Bright flash...KAAA..BLOOEY!

[kiddznet]

...came from this area after replacing fuse and test power on
Any ideas what to try for and how to test please?

HO!.. the square black thingymyjig on the left with 3 legs has a short across all 3 legs, The others 2 measure a resistance of 2.65 on the 20k scale across the outer legs

[shovenose]

Re: Bright flash...KAAA..BLOOEY!

Oes it still work ifyou replace the fuse?

Yeah i wold say one of the heatsinked black things ia fryed.

[kiddznet]

Re: Bright flash...KAAA..BLOOEY!

This is the thing I mean MOSFET thingy.
Fuse blew instantly

[Khron]

Re: Bright flash...KAAA..BLOOEY!

That looks like the 5VSB mosfet. Source an equivalent replacement, replace it, and retest...

[kc8adu]

Re: Bright flash...KAAA..BLOOEY!

correct on 5v stby but when you get one blown like that more often than not there is lots more damage and an instant death sentence for the new mosfet.BANG!! (sound of bits bouncing around in the case)

That looks like the 5VSB mosfet. Source an equivalent replacement, replace it, and retest...

[kiddznet]

Re: Bright flash...KAAA..BLOOEY!

Thanks all got the thing out and its definitely shorts across the connectors and to the case
Its marked C 5027-R will see if I can find one.

[kiddznet]

Re: Bright flash...KAAA..BLOOEY!

Probably old news but I came across this http://www.repairfaq.org/REPAIR/F_smpsfaq.html

[everell]

Re: Bright flash...KAAA..BLOOEY!

Your problem is definitely the 5vsb sircuit, using the two transistor design. I have attempted to repair several, most of which just blew out again.

Just this week I attempted to repair a Rosewill RP550-2-S. Replaced one bad transistor and one burnt resistor. Powered it up, no 5 volts, then a few seconds later it sounded like pouring milk on rice crispies, and sparks flying everywhere like a sparkler on the fourth of July. Power off, and I found one resistor blown completely off the board, four other resistors blown apart, the big mosfet transistor shorted, and the smaller transistor resistive.

Next step is to gut the 5vsb circuit and install a mod using a pwm chip (and a few other components) mounted on a small piece of perf-board. I have done this many times, and so far it has always worked, and the pwm chips don't blow up like the two transistor circuits. They don't go overvoltage either.

[kiddznet]

Re: Bright flash...KAAA..BLOOEY!

everell

?(pwm chip) Are you able to post the details here?


( Taylorcraft, good.)

[everell]

Re: Bright flash...KAAA..BLOOEY!

Yes, it is a Taylorcraft. Paul Clawson did a flightsim of the BC-12D modeled after the one my dad flew back in the early fifties. I can tell you are quite observant, and not a teenager!

I have not fixed my psu with a mod yet - hopefully will get some time to work on it this weekend. I will let you know some details as the project progresses.

Do I understand correctly that you are from Australia?

[kiddznet]

Re: Bright flash...KAAA..BLOOEY!

Do I understand correctly that you are from Australia?

Correct .

Not a teen, correct.


I was flying a little after yer Dad was in the 60's
40 years in fact now retired

[momaka]

Re: Bright flash...KAAA..BLOOEY!

Just wondering, is this PSU a Macron Power by any chance (UL number E199529)? Reason I'm asking is because the design of that section in your PSU looks identical to a Macron Power MPT-301 I have, except mine uses beefier components. If it does turn out to be a Macron, let me know if you need to know part numbers or specs of burnt components. Mine is recapped and well working (so far).

@Everell: This is indeed a 2-transistor design, but unlike the other 2-transistor 5vsb circuits I've seen, there is no critical cap anywhere to be found near the 5vsb. The primary side of the PSU only has 2x 10uF, 50v caps, but those are part of the driving circuit for the BJT transistors (half-bridge topology). Secondary side has a few more 10uF, 50v caps, but none seem to be directly connected to the optocoupler. Any ideas?

[kiddznet]

Re: Bright flash...KAAA..BLOOEY!

Indeed I got a BANG! fuse blew after I replaced the transistor
Obviously, as has been stated, there are more gremlins in the works I will keep prodding away with my multimeter
Now its catching...have another PSU here that tests ok for 5vsb only?

[everell]

Re: Bright flash...KAAA..BLOOEY!

Easier to fix a 5vsb than some of the other more complicated problems in the main circuits. Yes, sometimes they are easy fixes, but the ones I end up with seem to be the bummers!

I worked on the RP-550 last night. Removed the excess parts and installed a mod board with an Infineon pwm chip. No 5 volts, and lots of strange voltage readings. So this morning, I removed the Infineon chip and installed a mod board with a DM311. I have had great results with the DM311 chip in the past, the Infineon is new for me.

On power up, the voltages on the DM311 looked OK, the 5vsb was only reading .87 volts output. So I must have a problem on the output side of the 5vsb circuit. The mod board with pwm did what was needed - doesn't go overvoltage, and doesn't blast transistors and resistors! Once I get this problem resolved, I will post you some information on how to do the mod.