Replacing PSU capacitors

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wyerd
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Replacing PSU capacitors

Postby wyerd » Fri Mar 27, 2015 1:33 am

I have a 110v PSU that I'd like to install in my STE which currently has a working 240v PSU as I now live in the USA and I'd like to stop using the step up transformer. The 110v PSU doesn't work as I've tested the output, but I suspect this is down to the old capacitors and at least one of them has a bulging top (8). I've looked at Exxos's website and what are the recommended replacements, but the values on my PSU are different and I'd like to make sure I replace them with the correct ones. Here's a photo of the PSU. I've number the capacitors and listed their values:-

Image

1,8 - 250v 47mF
2,5,6 - 35v 330mF
3 - 25v 100mF
4,7 - 16v 4700mF

Should I be looking at replacing the ceramic capacitors as well?

Lastly, where is the best place to order electronic parts mail order in the US?

Thanks for any advice,
Dave.

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Re: Replacing PSU capacitors

Postby 1024MAK » Fri Mar 27, 2015 3:57 am

The unit "mF" is not used in modern electronics (and yes, the Atari ST PSU is considered modern in this context!)
Electrolytic capacitors are normally specified in micro farads, using the micro "µ" symbol, hence 47µF. Where the µ symbol is not available, a "u" is used instead ( so 47uF).

If you look carefully on the printed circuit board (PCB) next to the capacitors, you will see the reference number of the component.
Capacitors on boards designed by English speakers have the prefix "C" followed by a number.

So in the bottom left of your picture, the capacitor you have called "8" has a reference "C5".

In the vast majority of cases (99%), the ceramic capacitors do not need replacing (unless of course you can see damage).

All the capacitors on the output side (all the ones rated at less that 50V) should be low ESR types (ESR means Equivalent Series Resistance).

It is also a good idea to buy quality types with a temperature rating of 105°C (they last longer).

The replacements do not have to have exactly the same ratings as the old ones. The voltage rating should be equal or greater than that of the original.
The capacitance value (in µF) should be equal or greater than that of the original.

330µF are not very common. So use 470µF instead.

There are various electronic suppliers. I will leave any recommendation to someone who lives that side of the world.

Mark
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Re: Replacing PSU capacitors

Postby exxos » Fri Mar 27, 2015 9:41 am

I do sell caps & upgrade kits in my store, I can mix and match what is needed. I also list a lot of capacitor values and upgrade ideas on my website http://www.exxoshost.co.uk/atari/last/psu/index.htm If you want to obtain parts yourself.
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http://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
http://www.exxoshost.co.uk/atari/last/storenew/ - All my hardware mods for sale - Please help support by making a purchase.
http://ataristeven.exxoshost.co.uk/Steem.htm Latest Steem Emulator

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Re: Replacing PSU capacitors

Postby Hippy Dave » Fri Mar 27, 2015 5:10 pm

You can conveniently purchase electronics parts in North America from Digikey, Mouser, and Newark.
http://www.digikey.com/
Use your credit card over the phone and have the parts arrive at your door the next day.

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Re: Replacing PSU capacitors

Postby wyerd » Sat Mar 28, 2015 1:11 am

The Pico PSU is a great idea. I'll have to look into it further. I've done something similar with my TI-99/4A's Peripheral Expansion Box as it had a faulty PSU and I replaced it with an AT PSU for $20. http://atariage.com/forums/topic/234391-how-to-replace-peb-psu-with-new-atlpx-psu/

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Re: Replacing PSU capacitors

Postby wyerd » Sat Mar 28, 2015 1:12 am

Hippy Dave wrote:You can conveniently purchase electronics parts in North America from Digikey, Mouser, and Newark.
http://www.digikey.com/
Use your credit card over the phone and have the parts arrive at your door the next day.


Thanks Dave.

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Re: Replacing PSU capacitors

Postby 1024MAK » Sat Mar 28, 2015 10:55 am

@ Dave - it may be possible to repair your power supply unit (PSU).

It comes down to two things - time and money. The quickest repair is to replace the PSU with a known good working PSU. Either an original or with another type. Some Atari folk will even give you a discount if you exchange your defective PSU at the time you buy a replacement. Or instead they can repair yours for a price.

If you have the time and are interested in learning about electronics, repairing your PSU can be cheaper if you are successful and your efforts result in a working PSU.

During the repair process you can connect the PSU to a "dummy load" so there is no danger to any Atari ST main board.

The original bridge rectifier is suitably rated for this application (see datasheet) but as with all components connected to the mains supply, can be damaged by over-voltage spikes on the mains supply.

If the power supply was that bad, my original STFM would not have survived being left on for weeks at a time...

Electrolytic capacitors do degrade over time, and the hotter environment (for them), the quicker they degrade. This is a known limitation of this type of capacitor. So with all switch moe power supply repairs the first step is to connect it to a test load to see what happens. Do some voltage checks (beware of the mains voltage and the up to 340V dc voltage on the high voltage circuits) then after the existing capacitors have discharged (or been discharged) replace ALL the electrolytic capacitors. Check all the solder joints on all the components for dry joints. Resolder as required, then test using the "dummy load" :wink:.

Mark
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Visit the Atari-Forum Wiki. Lots of technical info at DrCoolZic Atari ST Site :D

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Re: Replacing PSU capacitors

Postby wyerd » Sat Mar 28, 2015 11:46 pm

I've had another look at the PSU and the PCB does look darker in the middle area and indicates that it has been subjected to long periods of heat.
Image
Image
Replacing just the capacitors may resolve the issues, but it's a gamble that I'm not willing to take as I don't have the facilities to test it out on another load, or the experience. Fiddling around with a mains voltage device could cause a disaster for a novice like me. It's not that I'm not willing to learn, it's that I know that you have to respect electricity, especially mains voltage.

The Pico PSU idea is definitely the solution that I'm going with. It's an up to date device and it's not mains voltage. Plus it's more stable than the old Atari PSU's and it has the added advantage of expandability as it has molex and sata power connectors. Ideal as I now have Alan's IDE board installed.

Out of interest, I've emailed Best for a price and asked if they're NOS or refurbished as it'll be interesting to know.

Thanks for all your Mark and Exxos. It's interesting to hear everyone's point of view!

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Re: Replacing PSU capacitors

Postby wyerd » Sat Mar 28, 2015 11:53 pm

Mark - the PSU capacitors do have the µ symbol. I used mF as I wasn't sure how to find it on the keyboard - I just cut and pasted yours!

I just need a 110v PSU for my Memotech MTX now......

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Re: Replacing PSU capacitors

Postby 1024MAK » Sun Mar 29, 2015 1:06 am

wyerd wrote:I just need a 110v PSU for my Memotech MTX now......
Well, that is possible. If you are a member of Memorum, in April (I hope) I will be posting more details of my design of a replacement. The only difference for 110V / 120V operation is the transformer :wink: .

Mark
Falcon, Atari 520ST, 520STFM, 1040STE, Mega, TT and more PC's than I care to count and an assortment of 8 bit micros (nearly forgot the Psion's).
Visit the Atari-Forum Wiki. Lots of technical info at DrCoolZic Atari ST Site :D

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Re: Replacing PSU capacitors

Postby wyerd » Sun Mar 29, 2015 1:27 am

1024MAK wrote:
wyerd wrote:I just need a 110v PSU for my Memotech MTX now......
Well, that is possible. If you are a member of Memorum, in April (I hope) I will be posting more details of my design of a replacement. The only difference for 110V / 120V operation is the transformer :wink: .

Mark

Great. Yes, I'm subscribed. I look forward to your announcement.

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Re: Replacing PSU capacitors

Postby troed » Sun Mar 29, 2015 6:54 am

wyerd wrote:The Pico PSU idea is definitely the solution that I'm going with. It's an up to date device and it's not mains voltage. Plus it's more stable than the old Atari PSU's and it has the added advantage of expandability as it has molex and sata power connectors. Ideal as I now have Alan's IDE board installed.


Here's a description with pictures from when I did a picoPSU mod:

http://blog.troed.se/projects/atari-st- ... placement/

/Troed

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Re: Replacing PSU capacitors

Postby wyerd » Mon Mar 30, 2015 8:17 pm

troed wrote:
wyerd wrote:The Pico PSU idea is definitely the solution that I'm going with. It's an up to date device and it's not mains voltage. Plus it's more stable than the old Atari PSU's and it has the added advantage of expandability as it has molex and sata power connectors. Ideal as I now have Alan's IDE board installed.


Here's a description with pictures from when I did a picoPSU mod:

http://blog.troed.se/projects/atari-st- ... placement/

/Troed

Yes, I saw it when I was researching the idea. Very good write-up.

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Re: Replacing PSU capacitors

Postby wyerd » Thu Apr 16, 2015 6:36 pm

FYI replacement Atari 110v PSU from Best Electronics quote is in from Bradley

1 New Atari 1040ST Internal Power Supply U$D 75.00 (standard Atari 90 day Warranty)
Shipping to 12824 U$D 11.55
Insurance U$D 2.60
-----------------
Total U$D 89.15

Pico PSU is the way to go.......!!

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Re: Replacing PSU capacitors

Postby exxos » Thu Apr 16, 2015 6:52 pm

wyerd wrote:FYI replacement Atari 110v PSU from Best Electronics quote is in from Bradley

1 New Atari 1040ST Internal Power Supply U$D 75.00 (standard Atari 90 day Warranty)
Shipping to 12824 U$D 11.55
Insurance U$D 2.60
-----------------
Total U$D 89.15

Pico PSU is the way to go.......!!


8O Madness. Could buy a used one and mod it with new parts for half that price.

I do have it in mind to build my own PSU. I'm not a fan of the pico stuff personally.

Some Atari PSU's I have seen marked as 250V actually say 75V - 250V on the back. So assume they will work on 110V or 240V. I don't know offhand which ones they were, I never made a note of it.
4MB STFM 1.44 FD- VELOCE+ 020 STE - Falcon 030 CT60 - Atari 2600 - Atari 7800 - Gigafile - SD Floppy Emulator - PeST - various clutter

http://www.exxoshost.co.uk/atari/ All my hardware guides - mods - games - STOS
http://www.exxoshost.co.uk/atari/last/storenew/ - All my hardware mods for sale - Please help support by making a purchase.
http://ataristeven.exxoshost.co.uk/Steem.htm Latest Steem Emulator

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Re: Replacing PSU capacitors

Postby pedro » Fri Apr 17, 2015 10:16 pm

wyerd, although I’d suggest that you replace the capacitors yourself but seeing the condition of this PSU, taking it a local electronics repair guy is probably your best bet. Since there could be some other issues in this board besides the capacitor as well, some with exhaustive knowledge of PSUs could probably figure that out and change the right components for you.


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