CRATE retrofex rfx30 blown output IC

[goontron]

DISCLAIMER: i only have half a f**king clue when it comes to SS audio equipment, so bear with me, i exist in the world of valve radios.

i have a retrofex with a blown output IC, the visible numbers are:
TDA2050
88047VW
SGP4

along with the IC a 1 ohm resistor (R63) blew, if thats of any help, it usually is with valves but IDK about IC's. the fault was isolated to a bad (shorted) external speaker cord.

[diif]

Re: CRATE retrofex rfx30 blown output IC

Something like this ?
http://www.ebay.com/itm/like/180920315440?lpid=82

[goontron]

Re: CRATE retrofex rfx30 blown output IC

yeah, it looks like that would work....Thanks

[kaboom]

Re: CRATE retrofex rfx30 blown output IC

Is that 1-ohm resistor between either pin 3 or 5 and the neg or pos supply?

Make sure the new IC has both supply rails unless you like dumping one of them into the speaker.

[goontron]

Re: CRATE retrofex rfx30 blown output IC

Is that 1-ohm resistor between either pin 3 or 5 and the neg or pos supply?

Make sure the new IC has both supply rails unless you like dumping one of them into the speaker.

the resistor is at pin5, after a diode. pin3 goes to a cap and the ribbon.
this SS stuff is confusing...

[kaboom]

Re: CRATE retrofex rfx30 blown output IC

this SS stuff is confusing...

It gets easier, believe me...

After a few LM386 amps, I built a few TDA2002 ones back in the day.

It's funny- I tried building two amps on one board. The lousy layout resulted in GND and feedback via B+. One IC shorted and the other kept oscillating, even w/o it's "partner."

That was over 12 years ago- I've learned lots since then, and you will too.

It looks like they're clipping that signal with a diode (fed by that resistor) and sending part of it back down the ribbon. To the preamp for some kind of AGC?

Can you post a topside board pic? Pins 3 and 5 both go directly to their power feeds, doubled-up wires in the ribbon cable.

[goontron]

Re: CRATE retrofex rfx30 blown output IC

it has a DSP as well as an AGC, stand by for pics of all boards.

[goontron]

Re: CRATE retrofex rfx30 blown output IC

pics.

[kaboom]

Re: CRATE retrofex rfx30 blown output IC

Okay, those two diodes are the clamping diodes as shown in the datasheet.

Check the green poly cap for shorts. It and that resistor go from pin 4 of the IC (output) to GND. If that cap shorts, the 1-ohm resistor gets full output signal voltage.

Or, if the amp oscillates, the low Xc of the cap causes that resistor to absorb the parasites. If it keeps up for too long, the resistor smokes.

What's the value of those two electrolytics? From pin 3 and 5, to common.

I'd use ones no smaller than 470u, with voltage rating above the supplies. There should be a .1u MLCC across each of those decoupling 'lytics. Those two 'lytics should be low-esr- PW/HE/FC/FM, etc.

Those TDAs have a need to be tamed- that 1-ohm (R63) will not burn up like that unless the poly cap shorts or the amp oscillates.

Edit- See annotated pic.

[goontron]

Re: CRATE retrofex rfx30 blown output IC

the resistor is still good, just dark. the fault was a shorted ext speaker cable, as seen by it killing a valve amp too. (already fixed)

[kaboom]

Re: CRATE retrofex rfx30 blown output IC

the resistor is still good, just dark. the fault was a shorted ext speaker cable, as seen by it killing a valve amp too. (already fixed)

Do you want a callback, or do you want to fix it (hopefully) for good?

Now check that green poly cap.

[goontron]

Re: CRATE retrofex rfx30 blown output IC

Do you want a callback, or do you want to fix it (hopefully) for good?

Now check that green poly cap.

its failed, open. no capacitance, no resistance.

[kaboom]

Re: CRATE retrofex rfx30 blown output IC

its failed, open. no capacitance, no resistance.

And that means the replacement IC will oscillate and die.

The original IC oscillated for whatever reason, as evidenced by that smoked resistor. The current went thru the series combination of that cap and R63. After a while, the cap shorted, causing excessive dissipation in R63. Then, it opened, now leaving a fault (lack of parasitic suppression) that will take out the new IC.

Follow the suggestions in that annotated pic.

Just because you isolated a bad speaker cable doesn't mean you don't have more work to do.

Don't replace that IC without at least replacing that cap and resistor!

I had a TDA2002 amp, a Cebek module, with improper routing/bonding of the grounds, taking power GND a bit too near the input. Guess how high up it was oscillating? In the AM BCB! Only 2-3W out... Got 10W out (4-ohms) after redoing the GNDs.

[goontron]

Re: CRATE retrofex rfx30 blown output IC

shopping list: one (NLA) TDA2050, one 1/2watt 1ohm resistor, one .22uf 250v poly capacitor, and one 1amp 250v fuse.

[kaboom]

Re: CRATE retrofex rfx30 blown output IC

shopping list: one (NLA) TDA2050, one 1/2watt 1ohm resistor, one .22uf 250v poly capacitor, and one 1amp 250v fuse.

I typed "1-2W" meaning one - two watt, as in "a resistor between 1 and two watts," not a half-watt resistor!

At this point, go with a two-watter.

Mouser P/Ns:

660-MOSX2CT52R1R0J -R63
594-2222-368-25224 -Poly cap
512-UF4004 x2
80-C410C224K1R x2 -MLCCs to go across decoupling 'lytics, below
647-UHE1V471MPD1TD x2-if originals are 35V
647-UHE1H471MPD x2-if originals are 50V

The IC you'll have to get elsewhere:
http://www.ebay.com/itm/1-x-TDA2050-...-/301246868204

Is the fuse slow-blow? What size is it? 1-1/4x1/4 or 5x20mm?

[goontron]

Re: CRATE retrofex rfx30 blown output IC

I typed "1-2W" meaning one - two watt, as in "a resistor between 1 and two watts," not a half-watt resistor!

At this point, go with a two-watter.

Mouser P/Ns:

660-MOSX2CT52R1R0J -R63
594-2222-368-25224 -Poly cap
512-UF4004 x2
80-C410C224K1R x2 -MLCCs to go across decoupling 'lytics, below
647-UHE1V471MPD1TD x2-if originals are 35V
647-UHE1H471MPD x2-if originals are 50V

The IC you'll have to get elsewhere:
http://www.ebay.com/itm/1-x-TDA2050-...-/301246868204

Is the fuse slow-blow? What size is it? 1-1/4x1/4 or 5x20mm?

ok. the fuse wasn't a slow-blow, but it should be, that much i can gather.i found one floating in the bottom of my toolbox.

[goontron]

Re: CRATE retrofex rfx30 blown output IC

the lytecs have high ESR, rebuilding the whole daughter board.

[kaboom]

Re: CRATE retrofex rfx30 blown output IC

the lytecs have high ESR, rebuilding the whole daughter board.

You may have to use smaller caps than 470u, if space is tight. Don't go below 220u.
http://www.mouser.com/Search/Refine....d=nichicon+uhe

[kaboom]

Re: CRATE retrofex rfx30 blown output IC

Also, the stuff on the other side of that board can stay:

C34
C37
R58
R59

But change that coupling cap.