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Old 18 November 2014, 03:15   #1
dlfrsilver
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Amiga 500 PSU ref P.312503-03 singapore (Heavy PSU)

**** WARNING !!! *******

This model of PSU is more dangerous than the light A500 PSU and the A600/1200 PSU. For a simple reason : the electronic board is not spanned FLAT inside the PSU, but on its SIDE !

Any wrong manipulation could lead you to touch dangerous parts, so this means that you need to put the internal PSU board on a wood table FLAT !

There are only 6 capacitors to remove (that's the best part)

Tools needed :
--------------
- 'Current Protected' screwdriver (i use FACOM ones which support up to 1000V, so the 47 uF 400V capacitor won't do me any harm, as well as the other parts which could be charged).

* NEVER EVER TRY TO PROCEED IF YOU DON'T HAVE A PROTECTED TOOL/DEVICE TO DISCHARGE THE CAPACITORS ON THE MAINS, OTHERWISE IF YOU TOUCH A CHARGED PART, AND THAT THE CURRENT PULSE GET IN SYNC WITH YOUR HEART BEAT, YOU'RE DEAD AND I'M NOT KIDDING ! *

Capacitors list :
---------------

- 2x 2200UF 40V (replacement Panasonic EEUFC1H222 , 2200uF 50V)
- 1x 330UF 50V (replacement Panasonic EEUFR1H331L)
- 1x 330UF 25V (replacement Panasonic EEUFM1E331)
- 1x 470UF 16V (replacement Panasonic EEUFC1C471L)
- 1x to determine (small one)

1) Be sure that the PSU is not connected to the main /!\ /!\ and also that the PSU was not connected since 24H.

2) unscrew the 4 screws underneath it

3) press the power switch like if you wanted to switch on your amiga, this will help to discharge the big capacitor

4) Use the current protected screwdriver and pass it on the (+) and (-) poles of the big capacitors solder side.

5) prepare your solder station and use 400°C temperature for the iron

6) Pick your usual electronic-fluxed tin and use it if the solder points of the capacitors are reluctants to be desoldered

7) remove them one by one, and respect the polarity (!) to avoid any explosion, smoke, whatever

8) put back the plastic cover and the 4 screws

9) Time to test !
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Old 18 November 2014, 09:27   #2
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Did you measure the old caps with an ESR meter?
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Old 18 November 2014, 13:05   #3
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Nope, i have not checked them for a simple reason, the capacitors are just WAY too old, and must be replaced ; 30 years is beyond their time life.
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Old 18 November 2014, 16:44   #4
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I disagree to some extent. What a waste of time if they are still ok and will be ok for many more years. That early 2000s stolen electrolyte formula problem seemed to make all caps ticking time bombs. :-)
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Old 18 November 2014, 18:38   #5
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that's true, when i was working for Total in 2001-2003, i had to swap motherboards from my users IBM PC's : lifted or exploded capacitors, so bad that they never lasted more than 6 months....
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Old 18 November 2014, 22:17   #6
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I leave them alone unless they're the time bomb SMD ones or obviously cheap... but when it comes to a PSU I'd rather err on the side of new ones. (Or at least open it up and have a peek at what's there.)

Ofc there's always the slim possibility of replacing a serviceable original one with a dud new one, so I suppose an ESR meter is a good thing to have handy.
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Old 18 November 2014, 23:14   #7
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Hi dlfrsilver, thanks for your great tests Your experiments come just at the right time - my A500 PSU died last weekend and it's the exact same PSU that you have - 312503-03 made in Singapore.

The problem with my PSU is that the -12V line is dead, it only gives -1V. What do you think - would re-capping cure this? Or might there be something else broken?

Just by looking at the capacitors, all of them still seem to be okay No leaking, no dull solder joints, etc. Any hint / tip is welcome!
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Old 19 November 2014, 01:26   #8
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please post a picture of the inside of your PSU
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Old 19 November 2014, 22:56   #9
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Quote:
Originally Posted by dlfrsilver View Post
please post a picture of the inside of your PSU
Yep, will do. But I cannot work on my Amiga gear until Friday... Will post some pictures then
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Old 21 November 2014, 18:51   #10
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Yay, found the problem The voltage regulator that creates the -12V has had it.

The -1V I was measuring before was only my voltage meter going beyond scale In reality, it was around -21V, which is exactly the input voltage for the voltage regulator. I only noticed it after adjusting the scale. Since there are quite a few voltage regulators on the PCB, I wasn't sure which one to check, but following the trace from the -12V line was quite easy actually. I now ordered a spare part and will post how things work out

Nevertheless, here are a few pictures of the inside of my A500 PSU (312503-03):

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As you can see, the big capacitors really look nice - even after >25 years
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Old 21 November 2014, 19:43   #11
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Quote:
Originally Posted by amigasith View Post
Yay, found the problem The voltage regulator that creates the -12V has had it.

The -1V I was measuring before was only my voltage meter going beyond scale In reality, it was around -21V, which is exactly the input voltage for the voltage regulator. I only noticed it after adjusting the scale. Since there are quite a few voltage regulators on the PCB, I wasn't sure which one to check, but following the trace from the -12V line was quite easy actually. I now ordered a spare part and will post how things work out

As you can see, the big capacitors really look nice - even after >25 years
No capacitors were made to last 25 years. They must be replaced, and sorry to say it, but i have replaced capacitors even in my Atari STs, and they were in good exterior aspect, but once disoldered, there was leaking underneath them, meaning they're dead !!

So replacing them is the right thing to do
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Old 02 December 2014, 22:35   #12
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I desoldered one of the smaller capacitors in order to get room for replacing one of the potentiometers, and there was no leaking underneath it at all. Also there seems to be no leaking underneath the large ones either. For the time being, I will leave them alone. Let's see how things look like in another 25 years

Anyway, I just wanted to report back that I replaced the -12V voltage regulator and now my PSU works again like a charm I had the Amiga 500 running for almost 12 hours and it worked without any issues at all.

There are quite a few voltage regulators in this PSU and I really don't know why the -12V one died first. The only thing that caught my attention was that the aluminium cooler for the -12V voltage regulator is much smaller compared to the others. The reason for this is probably that there is only very little room left where the voltage regulator is placed on the PCB. I added an additional thin aluminium plate so that it gets cooled better than before, and I hope that this will make it last longer.

Here is how it looks like now:

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Old 02 December 2014, 22:40   #13
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It's probably not about space, just that normally very little current is drawn on the -12V line. Only a few components on the motherboard need that voltage. But extra cooling can't hurt
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Old 27 August 2015, 00:22   #14
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Ok guys, i have finally changed the capacitors in this model of PSU i own, and the result is great ! both my A1200 and A500 love it again !

PS 2 : I have also fully recapped my german A500 with superior quality capacitors (nichicon !) and wow, both sound and display are like when i remembered back in the day !

And the best :

- Since the capacitors replacement, the PSU is no more heating !

- The colors on the screen have never been so good.

Guys it's time for recapping !

Last edited by dlfrsilver; 27 August 2015 at 19:19.
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Old 27 August 2015, 19:18   #15
dlfrsilver
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Cosmos is back folks, he is now an entrepreneur, and he is selling kits for PSUs, as well as Amigas.

http://www.ebay.fr/sch/cosmosunivers...p2047675.l2562

Here is his main page.

One thing, before buying capacitors for PSU or computers, check carefully your motherboard revision, and your exact PSU model (check the images, in order to be sure between 3 same models that it match your model).

The capacitors are superior quality Nichicon.
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