UR6QW equalizer/audio toy back from the dead.

[nomadradio]

A long-time customer talked me into fixing his UR5QW equalizer/echo/etc audio gadget. Looks cool enough.

Said it went totally dead. No output of any kind. And no schematic to be found.

Sure enough, there's a tiny part that looks like either a surface-mount fuse or a PTC protector in line with the power input. Open circuit. And feeding power past it shows a short to ground. Sure enough the tiny SMT voltage regulator is dead as a post. No output. But if I feed it 5 Volts to its output pin from a bench supply, it comes on and functions.

I have no intention of replacing the tiny regulator. Just looks like maybe it wasn't big enough.

Overkill to the rescue. The dead regulator feeds 5 Volts to the chips. A 7805T regulator is rated at 1 Amp. These chips draw just over 1/10 that much current. I don't generally use the gray silicone "sil-pad" insulators, but this chip won't need heat sinking. Just need some place to bolt it down.

The 10uf cap goes from the input pin to the center (ground) pin. Any time the filter cap that feeds it is a distance away (like inside the wall wart) this is recommended to keep the regulator stable.

The foil trace that leads from the old regulator to the chips gets scraped to lap-solder the wire from the new regulator's output pin.

Finally, the old regulator comes out. No need to molest the blown fuse. The new wiring bypasses it.

And now it works. I have had poor luck with smt "power" components like this voltage regulator. Seems that using enough heat to loosen it always damages the ground foil under it. And then maybe it's the heat that caused the part to fail that destroys the glue.

Overkill in defense of reliability is no vice.

73

 

[brandon7861]

A long-time customer talked me into fixing his UR5QW equalizer/echo/etc audio gadget. Looks cool enough.

Said it went totally dead. No output of any kind. And no schematic to be found.

Sure enough, there's a tiny part that looks like either a surface-mount fuse or a PTC protector in line with the power input. Open circuit. And feeding power into it shows a short to ground. Sure enough the tiny SMT voltage regulator is dead as a post. No output. But if I feed it 5 Volts to its output pin from a bench supply, it comes on and functions.

I have no intention of replacing the tiny regulator. Just looks like maybe it wasn't big enough.

Overkill to the rescue. The dead regulator feeds 5 Volts to the chips. A 7805T regulator is rated at 1 Amp. These chips draw just over 1/10 that much current. I don't generally use the gray silicone "sil-pad" insulators, but this chip won't need heat sinking. Just need some place to bolt it down.

The 10uf cap goes from the input pin to the center (ground) pin. Any time the filter cap that feeds it is a distance away (like inside the wall wart) this is recommended to keep the regulator stable.

The foil trace that leads from the old regulator to the chips gets scraped to lap-solder the wire from the new regulator's output pin.

Finally, the old regulator comes out. No need to molest the blown fuse. The new wiring bypasses it.

And now it works. I have had poor luck with smt "power" components like this voltage regulator. Seems that using enough heat to loosen it always damages the ground foil under it. And then maybe it's the heat that caused the part to fail that destroys the glue.

Overkill in defense of reliability is no vice.

73

That's cool!

I always flow some lead solder into SMD parts before attempting to remove them. That lead-free stuff requires way too much heat without it. I think you made the right choice putting it on the heat sync though. When I put the arduino nano in the 980, the only 5v source was a transistor that looked just like your 5v SMD regulator and it ran on the warm side before I added the arduino. I figure if it blows, I'll have to do what you did there.

If you decide to sell that, I would be interested.

 

[nomadradio]

If you decide to sell that

It was a repair job for hire. Not mine to sell.

73

 

[Cable Guy]

I bought one over a year ago, it didn't work one day so I opened it up. The diode strung from the negative side of the power connector to the board had burned up. My fault, not from reverse connection. That device doesn't float the chassis or negative side of the power connector. Connecting it to a cobra 2k, the radio chassis and subsequently the antenna braid become ground. If, for whatever reason, your working on something like a radio or amp with a broken ground, it will pull it through your setup, the antenna, bench radio, ur6qw, which all ends up at that diode, to power it. The hint should have been, "hey, this radio comes on when all I have connected is the positive power." Long story short, I melted a diode in it because it combines chassis and ground through the mic wiring to the radio, and I pulled a butt load of current through it.

 

[N8YX]

A few thoughts on SMT stuff:

If you have to remove it, make sure you have the right tools. Chip Quik being one of them for boards you CANNOT afford to damage.

Nomad's observation vis the SMT regulator and heat are spot-on. Expect to see more of this kind of thing. Sadly, it isn't limited to the little guys. I have a 703+ in my to-do pile which suffered from a known design issue and will require replacement of an active device in the RF amp chain.

There's a time and place for through-hole components. I doubt the unit would have failed if it would have used a 7805T at the outset.