High voltages in final test on CS4 board

[dehringer]

I have some high voltages on one side of the CS4 board in my Eros 2 build.  All earlier tests in the build have passed.

IA: 217
IB: 215
OA: 144
OB: 158
OC: 141
OD: 107
OkA: 139
OkB: 102
OkC: 11.8
OkD: 1.8

I have gone back to check the solder joints on the board (although I could be missing a bad joint(s)).

Do you have recommendations on what to focus in on?  I’ve attached a few pictures.

Thanks for the help!

[Paul Birkeland]

Something like the Q2C center leg not getting adequately heated could cause something like this.

[dehringer]

Yes, after looking closer, the middle leg of Q2C didn’t have the solder flowing fully through.  I think I have resolved this but the voltages are measuring the same.

[Paul Birkeland]

I would reheat the rest of the resistor and transistor joints on that front PC board.  The LEDs generally solder easily and don't require extra effort.

[dehringer]

I’ve reheated all the joints 3 times and continue to get the same measurements.    I could only assume I need to worry about the joints on the side of the board with the measurement issues? 

I might need to take a break and come back with a fresh set of eyes unless you recommend anything else.

[Paul Birkeland]

A miswire or a problematic solder joint on that 9 pin socket could also cause some problems. 

[dehringer]

The lead on the 0 ohm resistor going through A3 was touching A4.  I resolved that and it brought OkC down a little bit to 5.2 volts but others didn’t change.  Would this issue have caused any damage to the tube?

[Paul Birkeland]

That could possibly damage the 2N2222 on that side of the small PC board.

[dehringer]

Would a damaged 2N2222 potentially be the cause of the high voltages I’m measuring? Or should I continue to try to track down potential a bad solder joint or mis-wire?

[Doc B.]

If you are not sure you should probably test the 2n2222 to see if it is shorted.

[dehringer]

I finally got a chance after the holidays to come back to this build.   I removed the 2n2222 transistor and it tested ok.  I also removed and tested all the other transistors on the same side of the board and I believe they all tested ok. 

I tried reflowing all the joints on that side of the board again.  I also reflowed all the point-to-point joints as well.  I’m still getting high voltages.  Current readings:

IA: 217
IB: 215
OA: 144
OB: 158
OC: 141
OD: 107
OkA: 140
OkB: 102
OkC: 4.5
OkD: 1.8

Do you have any recommendations on additional troubleshooting steps?

Thanks!!

[Paul Birkeland]

If you have the equipment to easily swap the 2N2222 transistors, I would try that.

[dehringer]

I don’t have a component readily available but I can get one and give that a try!

[dehringer]

Thanks to being able to borrow a 2N2222 from a new kit that arrived today , I was able to try this out faster than anticipated.

Unfortunately, with the new 2N2222 the voltages remain the same.     Could any of the other transistors have been damaged? None of them tested as being shorted. 

[Paul Birkeland]

Generally high voltages on the output of the C4S can be attributed to the center leg of Q2 not being sufficiently soldered.

In your case, the voltage isn't so high that I believe this is the problem.  This is more likely to be something like a swapped resistor or backwards component throwing things off.  I cannot ever remember building a C4S board and just randomly having a defective transistor (and I've been somewhat regularly doing that for 23 years).