Magnavox DTV converter won't stay on

[MagnumOpus]

Hi all:

DTV converter is a Magnavox TB100MW9, manufactured by Funai.
It got very light use for about two years, and then it started powering off by itself.

This appears to be a common problem, as I've seen posts in other forums, but no solutions offered.

Typically, one would first suspect the power supply, but there is none.
110v leads are soldered directly to the board.

I visually examined all caps; there are no apparent signs of failure.

So my question is:
Has anyone else encountered this problem, and if so, are there any solutions?
Thanks.

[tom66]

Re: Magnavox DTV converter won't stay on

There IS a power supply. It will just be integrated onto the main board in some way.

[MagnumOpus]

Re: Magnavox(Funai) DTV converter won't stay on

OK, thanks; I see what you mean.

Part of the board is labeled "HOT" and contains (among other things) a 200v cap and what appears to be a transformer.

I also need to clarify my initial post:
It shuts down to standby mode, not completely.
The power switch needs to be turned off for complete shutdown.

Next question(s):
Is there any specific component on the board that's most likely to cause this shutdown problem, and is it necessarily limited to the "HOT" side?

[tom66]

Re: Magnavox DTV converter won't stay on

Can we see some pictures first?

[MagnumOpus]

Re: Magnavox DTV converter won't stay on

OK, this is the closest I can get without losing focus.

[MagnumOpus]

Re: Magnavox DTV converter won't stay on

Also, the brown substance next to that cap doesn't appear to be from it.
(It's actually next to it.)

I noticed that right away, the first time I opened the unit.
I believe it's some sort of glue or sealer.

[bluto]

Re: Magnavox DTV converter won't stay on

Take a good look at all the components and look for anything that looks like it got hot or looks slightly burnt. Look at the tops of all of the capacitors for any signs of bulging or leakage at the bottom. You might also look on the opposite side of the board for bad solder joints. If everything looks good, I would probably start to check for bad caps. If you don't have a capacitor checker, then you may just have to shotgun replacements. The 7 caps around the yellow transformer are for the secondary side of the power supply and would be likely suspects. If you are going to replace them, I would also probably bump up the value of the primary filter cap (the one with the white sealer goo) slightly.

[tom66]

Re: Magnavox DTV converter won't stay on

Wow, that's cheap. It's got a self-oscillating power supply. WHY do Funai (make lower end Magnavox stuff) insist on still using these, I do not know.

There are some voltage check points like AL-3.3V, have tested these?

[MagnumOpus]

Re: Magnavox DTV converter won't stay on

bluto wrote:
Take a good look at all the components and look for anything that looks like it got hot or looks slightly burnt. Look at the tops of all of the capacitors for any signs of bulging or leakage at the bottom. You might also look on the opposite side of the board for bad solder joints.

I did that before starting this thread, but went back to double-check and verify that I didn't miss anything.

Everything appears OK. I even desoldered the cap next to that aforementioned brown goo to verify that it wasn't coming from that cap; it's not.

Shotgunning replacements would be my only option as I don't have a capacitor checker.

tom66 wrote:
There are some voltage check points like AL-3.3V, have tested these?

At one point, I could have, but no longer. Things have gotten worse; now the box powers off to standby immediately, so there's no time to check.

Would it be possible for me to solder the wiring from an AC-to-DC adapter directly into the board, bypassing the power-supply circuit? Or might the transformer have multiple voltage outputs (which would render this idea useless)?

Much thanks to both of you!

[tom66]

Re: Magnavox DTV converter won't stay on

At one point, I could have, but no longer. Things have gotten worse; now the box powers off to standby immediately, so there's no time to check.

You can still check the voltages in standby.

Would it be possible for me to solder the wiring from an AC-to-DC adapter directly into the board, bypassing the power-supply circuit? Or might the transformer have multiple voltage outputs (which would render this idea useless)?

This would probably not work because the power supply has multiple outputs.

[MagnumOpus]

Re: Magnavox DTV converter won't stay on

tom66 wrote:
You can still check the voltages in standby.

OK, thanks...here we go:

Multitester is analog, so voltage readings are approximate.
Markings are in quotes, next to jumper numbers.
These are the only ones that show voltage:

J602 7v "VT"
J612 7v "VT"
J621 .5v "SAFTY" (mispelled, I suspect)
J622 1.65v (under the circuit board)
J631 .25v "D-1.8V"
J638 3v "VMUTE"
J644 .05v
J647 3.3v "DTV-S-SIN"
J649 3.3v "D-ALL3.3V" (under the sticker)
J650 .5v "SAFTY"
J651 .05v "9V"
J655 2.5v
J657 3.3v "D-ALL3.3V"
J659 3.3v "D-ALL3.3V"
J661 7v

[VladC]

Re: Magnavox DTV converter won't stay on

So is this thread still alive? I have the same two boards which do not turn on. I can see generation on quarts and voltages look like OP posted. One board is blackened under the D620, but the diode works (other board no visible damage). I hope it does count as my first post. I have some knowledge about electronics and tools and skills but I need help. Please do!