Also I realise now how I toasted that resistor, I borrowed a KSC1815 not an KSC1845, oh well it could have gone worse.
Yep, KSC1815 is similar to 2SC1313 voltage wise, still unsure why changing it would have the effect of burning R635.
Also I realise now how I toasted that resistor, I borrowed a KSC1815 not an KSC1845, oh well it could have gone worse.
So something still isn't right.Found it
RS Stock No. 851-2693
Mfr. Part No.PR01000106809JR500
Brand Vishay
These are 1W, 68Ω, 5% resistors - they are quite small but don't discolour - I was able to order just 10.
I have just been on the RS AU website
You can get these
Vishay PR01 Series Axial Metal Film Fixed Resistor 68Ω ±5% 1W ±250ppm/°C
RS Stock No.683-5565
Mfr. Part No.PR01000106809JA100
Brand Vishay
$0.253
Each (In a Pack of 10)
https://au.rs-online.com/web/c/pass...ors/?applied-dimensions=4293491270,4294869117
Which seems to be the same thing.
Are you sure these are the correct resistors? They seem a bit small to me but I'm not sure if that matters with new components.
That's interesting because I didn't unplug many cables when I installed the parts that fried the resistor, no capacitors were changed and when I originally unplugged the EQ or Phono cable I marked them with coloured tape so I couldn't mistake them. Also when I did desolder a lot of cables it worked fine when reassembled.I think so, I went back through my orders and checked, they are small but are rated as 1W which should be plenty. (and is double the rating of the originals).
Even when everything is running right they do get very hot, I suppose it is possible you have something pulling a bit more current, but the only time I have seen that resistor burn up is when there has been a misplaced connector or other fault (like a reversed electrolytic). The two connectors on the EQ or Phono input board are really easy to mix up and cause this exact issue - but don't swap yours without checking first.
While finding the cause you might find it helpful to use insulated wire to extend the connections to that resistor, so you can change it quickly, while you track down the root cause.
I did discover I forgot to replace a 2SC1313 transistor at TR612 with a new KSC1815, could it have blown and be causing the new problems?
Yep still just R635. I'll swap it out for a new one as well as that rogue 2SC1313 now and report back.It is possible - especially if the resistor that's burning is still R635?
BTW: Did you notice the incorrect silk screening on the PSU/Protection PCB for C615 (220µF 35V) - the PSU output filtering capacitor for the -ve supply - if you installed the replacement capacitor as per the silk screening it is back to front! - this could be your problem.Replaced the transistor and resistor and tested it but the new one began to smoke instantly after powering on.
Thanks for the suggestion, I just tried disconnecting the Tone control board and phono board and powering on, it wouldn't pass protection and I could see that poor resistor turning red very quickly.OK, you need to take the load off the PSU and begin to find out why that resistor is taking such a beating.
Try disconnecting the power to the Phono board, and then to the Tone Control board - see if you can get to a position where you can power up without burning that resistor.
Yep I noticed that misprint at the time, I swapped each capacitor with a new one the way they were, it was all original when I got it, plus I recapped this amp back in 2013 and it had been working daily without issue (mostly).See additional 'BTW' note in my post above - is that relevant?
Just replaced the burnt out 100ohm resistor at R621 with a new one and R635 still smokes immediately after powering on.