Replacing electrolytic caps for the power supply board of a 30-year-old computer

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Hi,

 

Besides playing with AVR microcontrollers, I collect vintage computers.  I have acquired an Atari 1040STF, and I believe the caps on the power board need to be replaced.  Some of them show signs of bulging.  The biggest cap (in size) and in value is 220uF of 200V.  The diameter is nearly the diameter of a US quarter.  Given that this cap is 30 years old, I have found new electrolytic cap in modern time of the same rating (200uF and 200V) but much smaller.   I am wondering if that is OK, as long as the ratings matches.  Are there other things I need to match, besides the ratings (uF and voltage)?

 

Also, there are two caps of 1000uF each but with different voltages, 10V and 16V.  Can I use 1000uF 16V to replace the 1000uF and 10V one?  Should be fine, no?  Even better to have a 16V rating.

 

Many thanks!

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I suspect the Atari power supply is a "classic" power supply, with a transformer, bridge rectifier, caps, and then the regulator circuitry, and not a switching power supply.

 

If that is the case, then matching the uF and voltage rating will be fine.

 

In a switching regulator, and some of the more recent linear regulators, the cap's ESR rating can be important.

I don't think this will be an issue for the Atari.

 

The two 1000 uF caps can both be replaced with the 16 V rating caps, no problem there.

 

Good luck with your project!

 

JC

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DocJC wrote:

I suspect the Atari power supply is a "classic" power supply, with a transformer, bridge rectifier, caps, and then the regulator circuitry, and not a switching power supply.

 

If that is the case, then matching the uF and voltage rating will be fine.

 

In a switching regulator, and some of the more recent linear regulators, the cap's ESR rating can be important.

I don't think this will be an issue for the Atari.

 

The two 1000 uF caps can both be replaced with the 16 V rating caps, no problem there.

 

Good luck with your project!

 

JC

 

Yes, it looks like a ¨classic¨ power supply, as it has all the parts you stated.  Attached is a photo of the power board.  Thanks for response.  I will try to match the ESR rating as well.  Is there a way to identify the ESR on the cap?  Since ESR has to do with resistance, it's likely a very small value.

 

Thanks!

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I don't think ESR will be an issue.

 

That said, the photo shows the Power supply board's model number.

You might be able to find a true schematic and bill of materials, with part numbers, from which you might find the spec's on the caps.

All very doubtful, however.

And I don't think that will be necessary.

 

JC

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DocJC wrote:

I don't think ESR will be an issue.

 

That said, the photo shows the Power supply board's model number.

You might be able to find a true schematic and bill of materials, with part numbers, from which you might find the spec's on the caps.

All very doubtful, however.

And I don't think that will be necessary.

 

JC

 

Thanks again!  Found the schematic from dev-docs.atariforge.org.  Attached is the image.  Unfortunately, it does not tell anything else besides the capacitance and voltage ratings. It should be fine, per your responses.

 

 

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It is a switchmode. Which capacitors were bulging? For the output caps, you want low ESR rated caps. Was the power supply working?

It is not so much the age (in years) of the electro but how much use it had. Switchmode supplies place high demands on electros and they have an operational life. Depending on the quality, rating and operational load, the age varies. At the end of life the ESR degrades, the capacitors get hotter and this causes the bulging.

Last Edited: Sun. Jul 5, 2015 - 10:30 PM
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Is the power supply the same at the one for a MEGA STE ? Then I thing I have some working supply's.

 

If you have the original monitor then there is a cap that have to be changes as well (known problem)  

 

I forgot I think I have a working 1040 (hole without some of the keys), but it's an American version, where are you placed? 

Last Edited: Tue. Jul 7, 2015 - 07:23 AM
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sparrow2 wrote:

Is the power supply the same at the one for a MEGA STE ? Then I thing I have some working supply's.

 

If you have the original monitor then there is a cap that have to be changes as well (known problem)  

 

I forgot I think I have a working 1040 (hole without some of the keys), but it's an American version, where are you placed? 

 

THank you very much, but I am in the USA.  The shipping cost can be a lot.  Yes, my 1040STF is the American/NTSC version.

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No problem in replacing a capacitor rated for 10V with one rated for 16V.

You could check on the Cap if there is a manufacturer and a family name, then you could try to find the exact specifications that way.

 

As you have a SMPS it puts more stress on the capacitors. First as it is constantly charching/discharging. Thus the lower the ESR the better.

But also in temperature. Make sure you get capacitors that are rated for high temperatures. If you need to buy, then I would suggest going for types that can do at least 85C but preferrably higher like 105C