Stock BeePre - two LED not light up and voltage issue

[ike]

Hi there,

I just finished building the kit. I ran resistance and voltage check.

The LED on B side D1 is not lighting up on both boards. Some of the voltage measurements are way off: terminal 2, 17, A2, B2, C3, D3, C7 & D7 (see below)

I'm not sure where the problem is. Please advise.

Thank you,
Ike

Here are the complete voltage measurements:
1) 5V
2) 0V
3) 0V
4) 9.8V
5) 0V
6) 180V
7) 0V
8) 0V
9) 0V
10) 193V
11) 191V
12) 0V
13) 0V
14) 0V
15) 194V
16) 5V
17) 0V
18) 0V
19) 9.7
20) 0V
21) 0V
22) 219V
23) 0V
24) 0V
25) 219V
26) 0V
27) 0V
28) 0V
29) 6.9V
30) 6.9V
31) 14V
32) 0V
33) 0V
34) 14V
35) 6.8V
36) 6.9V
37) 0V
38) 0V
39) 0V
40) 220V
41) 0V
42) 0V
43) 220V
44) 0V
45) 0V
46) 220V
48) 0V
49) 0V
51) 0V

A2) 0V
A3) 0V
B2) 0V
B3) 0V

C D 2) 0V, 0V
C D 3) 1.9V, 1.9V
C D 7) 183V, 192V
C D 9) 181V, 190V

 

[Paul Birkeland]

Check that you have the R1 resistors on each of the large C4S PC boards in the correct positions, as well as the jumpers on the bottom sides of those boards.

-PB

 

[ike]

R1 resistors is in correct positions and the jumpers on the bottom of the boards checks out as well. Still, one of the LED light on the board is not on

 

[Paul Birkeland]

Also check that the PN2907 transistors and 431 regulators aren't mixed up, as they look identical.

If that is not what's causing your problems, can you post some photos of the build?  Specifically the top and bottom side of each large C4S board (just unscrew them and tilt them over).

The lack of regulated voltage and available current tells me that there isn't the correct amount of current for the EL34s to do their jobs.

The overall voltage scenario also suggests that the 300Bs aren't working properly.  You have 9.8 and 5V at the appropriate terminals, which tells us that the 300B is heating up, but it isn't drawing any plate current.  This points right back to the large C4S boards having a miswire or improperly installed component (I hate to sound like a broken record, but this is just from my personal experiences of debugging and repairing these circuits).

-PB

 

[ike]

Thanks, Paul.

The PN2907 transistors and 431 regulators are in the right positions.

Here are some photos of the build, all around the 2 boards top and bottom as per your request.

Let me know if you need additional photos.

ike

 

[Paul Birkeland]

The first thing I notice on one of your photos is that I can see a wire soldered to an "OB" pad but the insulation is visible poking out of the hole.  That wire is essentially connected to nothing.

I also see long legs of PN2907 transistors poking through the boards.  Those should be trimmed close to the board so that it's nice and easy to see that there aren't legs shorted together.

Lastly, a lot of the connections I see on the terminal strips are just component leads passing through the terminals with solder over them.  We recommend at least bending the lead up so that there's a better mechanical connection.  Optimally, these would be bent up and around the terminal if possible (which isn't always an option on the lower terminals).  Without connections made like this, it can be difficult to tell which components may be loose.

-PB

 

[Doc B]

I will submit that the issue may be a need for a magnifier to see if the solder joints are good or not. There are indeed several connections in those closeup images that look like they could use a reflow and a bit more solder. I use a visor magnifier.

 

[Leland Hankins]

You need to have a hotter iron or you need to hold the tip longer in place, let the solder flow.  I use 850 to 900 degrees on each iron, and always clean the tips before use.

 

[ike]

Thanks everyone for your advice. I'll take a closer look and re-solder the connections.

 

[ike]

So, I re-soldered all the connections with a hotter iron. After that, I turned the amp on and no LED light on one board, a step backwards. Thought, the other had all 4 LED lights up, first time. I re-soldered the side that was not lit and I have 3 out of the four LED up. Here are the pics. Any other ideas?
Thanks

 

[ike]

I re-solder some more and took more measurements... Now, the board closest to the power switch, none of the LEDs are on.

 

[Doc B]

If it was on my bench I would look at every connection around that PC board with a magnifier. It sounds like you had one bad connection and have created another when reflowing. Running continuity tests from one end of a connection to the other can sometimes help spot a cold connection.

 

[ike]

Thanks Doc, I'll give it another go.

 

[Paul Birkeland]

It's also really tough to debug a circuit based on just the status of which LEDs light up.  Before and after voltage checks, specifically noting which voltages have changed (if any) will provide valuable information.