Tv power supply repair/mod (replacing an unkown IC)
Good day folks. I was going to post this under the TV section, but I thought it doesn't have too much to do with the TV itself as with its power supply: it's a Blaupunkt TV and it's got this power supply which looks more like a laptop power brick. The chap who brought it told me he took it someplace else to have it fixed, after a thunderstorm killed it, but the guys there didn't bother troubleshooting the PSU too much and just told him that they couldn't find a replacement PSU, which is true to a degree, as I couldn't find one myself, especially where I live, but being the kind and helpful chap that I am, I shall try to fix it somehow. Sure enough, the fuse was missing and (I believe) the actual problem comes down to the small switching IC having an internal short. The person who worked on it before me apparently removed the IC and then soldered it back, though they did a pretty poor job at aligning it as you can see. Anyway, I took it off once more myself and there's indeed a short between what in the second picture would be pins 1 and 2 starting from the top left of the IC. Using my general knowledge of SMPSs, by following the traces, I believe these would be what's commonly known as the VCC and OUT pins, which would cause the transistor to stay in its ON state all the time, since you've got VCC going into the Gate pin directly. Amazingly, the FET is not shorted, neither are any other components, at least on the primary, however I have a hard time believing those two pins are supposed to be connected like that. I can just about make out 73e18 on the IC, but I could not find anything helpful about this: just generic pictures of tape reels from China, which might hint that this part DOES exist, but it's very very obscure. I then started thinking about replacing it with an equivalent part, and this brings me to my actual topic: I slept on it overnight and realised that many of these controller ICs have the same basic pinouts:
-VCC and GND
-OUT which goes to the G pin of the FET
-HV which powers the IC briefly before the AUX winding starts producing voltage for the VCC pin
-FB which is the feeback from the optocoupler
That's 5 which I could identify so far, both on this IC and on some others I came across while fixing other TVs. I'm not too sure what the 4th pin does (again, it would be the bottom right one, counting from the top left and going in a clockwise fashion like many datasheets do). It goes through R37, which is a 100Kohm resistor to ground. Have a look at this thing and see if my idea is remotely doable or it would result in immediate smoke (lightbulb test first, of course). Cheers.
-VCC and GND
-OUT which goes to the G pin of the FET
-HV which powers the IC briefly before the AUX winding starts producing voltage for the VCC pin
-FB which is the feeback from the optocoupler
That's 5 which I could identify so far, both on this IC and on some others I came across while fixing other TVs. I'm not too sure what the 4th pin does (again, it would be the bottom right one, counting from the top left and going in a clockwise fashion like many datasheets do). It goes through R37, which is a 100Kohm resistor to ground. Have a look at this thing and see if my idea is remotely doable or it would result in immediate smoke (lightbulb test first, of course). Cheers.
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