Amiga.org - A4000 + A3640 SMD->Tantalum capacitor replacement 2 of 6

A4000 + A3640 SMD->Tantalum capacitor replacement 2 of 6

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Description: Audio circuitry capacitors. Can cause noisy/scratchy sound and worse!

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Posted by: da9000 at January 15, 2008, 08:00:35 PM

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Comments (5)

da9000 Posts:922	February 11, 2008, 09:10:43 AM OK, thanks to Castellen for his explanation, I think we're getting closer to closure on the polarized vs. non-polarized capacitors deal. Check here: http://www.amiga.org/forums/showthread.php?t=34336
da9000 Posts:922	January 21, 2008, 10:50:44 PM Thank you Orange. Yes, I agree, these alone cost me $20+. But any Amiga is worth it! :-) And at least I won't have to think about'em ever again! EDIT: Although I appreciate the kind words from another hardware hacker (Orange in this case), I have to admit that I did lift a trace (visible in the photo), but luckily since the capacitor legs don't bend easily and the other leg is planted well, it won't lift the trace up unless pushed really hard. One last detail which I hadn't done on that particular machine is to hot-glue the caps so as to avoid ripping any tracks in case a capacitor is somehow pushed too hard (while inserting an expansion board or something like that).
orange Posts:2794	January 19, 2008, 07:14:11 PM it looks great, very neat.. too bad the tantalums are expensive.
da9000 Posts:922	January 17, 2008, 08:38:43 AM Rodgerio, I know you've been a proponent of the non-polarized audio caps, and I know the schematics show that the current going through them will swing to opposite polarities, but there's no conclusive evidence or rhetoric for that matter that they must be non-polarized, and even the originals are polarized. In fact, one of the top experts on the matter, Castellan (http://amiga.serveftp.net/audio_repair.html) says: Quote "The AC output of the device swings both negative and positive around a centre voltage of approximately -1V. Ideally the 22µF output capacitors (C443, C433) should be bi-polar (non-polarised) types for this reason. Many argue that this is the primary reason for these capacitors failing in the first place. I'm not convinced of this, as there are other 22µF capacitors in the machine which are correctly DC biased at all times and they still leak as the ones in the audio stage do." He uses the word "ideal", and does not use "must". He also didn't say "must" when asked about it here: http://www.amiga.org/forums/showthread.php?t=28225 Furthermore, according to http://joj.home.texas.net/amigacap.html, the voltage swings will be on the positive side: Quote "If an amplifier is connected to a uni-polar supply, it is connected to a source like +12V and Ground. Then the output of this amplifier would swing from Ground to near +12V on the output. With an amplifier like this, we can use a capacitor on the output. The capacitor could be a polarized capacitor as the voltage potential on the capacitors' positive lead would always be positive." I don't quite buy this, because Castellan's oscilloscope shows the waveform centered clearly in the -1.2V range, but then again, perhaps there was a constant in his system offsetting the voltage. I don't know for sure. Now, I'm no all-knowing electronics expert, but I've asked around and I've not gotten any show-stopping answers. Yes, I'm aware that under extreme conditions the caps will explode if polarity is reversed, but I think that is only when it's continuous, and a decent amount of voltage and current in effect. Having said that, I'd love to hear a real technical discussion that will help us reach a conclusive end on this subject. I may start a thread on just that subject. Lastly, I've been using Amigas with the polarized caps on the audio circuitry for a while and never had a problem, nor an explosion, although granted, I've not played any weird sounds, but typical MODs and games. Any experts, please share your thoughts.
rkauer Posts:3263	January 15, 2008, 10:05:34 PM Those capacitors on the audio out must be non-polarized units! Even regular electrolytics units can be used (they are less sensitive to backward currents). If a tantalum device suffer a back-current, it simple explode!

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