magnavox 42mf438b/27

[Coinhunter]

Has anyone repaired a power supply board for this television? Just had one given to me and it is dead dead dead! I just pulled the power board out and it has a 50v 680 micro farad that is bulging and leaking. Since I am new to doing this I just wonder how many caps I should replace. There is about 9 or 10 at this location. I am attaching a picture of the board section with the bad cap.

[budm]

Re: magnavox 42mf438b/27

I would replace all the caps on the secondary side low DC power supplies (the right side of the black line), and low value caps (22uf, 47uf) in the primary side (left side of the black line) which are for start-up circuits. I do that so I do not have to do it again for years to come, use good caps such as PANASONIC FM/FC/FR series.

[Coinhunter]

Re: magnavox 42mf438b/27

Did as you suggested and replaced all the caps but I still have a problem. The power light comes on put there is no video, sound etc. Got anymore suggestions? I need them badly.

[budm]

Re: magnavox 42mf438b/27

Can we get good FOCUS pictures of those white connectors so we see the voltage labelling, that way we can tell what you should have at those connectors.

[Coinhunter]

Re: magnavox 42mf438b/27

Granddaughter borrowed my camera. Starting on far left on picture 2 connector 7 and reading from l-r gnd-boost-dim-inv_on-gnd-gnd-12ssb-12ssb next is CN6 -12v aud-gnd_aud-+12vaud-12vssb-12vssb-12vssb-gnd-gnd-gnd-standby-3v3 st next is CN5 gnd-gnd-12VB-12VB next is CN8 same as CN5, next is CN4 gnd-24v amb-gnd-24v amb- gnd- 24v amb. Connectors # 4,5,& 8 are not used don't know why. I have a total of 12 more caps to replace and every single one will be new. So far I have been lucky and found all NTE caps locally. They did substitute (2) 25v 470mfd for (2) 10v 470mfd. Hope that was a kosher swap, if not then I will have to hunt for the others. Thanks for all your help.

[selldoor]

Re: magnavox 42mf438b/27

So far I have been lucky and found all NTE caps locally. .

You may not have been as lucky as you think. Is your local shop Frys?

NTE caps are not low ESR and are not suitable for this application ( Power supply) - We would not even recommend them for use in a tv at all.

Budm did suggest which caps to use? if you cant source locally use digikey.

You say you still have some caps to replace if these are small caps on the primary (HOT) side then that will include a start-up cap that is important to get it all working.

[Coinhunter]

Re: magnavox 42mf438b/27

Oh Gee z, our local dealer is Shields Electronics and is the only place you can purchase parts near here. I felt their prices were high but reasoned them away thinking I was purchasing near top of the line caps. With all of their "experience" and with my telling them what the caps were for and that I needed low ESR they would have filled my order correctly or not at all. Truthfully I went to Digikey but was afraid they were a wholesaler only order site. Plus trying to locate stuff on their site was for me a pain. Mechanically I am fine...mentally I have visualization and recognition problems. If I can post a full size picture of the board could you possibly point out the cap you are referring to? I forgot my phone has a camera. Lol It probably won't matter since I am going to replace all of the caps anyway, but I will be learning what you teach me. I have already learned so much from this forum including what caps to not purchase from now on.

[Coinhunter]

Re: magnavox 42mf438b/27

The only way for pictures is to post several. Hopefully they are clear enough for all to view them. Thanks again for all the assistance.

[Coinhunter]

Re: magnavox 42mf438b/27

By the way the purple color means I still have to replace them plus others.

[selldoor]

Re: magnavox 42mf438b/27

This is a complex board - There are a number of possibilities I have marked with a red dot. They are often 50v and low uf (less than 100) 10 or 68 is common.

[Coinhunter]

Re: magnavox 42mf438b/27

Replaced a couple more caps today & checked for voltage on the low side. Connectors 4, 5, & 8 all have the correct 12 and 24 volts. Still don't know why they are not used... on connector 6 the 3.3 is right on, standby has 2.6v, both of the 12V ssb have 0 v, the 12V aud and the -12v aud has 0 v. On connector 7 both of the 12V ssb have 12V, the inv as well as dim and boost have 0 v. (reference picture 6 above)On the primary side at connectors 2 and 3 I have 0 v. (reference picture 8 above).
Sure would be great if someone could come up with a service manual for this TV. I have goggled it, binged it, and searched eBay as well as the forums and I have struck out everywhere. All of this and the Magnavox/Phillips plant was only 20 miles from my home at one time.

[budm]

Re: magnavox 42mf438b/27

Is there a chassis number on the tag where the model number is?

[Coinhunter]

Re: magnavox 42mf438b/27

Yes the number is LC8.1U la

[selldoor]

Re: magnavox 42mf438b/27

When you are testing the voltages are all the boards connected


download from here

[budm]

Re: magnavox 42mf438b/27

Magnavox and Philips use chassis number for identifying what is used inside that particular model, hence that how you find the service manual. Same model can have more than one chassis type.

[Coinhunter]

Re: magnavox 42mf438b/27

When testing at connectors 2, 3, 4, 5, & 8 yes. When testing connectors 6 & 7 I am testing at the pins with the cable disconnected for the ssb one at a time.

[selldoor]

Re: magnavox 42mf438b/27

When testing at connectors 2, 3, 4, 5, & 8 yes. When testing connectors 6 & 7 I am testing at the pins with the cable disconnected for the ssb one at a time.

Not sure what you mean for 6 & 7. but you should have all the boards connected.
Please list the results down the page - much easier to read

Like
Pin Desc Actual
1 12v 12.21
2 5v 4.70 and so on.

[Coinhunter]

Re: magnavox 42mf438b/27

Ok I understand what you want now

CN 6

expected
pin # value/id actual
1 3.3v 3.3v
2 standby .02
3 GND
4 GND
5 GND
6 12V ssb 11.92
7 12V ssb 11.92
8 12V ssb 11.92
9 +12V aud 13.36
10 GND
11 -12V aud -12.98


CN 7

Expected
Pin # Value/id Actual
1 12Vssb 11.92
2 12Vssb 11.92
3 GND
4 GND
5 Inv_On 3.23
6 DIM 1.70
7 Boost 1.47
8 GND

[Coinhunter]

Re: magnavox 42mf438b/27

Sorry, it changed my formatting when I posted. All of the boards/cables are connected when I tested. I am reading the manual page by page to learn what is going on. I am also trying to understand all the test points shown but I cannot figure out the values I should be expecting to see.

[selldoor]

Re: magnavox 42mf438b/27

OK those voltages look good can you place all the boards and connect the cables and take a picture of the whole back so we can see where parts are placed.

Also pictures of the other boards and list of the board numbers.