Speedball LED/Voltage Issues

[jarn221]

Hi all,

My unit was working properly as a Crack, but now it's having problems after installing Speedball. We've double checked the instructions of Speedball three times now, and we can't find anything wrong/missing with Speedball wiring.

There seems to be no power from 12 to 1 and 5.  Currently, the D1 LED is not lighting, nor are the LEDs on the small "A" tube are not lit. (In total 3 LEDs not lit.)  The rest of the LEDs are on. 

When it comes to voltage checks, here are the numbers we had from testing.

From 12-

1 0
2 181.8
3 0
4 181.8
5 0
6 0
7 63.8
8 0
9 63.8
10 0
11 0
12 0
13 182
14 0
15 189
19 -50.5
20 0

A1 0
A2 0
A3 0.7
A4 0
A5 0
A6 0
A7 0
A8 0.7
A9 0

B1 75
B2 182
B3 65
B4 0
B5 180
B6 60.9
B7 0
B8 0
 
Thank you so much for your help!

[Paul Birkeland]

First - triple check that you have the correct transistors installed on the correct boards.

0V at T1/T5 can also occur if the center leg of the MJE350 isn't well heated. 

-PB

[jarn221]

We reversed the position of both of the MJE350

[Paul Birkeland]

I believe now that you have the R1's swapped between boards.

[jarn221]

We're not quite sure what you mean by swapped between boards.   The r1 resistors are 237 ohms.  There is one on board a and on board b.  Also attaching an image of the resistors.

[Doc B.]

He means that you may have an R1 resistor from one of the small boards on the big board and vice versa.

[jarn221]

We rechecked the resistors as mentioned and they are correct.  There's a different one in the big board and two of the same ones on the smaller board.

[jarn221]

Just to follow up, we've checked again and have had no luck.  Unfortunately not sure what to do at this point.

[Doc B.]

If the MJE350s were installed backwards and the amp was run there is some chance that the 2N2907 on the bad board was damaged. There is a procedure for checking transistors to see if they are bad, but I am afraid I don't recall where it is on the forum. Basically you check across each of the three possible pairings of the transistor leads and look for high readings on each pair, if any read very low like 50 ohms or less the transistor is probably damaged.

You could also simply reflow every solder pad on the misbehaving board and see if it resolves the issue.

I think we need someone to create a definitive repository for these common technical support suggestions that we post several times a month or a week. It might make it easier for all parties involved.

[Grainger49]

Coming up with the voltages on the B, C & E of each type transistor would be a step forward.  Hopefully it could find bad LEDs and transistors.

I'm sure I will have more suggestions when I sort out the Speedball I installed.  It isn't working.  I'll start a thread about it when I have some good data.

[jarn221]

We've been trying everything but still no success.  Could you explain to me how we could check the voltages on the B, C, and E locations?  We're not sure which points to run from.  Thank you!

[Paul Birkeland]

We've been trying everything but still no success.  Could you explain to me how we could check the voltages on the B, C, and E locations?  We're not sure which points to run from.  Thank you!

Just remove and replace the transistors on the PCB.