exxos's Atari, Amiga & retro forum

Hello guys,

Just to give you a feedback on changing the STe CA4003290 motherboard capacitors.

Qty original new value
11 16V 47 uF 16V 47 uF
6 16V 100 uF 16V 120 uF
2 35V 10 uF 50V 15 uF
4 35V 4,7 uF 50V 6,8 uF
1 35V 470 uF 50V 560 uF (C216)
1 16V 4700 uF 16V 5100 uF (C103)
1 16V 22 uF 25V 68 uF (C102)

...and everything goes well. Of course, following Exxos' advice, I used branded-low ESR capacitorn (mostly Panasonic FR series).
I changed the TV before and after the modification but I have the feeling the image is much more stable. There is no more a micro-waves effects on the screen. You know, the pixels were dancing a little bit. It is now totally stable.

I don't mean what I did is the right way to do it or it is something we should consider, it is just to give you my experience, for people having the same idea. It works !

DocRV

Hi there, any recommendations on where to order those capacitors? Im having problems finding axial low esr items. Thanks!

Except PSU I don't see any point in doing a "preventive recapping" in ST. Caps used in STs do not leak, like ones used in A600/1200, and usually don't short. If there are any stability problems, of course, go for recapping, but if everything is fine, I wouldn't touch the caps. Even if they fail at some time in the future, they are not likely to damage anything else. On the other hand, soldering an old PCB is always a risk, especially if you don't have an experience and right equipment. If not done well, recapping may do more hurt than help. So remember - if it ain't broke, don't fix it

I mostly agree with don't fix things which are not broke. But the caps in the ST series are bad in lots of places.

EG:

Video caps

https://www.exxosforum.co.uk/atari/last/ ... /index.htm

Reset caps

https://www.exxosforum.co.uk/forum/viewt ... =17&t=2175

I can't speak for "all" capacitors as I have not investigated every capacitor on every Atari board. I doubt anyone else has either. But if several are bad on a STFM or STE motherboard, then likely others will be bad also. As to if these will cause problems or not, nobody has done any research into it other than myself, and again I have not researched every capacitor on every board.

The information I publish about changing capacitors is because I personally researched and have had many issues again and again. So then I recommend people change them. The ones in the mandatory fixes I suggest people change them for very good reasons. Of course if you do not have issues then it is really up to the user if they want to change them *all* or not. Unless somebody does a in-depth analysis of every capacitor we will never really know.


EDIT:

Also you have to make sure when buying re-cap kits on the Internet, that these people actually know what they are selling and not just some cheap rubbish. Unfortunately there are a lot of bad capacitors out there which can be even worse than the ones you are taking out. Just because someone sells a capacitor kit does not necessarily mean it is a good. Unless you are buying it from my store of course

@tzok FYI when recapping ST series motherboards I regularly test the old caps and find they have very high ESR over 1 ohm and a voltage drop over 1v, which is absolutely horrendous. So I wouldn't just make the probability of failure or leakage as the only reason to want to re-cap a vintage machine. Better caps will protect the components/ICs by providing better/cleaner voltage. It also makes the video and sound output cleaner.

@Steve - what do you mean by capacitors having a voltage drop of over 1V? In what period of time? Not all capacitors in the ST board need to be low ESR, and 1 Ohm ESR, even for a Low ESR 4.7uF capacitor is perfectly fine. Correct ESR depends on the nominal capacity and voltage of the capacitor. ESR is not the only important parameter, and is not always an important parameter. Another equally critical parameter is leakage current, at nominal (or working) voltage or, in other words, parallel resistance.

I only meant that most of the ST electrolytic capacitors (except ones in the PSU) are non-critical. Of course, I didn't mean they can't make the computer unstable or inoperative, but rather that their eventual failure is unlikely to cause failures in other components. So it doesn't matter if you replace them prior to their failure, or after. Capacitors in the PSU are likely to cause serious harm to other components, so their "preventive" replacement is highly recommended. When they fail, it may be too late to replace just them.

I also want to warn less experienced repairers - if you just got your ST, and don't know the conditions it was stored in, don't try to solder the board straight away, especially helping yourself with a hot air. You have to make sure the PCB is dry first. It can absorb moisture from air, and when rapidly heated, moisture can change into steam and delaminate PCB layers.

tzok wrote: ↑Sat Nov 13, 2021 1:57 pm I also want to warn less experienced repairers - if you just got your ST, and don't know the conditions it was stored in, don't try to solder the board straight away, especially helping yourself with a hot air. You have to make sure the PCB is dry first. It can absorb moisture from air, and when rapidly heated, moisture can change into steam and delaminate PCB layers.

Noted, it looks like the same as handle a classical guitar, that is sensitive to humidity in the air too...

tzok wrote: ↑Sat Nov 13, 2021 1:57 pm I also want to warn less experienced repairers - if you just got your ST, and don't know the conditions it was stored in, don't try to solder the board straight away, especially helping yourself with a hot air. You have to make sure the PCB is dry first. It can absorb moisture from air, and when rapidly heated, moisture can change into steam and delaminate PCB layers.

Hi, what he means is that the caps are dead. I have serviced quite a number of STF, STE, and also my Falcon 030, and the caps were tested are simply giving bad results.

In most STs, the capacitors were not good quality for a start. Atari never meant their computers to be used 20 years later after their release.

So instead of having strange behavior or imprevisible problems happening when you don't want them to, replacing the PSU caps and the caps on the motherboard is simply doing good to the computer.

My personal notice is that the caps in the PSUs are bleeding (leaking), and on the motherboard they dry !.

And at least if you don't replace most caps on the motherboard, replace at least the 2 big ones.

Ah and i forgot the best : on all machines, ST, Amiga, PC engine or whatever, once replaced, the machines are more stable, and the display is better than it was with the old dead caps.

I'm a firm believer in preventative maintainence and looking after stuff.

As I said before. You can drive a car for years on the same oil. At what point do you change it ? When the exhaust is bellowing out smoke ? When the engine totally fails ? The engine may not show any signs of apparent issues, are you qualified to make such a assumption ? but it's slowly killing your engine leading to an early fail. Some engines may run for 30 years on the same oil. How well is another matter. If it gets you from A to B then who cares how the thing runs ?

But it's really down to the individual. If you want stuff to run as best it can and last as long as it can, then look after the stuff. If you don't care about such things and just run until something blows up beyond repair, then it's your choice.

If people think they don't need to recap, then fair enough, your choice to do what the heck you like. In which case this forum probably isn't "for you".

Well, to a degree it's all about what you feel is the bigger risk.

With power supplies there's no real argument as not only failure could mean a fried machine but because the PCB itself is robust there's little risk of damage from replacing the capacitors.

On the main board, however, it's not as clear cut. What's the higher risk? Desoldering the original capacitors, manhandling and flexing the PCB, possibly breaking tracks, or leaving the dried out capacitors, which aren't in spec. but probably won't do anything terrible in the long term other than a bit of instability.

Myself, I err on the side of leaving it alone unless there's an obvious problem. However, that's purely my assessment of the balance of risk and others will have the opposite view, which is fine.