Polaroid PSU output power

[kenny1070]

This unit is a Polaroid FLM 3701 (monitor only / no tuner)
Build date 2005

It utilizes a KAS200-5s241812xL Power Supply (LC-37K7)

This thread is a carry-over from a blown PFC Film Cap (474k 450v), which has since been solved.

BACKGROUND:

Came home one day after a really bad lightning storm = TV won't turn on.
No power - no red/blue lights - dead.

Pulled out the Power supply board and replaced all the Caps with new ones from LCD Alt.
All but the 450v 150uf large cap - extremely rare to go (as I've been told).

During repair found the PFC 474k 450v Film Cap at the input of the power supply was melted.
After lots of help from others here - I found a suitable replacement.

The 5vdc standby power has now been restored to the set, and the red standby light illuminates (problem solved).
Progress.


Which brings us to TODAY:

The P/S is still producing very low or no output voltage during the power/on command.

24v only generates about 18v before shutdown (3-4 secs.)
18v only generates about 12v before shutdown
12v only generates about 0.7v before shutdown

Since there is a 5vdc standby being sent - and -
a 5volt return signal from the CPU (power/on) command switch,
I'm assuming that the problem still lies within the Power supply boards ability to generated the regulated voltages.

Without an accurate diagram, theoretical application is only getting me so far.

Anyone have any thoughts or ideas ???

[tom66]

Re: Polaroid PSU output power

Since 12V is so low, I would check the diode for the 12V output, and see if it is shorted.

[kenny1070]

Re: Polaroid PSU output power

Thanks for the help Tom66.

I'm assuming the diode for the 12volt is the D118.
I pulled it out and it tested good (about 750 & infinity).

I also pulled out what assume is the 24volt (D117).
It tested good as well.

I may have to start pulling out the transistors.
The upper casings where the screw hold downs are (to the heatsinks) appear to have melted. Not sure if that is actually affecting the integrity of the current flow.
Nor am I sure which transistor is operating which leg of the supply.

Any other help you could provide would be great,

Thanks

[kenny1070]

Re: Polaroid PSU output power

Just found this on the D116.

It is the flip side of the transistor on the right of the last picture highlighted.

None of the others appear to be like this - they all have good clean solders.

I'm not sure if this a factory designed bridge (?) - or the result of a power surge melting the solder into it.


Any thoughts ???

[kenny1070]

Re: Polaroid PSU output power

Success !!!!


That was it.

I put a soldering wick on the bridge and eliminated it.

Powered up the set --- and full function !


A year and a half and 25 bucks later - it lives once again

Thanks to everyone for helping.

On to the next one

[keats11]

Re: Polaroid PSU output power

I have a Polaroid FLM3201 I picked it up from CL this weekend with the same blue light symptom. Its is a power supply issue, and all the DC voltages are low. Instead of 24 V, I have 17. Instead of 12V I have 7 and Instead of 18V I have 13. I found the schematic that Tom had posted in one of the forums, but there aren't any voltages labelled in the schematic. Has anyone come across this issue? It seems to me the transformer T902 is not being driven hard enough to generate the full voltages necessary.

[tom66]

Re: Polaroid PSU output power

Check if you have 450V across main cap.

[keats11]

Re: Polaroid PSU output power

I don't, I onlyhave 150V across the main cap. Looking at the schematic, the cap seems to be connected to the output of a bridge rectifier, so I would have only expected 150V. There is some PFC circuit that seems to be connected in parallel to it, basically an inductor+FET that drives it, the inductor O/p is connected in parallel to the cap output. Is this somehow supposed to boost the voltage? Tom, what would be your next guess?

[tom66]

Re: Polaroid PSU output power

Correction should be 390V+/-10V, but either way it is bad.

You have a fault with the PFC section of PSU, so check around there. It involves a diode, inductor, MOSFET and controller IC, among other parts.

[xyloeye]

Re: Polaroid PSU output power

I don't mean to hijack this thread, but I have the same problem in a Poloroid FLM323 that normally outputs only 24v. The 24v is present but plugging in the main board swamps the voltage down to 16v and the inverter supply goes to nearly zero. I think I've narrowed it down to the PFC also since the voltage across the big cap is only 170v. I'm wondering about a defective diode or maybe the PWM controller. I just got a couple of parts in and I'll report back if I figure anything out.

[xyloeye]

Re: Polaroid PSU output power

Would the PFC boost voltage be that high (390) in the US where we start with 120VAC? tom66 is in the UK where it's 230VAC.

[budm]

Re: Polaroid PSU output power

It is the PFC Voltage booster (done by PFC Controller IC) that boost the DC out put to 370~400VDC range, without it the voltage on the filter cap will be only 170VDC (120VAC in), or 330VDC (for 30VAC in). That is why the cap is rated at 450VDC.

[xyloeye]

Re: Polaroid PSU output power

Oh, thanks, Bud. I didn't realize the boost was that much. I think I saw in another thread (could be mistaken) where you mentioned that the high voltage film cap is part of the 24v circuit. Is it necessary for proper function of the PFC?

[13919]

Re: Polaroid PSU output power

Great site, I just joined.Anyone know where the find a schematic with voltages for this power supply. ine is dead across the dotted line.

[13919]

Re: Polaroid PSU output power

Add I replaced all 6 of the 680uf caps because they were rounded on the top

[vinceroger69]

Re: Polaroid PSU output power

Add I replaced all 6 of the 680uf caps because they were rounded on the top

whats the exact power board numbers so we can see if we can find a schematic for it.

[13919]

Re: Polaroid PSU output power

kas200-5s2418112xl

[13919]

Re: Polaroid PSU output power

I guess my big question is what carries the voltage across the dotted line on the board. all the test points on the 110v side have power,everything on the slave side is dead.Looks like the only bridge components are a cap, a xformer. three tiny square thingies with 4 legs (technical term),and a coil.Trying to back trace to a dead part.

[vinceroger69]

Re: Polaroid PSU output power

kas200-5s2418112xl

schematic i think.

[budm]

Re: Polaroid PSU output power

Your power supply is just like the one as shown in post 3?