Replacement resistor ID problem, Popped car stereo

[Goldtooth]

Hi

I broke my car stereo (Brand: ABC; model: CDX-7613) while installing. I think I by accident reversed +ve and -ve, plugged in and popped a capacitor (1000μF, 16V; found the remnants) and fried a surface mount resistor. As far as I can see only these two parts are faulty. Could other parts have broken without it being visibly obvious?



If not, the only snag is that I cannot read the code on the fried SMD resistor to get a replacement.

It's snapped through in the middle near what could be a 3 (not so obvious in the photo). Might be upside-down in the image. Do these come in standard values? Can I speculate based on the size and what's left of the code? At this point I'm guessing it says 231. How important is it to get close to the original value?

I have almost no experience in electronics (one year of university physics), so any help (preferably in layman's terms) would be greatly appreciated.

 

[Harald Kapp]

Can I speculate based on the size

No. You can get all values in each size (o.k., almost all...)
If the code is really 231, this indicates a 230 Ω resistor (23*10^1)

How important is it to get close to the original value?

Impossible to say without having a schematic diagram at hand.

Could other parts have broken without it being visibly obvious?

Unfortunately yes. The semiconductor ics may have been internally damaged. Polarity reversal isn't something these chips take lightly.

 

[Goldtooth]

Thanks for the response Harald.

I guess I'll just stick a 230 Ω resistor back in and replace the capacitor and see if it switches on (with the correct polarity xD). Hopefully the chips have survived.

 

[73's de Edd]

Sir Goldtooth. . . . . . .

Zero information on that company products . . . . . is floating around.

Visibles:

That the RED connector is the AV input.
The large 9 pin U2 left rear is the units POWER amplifier and its ancillary support components in the front
suggests this just being a R and L power output unit with no power woofer output.
To verify, pass on its part number to us.

That audio output to speakers should account for at least four of the closest connections on that 12 connection WHITE connector.
Your 12VDC power connection must also come in at the other end of that WHITE connector and passes thru the nearby F1 YELLOW auto resettable fuse . . . . . . that might now be reduced down to being UN settable.

Down in your left frontal quadrant . . .trouble area . . . I suspicion U1 as being inclusive of a power FET that does the MAIN power switching of 12VDC power for the unit over to the U2 POWER amp.
Your R15 seems to be series connected into it.
Its value probably was marked as 2 comma 2 R . . . . . . .as you certainly CAN NOT burn open / scorch a 230 ohm resistor with but a mere 12VDC passing through it.

Wouldnt hurt to also give us the other 4 electrolytics positions and cap value / voltages.
Also the markings on the big U1 unit, as I suspicon that the nearby ACC on the right strip activates it .

A flat on, screen filled and squared in the frame photo of the foil side of the PCB might answer some other questions on the unit.


73's de Edd

 

[Goldtooth]

Hi 73's de Edd

Thanks for taking time to help.

Part number for U2:
(YD, 1028, GJEaS)


Electrolytics:


U1: (78M05, A1518)


Foilside:


Here's a diagram for the big white connector and how it links with the circuit board:



I'm bit confused about what you said about the SM resistor code. Did you mean it probably was marked as 2R2 (2.2 Ω)?

 

[davenn]

Its value probably was marked as 2 comma 2 R . . . . . . .as you certainly CAN NOT burn open / scorch a 230 ohm resistor with but a mere 12VDC passing through it.

sorry Edd, but that's rubbish

 

[davenn]

I'm bit confused about what you said about the SM resistor code. Did you mean it probably was marked as 2R2 (2.2 Ω)?

that is a possibility .... have another close exam of the resistor in different angles of light and under a magnifier and see if you can
determine any more info from the burnt area

 

[Goldtooth]

Hi davenn

Unfortunately the little SM resistor is gone, but I've examined it as best I can under magnification before and I could pretty much only see what is shown in my original post.

I have since soldered in a new capacitor and a 180 Ω resistor, being the one closest to 230 Ω that I could salvage from some scrap electronics, just to see what happens when I power it up again.
It responded with a "Hi" before showing "00:00" with the ":" flashing, which is good, however, all the buttons (including the clock button), except the power button, are unresponsive. And the power button switches it off but not on again (have to plug out and in again). This makes me think that part of the circuitry isn't working and that it's probably the resistor? It was really difficult soldering it on and it may be shorting out something, hard to see if the solder is only where it should be.

Should I pull out the new resistor and go for a ~2.2 Ω and re-test? Does this mean that the chips have survived?

 

[davenn]

This makes me think that part of the circuitry isn't working and that it's probably the resistor? It was really difficult soldering it on and it may be shorting out something, hard to see if the solder is only where it should be.

it's sort of indicating that some other part of the circuit has been damaged by the voltage reversal