New Electronics(auto stereo) question/problem!?

[TopCatGr58]

Hey there folks,

Okay, a few years ago my OEM double DIN(double height) Am/FM/CD player died....wouldn't eject the CD's. SO...I got and installed a single DIN Am/FM/CD-MP3/USB/SD card player in it along with an adapter=extra shelf to take up the space. It has worked for several years just fine. It has a detachable faceplate for security.

Recently, while driving to work, would play it, and all of a sudden it would go completely dead....no power!? Then after a moment or so it would come back on..but all of the station presets were lost. I would push on the faceplate and it seemed like it would react to that action, so first thought it was flaky connection with the pins in the faceplate and deck base. Then I thought it was something with the wiring... a chafed wire or such grounding....however, the Radio vehicle FUSE was not blown.

I pulled the deck back out of the dash, inspected the wires...they were all intact, but there were a couple of those fancy plugs for connecting other audio devices...and they had several pins in them, and the plugs and pins were exposed...so I thought that they might have grounded to the ground screw sticking out of the back of the deck, so I wrapped them in electrical tape to insulate them, put it back in, reset the channels. I also checked the separate FUSE in the back of the deck, it was intact as well. It seemed to work for the few days prior to my trip down to visit my Mom in Alabama prior to attending XS Southeast next weekend.

Well....during a "Sleepy" time of the 15 hour drive, I decided to crank the volume up to help wake me up...and after a few minutes at a fairly loud level, the thing just shut off again! Then just like before after a minute it came back on. I turned the volume back down, and it continued to play for the rest of the trip.

SO...apparantly there's a resistor or output amp/chip that is being overheated during the high volume activity, and eventually separating causing total loss of power, once it shuts off, then it's allowed to cool, and reconnects, and I have power again. As long as I play it at modest volume levels, it doesn't get hot enough to shut down.

Finally....here's the question: Can someone point me in the right direction as to what component I would be looking for/at ie. Resistor/Capacitor/ Amp chip or such...or would it be worth trying to fix it vs. just getting and installing a new one. This one was only like $70.00 and a replacement similar unit from Walmart will be the same price.

I don't have a soldering iron with me on this trip, and it's working as long as I don't crank it up too loud!

T.C.

[Tat2demon]

Me personally, I would either hit up Walmart or swing by a pawn shop and just grab something else. With todays electronics/prices its just not worth trying to fix.

[IanDMacDonald]

Hey TC- I had an associates in Electronics long ago. If you're 100% sure it is not a short in a power wire, it's usually an output thermal transistor. It's a thermal shut-off safety feature on stereos to prevent overheating, based off impedance. Once the stereo goes over a certain impedance, the transistor in-effect closes. Check your transistos, if not your power supply. I'd just buy another one though.

[TopCatGr58]

Hey Ian and folks,

I remember from decades ago "learning" about stereos and such, that it was important to match up the output Impedence of the AMP with the Impedence(resistance) rating of the speakers....ie. Amp=8 ohm, speakers =8 ohm or MORE, but not less otherwise it would pull too much power thru the output transformer/sisters and could burn up the AMP!

Again, I'm not at home, so I can't recall the impedence range of the deck, but I was pretty sure it said like 4-16 ohms....most of them are usually now made to cover a wide range of speakers. I did NOT check the impedence/ohms of my speakers in my SUV, and it's possible that they were/are rated LOWER than that....which could explain the overload on the output....but it worked fine for several years and I did crank it up often while driving with the windows down, head bangin', , etc.!

SO....I could pull it back out, and strip the electrical tape off and check the impedence, and also check the instructions/box of the deck....yes, I still have it and verify that it can handle the range or not? But like has been suggested, I'll probably end up replacing it in the not to distant future. The thing is this one was SD Card capable and I liked that, and I don't see/find that feature on the new ones now....just USB sticks or ipods.
With the SD I could have 255 songs per card to play, much more convenient than a CD.

T.C.

[IanDMacDonald]

Okay TC- Just out of curiosity, what kind of sd card? micro or regular? USB front mounts can take a flash drive, and then u can have millions of songs on them from your choice of sized flash/thumb drives.

With regard to impedance on the speakers, yes, uou are correct. However, I do know yhat the Xterra has decent factory speakers that should cover theimpedance range of what your deck supplies. as long as the speakers are within the wattange range of the deck (modern decks are usually 50w per channel, a 4 channels, 200w.)

I'd say upgrade to a different unit. I could go on and on about good units (Crutchfield is my Playboy), but goto ABC Warehouse, and get a $45 JVC unit with bluetooth, etc., and you are good to go.

[crazy steve]

TC, I'd just get another stereo. The fact that you're losing the presets when it 'glitches' tells me that there's issues in the boards/connections internally.

As to speaker impedance, keep in mind that those numbers are nominal, sort of an 'average' value. Impedance changes with frequency, and a 'nominal' 8 ohm speaker can be anywhere from 1 ohm to over 30 ohms depending on the frequency it's reproducing. If you like to turn up the bass, that can double or triple the power required. Not all amps are created equal, and limitations in the power supply and design can cause problems; this is particularly true of 'budget' car stereo. I personally quit buying the 'cheapies' years ago as they just don't seem to hold up.

And don't count on the OEM speakers being a 'standard' ohm rating; I've seen OEM speakers as low as 3 ohms (when they're even marked) which will be ok if volume levels are held down, but if you like to 'rock out' the amp will start clipping.

[TopCatGr58]

Update

Hey Steve and folks,

Okay, it's stopped raining enough here to where I could finally swap out the old Jensen system with the new Boss 612 US MP3 200watt total/50wt per channel AM/FM/SD-MMC/USB unit.

I made it a point to get to the speakers and check them out, and discovered the speakers were only 2 Ohms! SO...it's no wonder that I burned up the output amp. And the new system is rated for only 4 to 8 ohms!

SO...I had a spare set of old Pioneer rear deck speakers that are rated for 4 ohms, so I disconnected the OEM rear 6x9's and mounted and wired/spliced in the wedge Pioneer speakers for the rear.

The front OEM's are split....5" round in the lower door panel, and a 1-2" tweeter up on the front windshield frame! I checked those with the Ohmeter, also 2 ohms! But I don't have the $$ just yet to replace those. I went to Radio Shack and picked the brain of the salesman who had training in electronics....to see IF I could put a 2 ohm resistor in the speaker line to temporize and balance the system's front/rear pairs so I wouldn't burn up the AMP...but after he did about 15 minutes worth of calculating and such, he said that it wouldn't work! It would cause too much current draw for the rears or such??

Speakers are different than just regular electrical circuits/equipment because they run on AC current and not DC. Anyways, I'll just keep the volume down until I can replace the front speakers and get the Ohms matched to the rear 4 ohms.

T.C.

[CaptonZap]

Howdy TC,

If you used an ohm meter on the speakers, you didn't get the information you needed.
Speakers are rated as so many ohms impedance, which is sort of an AC equivalent to DC resistance.
The most reliable way to find out the impedance, without some sophisticated equipment, is to ask the manufacturer. Most reputable ones will mark the impedance on the frame somewhere, or list it in the catalog spec sheet.
A lot of amps will fuse the output to avoid such problems.
Good luck,

CZ

[TopCatGr58]

Hey CZ,

Thanks, that's interesting....because when I pulled the rear speakers out of the frame and flipped them over, they had printed on them 2 Ohms. But along with that, I put my digital ohmeter on them, and they measured at about 2 ohms also!? I tested the front ones thru the wires at the dash without taking them out, and they also measured 2 ohms, I'm pretty sure they will have that printed on them as well when I finally get around to replacing them.

The Pioneer ones that I had were listed as 4 ohms, and when I metered them, they also measured at right about 4 ohms as well. Now, I know that all a speaker is is just a coil of wire wrapped around a toilet paper dowel stuffed into a magnet with a diaphragm glued to it! I would be surprised that the coil of wire is so long as to have that much resistance..but because it is small/fine wire I could see how it could have that much resistance/impedence for the length of the voice coil!

As Steve said, this is just an inexpensive piece of equipment, not sure how long it will last, but want to try to give it a fighting chance to perform by at least connecting the right speakers with the right specs/ohms so as not to try to overload the amps output transisters and such. The new deck weighs next to nothing...but there's no heavy moving mechanical parts because it's not a CD player, just Radio and SD card/Usb card player/amp.

If I had a BMW, Vette, or something like that, then yeah, I would put out for a quality system of many hundreds of dollars, but it's just in my 10 y/o SUV, work commuter vehicle, so I'm not too worried about it this time. I am just a little pissed/miffed at myself for not checking the speakers ohmage prior to installing the first replacement system....I probably could have saved myself all of this trouble and would still be able to have my HD radio/CD/SD/Usb player.

T.C.

[crazy steve]

Ah, car audio.... that's where all the snake oil went when the FTC cracked down on the home audio manufacturers...

TC, you have to take any 'ratings' you find on car audio equipment with a large grain of salt, particularly the 'budget' stuff. Amplifier ratings in particular....

Unlike home audio where the manufacturers are now required to list the power output in RMS watts as well as the 'class type' of amp it is, car audio is free to use any numbers that are semi-close, sometime not even close. Nearly all car audio power ratings are 'maximum' or 'peak' numbers, with some of the better quality units giving you RMS watts (an accurate rating). The RMS number will usually be around 25%, so a '50 watt' really only puts out 12watts. Most budget stuff can be even less than 25%. If you go into the high-end gear, then the difference between 'peak' and RMS ratings shrinks. Also note that as speaker impedance goes up, amplifier output goes down.

And even if you 'impedance match', that still doesn't guarantee a happy stereo. Different speakers will have different power requirements, even if their impedances are the same. Voice coil construction, magnet size/strength, cone size/weight/surrounds, all will affect required power. A too-small amp driving a 'correct' impedance speaker will go into hard clipping and while that won't overheat the amp like a too-low impedance speaker will, it's still not good for it. By the same token, a low impedance speaker can be driven with a 'mismatched' amp if the amp has enough power; i.e. a 50W 'nominal' @ 2 ohm speaker will work if the amp can produce 100 watts at 4 ohms.

And rather than replace all your OEM speakers, you might be just as well off by getting an outboard amplifier or two that can drive them and connect those between your head unit and the speakers. The outboard amps are usually much better at driving 'difficult' loads.

[TopCatGr58]

Stereo Talk.

Hey Steve,

Thanks. I remember the good old days circa mid/late 1970's when the FTC cracked down on the stereo market, but I didn't know that it was only the HOME audio equipment? I learned about the basic info needed to make an informed decision with the home equipment...ie....the RMS wattage rating of the amp, the Sensitivity of the Speaker....x Decibels @ 1 Watt/meter distance from the speaker. I also learned that an amp can often output twice as much wattage in PEAKS vs. it's RMS rating, and therefore the suggested practice of getting speakers that can handle about twice the RMS amp rating. And as a clarification point, the RMS is the power that the amp provides at less than 0.1% THD(Total harmonic distortion). And this is over the range of human hearing which is usually stated as 20 hz to 20,000 hz... however that upper limit is more for "babies", most of "us" adults are lucky to be able to hear tones in the 10k and above range!

The "el cheapo" head unit that I got was rated like you said...200 w PEAK total, 50W/channel peak/max, and about 12 watts RMS which was similar to my previous unit anyways. I also learned that once you crank the volume up to 1 watt output, it then takes a doubling of the wattage to get a 3 db increase in volume( about the smallest amount of volume increase that the human ear can discern as a change/increase). SO..that wattage values in amps to look for are 2, 4, 8, 16, 32, 64, 128, 250, 500, 1000 .

This gets you increases of 3, 6, 9, 12, 15, 18, 21, 24, 27, 30 decibels above the base sensitivity of the speakers. SO...with 90 db 1W/1m rated speakers, the 12 watts rms gets me approx. 98 decibels of volume....more than enough to cause me hearing damage!

My understanding of clipping was the inability of the amp to reproduce the sound's waveform in it's complete form/shape, that when driving the amp to too much volume, the wave form starts getting "clipped" off at the peaks which introduces the distortion to the sound. So I'm thinking that you're saying that if I try to turn the too small amp up too far beyond it's RMS rated value/power that it will "clip" the sound and produce distortion...so I agree with that premise...and will endeavor to not crank it up too loud into the FUZZ zone!

I know you know all of this, I am stating it moreso for others who may not have learned or know this so that they may be a bit more prepared when they decide to go audio equipment shopping.

Here's a good article to review: http://en.wikipedia.org/wiki/Audio_power

It also states that a new ANSI standard for automobile audio is being phased into the industry by several manufacturers, but it still isn't a federal statute/requirement! SO...buyer beware!

BTW, I found some nice Alpine component speakers(90/91db sensitivity) in the 6.5" and 1" cone tweeter style for about $30.00 on ebay free shipping, and ordered them! Curious to hear how they will compare to the OEMs. The OEMS are now some 10 years old, and they had little ~6 oz magnets, the new ones have 20 Oz magnets, so the quality of the bass should improve.

T.C.