Troubleshooting a carstereo... - Page 1
Forum section: electronics / projects

author: Hagis2k
author_rank: Regular Contributor
timestamp: May 01, 2014, 03:13:09 am
content: So hi there well i am looking to find the fault in my friends car stereo, and it goes so so lol...Its a Parrot Rythm 'n Blue the device flashes when power is turned on then it is dead draws 100-150mA i have measured all voltages in it5V is present 3.3V also and 12V i start to think that maybe? the cpu is faulty?? because when i press reset then it draws 800mA and dropsdown to 100-150mA and my ordered oscilloscope is not coming until in the end of may so i could probe the crystals and see if it is alive?bummer wonder what else i can check under the meantime? capacitors lol :=)Circuit diagram i couldn't find either lol

author: Legit-Design
author_rank: Frequent Contributor
timestamp: May 01, 2014, 05:37:57 am
content: Detailed pictures taken from both sides of the board with good lighting? Camera phone is good enough if they are in focus and with enough light, so need new enough phone that has auto focus. When in doubt use the sun as lighting. Upload full resolution images toAlso additional information is always helpful, how is it "dead"? Screen doesn't turn on? How it is flashing? If it's flashing power led maybe there is some meaning to those flashes?

author: Hagis2k
author_rank: Regular Contributor
timestamp: May 01, 2014, 06:24:48 am
content: So here is a picture of the board:

author: Hagis2k
author_rank: Regular Contributor
timestamp: May 01, 2014, 07:01:27 am
content: Well it is completely dead will not power on no reaction on the power button neither the display comes alive or anything else, been measuring a bit more in it and afaik all voltages are present...But the 7808 is connected thru a 2sb1243 a -60V 3A transistor so i tested pulling the base low on it with a 10k resistor then i get 8V too in the unitbut it still does nothing so i just wonder as the cpu: s3p831bxzz-qxrb that has the white sticker on it if that one is dead then i assume the unit will not respondto anything as its the brain of the device...

author: Joule Thief
author_rank: Regular Contributor
timestamp: May 01, 2014, 11:23:39 am
content: Check the top of the 220uf cap in the pic below.Either it is a trick of the lighting or possibly the cap has spewed a little.

author: Towger
author_rank: Super Contributor
timestamp: May 01, 2014, 12:11:26 pm
content: There is another cap with what looks like the came 'glue' on it.The transistor q803, in the close up, looks like there is a crack across it about 2/3 of the way from the top in the photo.

author: SeanB
author_rank: Super Contributor
timestamp: May 01, 2014, 12:49:05 pm
content: Does look like the smoke came out. As this is a power switch PNP transistor it likely just died, or the regulator it supplies has failed as well. Not marked but is close to SK801. Interesting in how they replaced the regulator IC802 with a 300mA PTC Brightking thermal fuse.

author: Legit-Design
author_rank: Frequent Contributor
timestamp: May 01, 2014, 12:57:02 pm
content: Quote from: Towger on May 01, 2014, 12:11:26 pmYes, all the black capacitors seem to have been glued with yellow glue.Similar device to Q803 on top right corner has similar crack marks on it. Can't read the other one marking but it's below IC805 next to R821, Q80? something. I think it might be from manufacturing or both devices are faulty.Is the bottom right flatflex cable fully inserted? To me it looks like that flex cable is half out. Also make sure every connector is well seated, just go around reseating them even if they look good. Some flat flex cables might come like this.Quote from: Hagis2k on May 01, 2014, 03:13:09 amQuote from: Hagis2k on May 01, 2014, 07:01:27 amSo it was flashing something before? Now it's not even flashing anymore?How did it actually turn out to be like this? Did it just suddenly die when in use? Has the fuse been changed before, manual states it has 15 amp fuse and maximum power of 180W*.Maybe another picture from bottom of the board?Go around gently touching the parts when it's powered on, does anything heat up?

author: Towger
author_rank: Super Contributor
timestamp: May 01, 2014, 01:53:34 pm
content: Quote from: Legit-Design on May 01, 2014, 12:57:02 pmIt would not be the first time a car radio was plugged into the mains...

author: SeanB
author_rank: Super Contributor
timestamp: May 01, 2014, 03:01:30 pm
content: Quote from: Towger on May 01, 2014, 01:53:34 pmI take it you know a few boilermakers and fitters then..........I saw one that put a B22d lamp into an E26 socket, and actually had it lighting. Had to change the socket with the lamp though when it blew, the parts no longer separated.

author: Hagis2k
author_rank: Regular Contributor
timestamp: May 02, 2014, 02:14:13 am
content: No blown transistors, either capacitors leaking they are glued to the pcb there is two 7808 voltage regulators and afaik a low dropout voltage regulator named KIA378R33API pulled the base low on both transistors (2sb1243) activating the 12V supply to the 8V regs so i got both 8V 5V 3.3V present checked the voltage at the cpu getting 4.9VWell a neighbor wanted me to look into this and all it does when you put the power on it is to flash the illuminate leds 1-2 seconds same with the motor for inject / eject the disc thenit is totally dead nothing happens on the lcd at all sucks that the oscilloscope i did order was out of stock getting it in the end of this month.

author: Shock
author_rank: Super Contributor
timestamp: May 02, 2014, 05:39:11 am
content: Are you powering up and checking both the +12v rails from the plug?user guide here.It's fused at 15A so you need to provide plenty of current as well.

author: Hagis2k
author_rank: Regular Contributor
timestamp: May 02, 2014, 09:21:28 am
content: I connected both ACC and Memory to my variable power supply it draws 100-150mA until i start up the both 8V regs by pulling the two pnp transistors when i activate them both then it draws 600-800mA can supply 2A on 12V i know it cant deliver the power to the amp when you crank up the volume but it should be able to run the device at idle

author: Legit-Design
author_rank: Frequent Contributor
timestamp: May 03, 2014, 01:53:27 pm
content: Still no idea what's on the other side of the board? (in this case a picture literally tells more than 1000 words) Know it might be lot of work to disassemble it, but then you see all things and can make sure there no surprises there. Surprises like burnt tracks or just burn marks on the pcb.

author: Niklas
author_rank: Frequent Contributor
timestamp: May 03, 2014, 05:29:21 pm
content: My first tip would be to take out the PCB from the box and inspect the connector solderings very carefully for small cracks. Have a look at the connector SK801 up in the left corner, especially pin number 4 from the right hand side. There seems to be a very thin, circular line in that soldering.

author: Hagis2k
author_rank: Regular Contributor
timestamp: May 06, 2014, 11:24:11 am
content: Thanks everyone so farI took some more photos of the unit as requested:http://imgur.com/a/WnrawShall remove the circuit board today and inspect it deeper in details have looked over it with magnifying glass and so far i cant see any solder cracks will surely be easier with the pcb removedbut lets play with the thought if the cpu is dead then nothing would happen? i get 5V dc to the cpu, and i looked it up it shall also have a program to run anyway time to tear the stereo apart

author: Hagis2k
author_rank: Regular Contributor
timestamp: May 06, 2014, 01:01:47 pm
content: So spent a few hours looking at all connectors, no issues even resoldered some connectors made no difference, then i went to checking the esr of all small caps... 2.2µF 50V esr 5-8ohms so dried out then lol so i have to ask the owner if we shall try to replace 20-30 caps and see what happens