SS Amp no sound, .49DC out of speaker wires; blown caps changed

[Garrick]

Hi!

I have an Orange 35LDX that produces no sound. There was a blown 35v supply cap. The other 35v supply cap seemed slightly swollen. In that situation, there was absolutely no sound coming from anything, but the onboard tuner still worked and the power light still came on. I changed both power supply capacitors with their equivalent (3300uf, 35v). Now there's a slight hum at the transformer, and there's .49v of DC current coming out of the speaker wires. Still no sound.
I cant afford to go shooting in the dark too much, but want to save this amp. I love the sound, and it was gift from my wife, who isn't doing so well as the years go by.
Any tips on where to start troubleshooting?
Thanks so much for your time and expertise.

[Mick Bailey]

If you have a schematic or link to one, would you post it?

Are you now getting a steady +/- 35V? What about the opamp supply voltages (+/- 15v?) Also, does the headphone output work?

The 0.49v on the output is higher than I'd expect from an amp that uses an IC for the power amp. Is this measured with the speaker connected or disconnected?

[Garrick]

Thanks for helping! Apparently, Orange is really tight about sharing their schematics. The closest I could find available is attached, but it's not identical. The 35LDX has a tuner and effects chips. I unplugged those to give it a go, and instantly popped the first power supply capacitor the second I plugged it in.
The .49v I was getting at the speaker leads was with the speaker unplugged. Not getting anything with the leads on the speaker. It looks like the input transformer is putting out about 21v with 1.2 amps as described on its label. Haven't tried the headphone output- will do when I get a chance Wednesday (when some 50v caps arrive- figured it might be wise to up the voltage). I would just take it to an expert, but I live in a very rural location in SC. There was someone I made an appointment with about an hour away, but that fell through twice after quite a bit of driving. I greatly appreciate any and all advice!

[The Dude]

Are you sure you installed the filter caps with the correct polarity/

[Jon Snell]

If you had DC on the speaker jack BEFORE replacing the capacitors and assuming there are no nasty dry joints, replace the IC as well and use fresh heatsink compound and isolator washer/mica pad.

[Garrick]

Are you sure you installed the filter caps with the correct polarity/

Yeah, the caps were marked and the board thankfully is too.

[Mick Bailey]

It looks like the input transformer is putting out about 21v with 1.2 amps as described on its label.

That would be the AC voltage. What are the DC voltages? You should have the main power supply rails to the output IC (measured immediately after the main filter caps) as well as a lower voltage that powers any opamps in the preamp (if fitted), plus the effects circuit. It's important to check the voltages are correct after a problem has been fixed.

Usually, if the headphone output works then the preamp and associated voltages are OK, but you still need to check the main supply rails to make sure the power amp is getting the correct and balanced voltage.

[eschertron]

If Garrick's amp is like the schem provided by VintageKiki (post # 3) above, the headphones are tapped off the power chip's output.

Also, it looks like the shorting (output) jacks all need to be working correctly for the ground to get to the desired output. If either the headphone or ext speaker jack are not making good connection on the shorting pin, then the internal speaker will not work. This does not jive with finding voltage on the speaker wires, however.

[Mick Bailey]

The 35LDX is a lot more complex - looks to be 4 opamps and more ICs on the digital board, so I think the posted schematic is way off. Maybe though the basic topology is the same - the headphones may well come off the power amp.

[Garrick]

I am so blind! I was so wrapped up about the blown capacitor that I didn't notice a burned connector RIGHT NEXT to the caps I replaced!
Attached is a pic I took to make sure I have the negatives on the right side before I took the original blown capacitor out. You can see the burned connector right behind it. I took a pic with the new caps in and you can see the connector is burned all the way through.

Also attached is the general layout of the whole mainboard, minus the tuner and effects boards.

What would cause this? Is it from when the original cap blew or do I likely have another issue down the line?

I apologize if I wasted y'all's time. I can't believe I pulled those old caps, put in new ones TWICE before I noticed the burned out connector RIGHT NEXT TO THEM!

[Mick Bailey]

The burnt part is a jumper that's acted like a fuse. It possibly feeds the cap from the rectifier. Something has to pull more current than the jumper was intended to take and likely the faulty capacitor was shorting. If you'd checked the DC voltages you would have seen one of the supply rails to the power amp was missing. I'd also check the rectifier using your DMM on diode test mode to make sure it hasn't been damaged at the same time.

[Garrick]

Thanks! I will do once I figure out how. For now, I soldered in a new connector where the one had burned out, and the amp is functional again, sounding same as ever, even with different voltage caps. Hopefully I haven't made whatever caused the blown cap and short to occur worse. My optimistic thought is maybe the cap was bad, popped, and then there was too much draw and that burned the connector.

[Mick Bailey]

If the amp now works the rectifier is good. When they fail they usually short and pass AC, though sometimes they blow apart and can fail open if the fault is catastrophic. Looks like your amp is fixed and good for quite a few more years. BTW, the term for the burnt part is a jumper rather than connector.

[g1]

Quite surprised it could burn through a jumper wire like that without blowing the fuse.