Magnavox 42MF521D/37 - Dead

[tom66]

Re: Magnavox 42MF521D/37 - Dead

You can do a "smoke test":
https://www.youtube.com/watch?v=Xhqw...g&feature=plcp

[kevinm34232]

Re: Magnavox 42MF521D/37 - Dead

That is great I haven't seen that before! I will try that..

[kevinm34232]

Re: Magnavox 42MF521D/37 - Dead

Tom I pulled L5001 just for fun and still have that short on the OUT pin of 7003, and the other side of 5001 0.06 ohms. Multiple problems?

[tom66]

Re: Magnavox 42MF521D/37 - Dead

Pull the diode too and test. The IC itself could still be damaged but in a way that makes the rest of the board look shorted. I had this once with a DC-DC converter. It's really weird because there's no MOSFET between OUT and GND but some parasitic diode forms instead.

[kevinm34232]

Re: Magnavox 42MF521D/37 - Dead

Did that and no change.. Pin 3 INH has short to ground too though. Think I need a new main board

[tom66]

Re: Magnavox 42MF521D/37 - Dead

INH -should- be low. Low turns it on. Though if the IC is fooked, then it may have multiple shorts from being cooked.

[kevinm34232]

Re: Magnavox 42MF521D/37 - Dead

You think I should just try the new IC? I am concerned that I have 0.06 ohms to ground after the coil 5001 although that it looks that it is still tied in to the FB pin of 7003..

[tom66]

Re: Magnavox 42MF521D/37 - Dead

FB goes through resistors so it can't be that unless the resistors are shorted (I would doubt it.) Try the IC first, it is the most likely cause.

[kevinm34232]

Re: Magnavox 42MF521D/37 - Dead

I will. Kinda mangled the 5001 coil removing it but it should be OK.. Will let you know..

[kevinm34232]

Re: Magnavox 42MF521D/37 - Dead

OK I just reinstalled the new 7003 IC regulator. And I do not have L5001 installed. I'm still not getting the 12v OUT. Now it was not easy removing the old IC and I lost pads 2 and 3 from the board but I was still able to solder to pad 3 and it looks like pin 2 is not used. I do have the 17v input. Is there anything else I need to look at? I didn't reconnect inverter and tcon boards while testing it but it should still give out the 12v correct? Or do I need the coil installed in order for the FB circuit to work the chip?

Update: Yes obviously coil needed to be in the circuit, and now I have the 12V and TV is powering up. I need to reinstall everything now to see if it's all good.

[tom66]

Re: Magnavox 42MF521D/37 - Dead

You figured it out before I got the chance to reply. good luck.

[kevinm34232]

Re: Magnavox 42MF521D/37 - Dead

Well reinstalled everything and I got a picture for a second and then it shut off can smell burning... Now Im getting 15v instead of the 17v off the PS board and it won't come on again.. It's such as hassle working on this thing the way it all goes together, I have to unscrew it again..

[kevinm34232]

Re: Magnavox 42MF521D/37 - Dead

Looks like 7003 may have burnt up again had some white grease on top of there is a brown mark on the corner close to pin 8, looks like that's where it was damaged before. Now the input is a little low (15v compared to 17v) and no output.

16.5v off PS board when not connected to main board so it's being loaded down. Without L5001 in circuit before I had a 0.04 reading at 200k ohms on the 12VS does that indicate a problem down the line?

[tom66]

Re: Magnavox 42MF521D/37 - Dead

There might be excessive load -- did you do the short test as in the video?

[kevinm34232]

Re: Magnavox 42MF521D/37 - Dead

Yes I did, there is bulbling from freeze spray at 7003 where it looks burnt.

Is it odd that it wouldn't blow the fuse right out of that regulator?

[tom66]

Re: Magnavox 42MF521D/37 - Dead

Remove that IC, then try it over the rest of the board -- something else may be faulty.