a few LED's no longer light up [solved]

[Doc B.]

Something that was working when the preamp sat normally stopped working when you turned the amp up on edge. That would imply that a bad connection came loose from the movement. Try wiggling the tube and if that doesn't solve it try wiggling all of the new connections you made when you reinstalled the board.

[wesleyHK]

thanks for the advice doc, i tried that last night, but couldn't find anything.  got up early this morning and looked at it again.  decided to reheat some solder joints and that did it, the LED's lit up...  i am embarrassed    that that fixed it  .  i had to get to work, so will give it a listen this afternoon.  i'll be crossing my fingers  .

[wesleyHK]

   it only played for around 15 mins. and the big crackling sound came back.  i then looked underneath and again the 3 LED's were out.  i have double checked everything again and again.  there are no bad solder joints, plus i checked the grounds too, everything is o.k.  there were a few loose tube pins holderss, because i am using telefunken E88CC tubes which have slightly smaller diameter pins than the supplied russian ones, so i tightened them up.  i used the supplied russian tubes a couple of times and they enlarged the holders a bit.

since the amp was working a few days before i installed the shunt regulator board, my guess is to put the blame on the board.  i double checked the solder joints of the wires connecting the board and also check the resistors and they are fine.  i have no way of checking the other components.

i have noticed that when the LED on D1 does light up, the LED's on tube socket A do all light up as well.  do you think it could be something on that board that is at fault?  or is there an LED on tube socket A that might be at fault?  i am in a business where we use LED lamps (for the nail industry) from the states and we have found lamps with defective LED's from time to time.  they are supposed to last for hundreds of thousands of hours, but things do go defective.

regards,

wesley

[Paul Birkeland]

We would need voltage measurements under the conditions which produce these issues to make any real determinations. 

-PB

[wesleyHK]

paul,

at which terminals do you want voltage measurements?  do i leave the shunt regulator board in to take the measurements?  let me know.

thanks,

wesley

[Paul Birkeland]

Yeah, on the shunt regulator board, you can measure the voltages at IA/IB, OA/OB, and Ba/Bb. 

[wesleyHK]

IA  140.9
IB  141.0
OA  starts at 3.0, then slowly drops down to 1.4
OB  107.1
BA  0
BB  0

[wesleyHK]

   paul, i solved it!

since the voltage at OA was abnormal, i looked closely at the board.  looking from the top, i noticed that 2 solder points at the MJE5731A transistor were touching by a very, very minute amount, so i got out a syringe needle and scraped it a tiny bit so that they were separated and that did it. 

the voltages are now as follows.  the LED's now light up  .

IA  118.1
IB  118.0
OA  106.8
OB  107.7
BA  0
BB  0

thanks again for your help paul, GREATLY APPRECIATED .

[Paul Birkeland]

There's magic in them numbers!

I'm glad you got it up and running!

[airdronian]

  paul, i solved it!

since the voltage at OA was abnormal, i looked closely at the board.  looking from the top, i noticed that 2 solder points at the MJE5731A transistor were touching by a very, very minute amount, so i got out a syringe needle and scraped it a tiny bit so that they were separated and that did it. 

the voltages are now as follows.  the LED's now light up  .

IA  118.1
IB  118.0
OA  106.8
OB  107.7
BA  0
BB  0

thanks again for your help paul, GREATLY APPRECIATED .

Glad you and PB were able to solve this.  These sorts of posts are very helpful to those of us starting out.  Thanks. 

[wesleyHK]

  paul, i solved it!

since the voltage at OA was abnormal, i looked closely at the board.  looking from the top, i noticed that 2 solder points at the MJE5731A transistor were touching by a very, very minute amount, so i got out a syringe needle and scraped it a tiny bit so that they were separated and that did it. 

the voltages are now as follows.  the LED's now light up  .

IA  118.1
IB  118.0
OA  106.8
OB  107.7
BA  0
BB  0

thanks again for your help paul, GREATLY APPRECIATED .

Glad you and PB were able to solve this.  These sorts of posts are very helpful to those of us starting out.  Thanks.

you're more than welcome.  with a few builds under my belt, i thought i wouldn't encounter any problems, boy was i wrong.  life is about learning, no matter how old we are.