Just wondering if bad capacitors will make an A3640 not function and therefore computer not boot? Conversely, will A3640 work without capacitors at all like for example some motherboards?
Will A3640 work with bad capacitors? Without any capacitors?
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RetroNinja
Active member
My lack of Electrical Engineering degree says YES it will work. Will it work well and reliably? That's a different story. Capacitors perform a few functions. Their main use is to regulate voltage. As voltage surges and spikes flow through electrical equipment, capacitors help to trim out the highs and lows of the voltage. Capping the high limit and filling in when they drop low.
You can abstractly think of capacitors as tiny batteries in a circuit. The fluctuating house mains charge the 'batteries', while the 'batteries' give a smooth steady voltage to your IC chips.
As I understand it, when some capacitors fail they essentially turn into resistors which can affect the current level in a system. That can cause odd issues. Some people believe you should always replace 30yr old capacitors. The train of thought is there is a dielectric fluid/goo in them that may dry out over time. You would have to desolder each and every cap, then measure it to see if it is still good to know their state. If you're doing that you may as well just replace them.
I've never seen a mobo without capacitors. Keep in mind some are super small SMD while others are the easily identifiable round cans on a mobo. I have seen some modern boards that no longer have the canned versions.
Any EEs out there? Can you refine my answer?
You can abstractly think of capacitors as tiny batteries in a circuit. The fluctuating house mains charge the 'batteries', while the 'batteries' give a smooth steady voltage to your IC chips.
As I understand it, when some capacitors fail they essentially turn into resistors which can affect the current level in a system. That can cause odd issues. Some people believe you should always replace 30yr old capacitors. The train of thought is there is a dielectric fluid/goo in them that may dry out over time. You would have to desolder each and every cap, then measure it to see if it is still good to know their state. If you're doing that you may as well just replace them.
I've never seen a mobo without capacitors. Keep in mind some are super small SMD while others are the easily identifiable round cans on a mobo. I have seen some modern boards that no longer have the canned versions.
Any EEs out there? Can you refine my answer?
Thanks RetroNinja. I think your detailed explanation has the key clue - and that is that their failure turns them into resistors. That fact makes it that an A3640 with failed resistors could not work for this reason of resistance and insufficient voltage. So I guess the point here is that failed capacitors could result in non-working A3640. I ask this because as many posts as there are about the reverse capacitors and the required fix, none of the many posts I read state if A3640 will work without capacitors or if this actually causes the board not to work, unless they leak and cause trace issues. Hence, if they were to be removed - an A3640 without any capacitors on it - will it work/boot up at least? ...assuming the traces are fine and there is no leak damage of any sort?
As a sidebar: I took my 1942/1084 monitors to a classic TV/Audio repair shop that's been around for 4 or 5 decades for the switch replacement work. I just don't like the backs of CRT tubes...they make me nervous. Anyhow, I've also taken an audio piece or two there, and got chatting with the guy about...that's right...capacitors. His view based on decades of experience is, if it isn't broken, don't mess with it. And if it breaks, replace what's broken only. I don't know why this makes sense to me. Perhaps I'm just overwhelmed at having to worry about all those capacitors out there, until I need to worry about them.
As a sidebar: I took my 1942/1084 monitors to a classic TV/Audio repair shop that's been around for 4 or 5 decades for the switch replacement work. I just don't like the backs of CRT tubes...they make me nervous. Anyhow, I've also taken an audio piece or two there, and got chatting with the guy about...that's right...capacitors. His view based on decades of experience is, if it isn't broken, don't mess with it. And if it breaks, replace what's broken only. I don't know why this makes sense to me. Perhaps I'm just overwhelmed at having to worry about all those capacitors out there, until I need to worry about them.
FYI, I tripped across this old post below from 2010 in my search for answers, and asked the OP about it. He was kind enough to access his FastMEM and reply and noted that indeed, the card failed with the capacitor failure, and upon replacement it returned to full function. I guess what I'll do is take the capacitors off and pop it in capacitor-less and see what happens. Maybe...I'll open a time warp back to 1994!
www.amibay.com
Advice needed on A3640 repair - caps orientation
Hiya!!! I have here a good friend's A3640 accelerator: it was working fine, until it needed some reboots to have the amiga boot OK and finally it just stopped working. Naturally I suspect the aging caps... but what about their orientation? I have checked the old ones and they seem OK to me but...
www.amibay.com
Why? If you know how to desolder caps why not just replace them? Or did you have some other method of removal in mind?
What the TV repair guy said about caps may seem wise for general equipements easily replaced as TVs but we are talking here about rare and expensive retrocomputers and we all know by now that capacitors not only cease to fonction but also leak and destroy the card.
So it is about time that any serious Amiga stuff got the caps replaced, if not good working accelerators at least all the mobo.
So it is about time that any serious Amiga stuff got the caps replaced, if not good working accelerators at least all the mobo.
RetroNinja
Active member
FYI, I tripped across this old post below from 2010 in my search for answers, and asked the OP about it. He was kind enough to access his FastMEM and reply and noted that indeed, the card failed with the capacitor failure, and upon replacement it returned to full function. I guess what I'll do is take the capacitors off and pop it in capacitor-less and see what happens. Maybe...I'll open a time warp back to 1994!
Advice needed on A3640 repair - caps orientation
Hiya!!! I have here a good friend's A3640 accelerator: it was working fine, until it needed some reboots to have the amiga boot OK and finally it just stopped working. Naturally I suspect the aging caps... but what about their orientation? I have checked the old ones and they seem OK to me but...
I thought you meant new designs that may be cap-less.
In an existing circuit design, if you are pulling some out it is rather important that you replace them. While in theory there is parallel voltage to the caps and the next item (a lot of times an IC) it will be highly unstable. Maybe it would be fine to play a scrolling game or sit at a WB screen but anything more and random crashes are very likely.
Also there is a 'balance' in the
@Half-Saint - fully agreed. I guess I'm just looking for a quick testing method of some sort.
@Xanxi - 100%. What needs to be noted is that those tiny surface mount things aren't exactly an issue in older hardware. With all this environmental talk, can you imagine the amount of plastic flat panel TVs that get thrown in the dump each year because of these things? Brings a tear to my eye. As a side note, I just tripped into an Amiga 2500 that needs TLC, but the mobo is just stunning. And as I read about it, it seems the 2000s don't have capacitor issues as much (so far) could it be the lack of those tiny surface mount things? As another side note, reading about audio capacitors, I'm learning about reforming - interesting stuff.
@RetroNinja - yes, the goal I guess is just quick troubleshooting path. Snip the caps away and plug the board in to see if it boots or if there are other issues. If it boots, then the recap is worth it. OH brother...am I really trying to avoid soldering in 5 capacitors if unnecessary?
@Xanxi - 100%. What needs to be noted is that those tiny surface mount things aren't exactly an issue in older hardware. With all this environmental talk, can you imagine the amount of plastic flat panel TVs that get thrown in the dump each year because of these things? Brings a tear to my eye. As a side note, I just tripped into an Amiga 2500 that needs TLC, but the mobo is just stunning. And as I read about it, it seems the 2000s don't have capacitor issues as much (so far) could it be the lack of those tiny surface mount things? As another side note, reading about audio capacitors, I'm learning about reforming - interesting stuff.
@RetroNinja - yes, the goal I guess is just quick troubleshooting path. Snip the caps away and plug the board in to see if it boots or if there are other issues. If it boots, then the recap is worth it. OH brother...am I really trying to avoid soldering in 5 capacitors if unnecessary?
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By the way, does anyone know if it is true that Amiga 4000 motherboard will boot up without capacitors?
RetroNinja
Active member
What do you have against capacitors? Did a gang of hooligans named 'The Impedance Boys' steal your lunch money when you were young?
Capacitors do function like little batteries, true. Another important thing about them is that they do not conduct DC voltage but they do conduct AC voltage. When placed between the VCC and GND lines all of the DC voltage is unaffected but any AC voltage (which is just DC where the voltage is rapidly changing), is ideally conducted straight to ground - the device that the capacitor is near should see smooth DC only. When used in an audio circuit such as the two electrolytic capacitors near the keyboard connector on an A600/A1200 the reverse effect is used, the capacitor is in series with the audio signal. This stops any DC voltage from escaping the Amiga (which could damage your amplifier or other audio equipment) while allowing the rapidly changing audio signal to pass through.
@YouKnowWho I disagree with your guy - I have a 1081 and a full kit of capacitors for it, I will replace them before it gets much more use. When a capacitor fails it could go open circuit, it could go short circuit, or dramatically reduce in capacitance, or dramatically increase leakage current or just dump corrosive fluid in its vicinity. The cost of the capacitor is not the problem but what else in the circuit it could damage as it dies. I think it's a reasonable perspective if you're a TV repair guy who doesn't want to overcharge the customers but when looked at from the viewpoint of wanting to keep this irreplacable piece of equipment functioning it is not valid.
@YouKnowWho I disagree with your guy - I have a 1081 and a full kit of capacitors for it, I will replace them before it gets much more use. When a capacitor fails it could go open circuit, it could go short circuit, or dramatically reduce in capacitance, or dramatically increase leakage current or just dump corrosive fluid in its vicinity. The cost of the capacitor is not the problem but what else in the circuit it could damage as it dies. I think it's a reasonable perspective if you're a TV repair guy who doesn't want to overcharge the customers but when looked at from the viewpoint of wanting to keep this irreplacable piece of equipment functioning it is not valid.
@RetroNinja - I'm just looking at a quick path to verifying that capacitors are the function issue on a card or board before lovingly replacing them to find out nothing changed. By no means am I suggesting that this is the way to use the piece beyond troubleshooting and verifying that it was the caps. Capacitors are in the circuit for a reason.
@Aeberbach - fully understood and agree with your view. But at the same time...there are so many capacitors to worry about out there, and replacing them as a preventative measure does carry a cost and a risk. Additionally, in that conversation, he did note that in a piece all components age somewhat proportionally. You start putting new components in, it could also change things.
@Aeberbach - fully understood and agree with your view. But at the same time...there are so many capacitors to worry about out there, and replacing them as a preventative measure does carry a cost and a risk. Additionally, in that conversation, he did note that in a piece all components age somewhat proportionally. You start putting new components in, it could also change things.
In my effort to consolidate some info about this question, here is a post where the user claims to have a missing cap and A3640 would boot up.
One missing cap is normally not a problem. You're talking about removing all of them.
In an effort to consolidate info in one place, found another one...here user "mechy" notes in 2013: "Its been my experience the 4000 will boot with a 3640 with no caps for quick and dirty testing on 3640 trace repair."
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