SparkFun Forums

[3Dawn]

I have a Duemilanove and Mega. On both of them I accidentally reversed the voltage when using the Vin line (I think). The Mega blew the C6 capacitor. I have replaced it. Now on both units the input jack doesn't work. The units work just fine when connected through USB.

I'd like to try to replace components if possible (for my own learning), but is it worth it? Also, are there any likely culprits that would have blown?


Thank you for your help - I am new to electronics and I think I'm addicted.

[StigOE]

Get the schematics and check with a multimeter where you loose the voltage, starting with the voltage regulator(s).

[MichaelN]

Hasn't this already been asked (and answered)?

viewtopic.php?f=20&t=23785&p=110155

[3Dawn]

I replaced the C6, but it still doesn't work. Plus I didn't ask about the 2009 board. I thought there might be an easy answer.

[3Dawn]

OK, so I am checking the voltage on the Mega. Black lead on the input receptacle ground. The voltage is around 7V up to C6, then nothing on the other side of C6. If I check continuity across C6 it says that there is continuity. Also, the original Mega board had two caps next to each other. One blew up so I can't read it, but the other says 476D on the top. I have since learned this means that it is a 47microFarad capacitor. Yes? However, the Mega schematics show it as 100 microFarads. I replaced C6 with the following part number from Digikey: 495-1548-1-ND. Is that my problem? Also, I tried switching the two capacitors, C6 and C7, to see if that made a difference - it didn't.
Please help! Thank you!

[MichaelN]

If I check continuity across C6 it says that there is continuity.

Capacitors shouldn't show continuity when you check with an ohmeter. However, since you replaced these caps it is likely that this is another part of the circuit causing this (eg the regulator as suggested several times previously).

One blew up so I can't read it

Reversing polarity on electrolytic capacitors will commonly cause them to smoke / blow up.

...the other says 476D on the top. I have since learned this means that it is a 47microFarad capacitor. Yes?

Yes.

...the Mega schematics show it as 100 microFarads.

The exact value of electrolytic caps is normally not important.

I replaced C6 with the following part number from Digikey: 495-1548-1-ND. Is that my problem? Also, I tried switching the two capacitors, C6 and C7, to see if that made a difference - it didn't.

Why aren't you looking at the regulators??

[3Dawn]

Sorry but I didn't see any reference to the regulators. I will check them if I can figure out where they are.

[3Dawn]

OK, so it looks like both of the boards are getting 0V on the output. One thing I am confused about: When I look on the schematic for the Mega it shows IC4 and IC5 as having similar part numbers (MC33259xxxx). On the board they appear to be right on top of each other. Are they the same component? Digikey doesn't have any replacements in stock. I'll try looking elsewhere. Any suggestions?

Also, THANK YOU for the help. I appreciate it.

[StigOE]

Sorry but I didn't see any reference to the regulators. I will check them if I can figure out where they are.

I did say in my post 'check the voltage regulator(s)'... On the Duemilanove, the voltage regulator is IC4. On the Mega there are two voltage regulators, IC4 and IC5.

Stig

[n1ist]

As I mentioned in your previous post, the board allows them to use one of two different regulators. Only one of them is loaded at a time. This lets them load whichever they have in stock at the time. I'm not quite sure what you mean by

The voltage is around 7V up to C6, then nothing on the other side of C6

Do you mean that there is 7v on the trace between D1 and C6, and 0V on the continuation of the trace between C6 and IC4/IC5? If so, the trace is damaged, and you need to jumper across it. If you mean that the positive terminal of C6 measures 7V with respect to ground, and the negative terminal of C6 measures 0V with respect to ground, that's normal.

It looks like the LM1117 (Digikey part LM1117MPX-5.0CT-ND or similar) is a valid substitute for MC33269ST-5.0T3.
/mike

[3Dawn]

Hi Mike, yes, 0V on the ground terminal of C6. Thanks for you help. I'll order some of the parts you suggested from Digikey and see if that works.

[StigOE]

Looks like the Duemilanove uses a MC33269D which is a SO8 package so LM1117MPX isn't a substitute for this. I don't have a Duemilanove handy so I can't verify this.

Edit: Mouser has them in stock. Part number 863-MC33269D-5.0G