Are These Discolored Resistors a Problem?

[mushroom]

I have a Traynor DH40H IronHorse that stopped making any sound one day. I'm a total amateur when it comes to electronics but the subject does interest me so I tried poking around the amp to figure out what was wrong.

The power light comes on and I can hear the transformer hum. The tubes weren't glowing, so I took them out & put them back in, cleaned the contacts, bought brand new tubes, nothing. This amp has bias test points and they read 0V.
I then opened the amp and saw nothing out of the ordinary except for 2 discolored resistors. They are 1K 2W resistors that I believe are the screen resistors.
Pictures are attached.

I took it to the tech in my town but it fired right up on their bench, and they could find nothing wrong with it. They said it's fine for the resistors and PCB to be discolored because of the heat. They brought it back and it was silent again (they witnessed it, so they're taking it back to their bench).

I can't get rid of a little bit of anxiety about this mysterious intermittent issue. Could anyone here take a look at the attached pictures and tell me if you think the resistors being discolored is a problem at all? Or if you have any ideas about what could have been wrong with it?

Thank you for your time!

[sluckey]

The tubes weren't glowing

Does this mean you could not even see the filaments glowing orange? No filaments would explain a dead amp. Look for a bad connection where the filament wires attach to the pcb.

Burned screen resistors is often the sign of a failed tube. Those 1K resistors should have color bands of brown, black, and red, but the red band has been so hot the color has changed. I would replace them and not mount them close to the board. Let them stand up at least 1/2" above the board.

[mushroom]

Does this mean you could not even see the filaments glowing orange? No filaments would explain a dead amp. Look for a bad connection where the filament wires attach to the pcb.

Thank you, this is so helpful! Yes, no lights at all in either EL34.
Also no glow from the V3 preamp tube, not sure if/how that's related. V1 and V2 preamp tubes were glowing orange.

It looks like the filament wires are connected by a plastic clip, I'll check that if the amp comes back without an issue identified.

[tdvt]

The one end of R25 (towards R50) looks like a terribly degraded solder joint, maybe to the point of failure, though neither resistor's solder joints to that point look great. Cause or effect...?

Hopefully the PCB traces (conductors) are still OK. The outer ends look alright, worst case you may have to jumper from the screen voltage supply to that point in the circuit, if the traces are bad.


Kind of weird some tubes heaters were lit but not others, but not sure how the heaters are wired. 

[sluckey]

Yes, no lights at all in either EL34.
Also no glow from the V3 preamp tube, not sure if/how that's related. V1 and V2 preamp tubes were glowing orange.

It looks like the filament wires are connected by a plastic clip, I'll check that if the amp comes back without an issue identified.

V1 and V2 are dc heated from a different source. You need to troubleshoot the 6.3VAC feed to the EL34s and V3. Very simple circuit.

Tell your tech what you just told me about V1 and V2. He should be able to quickly fix the other heater circuit. Have him replace those screen resistors while he's in there.

[Latole]

". ..I took it to the tech in my town but it fired right up on their bench, and they could find nothing wrong with it. "

Sorry he is not a tech or he have no time for you.
See a qualifie tech.

[Merlin]

I can't get rid of a little bit of anxiety about this mysterious intermittent issue. Could anyone here take a look at the attached pictures and tell me if you think the resistors being discolored is a problem at all? Or if you have any ideas about what could have been wrong with it?

Sounds like a broken wire or joint somewhere, which was dislodged and 'fixed' itself when you lugged it into town. The resistors look fine, they go that colour after a while of being hot, but they don't look burnt. No harm in replacing them of course.

[Beezerboy]

I would absolutely replace those resistors. check the trace real close, it is probably damaged. I would consider a hard wire connection. at least scrape back the trace and solder a jumper from that to the new resistors. and as mentioned, get the lead connections up a bit off the board.

I also agree with the idea that there are cracked solder joints somewhere that is causing the intermittent. you say the preamp tubes don't glow... start at the power supply and check the whole path. re-flow any solder joint that look questionable. Traynor also uses a lot of ribbon connectors... check those too.


https://www.thetubestore.com/lib/thetubestore/schematics/Traynor/Traynor-DH40H-Schematic.pdf