected an led between pin 10 and gnd which dropped the voltage to around 2 volts. This solved everything, the unit powers up, the ccfl lights and everything works. Although this isn't good because its not a fix, only a hack.

Anyways all was well but now after about 30mins of running the 5v rail drops off. After tracing it back to the main board there is a smd 1A fuse.



I replace this fuse and the same thing happens again. I suspect it has something to do with the led i hacked in so what i need is some help to find the true cause of the problem. The driver chip has inbuild overload and underload protection and its seeing something on the feedback pin or pin 10 thats not right.

Hope i have explains clearly enough and hope you can help.

Mark