13.8V HW1200R-20A repair

[pdavid]

This thing was charging some accus when it just simply shut down. I changed the fuse and turned it back up and then it blew. On the primary one of the c3306 got a hole on it, the other next to it got shorted. Also the pcb got a nasty burn and two resistors and one diode got open. Secondary has two 30 amp schottky-they are fine, controller is a 494, filter caps are United.. everywhere. The box has a 12V fan, which turns on if there is like more then 7A of load.

I measured and tested everything. Had to change the transistors and diodes, both 2 ohm resitors and fuse and put some insulation tape on the pcb. Turned it on and it's working all day today so I guess it's going to be fine I don't know what caused it to blow up. It wasn't even overloaded.

[momaka]

Re: 13.8V HW1200R-20A repair

United caps are crap. While they may not be what caused your problem, I advice that you change them anyways.

Also, make sure to change the 50v, 4.7uF caps near the transistors on the primary. If the diodes you changed were the snubber diodes that are in parallel with the transistors, make sure you used ones that were rated for at least 1000V reverse voltage and are of the fast/quick recovery type.

[kaboom]

Re: 13.8V HW1200R-20A repair

Last one for me for tonight...

That's a good 'ol half bridge.

The two switchers are bad. The two freewheelers, two 'back-bias' caps (4.7u/50V) and 4148s, and the resistors associated with each switcher also have to go.

Sometimes, the freewheelers are OK, but the other "small components" take a beating when the switchers go. I had one supply go and one of the 3.9K resistors in the base ckt went open and a 2.7 ohm resistor exploded, leaving a mess behind. You *must* clean all carbon, etc down to bare PCB material if possible. Otherwise, the leakage may 'surprise' you.

-Paul

[pdavid]

Re: 13.8V HW1200R-20A repair

I cleaned the pcb til the glass fiber. Only one of the the 4.7uf caps got replaced, it measured something like 5uf so I left it alone...
The primary caps are ok, the ones on the secondary are in range too. The worst esr was 0.076, the one next to the output filter coil. Maybe I'll replace them sometime. This powers supply is 4 years old.
I replaced the diodes with the same type, some ultrafast type, I don't remember the numbers and it's not visible.
On a side note, the assembly of this box is a bit unfriendly. The screws are some non standard, probably to prevent users from opening it up. They have these notches on their sides.

[momaka]

Re: 13.8V HW1200R-20A repair

I cleaned the pcb til the glass fiber. Only one of the the 4.7uf caps got replaced, it measured something like 5uf so I left it alone...

The 4.7uF caps are part of the circuit that drives the primary transistors and they should always be replaced as a set. Mismatching them can lower the efficiency of the PSU and cause the primary transistors to heat up more than they normally should.
Also, while their capacitance may measure the same, the ESR on one of them could be too high.

I do see your point, though - if it works, why mess with it, right ?

[wmihelich]

Re: 13.8V HW1200R-20A repair

I have a power supply like this that when under load only has about 7 volts of output. 12 volts under no load. I am just a hobbist and could use some help in solving this problem Thanks!

[Mechdave]

Re: 13.8V HW1200R-20A repair

G'day All,
I know this is an old post, but I happen to have one of these HW1200 units as well with the same problem. So far I have found the transistors u/s, have replaced them with Fairchild 13009's and I have found the 2 ohm 1 w resistors open circuit. So far I have not replaced anything else. All the other components seem ok. Does anyone have any pointers? I am relatively inexperienced with this one and I need some help with understanding the diagram from kaboom. My issue is not understanding how the transformers work between the circuits. Any help would be greatly appreciated. Cheers

[ben7]

Re: 13.8V HW1200R-20A repair

G'day All,
I know this is an old post, but I happen to have one of these HW1200 units as well with the same problem. So far I have found the transistors u/s, have replaced them with Fairchild 13009's and I have found the 2 ohm 1 w resistors open circuit. So far I have not replaced anything else. All the other components seem ok. Does anyone have any pointers? I am relatively inexperienced with this one and I need some help with understanding the diagram from kaboom. My issue is not understanding how the transformers work between the circuits. Any help would be greatly appreciated. Cheers

Check the film cap C5 for proper capacitance.
Also, check the rectifying diodes on the secondary side of the largest transformer.

This type of PSU has the controller on the secondary. The controller drives a small transformer which drives the two power transistors.

[Mechdave]

Re: 13.8V HW1200R-20A repair

So really the controller circiutry will usually not fail when the two big transistors fail. The controller circuit is "protected by the transformer" yes? Also the secondary part usually will not fail because it is also isolated by transformers?

I have detailed and removed all components on the primary board area, cleaned the board and tested all the components, so far I have found the two 0.2 ohm 1W resistors were open circuit and all other components ok. I will replace the caps (electrolytic and ceramic. The big 470 uF caps seem u/s too). I have checked the rectifier diodes and they are ok, 0.470 odd volts when tested with multimeter diode function with no reverse feed through them. It seems rather strange that there seems to be no cause of the transistors going bang. The Q4 and Q3 transistors test ok (in circuit) too. I don't know why it has gone yet, I think I will get parts and reassemble and test. Hopefully it will all work. I don't understand the control circuit well enough yet to say whether it is broken or not!

[Kati-moa]

Re: 13.8V HW1200R-20A repair

Mechdave,
I have just fixed my HW1200, it was a bit of a mission but sounds like you might have similar problems. My output voltage varied around 6 volts. I replaced all the caps apart from the two large ones in the main 340V dc supply to no avail. Finally I checked the supply voltage to the 494 (pin 12) which should be greater than 7 volts - it was not hence the reg output could not get up to 5 V either (pin 14). Turned out Q3 (S8050s NPN) had gone leaky dragging down the 494 supply. I replaced Q3 and Q4 with a couple of BC337s and away it went.
Hope this helps

[Alkibir]

Re: 13.8V HW1200R-20A repair

Hi Kati-Moa, hope you are still around here.
I have a HW1200R (Ripmax O-IP2000 Version)
Output Voltage drop to 10 volt and a buzz sound from one of the two components hanging on Large Coolers ( I think).
Also the large Caps (470uy 200volt) have 110 Volt on their casing. That diagram is similar to what we have but is a different power supply which confuses some of us less experienced Folks.
I do not see any bulging Caps or does it smell of burning nor do I see any leakages etc. It might be in its early breakdown stages.
Any more tips?
Best Wishes

[euro-botics]

Re: 13.8V HW1200R-20A repair

hi David, did you found the issue ? i have the same issue .... this Ac-Dc doesn't give over 20A... reason where mine is dead... if you have any suggestion i will thank you

have a nice day