MSTE PSU RE-CAP FAIL

[exxos]

I had this power supply sent in for repair as after it was recapped , it failed to function correctly.

Upon arrival I saw that the capacitor legs were not particularly cut short enough and was sticking out a few millimetres. They did not short out on the metalwork case, but it is something to bear in mind for the people who are doing this work.

The power supply would turn on the 5 V would intermittently drop to 3 V or 0 V, and a couple of seconds later jump up to around 4.5 V.

I checked all the joints with a magnifier and basically seemed okay, I did not see any short-circuits.. However it wasn't long before I found the problem..

IMG_1918.JPG (138.8 KiB) Viewed 4415 times

On the top of the board it becomes obvious why this happened..

IMG_1919.JPG (133.57 KiB) Viewed 4415 times

Something sticking up on a little bit of a heatsink, very easily to get knocked and as there is no upper support for this part slight knock and it rips up the PCB pads..

So a wire link later...

IMG_1920.JPG (159.04 KiB) Viewed 4415 times

And....

IMG_1922.JPG (234.32 KiB) Viewed 4415 times

As a side note, power supply I had, had a cut track. I'm not sure what I was by design or just something which happened my mistake...

Though someone else posted some images here, the same power supply, which do not have the cut track..

https://www.exxosforum.co.uk/forum/viewt ... 2086#p2086

So bit of a mystery if this was a factory mod or just got damaged at some point..

[Icky]

As a side note, power supply I had, had a cut track. I'm not sure what I was by design or just something which happened my mistake...

Though someone else posted some images here, the same power supply, which do not have the cut track..

https://www.exxosforum.co.uk/forum/viewt ... 2086#p2086

So bit of a mystery if this was a factory mod or just got damaged at some point..

I have come across these two versions of PHIHONGS PSUs:

One is a REV-A1 which has the cut track and the centre post is isolated with cloth tape. This one the opto isolator is a CNY17-3Z and it is from an Atari TT REV H.

The other a REV-02 which does not have the cut track and the centre post is not isolated. This one has the PC111 opto isolator and is from and Atari MegaSTE.

I'll add pictures shortly as I am in the process of re-capping the REV-A1, the REV-02 is already recapped

[damanloox]

If you look closely on the other revision you'll see that track is not there (ie. exact same result as track cut on older revision).
I suspect the track needs to be cut to prevent ground loop...

[exxos]

If you look closely on the other revision you'll see that track is not there (ie. exact same result as track cut on older revision).
I suspect the track needs to be cut to prevent ground loop...

I've only ever had that one power supply personally so I don't know about any other revisions..

I suspect it was done to improve regulation or something. Feedback should always be done on the main output wires, I have not traced or looked at the circuit board much. it is possible it could cause some regulation issues of some kind. Or add some noise.

I guess if someone was bored enough, scope the outputs, re-solder over the cut, and try the outputs again and see what the difference is..