So i got back from a short vacation yesterday and my cars battery was completely dead (mom left a dome light on inside). While attempting to juice it up, i made one of the worst mistakes you could make; after hooking my car up, i hooked up my parents trucks battery backwards (positive to negative and vice versa). Needless to say, the cars didnt agree so i immediatly undid it and connected them correctly.

Long story short, My 95 850 glt still runs, but the headunit is down. I tried replacing the fuse, but it instantly fries it when i hook up the battery.

Has anyone encountered a problem such as this? And most importantly is my head unit fixable, or do i need a new one?

 

You might be able to fix it but it may or may not be worth the effort. The radio should have a reverse polarity protection diode on the circuit board just behind the connectors that runs between the + line and ground. The diode is meant to be sacrificial and it will blow up and short out in the event that the polarity is backwards to try to save the rest of the radio.

I don't know any source for actual component level schematics for any of the radios but when the diodes blow they are normally obvious just by looking on the circuit board. The blown diode is the one that is charred and cracked.

If you can solder they are easy enough to change or, for testing purposes, just snip it out and see if the radio works again.

What head unit do you have? If it is something like a SC-810 or SC-812 / 813 you can just buy a replacement for around $35.00 and it is plug and play. If you do have a SC-810 don't even try to replace it with the same radio since the SC-810 has a real problem with controls getting scratchy. A SC-812 or SC-813 will plug in and work just fine. The SC-815 and 816 units have the built in CD as well but they tend to go more in the $125.00 range.

...Lee

 

Time for a replacement.

What amp fuse is it blowing ??

 

15A, located in the #7 slot for the radio/amplifier


I have the sc-815

 

The reason I asked about the fuse was to make sure it was the "small" one and not one that might be feeding additional items. If it's popping that 15 amp fuse than it's very likely it's something shorted out inside the head unit. It would be cheaper getting a used one or replacing it with an aftermarket unit depending on your taste, skill and wallet !! There are some places that will repair radios but it's really expensive and unless you have a classic car where it needs to be original or just love the stock radio it isn't worth it.

I purchased my 850 with a AM FM Tape head unit and tried to get a stock Volvo CD player but finally gave up and put in an aftermarket CD unit I had laying around. If Santa was nicer to me I would have loved to get something with CD and GPS built in (will play DVDs too) but they start at around 500 bucks and I just can bring myself to spend that.

 

disassembled the head unit and found the fried diode. Any idea on where i could find a reverse polarity protection diode? my first guess would be radioshack lol.

By any chance would you know the input voltage for the radio so i could find the correct diode?

 

Radioshack

 

made the run to radioshack today, bought the diodes and some replacement fuses. The soldering job was not nearly as difficult as i was expecting it to be, as the underside of the board is covered by this metal piece which is soldered on.

put everything back together and into my car; no more blown fuses and radio works again. thanks for the help



the two points which the burn marks around them are the ones i soldered