Is my head unit dead?

[DerekTheGreat]

About four or five years ago I overhauled my Town Car's audio system. It has an aftermarket 5 channel JBL amp, aftermarket JBL speakers and an aftermarket Sony deck. Last year I got a bunch of static and noise from the rear speakers and right after the headunit just died, no display. It's died before, I just take the fuse out and it comes back to life without any of my settings of course. Anyway, Ashley and I were driving to Ohio when the front right speaker started making a thumping sound. Even when I shut the radio off completely, thump..thump..thump.. with the occasional crackle sound. I pulled the faceplate off and the sound went away. Before that, audio was playing fine and when I put the faceplate back on, audio was good again but I took the faceplate off the radio just so it wouldn't do that again. Question is, do you guys think this is the amp or the head unit which is dead? Suspicion leads me to suspect the head unit. F'n aftermarket POS..

[EaOutlaw1969]

My guess would be the amp may be the problem.

I used to repair electronics, car radios, amps etc,much of what I would find wrong with amps was cold solder joints that would lead to burnt parts if the amp was not repaired right away.

This being said car radios also suffer from cold solder joints as well.

When I was younger and still had good hearing I would never just install aftermarket audio equipment without checking the solder connections
I would sometimes upgrade the caps and circuit paths also. ( I never cared about warranties )

I have only came across one new never touched amp that looked like each connection was hand soldered and required no modification, I do not remember the brand but the circuit board was colored to look like a american flag. the craftsmanship and parts used were second to none, however that was back in the early 90s I have no clue who makes good amps or electronics today.

To find out what is wrong you will have to bypass the amp and run your speakers off of the radio if the problem goes away it has to be the amp.

[DerekTheGreat]

What makes you suspect the amp and not the thing providing it with a signal? Seems weird that the noise quit when the faceplate was yanked off. My gut says if it was the amp, it would continue making that sound. I'm about ready to put it back to factory, that shit was all new 4 years ago and not abused. I'm tired of aftermarket shit quality.

[EaOutlaw1969]

I really do not know for sure what is wrong until you start the process of elimination, I am 90 percent sure if you dig deep enough you will find bad solder connections.

If you had another audio source that you could quickly plug into the RCA connections you could find out for sure what piece is the problem.

The radios I have worked on in the past have had bad connections, bad power outputs and normally problems with cd player. I have yet to see a signal problem injected to a external amp because those parts are normally much smaller and not as prone to cold solder joints.

This being said anything is possible your phone could use a adapter to inject audio through the amp and speakers which would let you know if the amp is the issue.

BTW how high do you have the amplifiers gain adjusted to?

[DerekTheGreat]

I could just feed the amp output from my Ipod? Guess that is a great way to test things. I wasn't sure how to go about eliminating things short of putting a new radio in it and or amp.

Not too high, like no more than 2/3 of the way up and I do use the high pass filters. Sub might be higher though yet luckily it isn't the problem.

It just seems funny that I was listening to the radio when it started thumping, turned it off and it started thumping like 10 minutes later (sounded like a stylus skipping on a record) it only stopped when I yanked the face plate off the stereo.

[EaOutlaw1969]

Normally if your amp has short it will go into protect mode and a light will come on showing that, if caused only by a cold solder joint the amp may come on and play for some time before the circuit opens or creates too high of a load putting the amp into protect mode again.

The good news is the radio or amp can be repaired if needed with minimal money and tools if you have good eyesight a steady hand and basic knowledge of a DVOM.

[DerekTheGreat]

I'll tear into it this weekend or next. Guess if I take the amp or stereo apart I'll just look for the shit stains and resolder those?

[EaOutlaw1969]

If you find the radio and or amp needs work, look with a magnifying glass for dark or burnt spots on the board like you mentioned which is good.
but soldering only can make the problem worse if you do not check the components on the board for shorts or opens.
This is where you would break out your DVOM and measure across these parts looking for shorts with your DVOM.
A direct short will read the same or close to the same as touching the leads of your DVOM together.
So lets say you are testing a diode you would measure by touching the probes on either side of the diode one then reverse the leads one measurement should read infinite like no connection swapping the leads should show resistance.
If you find a direct short then remove one leg of the diode from the board then recheck to make sure only the diode and not the circuit shows shorted.
Normally if you find a burnt spot or multiple burnt spots on the board and shorted or open parts other parts in the same circuit may be damaged shorted or the values may have changed.
Because I never ever have schematics to go by for values I find a circuit that is still healthy to compare the values to.

The hard part for you will be checking capacitors, I have a special tool that can check caps on the board that measure if they are out of range I replace them.
without this tool you will have to look for signs that the cap is swollen, damaged leaking etc or just replace every cap in that circuit which is normally recommended if you find burnt parts.

Pretty much YouTube can be helpful when trying to diagnose and repair electronics.

My point is with your five channel amp not all your channels will be effected so use the known good circuits to compare the suspected circuits.
if and when you get around to soldering the board use masking tape to tape off the areas you are not working to avoid the possibility of bridging circuits with solder drips.
if possible only use a good quality soldering iron with a fine point and good quality thin gauge solder. and make sure to not get the board or parts too hot so solder a few spots then either wait or move to another section like you would when welding.

[DerekTheGreat]

LoL. I'll be sure to have a few shots of whiskey before I attempt this then, should it come to it.

[gadget73]

Confirm the power connections to the radio and amp before you get carried away with all this. I've had craptastic connections do things like this.

[DerekTheGreat]

Will do, I do kind of suspect that too. I didn't do the install so who knows what they did to make it happen. On the Brightside, it forces me to take the dash apart which is needed since I have to fix my big ole fucking clock that Town Cars were equipped with. I may not have a tach, but muthafuker I can tell you what time it is from the back seat!

[gadget73]

Yes, but you're only right twice a day. Mine is actually right.

[DerekTheGreat]

Haha well it looks like my clock will have to wait.
Update is that you dudes were right. I can't thank you enough for the troubleshooting tips and advice. Yesterday I finally got around to tearing the car apart, I was able to rule out the headunit from the system and traced my issues back to the amp. The headunit may have contributed somewhat though, I found a shocking amount of corrosion in the factory connector. I think the aftermarket harness adapter pins are made from aluminum and so galvanic corrosion had set in.. Lots of fluffy white stuff that definitely wasn't there when the radio was installed. Oh, turns out I did install it myself. I was admiring the wiring job thinking there was no way in hell I did that until I recognized the materials to be from my own stash lol..
Car Tunes did the amp installation and made the radio sit better in the factory hole, about the only good thing they did.. Anyway, turns out the amp's ground was loose but also the RCA inputs aren't tight.. I was able to reproduce that popping sound by hooking my iPod up to the RCA cables in the dash. If I didn't seat them tightly and jiggled, I'd get similar noise. So I dicked with those at the amp where they were loose, tightened the ground as best I could & buttoned it up after 20' of trouble free testing. I then had to relearn how to set my stereo up again but jammed out for another hour at least. When that stuff works, man is it pretty damn decent.. Thanks again fellas!

I've attached some pics, one of the corrosion in the harness and others showcasing the radio & how it looks when the headlights are turned off and then on. Decent radio if you want to go aftermarket. IIRC it's a Sony MEX810 something or other. I've always hated the knob and its illumination ring and that one ultra bright button to the left of it though, atrocious. No amount of dimming reduces it to a point where it doesn't look garish and the other buttons too hard to make out in sunlight or low light conditions where you need the headlights yet it's not totally dark yet.

Sent from my SAMSUNG-SM-G891A using Tapatalk

[gadget73]

Factory harness pins are tin-plated copper.

Possible its just solder on the amp RCA jacks. I've had a lot of those break over the years from vibration. A few minutes with the hot lead melty stick sorts it out.

[DerekTheGreat]

The pic doesn't really show the mess which was in the factory harness, looked like someone dipped the thing in powdered sugar. I cleaned up as best I could and put dielectric spooge and Krown T40 in the connectors before I put humpty-dumpty back together again.

I certainly didn't think about that, although the car has maybe 20k miles on it since the install and the components are only about four years old. Would be some real shitty build quality right there. However, the RCA inputs you could pull out with your pinky, that's how loose they were. Tight at the radio, loose back at the amp. Wires leading out to speakers weren't all that tight either so I got out the 1/2 impact and tightened them up until they were loose again, factory spec. /s