If you need some close up, ask away

An underside picture would be convenient. I suspect the burn is from an under trace.

 

Was going to ask for a picture of the bottom side (solder side) where all the traces are. Also agreeing with MrChips about IC901 being a likely culprit. But still just guesswork so far.

 

T901 - D901 - FB901 - IC901 - - - was this made by Binford? Everything Binford made was "The Binford 6400" model. Maybe the Binford 901 ? ? ? (Just making light. Ignore this post)

 

Was going to ask for a picture of the bottom side (solder side) where all the traces are. Also agreeing with MrChips about IC901 being a likely culprit. But still just guesswork so far.

I'm swamped with work right now, haven't had time to look at it, will have to dig up my multimeter first, I'll take a picture of the underside first, that will be quicker. Your help is very much appreciated.

 

Was going to ask for a picture of the bottom side (solder side) where all the traces are. Also agreeing with MrChips about IC901 being a likely culprit. But still just guesswork so far.

Here you go guys

 

I've rotated and reversed the image to match the picture in post #17. I've outlined the area and indicated associated components and jumper in the picture.

 

If convention holds true, T901 PIN 1 would be the pin with the square pad. This doesn't match the schematic. At least that's my observation. The diode (D901) appears to be connected to pin 6. R901 & C904 bridge across to pin 8 of T901.

I'd say "desolder the jumper" and remove the diode. Replace it with a cheap as snot diode. If it doesn't blow out then make sure you've gotten the diode around the correct way, Cathode (bar) next to the jumper. Measure the voltage between pins 6 & 8 with your meter on AC. You may have to desolder R901 and C904 to get a true reading. But before you desolder them set your meter to DC and check the voltage across C904 or R901. Once you know that voltage find a light bulb (not an LED) who's voltage is equal to or a little above that value and connect it in place of the jumper. If it lights up full brightness you may have a short on D902 (the big black cap). To be honest, I don't see a shorting pathway. TH901 provides pathway from BR901 to C902 and the jumper. Unless pins 6 & 8 along with C904 and R901 make up a tank circuit - I'm not familiar with tank circuits. Something is not adding up to me. I said "TO ME". That just means someone else may recognize something as common as shoe laces where I am as familiar with this circuit as Dentists flying fighter jets. Maybe D901 just got so hot it finally quit after long burning the board. It may have needed a heat sink. But I'm not the engineer to be asking that question. Or answering it.

Bottom line - I don't trust the schematic someone found. Not sure about IC901. Can't find it definitively unless it's the four legged device mounted on the heat sink. OK, yes, I think it is. On the drawing within the large blue box are pins marked "F", "G", "B" and "D". So the pin marked "D" on IC901 is where power from the ferrite bead goes to. I just don't see any obvious failure paths. The board is cooked. LONG TIME cooking is my opinion. (side by side comparason)

 

I have copied the schematic here so that we don't have to go back and forth.
It would appear to me that R901 would have prevented that catastrophic fire. There is about 340VDC from the bridge rectifier. I would check C904 for a short.

 

I have copied the schematic here so that we don't have to go back and forth.
It would appear to me that R901 would have prevented that catastrophic fire. There is about 340VDC from the bridge rectifier. I would check C904 for a short.

View attachment 305556

The schematic seems to suggest IC901 has six pins and all of them appear to be connected to something. On the board it appears IC901 has only four leads. Five if you count the heat sink. And I'll concede it's possible one of the pins of the IC were deliberately cut off at the body, but the board doesn't show any spaces for another lead. I remain suspicious that schematic is not accurate to the board the TS has in hand.

 

The schematic seems to suggest IC901 has six pins and all of them appear to be connected to something. On the board it appears IC901 has only four leads. Five if you count the heat sink. And I'll concede it's possible one of the pins of the IC were deliberately cut off at the body, but the board doesn't show any spaces for another lead. I remain suspicious that schematic is not accurate to the board the TS has in hand.

There are different versions of the SMPS board. The schematic shown might not be the exact correct schematic but I think that it is close enough to assist in the trouble shooting.

If the TS could post the marking on IC901 that would help.