Just bought my 1991 NSX. The stereo system is no bueno. How can I tell what's wrong?

[Import-Tooner]

So I just purchased a '91 one New Years Eve. The car has been parked since 2012. When I was inspecting the car I turned the radio and the antenna was not going up but you could hear that it was trying. I turned the radio off in fear that I was going to damage the antenna mast. After having the car home for a few days I decided I was going to unhook the mast and see how the radio worked. When I turn on the radio I just get a high pitched squeel and I can faintly hear the radio station that I'm on. The display comes on fine though. Also, when I fade left or right, left seems to have some sound but right has none. I know there are problems with the head units and the door amplifiers in these cars. The question I have is this, how do I find out if the problem that I have is in the head unit, the door amps, or both? I realize this has probably been covered but I have been searching and not coming up with too much. Thanks in advance!

 

[clutch1]

You can use an O-scope (or to a lesser extent, a multimeter) to go to the signal wires at each speaker/amp enclosure. Play some music and see if it's getting proper signal to them. If the O-scope pegs to some high Hz, then you know the headunit itself it sending that squeal to the amps, and not the amps having an issue and making the squeal themselves.
Also, have you tried playing a cassette to verify it does it on both sources?

 

[Import-Tooner]

You can use an O-scope (or to a lesser extent, a multimeter) to go to the signal wires at each speaker/amp enclosure. Play some music and see if it's getting proper signal to them. If the O-scope pegs to some high Hz, then you know the headunit itself it sending that squeal to the amps, and not the amps having an issue and making the squeal themselves.
Also, have you tried playing a cassette to verify it does it on both sources?

I haven't tried that. Although it is a good idea just incase. I will try your suggestion and see what I come up with.

 

[TURBO2GO]

member BrianK can help you out. He repairs these.

 

[NSX2398]

member BrianK can help you out. He repairs these.

Brian only repairs the amps .. not the head unit. I believe that Willman is a good source for head repairs/replacements. But in my experience, the problem is nearly always the amps.

If you have the antenna disconnected and the head unit is on AM you may get strange issues. Change it to FM or use the cassette player in your diagnosis. The L/R fader technique is about the only diagnostics tool you have without taking things out. I don't know how familiar you are with a BOSE systems but the head unit only puts out line-level signals and the amps are integrated with the speakers in a housing in each door .. plus there's an amp in the sub enclosure in the passenger footwell that also drives the one rear speaker on the back wall between the seats. I think Brian charges about $100 per amp .. your best bang for the buck. Check the Wiki for amp removal instructions.

 

[cmthomson]

The antenna and noise issues are separate. The noise is almost certainly blown capacitors in the door amps (and possibly also the center amp); the head unit is much more rarely the problem. As others have said try a cassette (if you can find one) or one of those MP3 to cassette converters, which you should get anyway. The antenna may just need a little finger help and then some lubrication.

 

[Old Guy]

The NSX has two antennas. One is the mast antenna and the second is on the glass in the rear hatch. If you have a reasonably close or strong FM signal, the mast antenna does not need to be up to test the operation of the radio. The on the glass antenna works just fine. I disconnected the power signal on my mast antenna a couple of years ago because I would on occasion catch it on the garage door if I didn't wait for the door to open completely before moving forward - impatient!

If you have the noise present in both channels and it disappears from one channel when you fade to the other channel and vice versa, I would put money on the noise originating in the head unit, not in the individual speaker amps. If one of the speaker amps fails, you should still get an audio signal on the other channel if the head unit is good. If both speaker amps are dead, diagnosis is more complex. You will need access to an oscilloscope or audio signal tracer to see if you are getting any signal out of the head unit (tech speak for a probe connected to a small amplifier and earphone).

If you search the Electronics forum, you will find a post of a member who went through the capacitor replacement process for the head unit.

 

[Wavey1]

A few points: Brian K is only rebuilding the speaker amps for $90 each, not doing head units anymore. Speedmaster discovered that you can purchase brand new speakers (boxes, speakers and amps) directly from Bose for $140 each (contact info is at http://www.nsxprime.com/forum/showthread.php/193817-New-speakers-and-AMPS). Willman is no longer rebuilding the head units, just doing the Clarion retrofit to the OEM head unit (pricey!)

 

[Import-Tooner]

I'm going to do a full aftermarket stereo. Keeping this part of the car original just isn't worth it.

 

[Wavey1]

Just a heads-up. By the time you do a head unit, an amp, a subwoofer with enclosure, and speakers with adapter plates, you'll spend as much or more. It's also VERY difficult to pull full-size speaker wiring into the doors (OEM wire is small-gauge because it only carries the line level), unless you want to do an amp at each speaker location (more $). Also, you'll have to cut the original console (a very expensive piece), or buy an aftermarket console. It's going to add up either way, and unfortunately there's no fast, easy or cheap solution to stereo issues with these cars.

 

[Import-Tooner]

It's going to add up either way, and unfortunately there's no fast, easy or cheap solution to stereo issues with these cars.

Ya I totally understand. I'm not looking for fast, easy or cheap. If I'm going to spend the money, I may as well have my car updated to the 21st Century. At least as far as the stereo goes. Pulling speaker wire through the door is the only thing that concerns me. I may need to loo into that a bit more.

 

[Wavey1]

One option is to use Willman's retrofitted head unit (modern Clarion guts), use the original signal wires to the doors, and add new speakers, new amps and new speaker adapter panels inside the door. Willman's unit includes the Clarion RCA outputs so it would be easy to do a short run to a new subwoofer. That way you don't have to modify or replace the console. Just a thought.

 

[NSX2398]

Just a heads-up. By the time you do a head unit, an amp, a subwoofer with enclosure, and speakers with adapter plates, you'll spend as much or more. It's also VERY difficult to pull full-size speaker wiring into the doors (OEM wire is small-gauge because it only carries the line level), unless you want to do an amp at each speaker location (more $). Also, you'll have to cut the original console (a very expensive piece), or buy an aftermarket console. It's going to add up either way, and unfortunately there's no fast, easy or cheap solution to stereo issues with these cars.

I did a bit of a compromise .. kept the head unit but put an aftermarket amp behind the driver's seat and bypassed the amps in the doors. As you point out, the wiring is light for hi power output but I'm not a head banger .. just wanted something a little more reliable as I use the car in wide temperature swings and had been through a few amp rebuilds. I kept the stock sub (bypassed it's amp too) but it would be a snap if I wanted to upgrade the sub. I found that mounting the amp behind the driver's seat had easy access to grounds on the firewall plus it was easy to run short power through a grommet back into the engine compartment and connected to the fuse block. Used the SOS adapter wiring to make that easy. So, all in, I think I was under $400 but I think I overspent on the Alpine multichannel amp.

 

[Wavey1]

Good plan, as long as the head unit keeps working.