Magnavox 42MF521D/37 - Dead

[kevinm34232]

I picked up this TV with the power supply board missing. The owner originally had someone come look at TV and replace some caps, that didn't fix it and apparently he didn't return the PS board back. So anyways I purchased a new PS board. TV still does not come on. Seems dead but have correct voltages off of PS board (16v and 24v going to main board and inverter boards). However, there is no standby light and no response when hitting power button. Also these voltages are immediately present when unit is plugged in.

Not sure where to go from here..

[kevinm34232]

Re: Magnavox 42MF521D/37 - Dead

Missing 12VS here on main board, have the 16V on VCC pin but 0v OUT.

[tom66]

Re: Magnavox 42MF521D/37 - Dead

Check INH pin should be logic HIGH (>1V)

[kevinm34232]

Re: Magnavox 42MF521D/37 - Dead

It's 0v, but Im not sure now if it's because I have the inverter boards and T-Con board unplugged because of this chassis design...

Nope it's not that, carefully plugged everything else in.. There is another chip close to 7003 labeled 7004. That has 24v on VCC abd 5v on OUT pin.

[tom66]

Re: Magnavox 42MF521D/37 - Dead

Should still be OK without those so the chip is at fault it would appear as INH should be high to turn off the converter.

Check 6001 for shorts and check 5001 appears low resistance (should appear like a dead short.)

[kevinm34232]

Re: Magnavox 42MF521D/37 - Dead

Arghh I think I was looking at wrong page, was trying to find where the 16v or 24v goes down to 12v, it's missing at the fuse.

[tom66]

Re: Magnavox 42MF521D/37 - Dead

The fuse is blown or OK?

[kevinm34232]

Re: Magnavox 42MF521D/37 - Dead

5001 is good. D6001 seems weird, it was reading .012 in both directions, and lifted one side and it reads .0L and .167. Same with D6002.

Fuse is good, but I don't have the 12v on either side of it.

[tom66]

Re: Magnavox 42MF521D/37 - Dead

You need to trace where the 12V comes from but I suspect it comes from that very DC-DC you were originally suspecting... note the DC-DC is a SOURCE not a SINK.

[kevinm34232]

Re: Magnavox 42MF521D/37 - Dead

That page is labeled VIDEO DAC. Not sure if that is the source or just another circuit. What is PWR-SAVING?

[tom66]

Re: Magnavox 42MF521D/37 - Dead

PWR-SAVING will be for standby mode but we have determined that since INH is low (previously my mistake; datasheet says LOW should turn on output) the chip should be working as long as it has 16V in. However as it is not generating the 12V something else is wrong other than the diode or inductor so I suspect the IC itself is failed.

[kevinm34232]

Re: Magnavox 42MF521D/37 - Dead

Hmm OK. Just added a power block diagram to post above, does that help you at all?

It looks like 12VS may be coming from the 16v?

[tom66]

Re: Magnavox 42MF521D/37 - Dead

Yes, the IC will be converting the 16V down to 12V, you need to find out why that isn't working -- the IC is dead or there is a short circuit on the 12V.

[kevinm34232]

Re: Magnavox 42MF521D/37 - Dead

Yea but the one we were looking at (7003) had 24v input so I was thinking it wasn't the one.. I just haven't seen anything else in the SM where the 16v goes to 12v. I took readings from the caps in the area does that tell you anything?

[tom66]

Re: Magnavox 42MF521D/37 - Dead

Either you have the wrong SM or there's been a design change. Am I wrong in saying you have no 12VS? Whatever the input voltage, 7003 ain't working. It is an ex-parrot.

[kevinm34232]

Re: Magnavox 42MF521D/37 - Dead

For some reason I thought I was getting 24v at VCC but its 17v, my bad. I just ordered a new regulator for that 7003 will let you know, thanks for the help!

[tom66]

Re: Magnavox 42MF521D/37 - Dead

Did you check 12VS for shorts first?

[kevinm34232]

Re: Magnavox 42MF521D/37 - Dead

Of course.. not.. I have a short to ground from the OUT pin of 7003.

[tom66]

Re: Magnavox 42MF521D/37 - Dead

So that's where the problem is, the 7003 is probably fine but something is wrong on the rest of the main board. Finding the exact failure will be tricky.

[kevinm34232]

Re: Magnavox 42MF521D/37 - Dead

Just looking at what is fed by the 12v it sure does look tricky.. And what's the odds it's not one of the flat pack IC's??