A4000D : please, check C433 & C443 polarity

[Cosmos Amiga]

Please A4000D owners, could you check the polarity of your audio C433 and C443 (22uF 16v) ?

No oscillo here, only my multimeter...

Seem inverted on all 4000, yes or no ?

Or bipolar caps solve that ?


Thanks,

[mechy]

Please A4000D owners, could you check the polarity of your audio C433 and C443 (22uF 16v) ?

No oscillo here, only my multimeter...

Seem inverted on all 4000, yes or no ?

Or bipolar caps solve that ?


Thanks,

Yes, install bipolar (npo) caps there.

[Cosmos Amiga]

Yes, install bipolar (npo) caps there.

On the A600 & A1200, bipolar are not required, so why on the 4000D ?

[mechy]

On the A600 & A1200, bipolar are not required, so why on the 4000D ?

I'll let anthony answer:) i have always followed this.

http://amiga.serveftp.net/audio_repair.html

[Cosmos Amiga]

I'll let anthony answer:) i have always followed this.

http://amiga.serveftp.net/audio_repair.html

Oh, yes :

"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."

[Hanzu]

Maybe they all leak also because they should have used the ones with a little higher capacitance in the design.

And why did they not use tantalum SMD capacitors in the first place that would have eliminate a lot of service need? Maybe partly because of the high price at that time.

A1200 Rev 2B has one tantalum SMD capacitor in the place (close to VIDEO port) where there was of an electrolytic SMD capacitor in the previous motherboard revisions. I also saw one assembling his empty A4000T motherboard with tantalum SMD capacitors only. This clearly is not recommended since it is not more common. Why?

[mechy]

Maybe they all leak also because they should have used the ones with a little higher capacitance in the design.

And why did they not use tantalum SMD capacitors in the first place that would have eliminate a lot of service need? Maybe partly because of the high price at that time.

A1200 Rev 2B has one tantalum SMD capacitor in the place (close to VIDEO port) where there was of an electrolytic SMD capacitor in the previous motherboard revisions. I also say one assembling his empty A4000T motherboard with tantalum SMD capacitors only. This clearly is not recommended since it is not more common. Why?

The capacitance is not the issue ,maybe higher voltage would of been better,but the 90's was a time for loads of bad caps in everything. I think it was cheap caps or overheating when soldering or both.

Tantalums can absorb moisture. there is a reason the engineers used electrolytics. Nasa even tested the effects of moisture on these. Personally i dont think subbing tantalums for electrolytics is good in most cases.

[Hanzu]

The capacitance is not the issue ,maybe higher voltage would of been better,but the 90's was a time for loads of bad caps in everything. I think it was cheap caps or overheating when soldering or both.

Tantalums can absorb moisture. there is a reason the engineers used electrolytics. Nasa even tested the effects of moisture on these. Personally i dont think subbing tantalums for electrolytics is good in most cases.

After reading this: https://en.wikipedia.org/wiki/Tantalum_capacitor I realized we should talk about tantalum electrolytic capacitors (my bad actually) Seems like the moisture goes inside the case in the manufacturing process of the component, not in the use of the component. (https://en.wikipedia.org/wiki/Tantalum_capacitor#Leakage_current) If component is throghly tested in production I can't see this as a big problem. CMIIAW.

The greatest drawback I have seen personally for tantalums is that they seem to burn and not explode when accidentally assembled reversed in production or if driven with too high current. I once saw one burn a hole in the PCB. When normal electrolytic capacitors just burst open.

If one needs big capacitance polarized capacitor with small size, then modern tantalum is an good option, but maybe you agree tantalum electrolytic capacitor is better option for ceramic capacitor http://www.kemet.com/Lists/TechnicalArticles/Attachments/93/2008-11%20Update%20-%20Ceramic%20versus%20Tantalum.pdf than it is for normal electrolytic capacitor.