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Old 12 July 2013, 13:02   #1
Loedown
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A500 / A600 / A1200 PSU Tester

The last thing anyone wants to do is plug in their precious Amiga to a bad PSU. I have made a little tester which puts moderate loads onto the + / - 12 volt lines and +5 volt lines

I grabbed a few of the power resistors I have lying around and snagged a power connector off an old A600 scrap board I have here and a 4 pin Molex socket off an old dead PC PSU.

8R2 @ 5W for +5 to GND

66R @ 6W ( 2 x 33R 3W Series ) for +12 to GND

500R @ 1/2W ( 2 x 1K 1/4W Parallel ) for -12 to GND
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Old 12 July 2013, 13:16   #2
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Thanks for the idea, Paul!
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Old 13 July 2013, 11:42   #3
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Ohh sell a kit =)
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Old 13 July 2013, 12:28   #4
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but that doesn't load anything (unless you short out pins in the molex connector)..

also, overvoltage is what usually kills things, which this thing doesn't test..

or am I missing the point of this thing?
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Old 13 July 2013, 16:37   #5
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but that doesn't load anything (unless you short out pins in the molex connector)..

also, overvoltage is what usually kills things, which this thing doesn't test..

or am I missing the point of this thing?
Yes you missed the point, it provides resistances on the three voltage rails to GND, provides modest load on each rail. The Molex connector is just a convenient place to pick up the voltages from as the Molex pins are a good size to put your multimeter probes and if the PSU has gone overvoltage the worst you will do is burn out a 60 cent resistor or the main fuse in the PSU.

610mA on +5 ( 4.3A max)

181mA on +12 ( 1A max )

2.4mA on -12 ( 100mA max )

Not ideal by any means but with what I had lying around. Better values would be;
3.3R 10W for +5 ( 1.51A 7.57W )
18R 10W for +12 ( 667mA 8W )
150R 2W for -12 ( 80mA 0.96W )

The resistors will get hot so keep this in mind when running cabling and use appropriate wire for the current capacity.
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Old 13 July 2013, 18:04   #6
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ahh, of course.. I had a quick glance at the photo and it looks like the resistors are in series with the power rails ;-)
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Old 14 July 2013, 06:48   #7
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Ohh sell a kit =)
A bit hard to do unless someone has a reliable supply of square DIN sockets.
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Old 18 July 2013, 17:53   #8
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http://www.amistore.de/Amiga-Hard-un...eu::28462.html

Dont know if that is reliable or how many they have in stock. My german suck a bit.
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Old 18 July 2013, 22:35   #9
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http://www.amistore.de/Amiga-Hard-un...eu::28462.html

Dont know if that is reliable or how many they have in stock. My german suck a bit.
My German is passable, but how did you get hold of that link? It now gets you to the index page, because it appears thsat they no longer have the A500 version in stock. Did you buy the last one?

However, they do still have the CD32 version!

http://www.amistore.de/Amiga-Hard-un...eu::28463.html
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Old 19 July 2013, 09:53   #10
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Hrmp. The link certainly worked yesterday. They must have run out and removed the link. And no, it wasn't me =)
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Old 19 July 2013, 12:16   #11
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Resistors can be replaced by bulbs (car standardized are preferred).
Nothing can be comparable with something like this http://www.edn.com/design/analog/436...power-supplies

http://www-d0.fnal.gov/hardware/cal/...nfo/curr_load/

http://www.eevblog.com/forum/project...y-load-tester/

http://www.edn.com/design/power-mana...s-as-low-as-2V
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Old 19 July 2013, 13:18   #12
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i had a quick look at the schematic in the third link you posted pady71,the zener at point d1 is shorted by the look of it.(it should of went to ground i think)

i didnt read the comments in thread though to see if anyone noticed it.

using car bulbs is a good idea for low amp supplys for load testing,brake lights are good for this.(its sinple to setup for multiple rails)
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Old 19 July 2013, 14:35   #13
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For low amp - LM317 or similar configured as current source can be used - this is one resistor, one LM317 (and counterparts - LM337, LM350 - or for voltage higher than reference even 7805 etc)

Just set this on decent radiator/heatsink (those from Pentium 4 can be bought as real bargain on ebay and most of them is capable to spread over 100W easily).

http://www.eevblog.com/2010/08/01/ee...ttery-testing/

I mean my earlier links are just example relatively easy, high quality active load can be made if someone is interested in real power supply testing.

http://www.eevblog.com/2010/08/01/ee...ttery-testing/

I mean as a contradictory example - resistor load for PC PSU testing http://techreport.com/review/13271/e...ies-compared/4 - it looks quite odd but works...
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Old 20 July 2013, 05:50   #14
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It was just a quick tester and I have included resistor values for the A500 brick ending in 05.

Bulbs are good because they have a low resistance at start up and increase over time as the filament heats up / lights up.
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Old 12 August 2013, 14:47   #15
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This is what I need!

I tested my nos 1200 psu and I now know the wrong method was used, I had no load on it. The trouble is that means having an amiga connected, if the psu is bad then I will kill things doing so.

Would be brilliant to have a tester in kit form. Heck I would buy one and salvage the square din socket and solder it all myself
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Old 13 August 2013, 09:10   #16
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This is what I need!

I tested my nos 1200 psu and I now know the wrong method was used, I had no load on it. The trouble is that means having an amiga connected, if the psu is bad then I will kill things doing so.

Would be brilliant to have a tester in kit form. Heck I would buy one and salvage the square din socket and solder it all myself
A kit would be dead simple but I know that the circuit boards aren't cheap for starters, if anyone knows of a good place for doing a cheap PCB I will be happy to draw it up and get them made.
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Old 13 August 2013, 09:35   #17
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I found these a while ago, and it seems pretty cheap, although I haven't tried them yet:
http://imall.iteadstudio.com/open-pc...ototyping.html
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Old 13 August 2013, 11:22   #18
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I found these a while ago, and it seems pretty cheap, although I haven't tried them yet:
http://imall.iteadstudio.com/open-pc...ototyping.html
I assume that all new designs need to be ROHS to satisfy the European Union / Northern Hemisphere?

A show of hands, if I get interest from 10 members I'll sort it out.
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Old 13 August 2013, 12:37   #19
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*Hand up*
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Old 13 August 2013, 13:02   #20
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I assume that all new designs need to be ROHS to satisfy the European Union / Northern Hemisphere?

A show of hands, if I get interest from 10 members I'll sort it out.
I don't think ROHS is mandatory for DIY projects. If you were building and selling them, then that's a different story. However, I think all PCB production today is ROHS since most markets require it.
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