The only components I haven't been able to verify (because they're on the circuit) are C33/34. I suspect those could be out of spec, I'll see what happens if I can replace those.
All 4 are heating up the same. No heat from another source. Ok so it sounds like these capacitors should not be getting this hot in this circuit?
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They aren't backwards, are they? Just thinking that caps get hot when reverse biased, but a low voltage cap usually doesn't blow up.
Oh just checked the area next to the chip resistors and it’s really hot! Maybe it is the chip resistors (R38 and R39)after all.
So it I think I've been focusing on the wrong area all along and the chip resistors are the heat source which radiates through the pub through the PCB the capacitors. I didn't think it was possible until I touched the pcb next to the chip resistors and that was too hot to the touch. I also noticed those resistors have large pads apparently for heat sinking. Would replacing those with higher power rated resistors (3-4Watts) reduce the heat?
Ah that's right. The heat dissipation rises with surface. I see.
Appreciate all your help. I would have replaced those capacitors and left wondering why they were also running hot. I'm pretty sure its the chip resistors at this point and I don't know if I can fit a larger resistor to dissipate more heat.
I had hot resistors discolouring and burning the pcb. It turned out to be the caps leaking and the reduction in capacity causing high current ripple.
Ok I'll keep c33/34 on the radar. I think the electrolytic are ok because the symptoms were happening before with original stocked electrolytic.
It's amazing how much heat can be conducted through wires or traces into capacitors. I consider it an engineering 101 blunder, yet so many audio products have suffered from this. The classic example is voltage dropping resistors soldered directly to the leads of twist-loc cans. Lots of way to provide a thermal break, but they're always easiest to apply during the original design.
SMD capacitors of that vintage are dreadful... the seals deteriorate and the capacitors leak and go high ESR. I frequently replace these in vintage computer/gaming gear that was made in the 90s. Clean the board thoroughly with alcohol where the stuff has leaked. You will know if it's leaked if you smell a very fishy smell when you heat the area up with a soldering iron!
These smd capacitors were purchased from mouser and installed a few months ago. Good to know about the fishy smell.
Turns out it is not the resistors, or at least the resistors are not the main heat source and there are other sources. those resistors in the the right channel are twice the distance from the electrolytic caps.
What are twist-loc cans? Would you recommend those as a heatsink this in circuit? I don't know if they fit.
Twist lock capacitors. Basically the heat travels along the lead into the large cap where it increases the internal temperature and that's harder to get rid of in a single larger cap. Heat really shortens the electrolytic cap lifetime, where some are 1000h any shortening by design is daft.
Twist-loc cans are old tech, usually found in tube amps. The can had (usually) four metal ears that went through slots in the chassis or pcb. They got twisted with pliers about 90 degrees to lock the cap in place. Not typically found in new designs AFAIK. They had heavy lugs in the center to solder to, which were very convenient to solder dropping resistors to, thus the heat problem. Still, the problem can happen with any cap.
a - how do you know?
b - if that is the case, you have a serious problem, maybe electrolytics with significant overvoltage to their rating.
Jan
a- I used an IR temperature thermometer and I can rest my finger on the capacitor for about a second before its too hot. is around 80C too hot and unexpected for these electrolytic in the circuit?
b- I've measured 15 Volts across each electrolytic.
Are the caps in the wrong way around, + and - mixed up? That would explain it.
Are you sure they are not 10V caps - I saw a pic with '10V' on the top of one.
Jan
Are you sure they are not 10V caps - I saw a pic with '10V' on the top of one.
Jan