Collins PM2 Power Supply - Rebuild to service bulletin or not ?

  Hi,

Well, lots have gone on since my last blog, lots of repairs, lots of family stuff, and of course COVID-19 - arrgggh !!!

I thought I'd try and share some more of my experiences, mostly to record them for posterity, but also to help others as well a little, so here is a new post ;

I've blogged before on a PM-2 Upgrade, I've done several of these now for other people - contact me if you are interested! - but I recently got hold of a PM-2 which was clearly not working, thankfully no one had plugged it in, most likely as the cord was in a terrible state - just take a look ;

Looking at the date code on the capacitors this unit is quite an early one - 6047 for several of them which makes the capacitors made in late November 1960 - not surprising that the cord has now perished beyond any use after 60 plus years  !!

After removing the case several things were obvious.

There was no way that it could be used without a major and complete rebuild!

Looking at the photo (right) you can see how badly overheated the mainboard was - both the components and the board itself is pretty much shot and is not usable in my view. It's not too clear but the board is badly charred, possibly at least twice with the board being scraped of the carbon by the look of it !

I know that these units were given a hammering in the field and then also again in private hands, don't forget these are designed to be 'lightweight use and not a replacement for the 516-F - but are often used as if they were, unfortunately. It looks like this one has had rather a bad time, been repaired several times, one of them badly, at least in my view ! The capacitors are also showing signs of stress as well, not surprising really when they are nearly 61 years old -  just take a look at the first capacitor after the smaller 10uf ones - can you see the bump ? - definitely not to be used or reformed!

The unit itself looks like quite an early one - it doesn't have the service bulletin applied which moves the capacitors from below the board to under the speaker so that places it well before 1963

So what to do ? - should I try and salvage the board and rebuild it as is or should I update as per the service bulletin and make a new board that replicates the original collins board ?

I've asked for other collins owner's and restorers' views on the collins reflector group, but ultimately I'll make the final decision 😀 - watch this space for the next update.