Sunny SYS4047-1 Thin Client PSU Repair

[Richard_L]

Hello all,

Here's a write up of an ongoing repair I am engaged in. I've made some good progress so far, but have a few questions at the end...

A few weeks ago, I got lucky while poking around in the skips at the back of a local business that's undergoing refurbishment. They'd just upgraded their IT hardware (not software though, all their new kit looks like it's still running Windows XP!  ) and had thrown out their old thin client PCs.

I asked if I could have them and I was duly allowed to take them.





They're mostly Neoware CA9 thin clients purchased between 2006 and 2009 if you date them according the earliest PAT stickers they had plastered over their sides. Their spec is:

800MHz Via processor
512MB RAM
512MB DOM (Disk On Module - a flash drive plugged directly onto a 44 pin IDE motherboard header.)
3x USB
2x Serial
2x PS2
1x Parallel Port

The spec doesn't look too bad - if you think of them as a step up from a Raspberry Pi, They're both 800MHz, 512MB machines, but the Neoware has the advantages of a built in PSU, i686 architecture and the ability to boot from a proper hard drive connected to a proper hard drive interface.

If you want to know more about thin clients, there is a good site here: http://www.parkytowers.me.uk/thin/

The immediate problem was that they were all dirty and a very lengthy cleaning and de-stickering session followed. It was a case of

"Don't turn it on! Decontaminate it!"

Piles of PAT stickers, asset tracking stickers in triplicate, motivational slogans, the 10 step checklist that employees were supposed to follow before switching the PC on each morning... all had to be removed along with a thick film of dirt and after all that it turned out that they were silver machines, not matte grey! Thankfully though, the thin clients are fanless, so despite all the external muck, the insides weren't bunged up with 8 years worth of fluff and hair.

After cleaning them, I tested them all and discovered that around 50% are either dead or too unreliable to use.

I've started the process of repairing the faulty ones and the culprit is usually a failed power supply.

The power supply they use is a Sunny SYS4047-1 and I believe that a number of other thin clients have used this supply.







NB: The supply shown has already had most of its electrolytic capacitors replaced.

Electrolytic Capacitors

I've been lurking on this forum and watching Dave's videos long enough to know that a common cause of failure is electrolytic capacitors, and the Samxon brand ones fitted to these Sunny power supplies certainly didn't disappoint! Here's the earlier photo of the PSU annotated to show the capacitor designations and values:



If you have one of these power supplies that has failed, then replacing C2 and C3 with new low ESR electrolytics is usually sufficient to get it working again. Additionally, C3 should be encased in heatshrink. I would guess from what I've seen so far that C3 fails first, followed by C2. They don't bulge or burst when they go bad either.

Some of the power supplies have already been repaired by someone. Whoever carried out the repair put their own "Warranty void if removed" sticker over the join between the two halves of the case. Whether this was to hide their awful soldering (it even makes mine look good) or to hide their random choice of replacement caps for C3 and C2, I don't know!

Anyway, I've decided to replace all the electrolytics except for the really big 82uF, 400V one - partly because the big beasts seem to be ageing very well (on average measuring 10% less than their rated capacitance and ESR still looking good) and partly because replacing them would have doubled the cost of the repair.

On the PSUs I've replaced the caps on so far, apart from C2 and C3, the other Samxon caps usually have good ESR but the capacitance tend to be down to around 60-80% of their rated value.

Samxon RS series datasheet. I don't know if RS is different to RS(M) or whether it's the same series and it has just evolved over the years but the RS datasheet is missing a few RS(M) values and values are now in different packages.
http://www.manyue.com/upload/products/standard/39.pdf

I have replaced the capacitors with Panasonic FR or FM series ones.

Panasonic FR datasheet
http://industrial.panasonic.com/www-data/pdf/ABA0000/ABA0000CE132.pdf

Panasonic FM datasheet
http://industrial.panasonic.com/www-data/pdf/ABA0000/ABA0000CE108.pdf

Here's a spreadsheet of the originals and their replacements:
https://684fb26652a022831b44903d657d35e8d8de2f3a.googledrive.com/host/0Byy8KSn1BvppLU02NG9hTllzeEE/PSU_Capacitors.ods (ods format)
https://684fb26652a022831b44903d657d35e8d8de2f3a.googledrive.com/host/0Byy8KSn1BvppLU02NG9hTllzeEE/PSU_Capacitors.xlsx (xlsx format)

In a couple of cases, where space allows, I've been able to increase the voltage rating of the replacement capacitors, including the troublesome C3. The spreadsheet shows where that was possible.

Line Filter Capacitors

In addition replacing the electrolytics, I'd like your opinions on whether it would also be advisable to replace the two X1 rated line filter capacitors, CX1 and CX2. I was getting what I suspected to be nonsense measuring them in-circuit, so each time I've replaced the electrolytics on a supply, I've taken the opportunity to remove, test and return the line filter caps.

But having got nonsense measuring them in-circuit, I've got disappointment from measuring them out-of-circuit!

Both are Chiefcon brand, CKX series, X1 rated, metallized polyester capacitors. Datasheet here:
www.chiefcon.com/download/ckx.pdf

CK1 = 470nF, K/10% tolerance, 15mm lead spacing, LxWxH = 17x11x19
CK2 = 150nF, M/20% tolerance, 10mm lead spacing, LxWxH = 13x6x12

Measured values (nF) for the ones removed & tested so far:
CK1 = 335, 439, 2.1, 464, 119, 259, 225,
CK2 = 8.6, 1.2, 66, 80,  112, 82, 61,

I'm not sure if ESR matters particularly for these but it also varies wildly for the ones tested.

If I am to replace these, I'm having real trouble finding suitable replacements.

Chiefcon sell direct (on Alibaba), but with a MOQ of 1000. That's a few too many for me to buy.
So far, I've not found anything of the same capacitance in the same package from TDK, Panasonic and Vishay. The narrow 15mm and especially the 10mm lead spacing remove most choices even before you've started looking at the LWH dimensions. There's also no room on the board to squeeze larger packages in. They are the two green boxes in this image:





For CX1, I think the best I can find is a 330nF, 20% tolerance cap from TDK, or there are two or three alternatives at 220nF & 10%.
For CX2, I haven't found anything yet.

How low a capacitance can I use for a replacement? From measuring the old ones, it's clear that the power supplies will still work with much lower capacitances, but whether it's any good for the supply, I don't know.

Other Observations

Out of all the places the soldermask could be absent - it has to be between the pads for capacitor C3! In the photo below, look to the left of the silkscreen text "ZD4"



On a number of the boards I've examined so far, there is a L-shaped, partially-routed channel between two pads. Is this a routing error or some sort of carved bodge to achieve the required isolation between two pads?



Other Questions

So far, replacing the electrolytics has usually resurrected a dead supply. But I've now got one or two power supplies that are working but unreliable after the cap replacement, with the PC rebooting at random intervals. Any suggestions about which components to start checking next?

There's an old thread on BadCaps about a similar supply, but between them the respondents have named just about everything else on the board as the problematic component.  http://badcaps.net/forum/showthread.php?s=b4e6a0c7a62aa10dc8beb10e266e9d80&t=6761&page=1

Also, there is no relay on the board so what component is it that makes a very mechanical sounding "click" when the PSU is turned on?

I hope someone may finds my experience with these thin clients helpful now or in the future - it's taken a long time to get this far and my intention of upcycling these machines is turning into something of a labour of love.

thanks,
Richard

P.S. If the images are too large, I'll make them smaller if people complain. I thought they would appear as enlargeable thumbnails but on the preview, they are full size straight away.