Amiga 500 PSU ref P.312503-03 singapore (Heavy PSU)

[dlfrsilver]

**** 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 !

[Jope]

Did you measure the old caps with an ESR meter?

[dlfrsilver]

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.

[Jope]

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. :-)

[dlfrsilver]

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....

[Damion]

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.

[amigasith]

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!

[dlfrsilver]

please post a picture of the inside of your PSU

[amigasith]

Originally Posted by dlfrsilver

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

[amigasith]

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):







As you can see, the big capacitors really look nice - even after >25 years

[dlfrsilver]

Originally Posted by amigasith

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

[amigasith]

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:

[ajk]

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

[dlfrsilver]

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 !

[dlfrsilver]

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.

[e5frog]

Not sure about the policy here, continue a subject in old thread or start a new one on the same subject?
I chose to continue.

Had used an Amiga-PSU for other stuff, just sold my A600 and with it the "everyday" switched A600 PSU. When now restoring the heavy Amiga 500 312503-03 I thought I'd swap caps.

Not sure if the late 80's Marcon and Necon brands are still any good but for such an important detail it's worth spending a few dollars to keep the other end safe (which is a lot more $), it's been over 32 years...
Marcon seems to be OK in general, Necon... don't know.

The six original caps in this one, all of them Marcon, 105 degree except C10 which is Necon.
I have added diameter and raster (distance between pins) values to the list as it's a very important detail when you try and fit them. Modern capacitors are generally smaller but the proper raster measurement is nice if you don't want to bend pins here and there.

It's my understanding the caps should have ESR less than the old ones, preferably as low as possible. Ripple current tolerance is another detail, highest possible.
Can't really find any proper specs on these - so, guesswork regarding the ripple? I guess I'll get the best and hope it's enough.

C1: 40V, 2200µF, D 16mm, raster 7mm, ESR <0.06 Ohm, V-L: 1.9%
C2: 40V, 2200µF, D 16mm, raster 7mm, ESR <0.07 Ohm, V-L: 1.6%
C5: 16V, 470µF, D 10mm, raster 5mm, ESR <0.24 Ohm, V-L: 4.6%
C9: 25V, 330µF, D 10mm, raster 5mm, ESR <0.21 Ohm, V-L: 3.9%
C10: 40V, 330µF, D 13mm, raster 5mm, ESR <0.32 Ohm, V-L: 1.5%
C11: 50V, 10µF, D 5.5mm, raster 2.5mm, ESR <4.3 Ohm, V-L: 8.4%

So... _seems_ pretty much OK, all of them measure above printed capacitance except C5 and C9, which also have the highest V-Loss. However, all are within the usual tolerance of 20% regarding capacitance. Measurements has not been made at the voltage they are used so... measurements like this doesn't give all the information. Getting in there with a 'scope and checking the details could be done - but... naah.

Important is also to buy from a reputable source, perhaps not get those cheap Panasonic caps from a Chinese seller at 1/10th of the price for the same thing at DigiKey - then they are likely fake or actually called "Pansaonic", "Ponasonic", "Penisonic"... or something like that...
;-)