B+ issue

[i4004]

this philips tv was dead. all voltages after the trafo were heavilly dampened. i unhook the b+, and sure enough stby lamp comes on.

but the issue is this: i don't see short circuit on b+. it has about 45ohms. h.o.t. doesn't seem to be blown either(40ohms between pins), so i'm wondering what can cause such behaviour?

ie b+ is choking the smps but no obvious s.c.

[arneson]

Re: B+ issue

'This Philips TV' is not very specific.
I have a 60' rear so I've een paying attention to them.
They had a large screen capacitor problem one year ago in some models that resulted in a huge recall.
It was an overheat of a backlight cap failure,
but not for the one I have.

[i4004]

Re: B+ issue

it's 20" crt pal model made in poland.
now you know it?
hehe....

it's not really model specific, what i'm really asking what the expected resistance of b+ against ground (-) when b+ rectifier diode is not connected...
i don't wanna check h.o.t. if that's normal(offcourse, in the ballpark..doesn't need to be exact..)...
hehm..perhaps it's short circuit somewhere on secondary side of flyback...uhm..don't you just like short circuit situations on unfamiliar model...
that and intermittant errors...huh

[kc8adu]

Re: B+ issue

45 ohms to ground may as well be 0.0 on the b+.
what is it on that set?130v?
pull the hot and check again.if no go lift the b+ pin of the fly.

[i4004]

Re: B+ issue

i see 185V mark next to one diode in h.o. section...

will check those 2 tomorrow.

[i4004]

Re: B+ issue

removing hot does nothing. removing b+ from flyback(while hot was removed) restores normal voltages(b+ is 115V).
this suggests flyback is shorted, right?

presuming i can find replacement(need to check), how in the world do i desolder with such reinforced holes(see attached image)...

[Krankshaft]

Re: B+ issue

A nice high wattage soldering iron and some desoldering braid always did the trick for me.

Don't forget to loosen the mechanical connection from the flyback to the board out of all the flybacks I've removed most of them have had a screw or clip to prevent the flyback from flexing too much and cracking the joints or board. Sometimes the flyback is secured with a single screw to the rear cover when its installed.

You should try doing a ring test on the flyback (if you have the Dick Smith tester).

[i4004]

Re: B+ issue

don't have flyback tester, i can only check resistance against a good one, if seller agrees to do it prior to selling it to me(which they probably will).

some methods are explained here
http://www.repairfaq.org/sam/flytest.htm
and here
http://www.noahtec.com/testing-flyback-transformer.htm

but none of this is real easy.
i should find a schematic and try to see if there's excessive load on it's outputs, then remove and test it....somehow....uhm...

[i4004]

Re: B+ issue

got a tip from another forum(otherwise this would be a bitch to diagnose..i would probably unhook everything from secondary and suspect trafo if that didn't help...):

shorted ceramic cap..removing it brings telly back to life.

b+ branch now looks like lytic to ohmmeter....