[FIXED] Mastech DC Power Supply HY3005DX (Rebranded PS305D) - Blown by 220VAC

[Zucca]

2 Bad decisions:

1) Buying a crap PS like this:
https://www.eevblog.com/forum/testgear/mastech-dc-power-supply-hy3005dx-cheap-and-very-impressing!/

2) Thinking the outputs are isolated from the mains. I forgot there was a little metal tab between the - pole and the earth ones in the middle.

Short Story: I completely forgot the minus pole was connected to earth (by a metal tab), and I ended up in my setup to connect the 220VAC main to the minus... BOOOM!
The crappy PS did not survive: after turning it on it was going at 40V output and then decrasing to 0V, no response from the adjunting knobs.

I opened the unit expecting to find a black burned spot somewhere, no no it looked just fine crap as always, so next step I got the schematics from here:
https://www.eevblog.com/forum/repair/new-power-supply-ps305d-not-regulating-and-running-over-voltage-and-current/

Few measures laters I understood the protection circuit balcony (not reported in the schematics)

was kicking in by cutting the power after the diode bridge BD1. That's why I was getting  40V and then 0...

By excluding the protection the output was solid at about 47V with no response to the adjusting knobs. After a few second I was powering down the unit because I didn't  want to damaging it further somehow.

So I started to check components left and right (the the brain turned on...) and I found the bad guy: D116 1N5399 was shorted. Replaced with a bigger one ECG5804 (didn`t have the exact replacement) and ready to go.

Here what I learned:

1) If the R106 is burning hot and there is decoloration on it, it`s a design feature not a failure (in all the pictures I saw has that resistor color looks cooked).
2) They don't even bother installing proper connectort between the different bards (ie protection balcony and main board), just use some hot glue to hold those thin cables down.
3) The big 5W power resistors R104 and R103 marked 5WR18J are supposed to be 180mOhm and they are not shorted. I didn`t know "R"="."
4) Check all the solder joints, some of them are scary.

This power supply in general has a quality level comparable to a "steaming pile of HS" (quoting Louis Rossman).

Since it could be a popular unit to beginners, I wanted to share hoping to help somebody out there.

[station240]

Actually I'd expect you'd have a lot more to fix if they hadn't tied negative output to earth.

This sort of product build quality was standard, back in 1993. Really no excuse these days for shoddy wiring, glue as a cable restraint, and useless solder joints.