Polymer Capacitor Advice (A1200 or any Amiga)

[Zippy Zapp]

Hi All,

I am going to recap 2 Amiga 1200's because I am pretty sure they have not been recapped. 1 is an Original Commodore branded PAL and 1 is an Amiga Technologies NTSC. They both work fine but I know if they haven't started to leak, they will.

I see many opinions on cap replacement. Some are even using ceramics and surface mount tantalum caps. I would not switch to ceramics because to me it doesn't seem ideal. I am leaning toward Aluminum surface mount Polymer caps and Polymer through hole for the the non surface mount caps.

I like the idea of these caps because, they are supposed to never leak as they are solid and not liquid and they are rated to last a lot longer then regular electrolytic caps. Most modern decent quality PC Motherboards are pretty much using all polymer caps where they used to used electrolytic.

I know there is a service on eBay that replaces caps with Polymer and I have read that this is pretty reliable but thought I would ask if anyone has done it and if they have any comments on any cons or sizing problems?

Thoughts? Does anyone have a list of part numbers they used that work well, size and etc? This could apply to any Amiga really. Polymer caps are available in through hole too so A500/2000/3000 could apply.

Thanks!

[Zetr0]

@Zippy Zapp

I will be honest my friend, I do prefer like-for like and I wouldn't replace any capacitors with ceramic / tantalum based units as the circuit is not designed for that level of tolerance.

When I do repair work I usually use identical items but with 105c tolerance capable "Panasonic" capacitors - yes I am a Panosonic fan-boy I admit that However I have to admit I would like to try a complete poly replacement and run that through some tests.


Re: A500 / A1000 / A2000 : Through Hole Capacitors

To be absolutely honest here, as long as there is a power cycle every so often of the above devices its unlikely a capacitor will go bad - simply because that is confirmed, refined 60 year technology there - they might dry out and die in that manner but its proven 60 year old technology in these things - replacing these with a like for is the better way to go in my humble opinion.

[Zippy Zapp]

@Zetr0,

Thank you kindly for your experience! I am with you, I usually go like for like when I am replacing Through-Hole stuff. And I agree that with the TH stuff I don't see a problem not replacing them. My thoughts were that some people like to replace old caps even if they are not bad but just because they are old. If they used poly I would be curious the result.

Hey I like Panasonic too, it is usually my first choice followed by Nichicon and Rubycon mainly because I usually buy from Digi-Key, not because I know any better.

Since it doesn't seem like there is any harm going with full poly, except for some of the TH stuff in the A1200 that may not be available in poly, I am going to order a set, well probably multiple sets of poly caps to try it out. My only concern is size as some of the spots were caps go are on the tight side so an exact size replacement is going to be ideal.

This will be the first time I have replaced traditional electolytics with poly so I hope it goes ok. I am always nervous when it is a treasured computer. I have done many 20xx era power supplies, LCD monitors and a few older Macs with bad surface mount caps but not an Amiga yet so hopefully I don't screw it up!

Thank you for your comments and I will be updating when I get the caps and get time to replace them.

[wmsteele]

Have a look here...
http://www.amibay.com/showthread.php...hlight=premium

[idrougge]

I have replaced the capacitors of an A4000 with stereo-quality polymer capacitors, but haven't been able to discern the result due to PSU troubles.

Nevertheless, one must keep in mind that capacitors have other characteristics than just capacity. Some parts of a circuit may want a low ESR, while certain other parts may prefer the ESR to be higher. Different capacitor types have different characteristics when it comes to load under common circumstances, load under other circumstances and overloading. This may not matter in most circuits, but may cause problems in reset circuits or audible issues in the audio circuits.

[Zippy Zapp]

Cool. Thanks for the information. In regards to the A1200 circuits any issue that you can see with Poly caps? Of course I think for the through hole caps, I see no reason not to use standard electrolytics but the rest of the surface mount I am going to try polymer caps. But I am far from an electrical engineer. I am just a hack that likes to do it myself to learn.

[Zetr0]

@Zippy Zapp

I have to admit I am quite excited as to where your experiment leads too - and I most certainly will champion the "I give that a go" nature! =)

Indeed idrougge raises a good point about ESR - but from my knowledge of the A1200 cuircuits the only one I would be concerned about would be the VIO circuit.

The VIO circuit provides a limited analogue voltage corridor for the analogue video to ensure that a violent potential difference doesn't destroy the TV (Display Panel) or the Amiga - now while I doubt replacing the radial capacitors for polymer based units will change much in this - it is something to keep an eye on =).

Have a look at the motherboard spec-sheet and you will see what I mean. but that is all I can really say that would be susceptible on the A1200 circuit in regards to ESR/ESRD.


Good luck, I am trully excited to see the results of your experiment(s)

[bebek]

Originally Posted by zetr0

@zippy zapp

i will be honest my friend, i do prefer like-for like and i wouldn't replace any capacitors with ceramic / tantalum based units as the circuit is not designed for that level of tolerance.

When i do repair work i usually use identical items but with 105c tolerance capable "panasonic" capacitors - yes i am a panosonic fan-boy i admit that however i have to admit i would like to try a complete poly replacement and run that through some tests.


re: A500 / a1000 / a2000 : Through hole capacitors

to be absolutely honest here, as long as there is a power cycle every so often of the above devices its unlikely a capacitor will go bad - simply because that is confirmed, refined 60 year technology there - they might dry out and die in that manner but its proven 60 year old technology in these things - replacing these with a like for is the better way to go in my humble opinion.

+1

[Zippy Zapp]

Originally Posted by Zetr0

@Zippy Zapp

I have to admit I am quite excited as to where your experiment leads too - and I most certainly will champion the "I give that a go" nature! =)

Uh Oh, pressures on! Actually I am excited to try it out. I think today I will have time to take detailed pictures and check all the capacitor spots on my PAL unit. I don't even remember which revision is in there.

Indeed idrougge raises a good point about ESR - but from my knowledge of the A1200 cuircuits the only one I would be concerned about would be the VIO circuit.

The VIO circuit provides a limited analogue voltage corridor for the analogue video to ensure that a violent potential difference doesn't destroy the TV (Display Panel) or the Amiga - now while I doubt replacing the radial capacitors for polymer based units will change much in this - it is something to keep an eye on =).

Ok you lost me there. Is there a cap number location for this section? Is it a TH cap? Would you recommend I put a like for like in this section? I have heard the terms ESR and Low ESR but I am not that experienced to know what the consequences are. I usually just look at the capacitor I am replacing and find a matching one on Digi-Key. But I have been reading here for a few years and I definitely, without a doubt, trust the experience you guys have, Zetr0, idrougge, Daedalus, Jope and many others that I have learned a great deal from. So, Thank You!

Have a look at the motherboard spec-sheet and you will see what I mean. but that is all I can really say that would be susceptible on the A1200 circuit in regards to ESR/ESRD.

I found the Amiga 1200 schematics but maybe that is not the same thing? Is it in the Video Coupling area? This is a little, no this is a lot over my head.

Good luck, I am trully excited to see the results of your experiment(s)

Thanks! I hope it goes well too!

[wiz12]

Where do you guys buy your capicitors?

[Zippy Zapp]

Originally Posted by wiz12

Where do you guys buy your capicitors?

I guess that depends on where you live. I usually use digikey.com, in the USA but I have also used mouser.com and jameco.com. So far I have been very satisfied with Digi-Key.

I have taken several pictures of the board, mine is a 1D.4. I am just comparing the values with the lists I have found on line. Then I can work up a part number list and I will post that on here for comments. I want to submit the order sometime Sunday so I can get them by Wed/Thur.

I have to say that this board is really clean and all the surface mount solder points on these caps are shiny and I see no evidence of any leakage. Makes me wonder if it is a necessity as much as I have read about online? Or is it simply some spots could be hiding the leakage?

Nervous as these are fairly tight places. I mean I am pretty sure I can do it but the others I have done had a little more wiggle room. Ah well it's the only way to improve your skills I suppose.

I have attached 1 picture that shows 4 caps of the same value. According to the lists I have found on line they are stating that these are 22uf 25v. To me they look like 22uf 35v. Am I reading these values wrong? Here is a Digi-Key link for a Panasonic Polymer cap with same ratings and size. Does this look like a good replacement?
https://www.digikey.com/short/3w5m1m

[idrougge]

Originally Posted by wiz12

Where do you guys buy your capicitors?

Reichelt.de or demand.nu.

I usually buy all kinds of things from China, but when it comes to capacitors, I don't want to end up with pirate goods, so I buy from sources I can trust to supply real Panasonic or Nichicon capacitors (or Elna for through hole) and not Pamasonyc or Nitchycom.

[idrougge]

Originally Posted by Zippy Zapp

I have attached 1 picture that shows 4 caps of the same value. According to the lists I have found on line they are stating that these are 22uf 25v. To me they look like 22uf 35v.

It's not uncommon to see 35V capacitors mounted on A600/A1200 boards where the schematics say 25 V, and it certainly doesn't hurt.

When replacing capacitors, I usually up the voltage rating a step to make sure they won't be overworked and hopefully have a longer life. So I replace 16 V caps with 25 V and 25 V caps with 35 V…

[Zippy Zapp]

Cool. So I think I will leave them at 35v as you say it can't hurt. One thing I am checking now is the impedance.

On one of the lists I found for the caps for A1200 it was recommended to use Extremely Low Impedance on the through hole caps. The impedance on the referenced part number is 60 mOhm. Is that considered low and does it have anything to do with Low ESR? I am thinking they go hand in hand but I could be wrong. Most of the Poly cap replacements I have seen seem to be in the 30-80 mOhm impedance range.

[xArtx]

If you're that keen, there are a couple of electrolytics in the
audio path that should have been bipolar, but aren't.
For A1200 revision 2, they are C324 & 334, both 22mfd.

[Zippy Zapp]

Thanks for the tip. Of course those are the hardest to get to. 334 is right behind the keyboard connector. fun.

I did find one cap that has a slightly dull appearance on one solder leg. So I am glad I am doing this.

[Daedalus]

Impedance and ESR aren't really the same thing but they do tend to go hand-in-hand - low-ESR capacitors generally speaking also have a low impedance, and for less critical things can be considered equivalent.

As for the non-polarised capacitors on the audio outputs... They're marked as that on the schematics, but weren't fitted from the factory (not that that's an indication of anything). However, according to some, there's a DC offset coming out of the op-amps which puts the near terminal of the capacitor always in the positive. I can't remember who pointed this out, but I remember someone scoping it and showing that it never goes negative, meaning that polarised capacitors should be fine. Also, most Amigas have a similar output stage but don't specify NP on their schematics like the A1200 does.

I'll try to dig up where I read this as I haven't probed it myself (but will do when I next have an A1200 open). My guess though was it was someone who really knows their stuff - Stedy comes to mind...

[wiz12]

Is it possible to test capacitors in-circuit without removing them?

[Daedalus]

Hmmm... It really depends on the circuit the capacitor is in. If it's in a situation where there are no parallel capacitors or other components, then it's possible to check them with an ESR meter. But most capacitors are across the power rails, which means the meter will be put off by all the other capacitors so really the best bet is to remove them and test them out of circuit.

If you're removing them though, you might as well just replace them - SMT capacitors in any Amiga need to be replaced at this stage if they're still the original factory-fitted ones. If they haven't failed yet, they will soon.

[Zippy Zapp]

@Daedalus,
Thank you for the explanation, that is very helpful.

I have ordered a set of regular electrolytic caps. I have run into a few problems with Polymer selection:

1. I am finding with Polymer that some of the values that you need tend to be wider in size, like the one right next to the keyboard connecter. Even a couple of MM can make a difference there as it is tight. At least to me.

2. For the values in the A1200 so far on digikey they are not rated any higher for lifetime. I have no problem finding all of them in standard form with 7000hr rating. But with Polymer most of the values seem to be 2000hr for the exact model I need. I have found one that is 10000hr but the rest are not. So that kind of negates it a bit.

3. The price on some of these are 4 times the cost. Ouch.

It doesn't sound like a good idea but is there a problem with using Polymer and standard electrolytic caps in the same board? Polymer are *supposed* to be drop in replacements. The through hole caps are still standard electrolytic.

I am looking at other sellers right now to see if I can find a better mix.