Amiga PSU failure and resurrection - well almost

[tbtorro]

OK - so today I've noticed that one of my brand-new looking Amiga PSU seemed dead. Upon flicking the mains switch, my A500 test board would give no sign of life. So I tried to measure the output, and true enough, no voltage whatsoever was detected neither on the 5V nor on the 12V pins.

So I took the PSU apart and saw that the fuse was blown. Hoping for a quick fix, I have digged around for another fuse, but all I found was a 6A - so I took a calculated chance. I've inserted the fuse, took a deep breath, flicked the switch - and then POP! - and some burning smell and smoke. (but at least the fuse was intact icard). Basically, one of the ferite coils have melted down - due to an unknown reason (unknown to me at least).

If you have any idea what could have caused this - please do drop me a PM - I have another PSU with the same symptom - fuse burned, then burned immediately upon new fuse. (In this one I was now smart enough to insert a correct fuse)

So I was thinking, it's not really worth it to try to fix this, but what do I do with the case? Then I've remembered that few days ago I scored a DVD player from the scrap station dowstairs, and as good retro-head took everything from inside I could forsee a use for - including a small switching PSU board. A quick check showed that it was working, and conveniently the output voltage pin values were silk-screened on the PCB. So it was quite straightforward to hook it up to the Amiga cables:

The bare A500 motherboard I was using to test this came to life! But will this small board be able to supply enough current on the long run? I have noticed that one of the diodes was especially hot - so I thermo-glued a small heat sink to it. Also the surrounding filter capacitors and the transformer are quite hot - but not as hot as before the heat sink. (I can touch them without burning my fingers - so guessing around 70-80C). Anyone has a guess if this will hold? I have no idea what load this PSU was designed for.. I have marked those parts that seem a bit too hot:

To be able to secure the board inside the case, I have decided to keep the old PCB, since it had holes that matched the screws that secure the plastic pieces together. So I've just stripped the board clean of components, then drilled some holes in it to secure the new board piggyback style:

As you can see the two boards fit very nicely inside the old case - the only thing left is to place the four original case screws in the corners and done!

In the end I have added a keyboard, mouse, and a floppy drive, and loaded some demos. I've been running the bouncing ball man demo for a couple of hours now - and while the mentioned components are hot - they don't seem to get hotter. Please do comment if you think this will hold - if you have any suggestion how to find out the performance rating of the PSU. Thanks for watching!

 

[roy_bates]

i dont want to sound negetive,but you didnt actually resurrect the power supply only the case was reused.

but its still a good job.

but i have to ask,why bother removing all the parts from the old pcb to use it to hold the new one?

 

[rkauer]

A DVD PSU will not last much longer than a couple of days. But it might just "fit" in the power requirements of a vanilla A500.

Don't try to add other accessories.

 

[demolition]

Do you still have the case from the old DVD player? That way you could check the power rating. While it may not give much information, it will provide a little. If it says 20W, it is probably a bit too small. I think that PSU looks a little small for an Amiga and also I would expect a DVD player to use a bit less power compared to an A500.

It seems to work, but it might die after a while if it runs too hot. The caps will degrade quickly if they're too hot. Notice that burning your fingers on them does not mean they're too hot as they should be able to cope with 75 deg. C (which will burn you) for a long time. Often it is 5000-15000 hours at 85 deg. C, and could be much higher for 125 deg. C types.

 

[tbtorro]

i dont want to sound negetive,but you didnt actually resurrect the power supply only the case was reused.

but its still a good job.

but i have to ask,why bother removing all the parts from the old pcb to use it to hold the new one?

You are right - not much I of a resurrection, but still I have the illusion of saving the psu.. Once I screw it back together it looks exactly like an Amiga PSU - as opposed to a clunky PC psu box or a hacked enclosure.

The reason I kept the old PCB is that it has screw holes in the corners that match the plastic case. So the same screws that hold the case together also hold the PCB in place. So the case holds the old PCB and the old PCB holds the new . Otherwise I either would have to hack some kind of mount inside, or the new unit would just rattle free. So I judged this was the simplest and most elegant solution.

---------- Post added at 10:52 ---------- Previous post was at 10:50 ----------

A DVD PSU will not last much longer than a couple of days. But it might just "fit" in the power requirements of a vanilla A500.

Don't try to add other accessories.

Definitely won't.. Was thinking this is good enough for a test setup - and not for prolonged use..

---------- Post added at 10:56 ---------- Previous post was at 10:52 ----------

Do you still have the case from the old DVD player? That way you could check the power rating. While it may not give much information, it will provide a little. If it says 20W, it is probably a bit too small. I think that PSU looks a little small for an Amiga and also I would expect a DVD player to use a bit less power compared to an A500.



It seems to work, but it might die after a while if it runs too hot. The caps will degrade quickly if they're too hot. Notice that burning your fingers on them does not mean they're too hot as they should be able to cope with 75 deg. C (which will burn you) for a long time. Often it is 5000-15000 hours at 85 deg. C, and could be much higher for 125 deg. C types.

Great idea! Of course, I will check after work, and report back.

Any idea based on the description what caused the original meltdown?

 

[demolition]

Any idea based on the description what caused the original meltdown?

Hard to say..

 

[roy_bates]

if you have removed all the parts from the original that does make it a bit easier to check for shorts,broken diodes and duff capacitors.