Potential Manufacturing fault in Marshall DSL40s

[DaiTheFlu1967]

Hey DrGonz78, thank you very much for taking a look. I hadnt noticed R14's crack! And like you said its probably not a big deal but im pretty sure i have some high watt low ohm resistors that might be a match, ill look at the schematic in a minute and check the value. If i dont have one ill order one alongside my next mouser order. And as far as the glue goes im with you on that as well. I think i just wanted to hear that im not being overly cautious before i started cleaning up the rest of the glue thats starting to look like the glue around R8 and more so R9. If you dont mind i have one more question. So is this glue used solely for populating the board more easily? Like are the larger filter caps just glued in place so they wont fall out/off while the machine is soldering everything? (I assume at this price point population and soldering isnt dont by hand lol). Or is the glue there to keep the capacitors from movement which could weaken their leads? I ask because im wondering if the glue should be replaced (but with an appropriate glue that wont become conductive down the line).

Again thankyou, your input was really helpful. And i love your handle, one of my favorite books is "The Curse of Lono" by the man himself Hunter S. Thompson. The first time i read it was when I was about 16 years old and i was really sick so i was in bed and had nothing but time to read so i read it all in a day. The island of Hawaii and the adventure was described in such great detail that i felt like I was right there experiencing it all. I came away from that book feeling as if I had just landed back in Texas after vacationing in Hawaii lol.

EDIT: Lol i just realized the picture of R14 was part of the quote i posted replying to the tech who posted it. Luckily that wasnt my amp but none the less your observation made me decide i should look over all those larger resistors in my amp whenever i go in this week to carefully remove the rest of the suspect glue.

[SoulFetish]

If you dont mind reading my post above this one replying to the OP and giving me your professional thoughts about removing the rest of the dark glue from around the board I would appriciate it. My amp is one of the first off the line (bought second month after release serial date of 11-17). And i had this failure happen over a year ago and its been working flawlessly ever since i fixed it but im questioning if i should remove the glue from the other high voltage area just to be safe. I put a choke in a few months ago and when i was removing the choke resistor (i know thats not the correct terminology but im drawing a blank) i noticed another resistor pair close to the other set of filter caps that is starting to look the same as the pair that had the arch occur. If youd like pictures or for a more specific explanation let me know and ill look at the schematic and we can figure out what kind of voltage that other pair is close to. Thanks for your help!

I would recommend replacing those other bleeders for sure. Remove the glue from the area and install new resistors leaving 3/4” or so space between the resistor and board.
I think on a previous amp, the fault occurred in the area you are talking about.

[Helmholtz]

. Or is the glue there to keep the capacitors from movement which could weaken their leads? I ask because im wondering if the glue should be replaced (but with an appropriate glue that wont become conductive down the line).

That.

[g1]

Am I correct to think that not only is the glue becoming conductive, it is breaking down the conformal coating as well?
Or is it just that the conformal is not rated for higher voltages?

[SoulFetish]

So, a resistor has 2 (sometimes 3) parameters for voltage rating. if memory serves, data sheets usually list these as the insulation withstand voltage, breakdown voltage, and sometimes nominal working voltage.
Im suspicious that the glue is breaking down the insulation. Clearly the glue having a reaction to areas where the voltages are the highest and currents are the highest. The glue is discolored right at the ground nodes of the filter caps and along HV pcb traces.

edit: I just checked a generic yago 220k/2W carbon film insulation rating and it lists 1000V for 1W and above

[tdlunsfo]

In my case I remember the removal of all the glue to be pretty time consuming and outside my clients budget so I scrapped away any glue that was touching other components leads or on top of other HV traces. I did worry about what the glue was doing to the capacitors and cap leads but so far everything seemed to be kosher.