A1200 power input capacitors

[ShK]

Is it possible to increase the capacitances of C408, C811 (+5v) and C821 (+12v) and C822 (-12v) for the stronger power feed or does it just harm the power input circuit?

I was wondering if it would make any sense to do this? Will there be a problem with the cold start or reseting A1200?

1000μF 10v -> 3300μF 10V
47μF 16v -> 220μF 16V

Amiga 1200 Rev. 1D4 ( Artwork 364720-05 ).jpg

#  Location Original  Size
13 C408     1000μF    10v Through Hole 10mm (Lead Spacing 5mm, H 15mm)
16 C811     1000μF    10v Through Hole 10mm (Lead Spacing 5mm, H 15mm)
17 C821     47μF 16v  6.3mm
18 C822     47μF 16v  6.3mm

[Sandro]

you can increase the capacitance if you want but there is no need to do that because the power supply have own capacitors to rise that lines
those caps on the A1200 adds more capacitance..that's all
in the case of 5v yes increase it, because is the vital line the more capacitance the better
12v is used only for the floppy drive 100mf will be ok but increase it for a stable line
-12v I don't know for what is used but I assume 100mf will be ok you can increase to 470 if you want

[ShK]

So, 100μF 16V is proper for C821 (+12v) and C822 (-12v).

But, does 3300μF capacitor(s) in +5v line have enough time to be charged before the cold start sequence's 'reset hold' is released?

[Sandro]

Originally Posted by ShK

So, 100μF 16V is proper for C821 (+12v) and C822 (-12v).

But, does 3300μF capacitor(s) in +5v line have enough time to be charged before the cold start sequence's 'reset hold' is released?

I don't know what you mean when reset hold is released
but please note that the more capacitance is better...so you can try it safety
in the case you will note something rare you can return to the originals caps

for example intel ATX 2.2 specs they recommend 10.000 mf for each line +12v +5v +3v
but if you open any power ATX supply you will found as maximum 4700 mf on each line even on the best power supplies
on the A1200 for example on the 5v line you have 2 caps at 1000 mf each ( total 2000mf) add the capacitance of your power supply and you will have at least 4000 mf in the 5v line...that's enough for proper operation

[chaos]

There are big rectifier capacitors in the power supply, so there's no need for any big capacitors on the Amiga side, just filtering capacitors.

The 1000uF is big enough, no need for anything larger. I would rather bump the voltage rating to 16V, if such a capacitor would fit inside.

Placing a capacitor with bigger capacitance will change the time constant and possibly increase the charge / discharge current. Of course, there shouldn't be a problem replacing them with something that is close in value if that is what you have available.

[chaos]

Originally Posted by Sandro

but please note that the more capacitance is better...so you can try it safety
in the case you will note something rare you can return to the originals caps

More capacitance is not necessarily better. You should use ~4500uF recitifer capcitors for each Ampere of output current in your power supply, near the rectifier diodes. Next, a pair of ~50uF and ~500uF after your regulator. And next to any relatively high-speed digital IC, a triple of 1nF, 100nF & 1uF on each power supply pin. These are just rule-of-thumb values, of course. You do need more than a single capacitor in practice (in theory, they could be replaced with a single value), as each has its own characteristics.

I'm pretty sure the Amiga board designers knew what they were doing, so I wouldn't change the capacitors without a good reason. Certainly not without a reason. But you could always try and prove me wrong

[ShK]

Originally Posted by Sandro

I don't know what you mean when reset hold is released

I meant that does the +5v line have enough time to get up before Amiga try to the start. Does big capacitor in the power input circuit harm the boot up with its charging time? Is it multiple resetting needed to weak up the Amiga?

[ShK]

Originally Posted by chaos

You should use ~4500uF recitifer capcitors for each Ampere of output current in your power supply, near the rectifier diodes. Next, a pair of ~50uF and ~500uF after your regulator. And next to any relatively high-speed digital IC, a triple of 1nF, 100nF & 1uF on each power supply pin. These are just rule-of-thumb values, of course. You do need more than a single capacitor in practice (in theory, they could be replaced with a single value), as each has its own characteristics

I have A600's large case sizes PSU, here is list of its original capcitors: A600 PSU 391029-03, 3.0A (PWB30300-001 REV A04).jpg

Is it ok to change all those 1000μF 10v capacitors to the 10v 3000μF ones?

Is there any sense increase others capacitor capacitance for the stronger power feed?

A600 PSU 391029-03, 3.0A (PWB30300-001 REV A04)

#  Original  
1  1000μF 10v
2  1000μF 10v
3  1000μF 10v
4  1μF 35v
5  1μF 50v
6  330μF 35v
7  47μF 385v
8  82μF 35v
9  82μF 35v
10 82μF 35v

Wires from PSU    Voltage
WHITE             -12V
YELLOW            Shield
BROWN             +12V
BLACK             0V/GND
RED               +5V

[Loedown]

Cold reset time is the value that the unit takes to come out of the reset state after power has been applied so that the PSU voltages have stabilized. If your power supply takes 50 mS to come up to stable power on all rails and your reset circuit is set for 30 mS then you will have problems but if the numbers are reversed, the PSU takes 30 mS and the reset circuit is 50 mS then it's all good.

[TomCrazy]

Originally Posted by ShK

Is it possible to increase the capacitances of...

Possible - Yes

Originally Posted by ShK

for the stronger power feed

Could you elaborate on this a bit? I'm not quite sure what you mean here.
Putting more capacitance in there will not increase the power going into your motherboard. Power is a function of voltage and current, and since the voltages are already set (the PSU is, after all, a constant voltage source), the power factor is determined by how many amps your Amiga is pulling and how many amps the PSU is able to deliver. It has nothing to do with the capacitors in that sense.

Originally Posted by ShK

...or does it just harm the power input circuit?

No, it will not harm the power input circuit or anything else in the Amiga for that manner.

Originally Posted by ShK

I was wondering if it would make any sense to do this?

Nope, it doesn't make any sense at all to do this since there is no advantage whatsoever to doing it. On the contrary, there could be disadvantages.

It surprises me that noone has mentioned the resonant point of a capacitor yet. I don't know how much details I should go into here, but I will try to explain it briefly.

The total impedance of a capacitor changes with frequency. A capacitor has a capacitive reactance which dominates at lower frequencies and an inductive reactance that dominates at higher frequencies.
Since the reactance is something that makes up for the total impedance, the total impedance of the capacitor will increase as the reactance increases.
A capacitor has a special frequency point where the capacitive reactance and inductive reactance is about the same. This is called the resonant frequency of the capacitor.

Take a look again at the schematic. Do you see the two capacitors to the left of C811, the ones that are designated C801 and C804?
So as you can see, we have three capacitors in parallel here:

0.01µF --> 0.22µF --> 1000µF.

So why have they done that? Why have three capacitors of different values there when they could have just one?
It's because of what I just explained; The resonant frequency of the capacitors.
By having several capacitors in parallel like that, it's possible to achive a much lower impedance over frequency than if you have just one capacitor in there. If there was only one capacitor in there, then the filtering would work best only around a certain given frequency.

So where does this come into play? Well, the resonant frequency of a capacitor changes with the capacitance.
This means that if you choose a capacitor with a higher capacitance, you have suddenly decreased the resonant frequency of that capacitor.
Since you still have the same capacitors at position C801 and C804, you will not have changed the resonant frequency of those capacitors.
Since C804 is of a pretty low value (0.22µF is quite far from 1000µF), there will be a certain frequency gap between these two capacitors in terms of resonance point where the impedance is not that low.
By replacing C811 with a higher capacitance value, you will be lowering the resonance point of that capacitor, creating a bigger frequency gap between the capacitors that are hooked up in parallel, with lower filtering properties in that certain frequency range as a result!

So unless you carefully go through the datasheets and verify that the bigger capacitance value will not sacrifice any other important characteristic within the power input circuit, then no, it's not a good idea to replace the capacitor with another value.
If you absolutely feel that you want to add capacitance to the system, you would be better off soldering another 1000µF capacitor in parallel with the already existing one. That way, you would not have to sacrifice the filtering abilities over frequency, which is something I'm sure the engineers at Commodore included in their calculations when designing the Amiga 1200.
But trust me, you don't need more capacitance there. There is no benefit at all in adding more capacitance to the power supply input.
If you have a high ripple on your voltage rails and there is nothing wrong with your original capacitors on the motherboard, you most probably have an issue with your power supply and need to have a look at that.

In power supplies on the other hand, if there is only one capacitor for any specific voltage rail and you wish to increase the output capacitance to create a bigger energy reservoir in order to achive better filtering at heavy loads, then I see no problem in doing that since the larger capacitance will more than make up for the change in resonance frequency of the capacitor, especially at heavy loads. So the resonance frequency would not be of much significance in that case. But then again, I would still hesitate a lot before changing values myself because there might be something that the designers have thought about that I'm not thinking about.

So again, if your motherboard is working as it should, then I recommend you to leave it as it is. As a general rule of thumb, don't try to fix something that isn't broken. And I recommend you to not make any changes unless you're 101% sure what you're doing, because making changes to a circuit can change things in a negative way. Things that have to do with concepts within electronics that you maybe didn't even know existed.

Originally Posted by ShK

Will there be a problem with reseting A1200?

Resetting the Amiga? Definitely no problem.

Originally Posted by ShK

Will there be a problem with the cold start?
Does 3300μF capacitor(s) in +5v line have enough time to be charged before the cold start sequence's 'reset hold' is released?

It depends, but the quick answer would be; Yes, the capacitors will probably still have time to charge up quick enough in order for your motherboard to boot up fine during power on. As you can see in the schematic, the A1200 doesn't have a 555 timer-based "reset on power up"-circuit as the A500 and A600 have. Instead, it has a a circuit labeled "power OK" which is basically an OP amp configured as a comparator.
I don't know the characteristics of the OP amp used in this circuit (don't feel like checking it now), but according to the schematics, the time constant of the reset hold at power on will be a function of the input voltage on an A1200, rather than a function of a determined RC time constant in a 555 timer-based configuration. (But then again, the voltage will still have an effect on an A500/A600 too because of the voltage-current relationship affecting the RC time constant, but we're talking tiny details now so let's not take that into account.)

If you use a proper power supply, that power supply should be able to charge up a 3300µF capacitor in notime, making it have very little or completely no effect on the system.
However, if you use very thin wires between the power supply and your motherboard, or if you use very long wires, then you have a higher resistance in those wires than you would normally have. The resistance of the wires and the input capacitor on the Amiga motherboard then creates an RC time constant that is longer than if you would have the original 1000µF capacitor in there.
Could this be a problem? Well, that all depends on how well the "power OK" circuit is doing its job. It's impossible to make any kind of estimation just by looking at the schematics without knowing the exact characteristics of the OP amp being used.
The best way to find the answer to this question is simply to try it out. It will not damage your Amiga. In worst case, it will simply not boot up properly during power on, and you will have to do a keyboard reset in order for it to start up.

But then again, because of the reason I mentioned earlier, I do not recommend you to change the value of this capacitor. I would certainly never do it on any of my Amigas. Commodore made a few mistakes on some Amigas by e.g. putting electrolytic capacitors on the motherboard in the wrong direction. But for the most part, I think we can trust that the engineers knew what they were doing.

Originally Posted by ShK

So, 100μF 16V is proper for C821 (+12v) and C822 (-12v).

That doesn't seem to be an ideal capacitor to me, especially not for this application.
They have written that this capacitor has 1.1 Ohm impedance. I really don't like it when they write like that, because the impedance of a capacitor changes with frequency, so they have to put a frequency in there if they're going to write it like that. Like for example "Impedance: 1.1Ohm @ 100kHz" or whatever. But anyway, I suppose they are talking about the ESR here. And if so, 1.1 Ohm is a very high ESR for filtering applications. That will only lower the filtering capabilities of that capacitor even more!

Originally Posted by Sandro

but please note that the more capacitance is better...so you can try it safety

I agree that it's safe to try it, but as Chaos pointed out, it's certainly not true that "more capacitance is better". If that was true, then all electrical engineers would just throw as big capacitors as they could possibly fit on the PCBs they are designing. (Physical size of an electrolytic capacitor increases with capacitance.)
But electrical engineers don't do that, and there is a very good reason for it, and that is simply that it's just not that easy. It just doesn't work like that.
You can be sure that when they choose a capacitor in their design, they take into account all bits and pieces like ESR, ESL, temperature coefficiency, impedance over frequency, and even things like leakage current, dielectric absorption and parasitic capacitance and inductance, just to mention a few.
Capacitors are so much more than just capacitance and voltage rating.

Originally Posted by chaos

There are big rectifier capacitors in the power supply, so there's no need for any big capacitors on the Amiga side, just filtering capacitors.

I've never heard the term "rectifier capacitor" before. Which capacitors are you referring to here, the input capacitors or output capacitors of the power supply?
In either case, these capacitors are usually called either smoothing capacitors or filter capacitors. Rectification is not achieved in the capacitor, the capacitor is only filtering (or "smoothing out") the already rectified DC voltage. Rectification is usually achieved through a diode bridge.
If you were to try rectifying an AC voltage by using a capacitor alone, you would blow up the capacitor pretty quick.
Are you using the term "rectifier capacitor" to refer to capacitors with low ESR, perhaps?

But yes, I agree. Since rectification is done already in the PSU (taken the PSU is working as it should), there is no need to have bigger capacitors on the Amiga motherboard.
The bigger 1000µF capacitors on the motherboard (reservoir capacitors, filter capacitors, or whatever one prefers to call them) will hold a charge big enough to supply the whole motherboard with power a few micro seconds or however long it takes for the power supply to react to the change in current that the system is drawing.

Originally Posted by ShK

I have A600's large case sizes PSU, here is list of its original capcitors:

The thread started talking about changing values of the capacitors on the A1200 motherboard, and now we're talking power supplies?
But anyway, I just want to mention quickly that you shouldn't place your electronic equipment on a carpet like that (or whatever it is - it doesn't look like an antistatic mat anyway). An electrostatic discharge can easily damage components. Some of them might be more sensitive to ESD than others, but putting an exposed PCB on a carpet like that is generally not a good idea. You should use a proper antistatic mat instead. Just a bit of advice there.

Originally Posted by Loedown

If your power supply takes 50 mS to come up to stable power on all rails and your reset circuit is set for 30 mS then you will have problems...

It only matters on the 5V rail I think, not all rails. The 5V rail is what is powering the whole system, including the reset circuit and most of the chips on the motherboard. It would probably not even matter the slightest if the +12V rail was getting stable a few milliseconds behind the 5V rail, and I know for a fact that it totally would not matter if the -12V rail was as much as 5 seconds late or even more, because the whole system can run even without the -12V supply. The -12V supply is basically only needed for the RS232 interface and the dual rail supply for the OP amp in the audio circuit.

[Sandro]

Originally Posted by ShK

# Original From PSU Voltage
1 1000μF 10v WHITE -12V
2 1000μF 10v YELLOW Shield
3 1000μF 10v BROWN +12V
4 1μF 35v BLACK 0V/GND
5 1μF 50v RED +5V
6 330μF 35v
7 47μF 385v
8 82μF 35v
9 82μF 35v
10 82μF 35v[/CODE]

only 1 mf for the 5v line ?
the cap No 2 in Shield ???

are you sure this is correct ?

[ShK]

Originally Posted by TomCrazy

[... tons of details ...]

Thank you for your good answer. It was an interesting read.

Originally Posted by TomCrazy

Could you elaborate on this a bit? I'm not quite sure what you mean here.

By stronger power feed I meant that increase the output capacitance will create a bigger energy reservoir in heavy loads.

Originally Posted by TomCrazy

The thread started talking about changing values of the capacitors on the A1200 motherboard, and now we're talking power supplies?

The idea of changing capacitors capacitances started that fact that it is easy to do at the same time when recapping motherboards and psu's (carpet wink ACKED)

Now I understand that it is not easy to do in the right way.

I was originally looking for the best possible capacitors that stays operational condition without active use and do not damage the A1200 motherboard. I asked Tips for that from the Badcaps Forums, but it seems that all the experts are here!

[ShK]

Originally Posted by Sandro

only 1 mf for the 5v line ?
the cap No 2 in Shield ???

are you sure this is correct ?

Oh, I have the hard times to make tables on vBulletin. Wire colors are meant to be in their own list.

[Sandro]

Originally Posted by ShK

Oh, I have the hard times to make tables on vBulletin. Wire colors are meant to be in their own list.

seems interesting,seems the capacitance of -12v line is vital for proper operation in the A1200 that's because it have the bigger and safe cap there
Vital at least for the audio, maybe for video as well

as norm all ATX power supplies in the -12 v rail they have a small cap rated at 330 mf or 470 mf
so if anyone is using ATX power supply must increase the 470mf to 1000mf in the -12 v rail

also seems the power supply have small capacitance in the 5v rail because the capacitance on such rail will be after in the mother board using 2 caps at 1000uf

[ShK]

Originally Posted by Sandro

seems interesting,seems the capacitance of -12v line is vital for proper operation in the A1200 that's because it have the bigger and safe cap there
Vital at least for the audio, maybe for video as well

as norm all ATX power supplies in the -12 v rail they have a small cap rated at 330 mf or 470 mf
so if anyone is using ATX power supply must increase the 470mf to 1000mf in the -12 v rail

also seems the power supply have small capacitance in the 5v rail because the capacitance on such rail will be after in the mother board using 2 caps at 1000uf

I Separated the lists. I hope they are now easier to read. White -12V wire comes near of the cap #10 which is 82μF 35v.

[ShK]

Originally Posted by TomCrazy

That doesn't seem to be an ideal capacitor to me, especially not for this application.
They have written that this capacitor has 1.1 Ohm impedance. I really don't like it when they write like that, because the impedance of a capacitor changes with frequency, so they have to put a frequency in there if they're going to write it like that. Like for example "Impedance: 1.1Ohm @ 100kHz" or whatever. But anyway, I suppose they are talking about the ESR here. And if so, 1.1 Ohm is a very high ESR for filtering applications. That will only lower the filtering capabilities of that capacitor even more!

What is the maximum Equivalent Series Resistance (mOhm) value, which do you recommend generally for the A1200 recapping?

For example, is the Nichicon PW-series good for 'Through Hole' caps and the Nichicon CW-series for SMD caps a good choice? What do you recommend?

[TomCrazy]

@ShK
There is no such thing as a maximum ESR value. The general rule of thumb is simply; The lower the ESR, the better.

An ideal capacitor consists only of capacitance and nothing else. However, there is no such thing as a perfect capacitor. ESR is one of the unwanted properties of electrolytic capacitors. A high ESR will have negative effects on the operation of the capacitor and its lifespan.
Therefore, it's always best to get a capacitor with as low ESR as possible. The lower the better. How important this is depends a lot on the application, but you want to choose a capacitor with low ESR especially for decoupling/filtering/smooting applications.
In most cases, you should have no problems whatsoever finding an electrolytic capacitor with a lower ESR than 100 mOhms. Often you can find capacitors with an ESR of around 50 mOhms or even lower.
Always check the ESR of a capacitor before ordering it.
And try to always choose Japanese branded capacitors. I personally don't trust Chinese capacitors that much, but you can never go wrong if you choose a Japanese brand of capacitors. Check the origin of the capacitor before putting it in your shopping cart when browsing the website you're ordering from.

[Sandro]

yes the low ESR the better
chinese caps are useless the best caps are japanese being rubycon and panasonic the best of the best

nichicon or chemicon are good ones but not the best not even close,some series are really buggy ex chemicon KZG and KZJ series or nichicon HM and HN

[Jope]

Low ESR isn't an end-all golden bullet solution. Use low ESR where they are needed (switch mode PSUs for example) and use high quality regular caps where low ESR is not needed.

And also, unless you have measured the caps to be broken such as the original poster, it is not necessary to swap them every time.

[ShK]

Originally Posted by Jope

Low ESR isn't an end-all golden bullet solution. Use low ESR where they are needed (switch mode PSUs for example) and use high quality regular caps where low ESR is not needed.

And also, unless you have measured the caps to be broken such as the original poster, it is not necessary to swap them every time.

Does ~50mOhms or lower ESR make any problems on the A1200?

What do you mean with the high quality regular caps? Is it a Lifetime @ Temp -values or just using Nichicon and Chemicon brand?