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Old 05 February 2020, 13:58   #1
CubeTheory
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A500 Recapping Questions

Hi.

As I mentioned in my intro post, I have recently returned to the scene having got my original (bought new) A500 back off a friend I gave it to.

I know the A600 and A1200 definitely need recapping, but the general feeling i get is the A500 does not. I haven't looked for a schematic for mine yet (Rev6a Fat Agnus) so my first question is this:

Why does the A500 not need recapping generally? I ask this because coming from the ZX Spectrum world, and having restored a few, this is very much a must as powering up a spectrum that's been sitting for about 30 years without having recapped or at the very least performed some preliminary test, is a big no.

My next question is: who has or hasn't recapped the A500, and specifically why did/didn't you?

I have inspected mine and the Caps look ok, and everything seems to be working so far, so I'm inclined to leave it.

Apologies if this has been covered, but I did a search and found nothing,

Thanks
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Old 05 February 2020, 14:36   #2
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Never bothered, because my old A500s seem to work fine and the general consensus is that they don't need doing (the problems are more with the surface-mount caps). Also I'm cheap.

I imagine it wouldn't hurt though.

Nobody seems to talk about PSUs but I've heard of recapping those too. One of mine caught fire so if you're in the mood to solder something maybe start there!
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Old 05 February 2020, 14:40   #3
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The capacitors on the A600 and A1200 are fairly early surface mounted electrolytic caps. The seals on them are not that great, and over time caustic electrolyte will leak out causing damage to the PCB.

The A500 uses through-hole capacitors, a very mature technology even at the time, and they very rarely leak.

Additionally, almost all the electrolytic capacitors on Amiga motherboards are only there to provide voltage stability and are not that critical to operation as long as the power supply is good. In fact, you could run the systems with all caps removed* and they would work more or less normally.

Therefore, even if the capacitors on an A500 have aged, it doesn't usually cause issues. However leaking capacitors (on the A600 and A1200) are a problem because that will ruin the board.

Aging capacitors in power supplies are an entirely different matter and those should definitely be serviced, but on the Amiga all power generation is external.

Personally, I have recapped one of my A500 boards because I was working on it anyway. But there was no particular reason that demanded it.


* There may be some exceptions; I think the A600 has one electrolytic capacitor involved in the reset circuitry and that probably can't be left out
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Old 05 February 2020, 14:45   #4
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Some A500s have blown a few caps, but there's no need for mass hysteria like with the SMD Amigas.

We'll see if/when they start failing more often.
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Old 05 February 2020, 15:05   #5
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Can a electrolyte capacitor not leak but still be deead?
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Old 05 February 2020, 15:55   #6
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Quote:
Originally Posted by Gordon View Post
Can a electrolyte capacitor not leak but still be deead?
I recently pulled a big axial capacitor out of a Dragon 32 power board that had leaked, but was still working. It was outside of normal tolerance and a lot higher than its rating.

Just before that I pulled a 2200uF cap from a TV that had obviously leaked and that registered 83pF!

But caps can fail but not necessarily leak, causing shorts, etc. I've seen this in some of the Spectrums i've recapped, and in the Beeb psu. There's loads in there, but normally the 2 x2 caps and the startup electrolytic cap is all that's needed. I had to replace all the caps on the output stage across all 3 rails to get the psu stable again.

Last edited by CubeTheory; 05 February 2020 at 16:02.
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Old 05 February 2020, 16:21   #7
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Originally Posted by E-Penguin View Post
Never bothered, because my old A500s seem to work fine and the general consensus is that they don't need doing (the problems are more with the surface-mount caps). Also I'm cheap.

I imagine it wouldn't hurt though.

Nobody seems to talk about PSUs but I've heard of recapping those too. One of mine caught fire so if you're in the mood to solder something maybe start there!
Yeah, I tend to recap PSU's as a matter of course, though I haven't done my A500 Type 1 yet. I did put a Meanwell in a spare case i had though, so im using that at the moment.
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Old 05 February 2020, 16:22   #8
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Quote:
Originally Posted by ajk View Post

Additionally, almost all the electrolytic capacitors on Amiga motherboards are only there to provide voltage stability and are not that critical to operation as long as the power supply is good. In fact, you could run the systems with all caps removed* and they would work more or less normally.

Therefore, even if the capacitors on an A500 have aged, it doesn't usually cause issues. However leaking capacitors (on the A600 and A1200) are a problem because that will ruin the board.
Thanks for clarifying. I haven't gotten hold of schematic yet, so I wasn't clear on this point, that's good to know.
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Old 05 February 2020, 18:47   #9
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Quote:
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Can a electrolyte capacitor not leak but still be deead?

Hello!
Yes, a capacitor can look like new and be completely dead.
There are special tools to measure the capacity and resistance of a capacitor. They are expensive tools if you want them to be reliable.
Changing capacitors on the A500 is not necessary unless they show visual signs or the machine does rare behaviors.
In the PSU it is completely different, my recommendation is, if you do not have tools to measure the status of the PSU capacitors, then change them all.
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Old 05 February 2020, 18:56   #10
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In this image you can see a 220uF capacitor that has no signs of being bad but the meter accuses that its capacity is zero.
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Old 05 February 2020, 20:19   #11
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I had an A500 that refused to boot and gave a green screen RAM erorr.After much faffing around replacing and testing RAM chips it turned out one of hte caps on the 5V rail had gone bad and was causing the power line to the RAM to fluctuate.. After replacing all the caps (just to be on the fase side) the machine boots and runs without a problem.
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Old 05 February 2020, 23:44   #12
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Originally Posted by Vypr View Post
I had an A500 that refused to boot and gave a green screen RAM erorr.After much faffing around replacing and testing RAM chips it turned out one of hte caps on the 5V rail had gone bad and was causing the power line to the RAM to fluctuate.. After replacing all the caps (just to be on the fase side) the machine boots and runs without a problem.
Did the original ram turn out to be ok? or did it fail as a result of the bad cap?
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Old 06 February 2020, 05:29   #13
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Unlike 1200/600/4000/CD32, caps only need to be replaced (mandatory) when they fail on older Amigas! They don't leak like SMD caps. The can go bad and leak but extremely rare.
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Old 06 February 2020, 07:08   #14
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^ I've tested many with an ESR meter and encountered a few bad ones, but it's rare.

Worst case for vintage through-hole was an Atari 1200XL, some of them came with a Chinese brand capacitor (can't recall the name) and every one of them had leaked. As we all know, the Amigas got the good Japanese stuff (from what I've seen, here anyhow).

I agree that original PSUs are an exception, I won't use them otherwise.
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Old 06 February 2020, 12:12   #15
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Did the original ram turn out to be ok? or did it fail as a result of the bad cap?
The original RAM turned out to be fine, fortunately the voltage bounce was just in the downward direction so there was no overvoltage.

having said that, when I was building my A500++, some sloppy trimming of capacitor leads meant two adjacent caps had touching legs which ended up sending 9V to the clock chip. Amazingly the chip survived.
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Old 06 February 2020, 22:24   #16
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I have recapped 4 of my Amiga 500s. Kinda regret it. No point as long as they are working correctly. I ripped a couple of through hole vias on one of the boards when doing the recapping. Had to use a few bodge wires to fix it. A500 boards has huge ground planes aswell so it requires quite a bit of heat from the soldering iron. Well, it's done anyway so don't need to worry about them anymore. Still have 3 more A500s that I haven't recapped. I think I will just leave them alone for now and instead focus on recapping power supplies. Already did an A600 power supply that had fish smell and showed some interference on the screen in certain games. Recapping fixed it. Fish smell went away aswell.

A600/A1200 on the other hand is in great need of recapping.

so my suggestion as to A500s, leave the caps alone if it works fine and you see no leakage or anything. No point really. If you are skilled at soldering and have the caps and nothing better to do, then by all means.
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Old 07 February 2020, 10:14   #17
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Thanks for all the hints, tips, and views on this. Really appreciated. Mine is working fine. I'm just gonna leave it be and keep an eye on it.

I will be recapping the PSU, though. But no rush, it's been running on the Meanwell for the last 2 days and seems happy enough.
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