Polaroid FLM-3234B Power Supply

[tom66]

Re: Polaroid FLM-3234B Power Supply

No, you still have a short. No power board should read shorted on the bridge outputs. Test the filter cap for shorts - try removing it if possible.

[kevinm34232]

Re: Polaroid FLM-3234B Power Supply

Main filter cap was replaced aswell. Can you look at my last post on page 1 I think u missed it. Earlier I removed the small transformer T1 and still had short, should I remove the other 2 transformers and check it?

[tom66]

Re: Polaroid FLM-3234B Power Supply

Try that -- will isolate the short down to one section or another.

[kevinm34232]

Re: Polaroid FLM-3234B Power Supply

I will do that now. Did you look at my post #20 I just wanna make sure Im doing the lamp test correctly. ? Can you quickly explain the concept of it, why would the bulb light up but not blow, yet the fuse would, and how would that protect the components?

[selldoor]

Re: Polaroid FLM-3234B Power Supply

I see you replaced Z2 - have you checked it again since the fuse and Z4 blew.

[tom66]

Re: Polaroid FLM-3234B Power Supply

Think about a short circuit, what is the simplest short circuit? A piece of wire.

So you are just connecting the bulb in series with a piece of wire when the PSU is shorted.

The bulb acts to limit current to a level at which a typical short will only cause heating of the board, not catastrophic damage. A 100W bulb lets around 800mA flow.

[kevinm34232]

Re: Polaroid FLM-3234B Power Supply

I removed both transformers still a short. I have to be missing something there are not a whole lot of components unless something shorted again I will re-check everything.

[kevinm34232]

Re: Polaroid FLM-3234B Power Supply

I dunno unless it's some SMD component on the bottom of the board everything seems OK on top now. It seems no matter what I remove besides the bridge rectifier it is shorting..

[tom66]

Re: Polaroid FLM-3234B Power Supply

A bad controller IC could cause this, if its output is stuck permanently high.

[kevinm34232]

Re: Polaroid FLM-3234B Power Supply

OK a little progress I removed Q2 which I replaced also (see post #1), with a different part # (18N50). I installed a mica insulator between the unshielded screw mount but I also put the screw in, is that the problem? Do I have the wrong transistor or the pin layout different?? Without Q2 no short and 120vac at rectifier.

[tom66]

Re: Polaroid FLM-3234B Power Supply

Is the original transistor insulated type?

[kevinm34232]

Re: Polaroid FLM-3234B Power Supply

Yes. And I just put original Q2 back in, and no short yet, and now 166vdc at main cap. I don't think Q2 was originally shorted. I will now put transformers back in and see what happens.

Hey so by putting that screw in is that what was happening?? Or do you think the pin layout was different? I didn't look at them..

[selldoor]

Re: Polaroid FLM-3234B Power Supply

As well as the mica plate you will need an insulated collar on the section of screw that goes through the mosfet metal plate.

[kevinm34232]

Re: Polaroid FLM-3234B Power Supply

Didn't do that.. I usually replace with same part # so didn't know about this...

Can I try to power TV up with lightbulb still in circuit?

[tom66]

Re: Polaroid FLM-3234B Power Supply

It will power into standby mode usually, but not start up as the bulb severely limits the power the TV has to light the backlights etc. Maximum power available is 50W for a 100W light bulb (half power in each; TV drops 60VAC and bulb drops 60VAC.) Think a 120VAC TV will work on 60VAC, with just 50W available?

[selldoor]

Re: Polaroid FLM-3234B Power Supply

Lightbulb across the fuse - with the old mosfet in- yes - go for it

[kevinm34232]

Re: Polaroid FLM-3234B Power Supply

OK finally no more blown fuses! But now, with lamp still in place red standby light came on and turned blue when I hit power button but no backlight or anything. Put in new fuse, and same result, standby light goes from red to blue, but no backlight or anything. No 12 or 24v from PS. Also would not go back to standby when hitting power button.

[tom66]

Re: Polaroid FLM-3234B Power Supply

Yeah, of course. A bulb like that limits the current the TV can draw by a substantial amount. It will not start up with the bulb in series, you need to run it without it.

[kevinm34232]

Re: Polaroid FLM-3234B Power Supply

I did I took it out and put a new 4A fuse in and it did same thing... I tried first with the bulb to make sure nothing blew up! But it looks like I have more problems...

[kevinm34232]

Re: Polaroid FLM-3234B Power Supply

Now Im not sure why Im not getting the 12 and 24v the voltage at the main cap remains constant around 166vdc when in standby and when turned on..