psu.why & how to replace the dreaded capacitors in ATARI ST!

[KLund1]

Excellent page! Well done.
If there was something like that for the other ST's. I'd like to redo my MSTE, STE, falcon, Stacy

[exxos]

Excellent page! Well done.
If there was something like that for the other ST's. I'd like to redo my MSTE, STE, falcon, Stacy

I have a falcon, but since CT60 I have not used the PSU which came with it. The STE PSU is the same as the STFM, just there are many "versions" of the PSU. I did the page with the PSU I saw the most of though my workshop over the years.

[anodyne]

I have a TT that was having intermittent problems booting, and eventually it wouldn't boot at all. Fortunately I had a known-good P/S to swap in, and that showed that the P/S was the problem. As noted many times, on old power supplies, it's typically the electrolytics which go, so I replaced them all. I'm glad to say that everything now works great.

One of the earlier posts here had a very helpful list of capacitor values & numbers which helped me greatly. As a bit of pass-it-on for others contemplating the replacement, I've attached my own PDF with the details of the original capacitors and the replacements I used. I've also provided the Digi-Key part# for folks in North America. Total cost was under $30 including shipping, plus 3-4 hours of my time.

Another probably-viable option is to replace the P/S circuit board. Although the original supply (PSM-5341) is not being made any more, the Phihong company still exists and they have a bare P/S model PSA4541 which provides all the correct voltages and even has compatible mounting holes. It is available from Digi-Key (though not normally stocked). The only real issue is the +5V load, which is spec'd at no more than 5A, whereas the original Atari P/S provides 7A. However, I suspect that there won't be a problem as long as you don't use a really old & power-hungry hard disk. Minor issues include no connector for the fan, but that's simple to fix. I will probably try this option next time I have a TT P/S problem.

[KLund1]

anodyne,
Excellent post. That PDF listing is perfect. If there were addition PDF's for the other Atari models, it should be put as a Sticky, or in the Wiki. Having the order numbers is beyond helpful. Well done!

[rocket-dog]

My STE display looks better! I use a Veiwsonic LCD monitor connectd with a ST to VGA adapter and there always has been vertical lines in the desktop display since I did this. They are now GONE! I can only imagine that the poor power condition contributed to some crashing issues I occasionaly experience..

Seek and you shall find. That's what happening to me. I thought I had video and PSU problems.

(Yes I know it is an old post. Sue me. )

[k2500x]

As I mentioned in this post, I've been having problems with getting a solid image from the VGA cable on my 4mb 1040STe.

After seeing this thread I decided to take a look at my PSU. It's a model ASP34-1. I'll include the picture below.
I'm really no expert at soldering, however I did replace the caps on an external PC sound card and fixed my problem with it. But the caps on the sound card were clearly damaged, where as on this Atari PSU I can't really tell. i.e. they look ok to me.

From what I've visualized, the caps are:
2x 47uf 250v
3x 330uf 35v
1x 4700uf 16v
1x 2200uf 16v
1x 100uf ?v ... it's the really small one at the bottom center.

Do you think this is my problem? I'm from the US so I would be ordering parts from DigiKey. Can anyone help me with a parts list?

[exxos]

http://www.exxoshost.co.uk/atari/last/psu/index.htm

[k2500x]

exxos,

I of course read that web page first, but it's not the same power supply as mine. ASP34-1 Rev6 vs ASP34-2 Rev5.
Yours has somewhat different caps than I what I found on mine. Plus yours is the UK model as you mentioned, but mine is the US.
That's why I posted a photo to see if someone could spot the problem, and do they think it's the cause of my graphics issue?
My PSU doesn't make any "loud ticking sound", and it seems your repair of this PSU didn't seem to make a big difference in the end.


I do have a basic multimeter, but I'm not exactly sure what to test without pulling the caps off the board.

[exxos]

Your PSU is 99% identical. Capacitors I list even for other PSU types are generally the same. USA is of course lower voltage input, but thats not a problem anyway. You can still get a idea of parts needed. There won't be much difference. My PSU wasn't faulty to start with, I just changed the caps to show how to do it, and compare quality of PSU types and see how well they "aged". All the info you need can be found on that page.

[FedePede04]

I don't know if you are in Europe exxos and i don't know if it can be done, maybe you could change it to an European PSU ?

[exxos]

Some of them will run down to 110V, even down to 75V, but I did not make any notes of this. I would just change the caps etc as replacing a old PSU with another old PSU is a bit pointless IMHO.

[FedePede04]

you are right, i did not see that he wrote he was in the US, i only read the the Atari was and US model.
so i thought that maybe it was an US model running in Europa, and thought that it maybe would be easier to change the hole PSU.
so sorry for that I interfere, I just need to learn how to read a little better

[k2500x]

Thanks exxos,
Is there any way of knowing if my PSU caps are the problem, or do I just assume it is because it's so old?
Do I only need to replace the caps, or also the BU508 transistor that you mentioned?

Regarding the caps themselves, is it best to choose the exact match for the cap, or all caps from the same series? For example I'm looking at the Panasonic caps on digikey, and search by uf and volts. I was basically looking for FC series, but sometimes it's only available in FR, EE, FM, or a combination of availability from different series.

Check HERE for the listing.
What kind of Ripple Current and Impedance values I should be using as my cutoff? I see ESR, but nothing is listed there. Any other values I should be considering (>5,000h at 105deg)?

[exxos]

Generally I go for high ripple current and high temps. As you can see there are a lot of series of caps, I had to go though endless pages of caps, not just Panasonic to make my choices. Though generally Panasonic offer the best specs so I don't even bother looking at any other manufactures now. Though Panasonic do make some pretty dire "cheap" caps also. Some caps specs can be worse than the ones already in the PSU, madness for modern stuff really. I do sell those caps in my store anyway. I don't list every kit simple due to they are all basically the same caps, though I have mixed and matched caps for people who need them. If you want to source them yourself, then you will just have to look though them all to find the best specs which are available to you.

[k2500x]

Well I found the ASP34-1 schematic HERE and noticed a few things.

1) The small cap C9 at the bottom of my pic is 100uF 25V
2) Cap C7, C14, C15 on my PSU are 330uF V35 - The schematic shows them as 25V. That should be ok, correct?
3) Cap C17 on my PSU is 2200uF 16V - But the schematic shows it to be 25V. It's my understanding that this could be a problem because it should be 25 volts or higher.

[exxos]

They mostly on the 5V or 12V rail, so anything over 16V is good. The ideal for 12V rial is 25V , but because of physical constraints, its not so easy.

I have updated my page with more PSU's and types http://www.exxoshost.co.uk/atari/last/psu/index.htm

[Fujiyama]

While fixing problems in my Mega STe (see separate thread) someone suggested I also look into recapping my power supply (which seems like a good idea in any case as the machine is probably around 30 years old!) even though my issues seem unrelated I'm sure it won't make things worse if done correctly and using the right parts.

I've opened up my Phihong PSM-5341 rev. 1 (PSM-5341 schematics PDF) power supply so I can measure their physical sizes and confirm their values according the schematics.
Farnell (which I'll be using) sells Panasonic capacitors, but they have a wide range of series -which type is best suited for this task?
UPDATE: I just read "The laST upgrade -part 6 -PSU update" by Exxos, where he suggests Panasonic's FR series, so I'll go for those then.

Also by Exxos, in his "The Last upgrade PSU" page, in the Mega STe PSM-5341 section he lists the replacement parts which differ from the original ones. I can understand using higher voltage/temperature rated ones, but not their capacity values. Are these indeed improvements over the original values (perhaps Atari made a some savings by choosing lower value caps than the ideal, but more expensive ones) and is it safe to do so? Or should I really get the identical (or as close as possible) capacities as the original parts? The article also lists Q1 (MTP6N60) being replaced with an SSP6N60 (600V 6A 1.8R N-MOSFET). Is this also a recommended/necessary replacement when the PSU already appears to be working fine.


I have an STe as well and see two electrolytic caps that go to the power supply connector on the main board. Perhaps their purpose is to further filter the incoming power?
C103 (4700uF/16V)
C107 (100uF/16V)

I see the Mega STe also has a similar capacitor with C227 (470uF/35V).
Is it a smart and necessary move to replace these too with high ripple types (Panasonic FR series)?

The STe will be put inside a different case with multiple hardware add-ons so all along I've been thinking a replacement PC type PSU will be in order but I now see that Exxos sells improved and redesigned ST PSUs, so this might be an option but so far I don't know how much power all the add-ons need.
Unless there's a high risk my STe can be damaged by the original (not recapped) PSU I don't see any reason to spend any money by recapping it. Better spent buying a high quality, new PSU Meanwhile I hope it'll keep going until I figure out which PSU to get.

[Fujiyama]

Which brand/series of capacitors have people here used to replace the 400V ones?

I'm trying to find 10uF/400V and 150uF/400V caps for my Phihong PSM5341 (Mega STe power supply), but searching through Farnell's offerings I can't find anything from Panasonic's FR series (or the lesser good, but still fine FM and FC series) nor Nichicon's HD, HM, HN series or Rubycon's ZL, ZLH, ZLG or ZLJ series. I understand all these are low ESR/high quality types.
Which alternatives could I look into?

UPDATE: I came across a Rubycon BXW-series which is described suitable for power supplies and in Rubycon's online catalog is categorized under "high ripple", "long life (10000-12000 hours) and capable of 105 degrees C. There's no specific ESR rating to be found though.
They have a 150uF/400V in that series, but no 10uF/400V. Will 12uF/400V work equally well?

[dlfrsilver]

check this one in nichicon :

http://www.ebay.fr/itm/UPH2G151MHD-Capa ... SwIjNXJJ-e

next capacitor :

http://www.ebay.fr/itm/10uF-400V-105oC- ... SwdpxUXQg0

[Fujiyama]

Thanks for your suggestion, but I've read numerous warning about buying capacitors off eBay because of all the fakes being sold. I'm not saying all sellers there supply fake ones but you never know, so I want to buy them from a trustworthy dealer instead. I'd rather pay a little more and have peace of mind and not risk having to recap in the near future again..

I'm going to order low-ESR capacitors from Panasonic's FR-series (as Exxos has mentioned he's using in an earlier posting. He specifically mentions the FR-series in "NOTE2:" at the top of this page) with a 10000 hour lifetime and 105 degrees C rating, with the values he suggested for this particular PSU (PSM-5341) I've added the capacitor part no. on the PSU PCB.

400V 120uF - Replacement 150uF 400V (C6)
400V 10uF - Replacement 10uF 400V (C7)
16V 1,000uF x 2 - Replacement 16V 1500uF (C15, C16)
10V 2,200uF - Replacement 16V 4700uF (C14)
16V 4700uF - Replacement 16V 4700uF (C13)
10V 680uF x2 - Replacement 16V 1500uF (C17, C18)
10V 100uF - Replacement 10V 100uF (C19)
22uF 25V - Replacement 10uF 50V (not a typo!) (C23)
3.3uF 50V - Replacement 10uF 50V (C20)
4.7uF 50V - Replacement 10uF 50V (C26)
25V 100uF - Replacement 220uF 50V (needs to be mounted higher due to resistor in way) (C8)
25V 220uF - Replacement 220uF 50V (C24)

Finding 400V caps with the same lifetime rating (10000 hours) as the other capacitors was difficult (marked in red in the above list), but I finally found something suitable. Not 150uF as Exxos has listed above though, but 120uF (the original value).
Exxos, if you're reading: would this cause a problem (interacting with the new replacement values for the other capacitors) or will 120uF/400V (C6) still be fine?

So, to complete the list above, here are the two final capacitors (the ones marked in red above) I'm going to order:

120uF/400V (C6) replacement: 120uF/400V Rubycon BXW-series (12000 hours, 105 degrees C) (C6)
10uF/400V replacement: 10uF/450V Panasonic EE-series (10000 hours, 105 degrees C) (C7)

I've discussed recapping in my Mega STe repair thread as well as there wasn't much response here.

I'm attaching a schematic of the Phihong PSM-5341 below, where I've added the component values (with changed values according to Exxos' new values) in bold.
And here's a BOM of the parts you need to buy (same as the above list, but with the total amount of components of each value).

NOTE: it just occured to me that I haven't included the physical dimensions (height, diameter and pin spacing) which is important in terms of the parts fitting inside or not. Fortunately Anodyne posted an attachement earlier in this thread for his TT power supply (apparently the same PSU used by both the TT and Mega STe) which includes that information.


Bill of materials (BOM) for Phihong PSM-5341 (Mega STe power supply)
1x 150uF/400V normal electrolytic capacitor (C6)
1x 10uF/400V normal electrolytic capacitor (C7)
2x 4700uF/16V low ESR (Panasonic FR-series) electrolytic capacitor (C13, C14)
4x 1500uF/16V low ESR (Panasonic FR-series) electrolytic capacitor (C15, C16, C17, C18)
1x 100uF/10V low ESR (Panasonic FR-series) electrolytic capacitor (C19)
2x 220uF/50V low ESR (Panasonic FR-series) electrolytic capacitor (C8, C24)
3x 10uF/50V low ESR (Panasonic FR-series) electrolytic capacitor (C20, C23, C26)

MSTe-power-supply--new-values.png

[ors0n]

Hi
I'm going to recap my Mitsumi sr98 PSU from 520 STFM. After disassembly, I saw that capacitors are Jamicon SK series (not low-ESR http://yustaltd.ru/wp-content/uploads/2015/05/SK.pdf). I'm wondering, why Atari used that series of caps. What do You think about it?

[dhedberg]

Hi
I'm going to recap my Mitsumi sr98 PSU from 520 STFM. After disassembly, I saw that capacitors are Jamicon SK series (not low-ESR http://yustaltd.ru/wp-content/uploads/2015/05/SK.pdf). I'm wondering, why Atari used that series of caps. What do You think about it?

Most likely for no reasons other than price and availability.

[Greenious]

Hi
I'm going to recap my Mitsumi sr98 PSU from 520 STFM. After disassembly, I saw that capacitors are Jamicon SK series (not low-ESR http://yustaltd.ru/wp-content/uploads/2015/05/SK.pdf). I'm wondering, why Atari used that series of caps. What do You think about it?

Most likely for no reasons other than price and availability.

Could also be because it's not really needed. At low frequencies the difference in powerloss (and heat) between low ESR capacitors and normal ones is neglible. And there is not an advanced high frequency high power switching PSU in the standard ST...

Look at this simple diagram:

dc ripple.jpg

After the power passes through the rectifier, capacitors are used to smooth the dc ripple. To make high power PSU's more compact, you either use smaller caps, and accept a higher ripple. Or... you increase the AC frequency before the rectifier to get a "switching" PSU, that can get away with smaller caps, and maintain or even lower the dc ripple. But as you increase the frequency beyond a few hundred Hz, ESR start to become an issue, since the losses (and heat obviously) inside the caps increases somewhat exponentially with the frequency. At some point low ESR caps becomes a necessity, at an earlier point it's not a bad idea, but at low freqs it's basically just a waste of money.

[ors0n]

Thanks for the replies
I didn't know that general purpose series of capacitors can be used in switched-mode power supply. I currently own Rubycon PK series (http://www.rubycon.co.jp/en/catalog/e_p ... m/e_PK.pdf) and I wonder if this is a good idea to use them instead of Jamicon or buy a new one e.g Panasonic FR series.

[Greenious]

Thanks for the replies
I didn't know that general purpose series of capacitors can be used in switched-mode power supply. I currently own Rubycon PK series (http://www.rubycon.co.jp/en/catalog/e_p ... m/e_PK.pdf) and I wonder if this is a good idea to use them instead of Jamicon or buy a new one e.g Panasonic FR series.

It's not really what I wrote/meant, but low ESR caps are overkill in normal regulated PSU's. (non-switch type)

In switching PSUs, some can probably work with normal caps, but most, if not all, work best with low ESR caps.

The ST/STE is not very power hungry and the PSU used is a normal regulated PSU, ie non-switching.

So your caps should work well in your Mitsumi sr98 PSU in 520 STFM, imho.