Gould MMG5-5 early-ish switched mode supply repair.

I was thinking about another Arduino Christmas post. I'd got a string of 50 WS2801 LEDs left over from another project, so I thought I'd write some code to display some pretty patterns. As it turns out the FASTLEDS library had just what I needed in the examples section, so I uploaded that to a nano, and hooked up the GND. CLK and data lines to the nano, and was enjoying the lightshow. 

I needed to power the LEDs from a bigger supply than can be supplied by the nano itself, as the LEDs draw a shade over 1 amp when flat out, so I got out a little 5V 5A bench supply I bought from a car-boot sale in days gone by. When I saw it at the bootsale, I didn't know what it was, but for the price, there was a nice case, a panel meter and, somewhat unusually, a keyswitch.

It's a useful little thing, but doesn't get used that often. Great for when the main workshop supply just isn't quite big enough for the job.

All was well. I left it running for a bit, and went to watch some TV... I thought I heard a pop from the workshop. I glanced over, and could see the LEDs happily flashing away.... then about a minute later , that smell of burning molasses. Ugh... somewhere there's a Rfia let go!

Sure enough, the smell was coming from the supply. I switched it off and opened the window, and closed the workshop door behind it. 

Once the air had cleared, I disassembled the unit to find a Gould MMG-5 power supply module inside. It's all very nicely made.

It proved a little challenging to get open, this plastic rivet must be removed ...

... this cover removed ...

... this flexible solder tag unsoldered ...

... and that recessed nut undone ...

The electronics can then be removed.  

There's a nice date on the transistor , 44th week of 1977.

Switch mode supplies were starting to get commonplace in television sets around this time, so the technology wasn't exactly new...

... although, this small daughter board seems to have optical isolators, which TV's of the time certainly didn't have. There's no bespoke switched mode controller IC here. It's made up from a logic IC and a slack handful of opamps. 

And there's the guilty party. Sure enough a Rifa! It's replaced with a brand new X2 Class Epcos branded part of the same value.

And another saved from landfill...

Incidentally, the meter has a shunt to read 0-10A, despite the supply only being capable of 5!