Fender Champion 20 Solid State Amp - lights up. no sound

[earache]

Hello

I have a Fender Champion 20 Solid State amp that lights up but makes no sound. I looked inside and there was a burnt resistor that I subsequently replaced - a 1 watt 22 ohm resistor, one of a pair of probably power resistors as they are mounted elevated off of the circuit board. The resistor in question was at R4 per the legend on the circuit board.

I checked out the input jack and the solder connection seems good. Anyone have a similar problem with one of these amps? It's one of the DSP effect equipped Fenders from around 2014.

I haven't been able to find a schematic online, so if someone could help there, that would be great.

Thanks in advance

[DrGonz78]

I think this might be the correct schematic. It has R3 and R4 as a 1 watt 22 ohm resistor.

[The Dude]

If R4 was open, I'd first see if the -15V supply is there (marked VEE on the schematic) after replacing the resistor.

[earache]

Hi Guys -

Thanks much for the correct schematic and your kind attention.

There is -15V at VEE after I replaced the 22 ohm resistor. It's actually measuring more like -19V

That resistor was pretty toasted, heated up enough to burn all the color coded markings off of it. I'm not sure what would have caused that.

[Marshtech]

The output power amp chip TDA2050 is likely shot if there's no sound. Did you test the speaker?

[earache]

Hi
Marshtech


Thanks for the reply!
Yes I did test the speaker, it works.

[earache]

Additionally, everything still lights up on the front panel, and the speaker 'clicks' when power is cycled

[g1]

Just a note of caution, most of the TDA2050's readily available are fake. If anyone has a reputable source, please post.

[earache]

Just a note of caution, most of the TDA2050's readily available are fake. If anyone has a reputable source, please post.

Even from Mouser? DigiKey?Jameco?

[g1]

Even from Mouser? DigiKey?Jameco?

It's an obsolete part. As far as I know, none of those places have stock anymore. That is why there are so many fakes available.

[DrGonz78]

I know this is eBay source but I chose to buy a 10 pack a few years ago. So I stand by my experience but yeah it’s still eBay. You never know 100%. Perhaps this guy bought up the last of a huge source when they were discontinued.

[Enzo]

Jameco lists stock on TDA2030 and 2040, but no 2050. Says they are made by ST. They have 369 TDA2030 in stock. TDA2040? they have ONE in stock.

Mouser has none

Digikey has none

B&D has none

Allied none

[earache]

So I believe that the output power amp chip TDA2050 is not the problem, as it has +19 and - 19 at the appropriate legs (3 and 5)

I'm able to get sound out of the headphone jack.

One thing that I didn't mention because I thought it was unrelated - when I got this amp, not only was resistor R4 burnt up, the "power on" LED that shows at the front panel was knocked off, as well as the bezel that covers it.

I replaced it with a different LED that I salvaged from another small solid state Fender amp that's DOA.

It works but doesn't shine as bright as the other original LEDs on the front panel.

I know that lots of times an amp will go quiet because the input jack is no longer soldered correctly, but that's not the case here, as I can play the amp and listen thru head phones.

I believe that the issue is the mute circuit. Could one of you folks give me an idea as to troubleshooting that circuit?

Thanks In Advance

[Enzo]

Why do you think the TDA2050 is OK? It needs the supply voltages, yes, but can still be defective. The headphones are not powered by the TDA2050, phones have a separate driver circuit.

There is however a cutout contact on the phones jack that puts the amp into mute. Check that.

The power amp appears to be on a separate board? Looks like maybe a shielded cable from the preamp to that? Is there signal present on that cable?

[earache]

So in testing the TDA2050 for a signal, the lead slipped and I popped the soldered-on fuse....duh...