Either something is touching that shouldn't be or that second 130 ohm resistor is blown and open.
[RESOLVED] Up in Smoke (resistor between 44L and 30L)
- Thread starter WK3K
- Start date
I don't suppose you have any other resistors sitting around? Ultimately you'll want to replace the 130 ohm resistors and be sure that no part of those resistors touches a lug where the striped end of a power supply cap mounts, as that will just blow those resistors up immediately.
With fresh resistors, you'll want to power up the amp with no 2A3 in that channel and that red wire pulled to see if those 130 ohm resistors hold, then we can start adding stuff back.
With fresh resistors, you'll want to power up the amp with no 2A3 in that channel and that red wire pulled to see if those 130 ohm resistors hold, then we can start adding stuff back.
WK3K
New member
Sounds good. I don't have any extra, but it sounds like @Jamien is going to send some over. If that doesn't pan out, I'll track some down.
Thanks again for your help. Now that I've pulled things apart I'm suspicious of that resistor between 30 and 27 touching the terminal strip or the black wire from the ground buss going into 29. I'll report back when I can replace the 130ohm resistors and then measure 27 again.
Thanks again for your help. Now that I've pulled things apart I'm suspicious of that resistor between 30 and 27 touching the terminal strip or the black wire from the ground buss going into 29. I'll report back when I can replace the 130ohm resistors and then measure 27 again.
WK3K
New member
Hi PB,
I replaced the 130ohm resistors, re-did all the resistance checks (all WNL), removed the red wire at 27U, removed the 2A3's, and powered the amp on with the black lead of my voltage meter to 8U and the red clipped to 27U. I'm getting 460v.
I guess the good news is that nothing popped or smoked this time... I should mention all my power transformer secondary tests were totally normal too.
Will wait further instructions from you before proceeding.
@Jamier — thanks again for the resistors! They got here quick as a wink.
I replaced the 130ohm resistors, re-did all the resistance checks (all WNL), removed the red wire at 27U, removed the 2A3's, and powered the amp on with the black lead of my voltage meter to 8U and the red clipped to 27U. I'm getting 460v.
I guess the good news is that nothing popped or smoked this time... I should mention all my power transformer secondary tests were totally normal too.
Will wait further instructions from you before proceeding.
@Jamier — thanks again for the resistors! They got here quick as a wink.
Go ahead and plug in the 2A3, then measure the DC voltages on that 4 pin socket.
Hey, that's great. You have both HV branches operating with both 2A3s.
Next you will want to attach the red wire back where it went, fire up the amp, then keep an eye on the voltage at pin 1 on the 4 pin socket on the dead side. If it settles to about 375 again and just sits there, then you can measure the output voltage of each side of the C4S board (easiest to just probe the metal tab on each MJE5731A). If they are both around 220V, then your amp is ready to listen to.
Next you will want to attach the red wire back where it went, fire up the amp, then keep an eye on the voltage at pin 1 on the 4 pin socket on the dead side. If it settles to about 375 again and just sits there, then you can measure the output voltage of each side of the C4S board (easiest to just probe the metal tab on each MJE5731A). If they are both around 220V, then your amp is ready to listen to.
WK3K
New member
Gents. Sitting in the living room listening to music!
Ran all the voltage checks and everything was right where it should be. Time to sit back and enjoy.
My best guess on the original issue is that the 130ohm resistor between 27L and 30L was too close to the terminal strip and one of the leads shorted against something wired into 28 or 29. This blew both the 130's on that side. Replacement resistors more carefully wired seemed to do the trick.
Thanks PB for all your help and to Jamie for the spare 130's that brought this baby to life. I'll post pictures and impressions once I have put in some listening over the long weekend!
Ran all the voltage checks and everything was right where it should be. Time to sit back and enjoy.
My best guess on the original issue is that the 130ohm resistor between 27L and 30L was too close to the terminal strip and one of the leads shorted against something wired into 28 or 29. This blew both the 130's on that side. Replacement resistors more carefully wired seemed to do the trick.
Thanks PB for all your help and to Jamie for the spare 130's that brought this baby to life. I'll post pictures and impressions once I have put in some listening over the long weekend!
I learned an important lesson about parts availability when I had my mishap with the 130/2W resistors. When I blew mine up, I ordered those resistors from Mouser, but they said they were out and the lead time was 12 weeks. I thought, surely, it couldn’t possibly be 12 weeks, right? So I placed the order and then called Eileen to see if she had any that weren’t already allocated to kits that were in process. She did have some that were available and she sent them to me. I got them in a couple days, put the amp back together and lived happily ever after (Eileen is, often, the best friend you’ll ever have). Anyway, having forgotten about the Mouser order, 12 weeks later those resistors showed up in my PO Box. So, the moral of this story is; when Mouser says it will take 12, or whatever number of weeks to get something, they aren’t kiddin’. That event also showed me the wisdom of using clip leads, instead of probes, when testing in tight spots. When that resistor blew it was like a firecracker goin’ off.
Jamie
Jamie
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