93 sc400 sound stopped working/ radio turns on

[jadesc4]

So the other day I got my exhaust done at the shop mind you, I sat there and watched the whole time. (this just adds to the context) I put my radio on and it works perfectly fine as I pull out after about a block down it works fine until I meet a friend lower the volume to the lowest and after 10-15 seconds I heard weird popping noises so I turned off the radio. Right after I try to turn it back on and no audio plays. The antenna went up the screen was lit and I was able to change stations, just no audio. I thought I would figure this out the next day (today) in which I thought I had done but didn't. Today when I started the car the screen was lit up but the antenna didn't go up when I tried to turn it on, also no audio. I checked the fuses under the hood and looked at a fuse map online for the radio fuse. Boom! Found it changed it and the antenna went up the screen displayed the numbers I could change the stations and everything. But still no audio. After changing the fuse I heard popping sounds like I did the other day but only when the radio was turned off. I looked around online and thought that maybe there is a fuse in the cabin that can help with the problem but haven't checked. I have also seen people disconnect the battery to restart the system. Would any of this help? Please help me figure this situation out im a poor 17 year old still paying off the car with 16 dollars under my name. LOL.

I have a feeling maybe I messed up the amp after reading someone elses post. there was liquid in the mufflers that i had in the trunk and they were on the right side of the trunk some had spilled out but only a very little amount could this be the case?

[RX400h]

The big question is why did the fuse blow. A loose connector would not cause this to happen, neither should a small amount of water in the trunk. I wonder if your audio receiver is simply used up.

[1990LS400]

There probably aren't many recent threads about this problem since there aren't very many SC300/SC400 still on the road but there were a number of threads "back in the day" about the SC amps getting damaged by water.

You could look for a good used on on eBay or maybe you can find a company that repairs them.

Do whatever you can to keep water away from the amp.  Trunk mounted Lexus telephone ECU's suffered a similar fate and often put the audio system in permanent mute.  If your SC400 has a phone ECU in the trunk, disconnecting it might solve your problem.

[sexyrexy71]

I just brought a nice SC300 home with only 112k on the odo yesterday. The sound is almost inaudible. There appears to be a amp box under the cd changer and yes, a little water in the trunk. I completely gutted the trunk trying to fix a inoperative turn signal. Also the gas cylinders for the trunk lid are weak. Does anyone have an idea where the water gets in? The seals look great. I guess I wanted a project bring home a 27 year old car, right?  

[1990LS400]

33 minutes ago, sexyrexy71 said:

I just brought a nice SC300 home with only 112k on the odo yesterday. The sound is almost inaudible. There appears to be a amp box under the cd changer and yes, a little water in the trunk. I completely gutted the trunk trying to fix a inoperative turn signal. Also the gas cylinders for the trunk lid are weak. Does anyone have an idea where the water gets in? The seals look great. I guess I wanted a project bring home a 27 year old car, right?  

The water is most likely getting in between the trunk lid and the gasket as it did on the 1990 and 2000 LS400's I drove for a total of 24 years.  I suppose you could replace the gaskets if you can find new OEM gaskets although new gaskets sitting on shelves for 25 to 30 years might not be in great shape.  Or you could look for similar aftermarket gasket sold by the foot.  I never replaced the trunk gaskets on my cars but I tried to get more proactive about removing the water with towels.  I also frequently cleaned and lubricated the trunk and door gaskets with spray silicon but I don't know if it helped that much.  There's not much that can be done to improve trunk and door gaskets after the become compressed and collapsed.  Water in the trunk and other places also contributes to high humidity which can cause corrosion in and failure of electrical components.  Maybe the solution is moving to Arizona!  

Edit:  One more thing.  Per my previous post in this thread, does your SC300 have or is there evidence that it had a dealer installed Lexus brand cell phone?  Failure of the phone ECU in the trunk can put the audio system in permanent mute mode although the audio can sometimes still be heard at a very low volume.  If it has a phone ECU in the trunk, remove it and check the pins in the ECU connectors for corrosion.  Even if it does not have a phone, check the connectors in the trunk for a phone and ensure that there is no corrosion on the pin in the connectors.  All Lexus SC of the 1990's were prewired for dealer installed phones.  The phone ECU connectors have a mute pin.  If this mute pin gets grounded by corrosion, the audio system will go into mute mode.  I've had substantial experience with this situation on Lexus cars of the 1990's.

[sexyrexy71]

Thanks for the info! I found this tinny coax back there not connected to anything. I bet it was for the cell phone. I disassembled everything back there, towel  dried it and let it set in the sun today. Removed the cd changer and what I assume is the amp under it. The one ground bolt back there I removed, cleaned the paint under it and re assembled with a newer bolt and corrosion preventative. Did that to the body ground by the battery and several grounds on the intake. I am going to do it to every ground I can find, had to do it to my 2002 celica. They dont spot remove the paint under the ring terminals, relying on threads and a clean bolt for contact. 
I will check fo a cell ecu. There is a funny yellow box by the antenna. 

[sexyrexy71]

I treated / reseated all the stereo connectors in the trunk and at least the front speakers came on. No rear speakers or subwoofer. The 12 disk CD changer refuses to play. What do you expect from 27 year old stereo electronics!?

[1990LS400]

14 minutes ago, sexyrexy71 said:

I treated / reseated all the stereo connectors in the trunk and at least the front speakers came on. No rear speakers or subwoofer. The 12 disk CD changer refuses to play. What do you expect from 27 year old stereo electronics!?

At least you're making progress.  Not that it will help but here an audio system diagram from Auto Repair Source that is supposedly for a 1995 SC300 although it doesn't indicate if it's for the standard or Nakamichi system.

 

[sexyrexy71]

I have a factory manual on order. I am a certificated aircraft mechanic so manuals and schematics are useful to me. I plan on keeping this car for maybe life. Thanks for the tips you helped me get at least the radio going. I will be swapping in a stock FRS head unit with bluetooth that is in my wife’s Echo. I don’t plan on spending any $ on the old stereo gear in this car. 

[bugjug]

The CD changer can cause issues. Disconnect it from the AMP and see if things change. I disconnected mine and fuses stopped blowing. Rear speakers are known to go out. I changed mine out for some Boston Acoustics S42 s in 2011. Almost a drop in replacement. I have an old post about this issue somewhere..