quick LED question

[moviedave]

Which small PC board on the speedball is connected to the LED going from the center pin to A3?

 

[Paul Birkeland]

Neither.

 

[moviedave]

The reason I asked is that is I installed the speedball and the LED connected to A8 didn't light up.  I unsoldered the small PCB boards and checked my work, and everything looked fine.  I put them back but swapped the which sides I soldered the boards onto.  After doing that, the LED on A3 didn't light up.  I will keep working.

 

[Paul Birkeland]

Always start with measuring voltages, the LED on A8 is indeed related to one of the smaller green PC boards.  Measuring the voltages at terminals 1, 2, 4, and 5 will tell us a lot about what's going on (and likely problems at terminals 6, 7, 9, and 10).

 

[moviedave]

Voltages were as follows

1. 85
2. 205
3. 0
4. 205
5. 0
6. 0
7. 124
8. 0
9. 94
10. 0

2 and 4 are a little on the high side, but the biggest issues are terminal 5 reading 0 and terminal 7 reading 124.

 

[Paul Birkeland]

You're not getting voltage out of one of the small green C4S boards, that is causing the rest of the problems.  Measure the metal patch on each MJE350.  When you find the one that is zero, reheat the solder joint on the center leg of that transistor.

-PB

 

[moviedave]

Are you sure that has to be the problem?  I did as you said, and found the thingy that had a zero voltage reading and resoldered the center leg.  It did not help.  Anything else that could be the source of the problem?

 

[Paul Birkeland]

Measure the voltage at the "I" solder pad on each small green board, they should be the same.

Also verify that the 2n2907's and 2n2222a's are in the correct places.

-PB

 

[moviedave]

The voltages are the same at the "I"'.  I will recheck my solder joints again.  I installed the speedball and had it working.  I later reverted it to stock to check the difference in how it sounded.  Deciding I liked it better with the speedball, I am putting it back.  I know everthing is where it should be on the board.  I just need to find out where the goof is.  Thanks for the help.

 

[Paul Birkeland]

Ah, OK, that is very helpful information.

You should be able to nail down that small green PC board.  Do note that a loose black wire on that board could cause the same problem.

 

[moviedave]

Solved that problem.  Re-soldered all my joints.  Now, I seem to have a new one.  Everything now has a reading, but a few are too high.

2. 201
4. 201
7. 123
9. 136
13. 201
15. 214
b2. 201
b3. 122
b5. 201
b6. 135

Any advice for this?  They seem to be higher in pairs.

 

[Paul Birkeland]

What are terminals 1 and 5 reading now?  These have a lot of control over how the rest fall into line.

 

[moviedave]

1. 83
5. 78

I didn't include them as they were well within the acceptable range, but what do I know.

 

[Paul Birkeland]

You're in operating range, I would go ahead and give her a listen.

-PB

 

[moviedave]

Only getting a hum from the left channel.  Where to go from here?

 

[Paul Birkeland]

Was the amplifier operating properly before the installation of the Speedball?

 

[moviedave]

yes it was

 

[Paul Birkeland]

Well, the good news is that the 12AU7 is operating properly, and the two small green PC boards are A-OK.

Moving on to the large green PC board, I'd give it a solid once over again to be sure you didn't miss any joints.  Do all 4 LED's light up equally brightly? 

It's a little strange, because your 6080 is drawing some current, but not quite enough.  It's also odd that it is the same for both channels.  This makes me suspect the red wire from 2U going to the larger green PC board is not making sufficient contact, or the red jumper from B+ to B+.

-PB

 

[moviedave]

Actually, the hum is coming from the right channel along with the music.  The left is silent.  The LEDs are all bright and the 2U and B+ to B+ jumper are soldered well.

 

[moviedave]

The 2N2222A nearest the small PCB boards feels loose all of a sudden.  Could that be the culprit?