ADJ disco light PFC60-12 Power supply repair

[garrymc123]

Hi trying to repair this power supply q1 was shorted on all pins it was an FHF8N60 and a resister I'm trying to check R9 resistor 5 bands no chart has the black band on it so looking for some advice on it

Thanks

[R_J]

Re: Power supply repair

Seems to be 0.15Ω 5% non-inductive, How does it check? Many times when the modfet shorts, the drive ic can be damaged, also check the components in the gate circuit.

[garrymc123]

Re: Power supply repair

Thanks for your reply how did u find this out as I couldn't find any calculator that had the black bands in it. The resistor reads 000.1. The driver chip is a 6853k11 ic but can't find any pinout on google for it to check it out is there a compatible replacement for this I can use.

Thanks

[SMDFlea]

Re: ADJ disco light PFC60-12 Power supply repair

The 6853 part might be this https://cdn.badcaps-static.com/pdfs/...3bdd796465.pdf .Can you get a close up picture of it and D3 as well,looks a bit charred

[PeteS in CA]

Re: ADJ disco light PFC60-12 Power supply repair

That critter looks to be flyback topology. Other than a ferrite rod inductor to reduce spike noise it has no output inductor (the "transformer" is actually a coupled inductor, and the "output inductor" is the primary winding).

More to the point, R9 was probably the current sense resistor and might have been damaged when Q1 shorted, depending on how quickly F1 opened (check F1, it's probably open). Source circuit current sense resistors are very low resistance.

D3 and Q2 may be in the gate circuit for Q1, and may have been damaged when Q1 shorted.

[momaka]

Re: Power supply repair

Thanks for your reply how did u find this out as I couldn't find any calculator that had the black bands in it. The resistor reads 000.1.

That's the tricky part sometimes - this was actually a 4-band resistor (brown, green, silver, gold - i.e. 0.15 Ohm 5%.) The "5th" band in this specific case isn't part of the resistance code. It's for something else, but I forgot what.
*EDIT*
I think I found the answer: according to the link below, last band being black means the resistor is non-inductive... which makes sense in this application.
https://electronics.stackexchange.co...-resistor-mean

Since it measures 0.1 Ohms on your meter, it means it's more than likely OK. As to why the transistor blew... who knows. But check all of the other components on the primary side as well, especially components connected to the Gate of that transistor. Might also be worthwhile to check the output rectifier as well and whatever else you can.

The driver chip is a 6853k11 ic but can't find any pinout on google for it to check it out is there a compatible replacement for this I can use.

Well, if bad comes to worse and you can't find a replacement, you can just replace the broken parts and try to see if the PSU works. However, one thing you should definitely do in that case... in fact, do this anyways when testing any PSU after working on it: use an incandescent light bulb in series with the input of the PSU, as shown here:
https://www.badcaps.net/forum/showpo...4&postcount=70
^ This will limit both current and power that can be drawn by the PSU, so you won't blow up any of your new components, if the IC or any other part is still bad and tries to make the PSU misbehave. Note, however, that you can't put a big load on the output of the PSU when you have the series incandescent bulb because... power limiting. Once you verify the PSU works well (voltages stable and nothing overheats if you leave it connected to the wall for a while), you can try removing the series bulb and then adding a load. Or if you want to go the safer route, you can put a few more incandescent bulbs in parallel to each other or just one strong halogen/incandescent bulb (200-300 Watts). This may allow you to connect a larger load to the PSU output to test it and see if everything works OK.

[garrymc123]

Re: ADJ disco light PFC60-12 Power supply repair

Hi, Guys thanks for all the info I will check all these parts when I'm back at the unit. I have attached a close-up of u1 D3 Has checked out ok but if I remember right it's probably me removing it to test then putting it back on is why it looks so charred but it has tested ok. My other question is where can ai get an equivalent replacement of FHF8N60 as I can only get them from China. Also, can someone confirm wich pin is the gate on the FHF8N60 as according to the datasheet middle pin is the gate but the middle pin on the circuit board goes to the transformer

[diif]

Re: ADJ disco light PFC60-12 Power supply repair

The middle pin of the 8N60 is the drain going by the Fairchild datasheet. I've got one if you can't find an alternative PM me.

[momaka]

Re: ADJ disco light PFC60-12 Power supply repair

TO-220 MOSFETs almost always have the Gate as pin 1 (leftmost pin when device front is facing the viewer.)

I don't see anything too special about the 8N60, so probably can replace it with just about any MOSFET that has similar current, voltage, and Rds_on ratings. Gate charge and turn On/Off delay shouldn't matter too much in this case, since PSU uses flyback topology and probably switching at relatively low frequency (<100 KHz). For testing purposes, you can probably even use something like IRFBC20/30/40, 02N70, 2sk2624, 2sk3767... or whatever else you may have in your junk box that came from the primary side of a forward-converter or flyback PSU. Obviously, if the MOSFET doesn't have the same or better current and Rds_on ratings as the original MOSFET, your replacement will probably run hotter. But again, for testing purposes, and with a lower or no-load testing, you can get away with a weaker MOSFET to see if at least the SMPS IC (U1) is good or needs replacing. Of course, use the dim bulb test, as mentioned above in my previous post.

[garrymc123]

Re: ADJ disco light PFC60-12 Power supply repair

Thanks to everyone for their help I have tested more components fuse is testing ok on the gate side of the ic
FHF8N60 on Q2 sot-23 ss8550 y2 I have a short between pin1- Base and pin3- Collector and on U1 I have a short between pin 1 Ground and Pin 6 out is there anything more I should be testing and where can I source these parts. DIFF is going to sort me out with a new FHF8N60

[garrymc123]

Re: ADJ disco light PFC60-12 Power supply repair

And yip got ma bulb tester at the ready for testing when the parts arrive