42mf231d/17 works when heated

[DavidOH]

I have this Magnavox. It will will power on with no picture untill I put some heat with the hairdryer on the power supply. I found 4 bulged caps. Three on the power supply.

The close up is the spot I have to heat. Two of the three caps in the row where bad . I changed all three. I can turn it on and push the menu button then put heat on it and the screen will come on. I've searched the hairdryer and startup cap threads. But I'm not sure where to find the startup caps. Thanks

[MisterD]

Re: 42mf231d/17 works when heated

you can buy a can of air usually used for cleaning computer motherboards,processors, etc. turn it upside down and it will produce cold spray, use it sparingly and try to isolate it down to a specific area by going back and forth from hair dryer to cold spray, it could be a bad solder connection or an actual component breaking down. known as thermal intermittent component. good luck!

[t.j.]

Re: 42mf231d/17 works when heated

startup caps range from 1uf to 47uf , an are usually 50v caps, so they a small one. check the service manual thread for your manual! there links there to couple differ sites that host manuals!

[DavidOH]

Re: 42mf231d/17 works when heated

I have the manual. The spot I'm heating is right on the three caps that I changed. I'll try to focus the air more to see if I can narrow it down.

[Mr Bill]

Re: 42mf231d/17 works when heated

what brand and series did you use to replace the 3 bloated caps? Will you post a picture of the bottom of the board where the 3 caps you replaced so we can verify there isn't a cold solder joint.

[DavidOH]

Re: 42mf231d/17 works when heated

Two of the caps were bloated one was not. The two that were are nichicon. The other is raido shack. I know bad idea. May put the old one back on as it was not bloated. I've looked for bad solder joints and touched all in that area. I'm going to look again. I just used a paper to focused the heat on different parts. I was able to get it to come on twice by heating the blue disk in the pic. I think it's a cap but not sure.

[Mr Bill]

Re: 42mf231d/17 works when heated

The blue disk is a ceramic capacitor.

http://www.digikey.com/product-detai...5PH-ND/2356735

[MisterD]

Re: 42mf231d/17 works when heated

Two of the caps were bloated one was not. The two that were are nichicon. The other is raido shack. I know bad idea. May put the old one back on as it was not bloated. I've looked for bad solder joints and touched all in that area. I'm going to look again. I just used a paper to focused the heat on different parts. I was able to get it to come on twice by heating the blue disk in the pic. I think it's a cap but not sure.

Look real close at all solder connections in that area, I suggest re-soldering all of the transformer pins ( transformer looks yellow in the picture, it's just to the right of the blue disc. capacitor) actually I would go over every connection in that area with the soldering iron. and make sure the mounting screws on all circuit boards are tight to ensure good ground connections.

[budm]

Re: 42mf231d/17 works when heated

That section is the standby power supply.
I would replace that start up cap C104.
Can you take the picture of that area but zoom out little more so I can see the parts in the primary side.
What you can do when the TV is working after warm up, use the canned air spray up side down and spray the Q-tip with the coolant until you see some icing, the you just touch the top of the suspect cap with the Q-tip to see if the circuit will stop working.
For spot heating, I use cheap soldering iron with adjustable heat see to low to heat up the top of the cap, not with the TV plugged in of course.

[DavidOH]

Re: 42mf231d/17 works when heated

I've rechecked all of the solder. I also sprayed it with coolant then pluged it in to see what warmed up. C110, C114, D105 were slow to defrost. I'll see about changing that cap as it sets next to a heat sink.

[budm]

Re: 42mf231d/17 works when heated

That heat sink is for the SMPS IC which drives the transformer for the standby power supply, the cap next to it is for filtering the DC generated by rectifying the output of the AUX winding of that transformer to keep the IC running after the circuits start running.

[DavidOH]

Re: 42mf231d/17 works when heated

I changed the cap C104. The only change is that it goes through the prestart better. I still need to heat the same area to get it to come on when cold. I'll have to keep looking.

[budm]

Re: 42mf231d/17 works when heated

From picture on post 10, I can see the standby transformer aux winding also supplies the power to the two caps and the regulator. Try to heat up just those two caps. Seems like yo u will have to try to isolate each section to heat up.

[DavidOH]

Re: 42mf231d/17 works when heated

Using a plastic funnel with the hair dryer I was able to heat parts of the board . I found if I heated then cooled with compressed air the caps on the upright board in the pic it will go on and off. I don't know which one is bad. But if I have to take it off to replace one I'm doing all four.
The place I'm getting the caps from is south of Dayton. They cost a little more than other places. But I live in Columbus so I can order then tonight and have them Firday.

http://www.mcmelectronics.com/

They've got a desoldering tool I'm going to get also. I'm tired of fighting to get caps off.

http://www.mcmelectronics.com/produc...-8240-/21-8240

Posted those in case anyone wants to take a look

[Mr Bill]

Re: 42mf231d/17 works when heated

Let me know how well that delsodering iron works. I'm wanting to get a station but i don't have a spare $150 with christmas approaching. I have the same problems fighting components off especially on multilayered boards.

[MisterD]

Re: 42mf231d/17 works when heated

Did you heat and cool IC102 (the one with the heat sink near the caps)? try putting something non-conductive like plastic or cardboard to shield the caps from heat while using your funnel with hair dryer to concentrate heat to the IC and then when you use the coolant spray press down spray button easily so the coolant only touches the IC102.

[DavidOH]

Re: 42mf231d/17 works when heated

Tried warming just the IC. Doesn't start.

[DavidOH]

Re: 42mf231d/17 works when heated

Let me know how well that delsodering iron works. I'm wanting to get a station but i don't have a spare $150 with christmas approaching. I have the same problems fighting components off especially on multilayered boards.

I just do this for fun. The reviews looked good for that iron. And it looked better than what Radio Shack has. Plus the board I need to take off has 27 solder points.

[randtek]

Re: 42mf231d/17 works when heated

In 33 years as a technician, I have tried a lot of different desoldeering aids. I always end up going back to desoldering braid (solder wick). It just seems to work best in my opinion. And it has no moving parts to fail!

[budm]

Re: 42mf231d/17 works when heated

30Watts is too small. I use Solderwick and soldepollit desoldering pump.