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Matt123
Posted: Thu Oct 06, 2011 3:06 am Reply with quote
Joined: 10 Feb 2007 Posts: 15 Location: Near Brighton
Hello, I have a slightly different PSU question about the TF5800pvrt.
Does anyone think I can pull an additional constant 8W from the 5V rail?.
Looking at the diagram - http://www.members.optusnet.com.au/toppytools/pwrcircuit.html - is appears like it might be able to ?
But I dont know what the coils can handle. And the ka1m0680rb might have to be replaced with something a little beefier because of the 4Amp limit.

I was thinking I will replace all the caps with Tantalum type caps, and putting a tiny fan in there (via a basic themo-resister, so the fan is not running all the time)

I would like to avoid using another 5v supply and try to use the built in PSU for a bad idea I have.

Matt
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mstombs
Posted: Thu Oct 06, 2011 9:43 am Reply with quote
Frequent contributor Joined: 31 Dec 2006 Posts: 938
Going to mount an nslu2 inside the box?

Do you mean solid polymer caps? These are used as marketing by graphics card and motherboard manufacturers to distance them from the industry failure in the use of cheap electrolytics - but from when I last looked they are smaller sizes lower voltages than needed by Toppy psu and the claims about improved life do not make it through to the spec lifetime - i.e. 2000 hrs @105 vs 8,000-10,000 on the better Rubycon/Panasonic good quality electrolytics.

Why don't you just try? And sure keeping all cool would improve life but one of the selling points of a toppy was lack of fan noise!
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andyfras
Posted: Thu Oct 06, 2011 9:50 am Reply with quote
Frequent contributor Joined: 25 Jul 2005 Posts: 3470
Check D10. On earlier PSUs it was MBRF760; on later ones it's MBRF1060 which gives it 3 more Amps capability. This enables the use of a higher capacitance for C22, which would be useful in your case. 'Facelift' Toppies use 2200uF @ 10V in this position (note that 16V is not necessary, as it's the 5V rail).

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alan_m
Posted: Thu Oct 06, 2011 11:19 am Reply with quote
Frequent contributor Joined: 18 Oct 2006 Posts: 3524
Matt123 wrote:
Hello, I have a slightly different PSU question about the TF5800pvrt.
Does anyone think I can pull an additional constant 8W from the 5V rail?.
Looking at the diagram - http://www.members.optusnet.com.au/toppytools/pwrcircuit.html - is appears like it might be able to ?
But I dont know what the coils can handle. And the ka1m0680rb might have to be replaced with something a little beefier because of the 4Amp limit.

I was thinking I will replace all the caps with Tantalum type caps, and putting a tiny fan in there (via a basic themo-resister, so the fan is not running all the time)

I would like to avoid using another 5v supply and try to use the built in PSU for a bad idea I have.

Matt


One thing to watch is that the 5V is used for a reference for all the other supplies and one of the common PSU failings is that 5V going low causes the others to go extremely high. If your extra 8W of loading causes the 5V to drop even by a relatively small amount this could stress other bits of the system.

Is 8W the maximum power after switch on or is the switch on power requirement greater? A peripheral taking a greater surge power at switch on may result in the Toppy's PSU not starting up correctly.

Why not experiment with a few resistors connected to the 5V line and measuring the resultant voltage? Start with a value that takes 3W then 6W, and then 9W.

You may need to check with something better than a cheap multimeter. You should check that the output is substantially DC with an oscilloscope when fully loaded. The multimeter may report 5V but the high frequency "ripple" on a heavily loaded supply may cause picture quality problems. As the other voltages are dependent on the 5V it may be wise to check them all in the same way, before and after.

You may consider taking up the values of the 1000uF capacitors to 1200uF, or possibly higher.

A constantly slow running (1000rpm) 80mm fan on the main board side of the box will take around 1W and in a quiet room you will be unlikely to hear it a couple feet away from the box. This knocks off around 10 to 15C in the box. This type of arrangement may be better than a badly designed control loop for a temperature controlled fan. I doubt if you will get any non active fan control to work well.

One of the main considerations with the power supply capacitors is a very low ESR (Equivalent Series Resistance) figure. The lower the better, especially if you want to take more power from the rail. Comparing the specs for the recommended capacitors and those for the (probably expensive) military specification Vishay 1200uF low ESR wet dielectric tantalum, the tantalum comes out better on temperature (125C) but the Panasonic has a much better ESR, by a factor of 8. You wouldn't be running your box at 125C so life expectancy is around the same.

What is the failure mechanism of a tantalum? In the distant past, when I repaired test equipment for a living, certain types of tantalum capacitors always failed short circuit, but this may not be true with the capacitors you are considering. Toppy's with PSU problems can be rescued in almost 100% of cases because the capacitor technology used doesn't fail short circuit.

Probably not worth the risk changing types.

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Matt123
Posted: Thu Oct 06, 2011 7:07 pm Reply with quote
Joined: 10 Feb 2007 Posts: 15 Location: Near Brighton
mstombs wrote:
Going to mount an nslu2 inside the box?
Exactly!, I'm going to try to turn it into a Media Server / DLNA-ish Server for a TV. I've bid on one on ebay and I hope I win it.


Cheers guys for all the info. It appears like my PSU was made in June 2006. I have no idea if the 'SC-0623C' transformer can handle it because I can not find a datasheet. So I'm going to take a risk and assume it will.


andyfras wrote:
Check D10. ... on later ones it's MBRF1060 which gives it 3 more Amps capability
Thanks for that tip, I think I'll do that in case it fries. Just in case I the 3v.


alan_m wrote:
"ripple" on a heavily loaded supply may cause picture quality problems
Thanks I'll check for that, I can see there is basicly no ripple on the 5v rail in the toppys current state. It looks like blip of 0.05v every 10us or so... But the 12v line is really messy (I assume you can guess why!), so I'll avoid using that voltage!
I'll check the riplle when I put the extra board in it.


I'll get some low ESR Rubycon/Panasonic caps to replace them with. It sounds better then my Tantalum type idea !
I see the stb used about 24w when its idle and upto 37w when the HD powers up.
Hopefully this '10 pound project' wont go over budget Smile

I'll post a responce when I get the NAS server and replace the caps, but it might be a while?
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alan_m
Posted: Thu Oct 06, 2011 11:10 pm Reply with quote
Frequent contributor Joined: 18 Oct 2006 Posts: 3524
Matt123 wrote:

I'll get some low ESR Rubycon/Panasonic caps to replace them with.


Andy (see his reply above) does a kit of higher quality capacitors for DIY repair and possibly may be able to supply a one off of other PSU components thus avoiding any minimum order charges with some of the reputable main electronic suppliers. To contact him hit the PM (Personal Message) button just below the signature in his posts.

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mstombs
Posted: Fri Oct 07, 2011 9:40 am Reply with quote
Frequent contributor Joined: 31 Dec 2006 Posts: 938
The nslu2 comes with a 5V2A psu that also fails due to poor electrolytic caps. Toppy destined 16V 1000uF work but are a tight fit and probably not worth the effort of surgical disassembly/reassembly required. What about the power supply to nslu2 attached usb disk? You need one to 'unsling' and serve files from, otherwise the slow usb transfer will hold you back.

The psu to my WD-500Gb also failed due bad caps (same cap worked) but I'm using the warranty replacement psu due to concerns over the future accident/insurance report about the fire behind the tv that seems to been started in an apparently repaired psu held together with cable ties...

Just used another of my Rubycon 1000uFs to temporarily fix a 2.5 year graphics card that had a failed 1500uF electrolytic (fz85 1500 6.3v).

I used to think there's nothings good about electrolytics, but now realise that they are not only cheap - they do tend to fail open circuit which allows me to fix them!

My only experience with Tantulum is the small bead type that look like match heads - they actually work reverse polarity for a while before they ignite and 'let the magic smoke out'.
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alan_m
Posted: Fri Oct 07, 2011 11:27 am Reply with quote
Frequent contributor Joined: 18 Oct 2006 Posts: 3524
mstombs wrote:

My only experience with Tantulum is the small bead type that look like match heads - they actually work reverse polarity for a while before they ignite and 'let the magic smoke out'.


I've seen them glowing red before the magic smoke emerged with a loud bang.

I once worked for short time for a valve amplifier manufacturer (Sound City) and the assembled chassis were powered on after manufacture for a few hours soak test. On one amp a capacitor of diameter 1.5 inches x 6 inches long had been incorrectly connected. The capacitor can hit the 30 ft factory roof when it decided to explode. At least these days they incorporate weak points in the can so that they tend to rupture before violently exploding

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Bizman
Posted: Fri Oct 07, 2011 12:02 pm Reply with quote
Frequent contributor Joined: 06 Apr 2010 Posts: 1707
Getting off topic, years ago I remember the dull thud of an electrolytic capacitor blowing. On raising the chassis to see what had happened, white smoke appeared which, when cleared, revealed the entire wiring had been coated with aluminium shorting out everything else. Embarassed

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Matt123
Posted: Thu Dec 22, 2011 2:30 pm Reply with quote
Joined: 10 Feb 2007 Posts: 15 Location: Near Brighton
Hello, I just thought I'll mention the conclusion of it. I install the board in the Toppy, added a slow fan, even extended the 5v diode heat sink. BUT it ******* caused interference on the aerial out. It caused a small faint pattern of red lines across the screen.
All that work for nothing! oh well lesson learnt.
Heres a picture of the inners if you are curious.
http://i41.tinypic.com/95y0sk.jpg
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