Curious about the amp relay I read about in the NSX manual

So, I see there is an amp relay under the hood (accorinding to the 1995 manual). I have a 1991 but assume there were no changes to the stereo electrical setup. That said, is the amp binary in that it either works or not? I just replaced the deck in my car (with a used one, but assume it is in good working order) but my speakers take time to "warm up" and are still crackling. I can replace the speakers (and the amps) but it occured to me that if the relay did not work, that may have an impact.

Will someone please educate me on the purpose/need for the relay?

Breathing life back into this question. I am curious if my OEM head unit, speakers or relay are bad. Stereo seems to warm up and give me better sound after about ten minutes. Am curious if this relay has anything to do with the performance of the system.

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Breathing life back into this question. I am curious if my OEM head unit, speakers or relay are bad. Stereo seems to warm up and give me better sound after about ten minutes. Am curious if this relay has anything to do with the performance of the system.

The power amp relay provides power to the two door amplifiers and the sub woofer amplifier. The head unit is off of a different power supply. If you are getting any sound out of your door or sub woofer speakers, the relay is working and is probably not the cause of your problems.

Solid state electronic devices can display temperature sensitivity if improperly designed; however, they generally don't require warm up. The OEM stereo in my 2000 works just fine on initial start up which suggests that there are problems with yours. During the late eighties some capacitor manufactures changed the formulation of the electrolyte in their electrolytic capacitors resulting in premature failure of the capacitors. Unfortunately, the failure problem did not materialize until the capacitors had been in service for some time (years). The Bose equipment in the NSX, and in particular the early model years seem to suffer from this capacitor failure problem. If you remove your door speakers and pull apart the amplifier, you will be able to tell whether you have this problem since the capacitor seals fail and ooze the electrolyte out of the cans. There is a vendor here on Prime (Brian K. I think) who offers a rebuild service for the amplifiers who has positive feedback for his service.

Old Guy said:

The power amp relay provides power to the two door amplifiers and the sub woofer amplifier. The head unit is off of a different power supply. If you are getting any sound out of your door or sub woofer speakers, the relay is working and is probably not the cause of your problems.

Solid state electronic devices can display temperature sensitivity if improperly designed; however, they generally don't require warm up. The OEM stereo in my 2000 works just fine on initial start up which suggests that there are problems with yours. During the late eighties some capacitor manufactures changed the formulation of the electrolyte in their electrolytic capacitors resulting in premature failure of the capacitors. Unfortunately, the failure problem did not materialize until the capacitors had been in service for some time (years). The Bose equipment in the NSX, and in particular the early model years seem to suffer from this capacitor failure problem. If you remove your door speakers and pull apart the amplifier, you will be able to tell whether you have this problem since the capacitor seals fail and ooze the electrolyte out of the cans. There is a vendor here on Prime (Brian K. I think) who offers a rebuild service for the amplifiers who has positive feedback for his service.

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Hmmm.....my head unit went silent yet all the lights illuminate and the tuner appears to lock onto stereo signals fine, so I'm thinking this relay may be gone. Where under the hood is it located? I don't see anything on the fuse box cover to tip me off.

EDIT: I found the section in the service manual that locates the amp power relay in the under hood relay box nearest the firewall but the diagram does not match the layout inside my box. Where it shows the relay to be located, there are not even any contacts in place for it. I have an '02 - does anyone know the correct location for this relay? If not, I will have to get out the multimeter this weekend and do some probing.

You say 'went silent'. Assuming we are talking about the OEM stereo, if the stereo system was working at one time the relay can't be gone (unless you mean failed).

Make sure that you have not confused the relay locations in the box. In the A relay box, for US vehicles there is an empty location where the dimmer relay on Canadian spec vehicles is located. On 2002 models the power amp relay is next to this vacant spot on US spec vehicles.

Old Guy said:

You say 'went silent'. Assuming we are talking about the OEM stereo, if the stereo system was working at one time the relay can't be gone (unless you mean failed).

Make sure that you have not confused the relay locations in the box. In the A relay box, for US vehicles there is an empty location where the dimmer relay on Canadian spec vehicles is located. On 2002 models the power amp relay is next to this vacant spot on US spec vehicles.

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Yes, by gone I mean "failed". I will give the relay box another look tonight and see if I can locate the relay. Thanks :smile:

Old Guy said:

The power amp relay provides power to the two door amplifiers and the sub woofer amplifier. The head unit is off of a different power supply. If you are getting any sound out of your door or sub woofer speakers, the relay is working and is probably not the cause of your problems.

Solid state electronic devices can display temperature sensitivity if improperly designed; however, they generally don't require warm up. The OEM stereo in my 2000 works just fine on initial start up which suggests that there are problems with yours. During the late eighties some capacitor manufactures changed the formulation of the electrolyte in their electrolytic capacitors resulting in premature failure of the capacitors. Unfortunately, the failure problem did not materialize until the capacitors had been in service for some time (years). The Bose equipment in the NSX, and in particular the early model years seem to suffer from this capacitor failure problem. If you remove your door speakers and pull apart the amplifier, you will be able to tell whether you have this problem since the capacitor seals fail and ooze the electrolyte out of the cans. There is a vendor here on Prime (Brian K. I think) who offers a rebuild service for the amplifiers who has positive feedback for his service.

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Hey Old Guy, thanks for the above.

Question for you...why do you suppose my CD player plays at a decent sound level immediately after I power up and the FM or tape deck takes 5-10" of on-time to get any decent sound? I don't understand the electronics in a head unit, but are they separate (or are there separate power supplies)?

Because I don't have the internal schematics, this is primarily an educated guess. The external CD player likely incorporates its own internal pre amplifier which provides a line level audio signal which is merely switched by the head unit when the CD player is selected and routed to the door and sub amplifiers. The head unit also performs control functions for the CD player; but, these are not associated with the audio signal itself. The net effect is that there are probably no head unit electronics in the audio signal path for the DC player. The FM / AM tuner and the tape player both require a pre amplifier to raise the audio signal to the line level for input to the door and sub amplifiers. If something is up with the preamplifier section in the head unit, then it will affect the audio signals from the tape and tuner; but, likely not the CD player.

If the CD sounds good on initial start up, you door and sub amps are probably OK. Perhaps time to send you head unit out for the Brian K fix.

Edit:

I was 'slightly out to lunch' in my comments. The CD player does have to feed through a portion of the head unit preamp since the volume, tone and balance controls on the head unit control the CD audio output. There will likely be a separate preamp in the tuner / cassette section that brings their audio signal to the same level as the CD player. You select from one of the three sources which then feeds into the tone, volume, balance control pre amp. It doesn't change the fact that the tuner / cassette portion of your head unit likely has some problems.

Old Guy said:

Because I don't have the internal schematics, this is primarily an educated guess. The external CD player likely incorporates its own internal pre amplifier which provides a line level audio signal which is merely switched by the head unit when the CD player is selected and routed to the door and sub amplifiers. The head unit also performs control functions for the CD player; but, these are not associated with the audio signal itself. The net effect is that there are probably no head unit electronics in the audio signal path for the DC player. The FM / AM tuner and the tape player both require a pre amplifier to raise the audio signal to the line level for input to the door and sub amplifiers. If something is up with the preamplifier section in the head unit, then it will affect the audio signals from the tape and tuner; but, likely not the CD player.

If the CD sounds good on initial start up, you door and sub amps are probably OK. Perhaps time to send you head unit out for the Brian K fix.

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Brian is not working on head units anymore. He referred me to [email protected]. I've spoken with Daryl on the phone and he seems like a good, knowledgeable guy but he's pretty pessimistic about being able to fix the OEM unit. He said that he has never been able to get a schematic from Alpine, who makes it for Honda, so troubleshooting is difficult.

If you are handy with a 15-25W pencil soldering iron (no soldering guns thank-you!) or you know somebody who is an electronics hobbyist, you could try removing the head unit and disassembling it. In the case of Speedmaster's head unit, it should be relatively easy to determine where the pre amp section is. Without test equipment such as a scope and a signal generator, it is pretty hard to diagnose a failure in semiconductor devices and if an IC has failed, you are pretty much buggered. However, discrete semiconductors and ICs have pretty low failure rates. The most common failure appears to be the failed electrolytic capacitors which you can usually spot by the fact that they are leaking electrolyte.

Taking the head unit apart is not incredibly difficult, just tedious. I took mine apart shortly after I bought my car because the inside of the display plate had coffee residue, or condensation from the AC, or something obscuring the plate from the inside. Unfortunately, I didn't really pay any attention to the electronics as everything worked (and continues to work) just fine. If you take yours apart, the one caution I will note is that be careful with the ribbon connector from the faceplate display / controls to the main chassis. I seem to recall I messed something up there when reconnecting the ribbon and lost the operation of a couple of the preset buttons. I had to take the deck apart and do something with the ribbon connector. Unfortunately, that was about 4 years ago so I don't remember the details.

The Williams guys may be reluctant to try to repair the head unit because they sell a service where they gut the head unit and put new electronics in it. Its probably lower risk and less customer hassle for them than trying to repair the unit.

Old Guy said:

You say 'went silent'. Assuming we are talking about the OEM stereo, if the stereo system was working at one time the relay can't be gone (unless you mean failed).

Make sure that you have not confused the relay locations in the box. In the A relay box, for US vehicles there is an empty location where the dimmer relay on Canadian spec vehicles is located. On 2002 models the power amp relay is next to this vacant spot on US spec vehicles.

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Something very strange is afoot under my hood Relay box A is not populated in the way that you and the service manual detail. Where the power amplifier relay is supposed to be located, not only is the that spot in the relay box empty, there are no contacts present to receive one. Does anyone know if there was an alternate location for the relay in a '02 model or an alternate relay box layout? The car has never been wrecked so no rewiring would have been done by an ignorant body shop electrician.

Additionally, I checked all of the relays in that relay box per the procedure outlined in the service manual and all are good. I'm so confused

The total # of relays in the box is the same as shown in the manual (assuming you did not buy a Canadian spec vehicle). Its pure speculation; but, maybe some assembly line wonk wanted to have some fun or there was an error in the line that assembled the boxes and the amp relay ended up in what should be the vacant spot between the O2 relay and the reverse lock out relay. Should be able to check by looking at the cable terminators. Otherwise, not a clue!

Just because I was curious, I went out to my car and popped off the cover of relay box A. My car is a 2000 US market car. It turns out that the relay arrangement in my car does not match the relay arrangement shown in the 1997 service manual or the 2000 service manual supplement (which are different). In fact, my relay arrangement looks very much like that of clean_green's 2002 with the exception that the three relay / two relay side of the compartment is switched front to back.

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As an observation, rather than trying to figure out what is going on with the relay arrangements in relay box A (pulling the box and checking the terminations as I suggested is going to be a hassle), if all you want to do is determine whether the power amp relay is responsible for your loss of audio, the easiest thing may be to get access to the subwoofer amp and pull the power supply plug to the amp. With the head unit switched on, you should be getting +12 v on the yel/red wire. If you are and you have no sound, then your problem is elsewhere.

Old Guy said:

Just because I was curious, I went out to my car and popped off the cover of relay box A. My car is a 2000 US market car. It turns out that the relay arrangement in my car does not match the relay arrangement shown in the 1997 service manual or the 2000 service manual supplement (which are different). In fact, my relay arrangement looks very much like that of clean_green's 2002 with the exception that the three relay / two relay side of the compartment is switched front to back.

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As an observation, rather than trying to figure out what is going on with the relay arrangements in relay box A (pulling the box and checking the terminations as I suggested is going to be a hassle), if all you want to do is determine whether the power amp relay is responsible for your loss of audio, the easiest thing may be to get access to the subwoofer amp and pull the power supply plug to the amp. With the head unit switched on, you should be getting +12 v on the yel/red wire. If you are and you have no sound, then your problem is elsewhere.

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Great advice Old Guy! I will give it a try. Thanks :smile:

If you turn the volume on the unit all the way up, do you hear very faint sound? i have repaired unit that was told could not be repaired, I have also done cap upgrades to working units, if you want to use me as a last resort hit me up. When the caps leak the acid makes its way all over the board and causes problems corroding stuff (All the broken traces need to be fixed), the header cables are fragile and also easy to damage, The face plate cable, not so much.

Scrapdog2grand said:

If you turn the volume on the unit all the way up, do you hear very faint sound? i have repaired unit that was told could not be repaired, I have also done cap upgrades to working units, if you want to use me as a last resort hit me up. When the caps leak the acid makes its way all over the board and causes problems corroding stuff (All the broken traces need to be fixed), the header cables are fragile and also easy to damage, The face plate cable, not so much.

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Thanks for your generous offer and I may take you up on it if Willman's can't fix it . No, there is no noise at all even with the knob turned fully up. I just stopped making sound while I was listening to it one day. No snap, crackle or pop was heard - it just went mute on me :frown:

In 2005, I had parked my NSX with the top off while shopping in a local store. A severe thunderstorm hit and in the time it took me to get outside and put the roof on, the coin tray had filled completely with water. A few days later, my radio quit. With some sequencing of removing and reinserting fuses, it would play for a few seconds.

I sent it to

United Radio Repair
5705 Enterprise Parkway
East Syracuse, NY 13057
(The above is their RMA address)

They fixed it for $210, and it has been working ever since. Unfortunately, I can't seem to find their phone number in my records.

Hope this helps.

ftuhy said:

In 2005, I had parked my NSX with the top off while shopping in a local store. A severe thunderstorm hit and in the time it took me to get outside and put the roof on, the coin tray had filled completely with water. A few days later, my radio quit. With some sequencing of removing and reinserting fuses, it would play for a few seconds.

I sent it to

United Radio Repair
5705 Enterprise Parkway
East Syracuse, NY 13057
(The above is their RMA address)

They fixed it for $210, and it has been working ever since. Unfortunately, I can't seem to find their phone number in my records.

Hope this helps.

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They have a website with contact info:

http://www.unitedradio.com/contact-us/

Old Guy said:

Just because I was curious, I went out to my car and popped off the cover of relay box A. My car is a 2000 US market car. It turns out that the relay arrangement in my car does not match the relay arrangement shown in the 1997 service manual or the 2000 service manual supplement (which are different). In fact, my relay arrangement looks very much like that of clean_green's 2002 with the exception that the three relay / two relay side of the compartment is switched front to back.

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As an observation, rather than trying to figure out what is going on with the relay arrangements in relay box A (pulling the box and checking the terminations as I suggested is going to be a hassle), if all you want to do is determine whether the power amp relay is responsible for your loss of audio, the easiest thing may be to get access to the subwoofer amp and pull the power supply plug to the amp. With the head unit switched on, you should be getting +12 v on the yel/red wire. If you are and you have no sound, then your problem is elsewhere.

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This past weekend, I did as Old Guy suggested and checked for voltage at the subwoofer power connector with the radio switched on. What I found was that it had power but only about 1/2 volt! Since power was present at all, I think I can rule out the relay being bad. So I pulled the head unit out and will take it over to Willman's today and see if Daryl can fix it.

clean_green said:

This past weekend, I did as Old Guy suggested and checked for voltage at the subwoofer power connector with the radio switched on. What I found was that it had power but only about 1/2 volt! Since power was present at all, I think I can rule out the relay being bad. So I pulled the head unit out and will take it over to Willman's today and see if Daryl can fix it.

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I am not sure that the problem is with the head unit. If you measured the voltage between the Y / R wire and the black wire (ground) at your sub woofer you should be getting +12v with the head unit switched on. The head unit has to be on because it controls the power amp relay. If the head unit is on and you are getting 0.5 v on the Y / R wire, it almost seems like the contact in the relay has failed or you have a very poor connection somewhere in the circuit.

As a thought, you may be able to find the location of the relay by having somebody listen to the relays in Box A while another person switches the head unit on and off. If its quiet enough they may be able to hear the click of the amp relay. That said, relays tend to be pretty dumb-ass simple devices and are not failure prone (notwithstanding the problems with solder joint failures in the main FI relay!).

One other thing to check. Does your power antenna go up and down? The power antenna gets its 'on' signal from the same pink / white wire that goes to the amp relay. If the antenna is going up and down then the control signal from the head unit is working and the amp relay should also be switching unless there is a broken wire some place. If your power antenna has stopped operating, then you could have a problem in the head unit itself or the pink/white control wire coming out of the head unit could be broken some where.

Old Guy said:

I am not sure that the problem is with the head unit. If you measured the voltage between the Y / R wire and the black wire (ground) at your sub woofer you should be getting +12v with the head unit switched on. The head unit has to be on because it controls the power amp relay. If the head unit is on and you are getting 0.5 v on the Y / R wire, it almost seems like the contact in the relay has failed or you have a very poor connection somewhere in the circuit.

As a thought, you may be able to find the location of the relay by having somebody listen to the relays in Box A while another person switches the head unit on and off. If its quiet enough they may be able to hear the click of the amp relay.

One other thing to check. Does your power antenna go up and down? The power antenna gets its on signal from the same

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I replaced the OEM antenna with the Shark II whip antenna long ago but it is getting no power. I had not thought about audible location of the relay so i will have to recruit help and see where that relay actually is! Thanks again :smile:

clean_green said:

I replaced the OEM antenna with the Shark II whip antenna long ago but it is getting no power. I had not thought about audible location of the relay so i will have to recruit help and see where that relay actually is! Thanks again :smile:

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Do you mean that the Shark antenna does not need power or that you checked and it is not getting power? I am going to assume the first. The pink / white wire that supplies the control signal to the amp relay and the antenna goes to the trunk where it would have been plugged in to the old power antenna. Because it is easy to access, you could check to see if you are getting the 12 v on control signal from the head unit at that location.

Also, its unlikely that its the problem; but, check the #61 20 amp fuse which supplies the power amplifiers through the power amp relay.

Old Guy said:

Do you mean that the Shark antenna does not need power or that you checked and it is not getting power? I am going to assume the first. The pink / white wire that supplies the control signal to the amp relay and the antenna goes to the trunk where it would have been plugged in to the old power antenna. Because it is easy to access, you could check to see if you are getting the 12 v on control signal from the head unit at that location.

Also, its unlikely that its the problem; but, check the #61 20 amp fuse which supplies the power amplifiers through the power amp relay.

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Yes, I found that power amplifier fuse and got really hopeful but it turned out to be fine. The Shark is an amplified antenna so it does require power but there is none there.

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clean_green said:

Yes, I found that power amplifier fuse and got really hopeful but it turned out to be fine. The Shark is an amplified antenna so it does require power but there is none there.

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Well, I just got back from taking my head unit to Willman's and he bench tested it for me while I waited. There is nothing wrong with the unit at all! It sounds like I really need to go on a quest in search of the hiding power amplifier relay. That may well be the culprit. A relay is much cheaper than a new or repaired head unit anway so I consider this good news. If I ever find the relay, I will post a red lined markup of the service manual page with the layout.


BTW, Daryl is a really nice guy and an NSX enthusiast! I would not hesitate to send him any future repair work. I saw him building his stereo retrofit, where he guts the OEM head unit and puts new Clarion internals inside. Wow! What a lot of hand labor goes into that! I think he isn't charging enough for those (video at bottom of page: www.willmanselectronics.com/nsx_sales.htm

clean_green said:

Yes, I found that power amplifier fuse and got really hopeful but it turned out to be fine. The Shark is an amplified antenna so it does require power but there is none there.

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When Willmans checked out the head unit, did they just confirm the operation of the audio components or did they also check the operation of the antenna control? If they didn't check the operation of the antenna control, before you do the final reinstall of the head unit, connect up the cables; but, put a back probe into #6 of the 16 pin connector on the back of the radio. This should be the pink/white antenna and amp relay control wire. Check for 12 v on the wire when you switch the head unit on. If you have 12 v here, then you should be getting 12v on the wire to your shark and the amp relay should be clicking - unless there is a wire broken some place. If you are not getting 12v on the #6 pin on the back of the radio, then there is something wrong with the switching mechanism in the head unit.

I know that Willman checked the blue wire for sure and it read 12V but I don't recall if he checked the pink/white. I will do that to verify. I also checked to see that I am getting 12V at the power amp fuse (20A) and it was also good.