Failed Final Voltage Check

[Dhouse7516]

Hi Paul and Doc, I'm in a predicament and hope you might have some advice.

After building and installing the shunt board, I did the voltage check and passed (I don't recall the actual measurements, it's been a while). I then proceeded through the rest of the build, passed final the resistance test, but failed the final voltage check on the C4S board. The B side of the board was fine, but all the values on the A side were off (If I recall correctly, they were low - apologies, but I did not write the actual values down at the time). I double-checked all the solder joints and connections on the C4S and A,B, and C sockets and they looked solid to me.

I found a couple of posts here where users had similar issues and Paul's advice was to remove the blue wires from IA and IB on the C4S and re-check the shunt board. I did that and got the following readings on the shunt board:

OA: 283
OB: 210
BREG A: 283
BREG B: 210
KREG A: 6.42
KREG B: 2.83

I was confused that I now had higher values on the A side, but went back and reflowed the solder joints on the D Socket and some that I thought might be problematic on the shunt board and terminal lugs, measured again and got the following values:

OA: 273
OB: 207
BREG A: 273
BREG B: 207
KREG A: 6.5
KREG B: 2.84

I read another post where Paul or Doc advised someone whose measurements were off to try going through the rest of the build to see if they evened out after doing the C4S Board. This obviously differs from my scenario but I tried hooking up the blue wire to IA and IB on the C4S again (hoping this wasn't a mistake), tested and passed the resistance test, and tried the voltage check again:

IA: 140
IB: 159
OA: 138
OB: 157
OC: 97
OD: 96
OKA: 97
OKB: 97
OKC: 1.76
OKD: 1.61

With the C4S connected, the measurements on the shunt board were:

OA: 161
OB: 140
BREG A: 161
BREG B: 140
KREG A: 3.73
KREG B: 2.63

I am assuming that the issue is with the shunt board or D socket, but would appreciate your thoughts. I walked away from the project for a couple of months and got the Eros back out today to take some pictures, which I will post shortly.

Thanks much,
Darren

[Dhouse7516]

Here are the pics. The D socket joints look a little funky in these post-reflow pics, but I double-checked and none are shorting. Also, that's dust you're seeing, not debris from the build - I didn't notice it until I started uploading the pictures. It has now been cleaned up  .

[Paul Birkeland]

It would be a good idea to try to get the board above the D socket working properly first.  Based on the information provided, I would expect there to be flaky solder joints at work that are preventing that C4S board from operating properly.

[Dhouse7516]

Okay, thanks. I will go back and look again. Do you see anything obvious in the pics of the shunt board or the D socket that I might be missing?

[Paul Birkeland]

Are Breg and +reg connected on the D socket C4S board?  It looks like they might be, but it's tough to tell.

Typically when I get these for repair, I will find a lot of soldering issues, and sometimes builders will focus on one spot and damage traces on the front C4S board by focusing their soldering efforts on a few specific parts.  I'd say in the last year I have dealt with that exact set of circumstances on Eros 2 kits at least four times.

[Dhouse7516]

That makes sense. I am fairly certain that BREG and +reg are connected via the 220 resistor lead on both sides, but I will confirm later tonight or tomorrow. I think that I will go ahead and disconnect that board and send you a picture of the underside.

[Dhouse7516]

Paul, I desoldered the shunt board and will post some images later. A question in the meantime: if the D5 and D6 terminals were shorting/touching, could that be the culprit behind the high voltage readings on side A of the board? Once I removed the board, I noticed that my re-soldering work was a bit sloppy on those two pins, and it’s conceivable that  D6 could have touched the stripped wire going into D5 when the tube was inserted. Thanks.

[Paul Birkeland]

That would drag either OA or OB on that D socket C4S down to about 56V.  It wouldn't hurt anything in the process.

[Dhouse7516]

Thanks. I think I found the problem. See the pics of the underside of the board below. I think that the red wire that connects OA to +reg was shorting against the middle pin of the MJE5731G. It's also possible that the red wire on OB was shorting against the middle pin on that side. See the red circles in the pics. Sloppy solder bulbs on my part! Would either of those scenarios explain the voltage issues? Regardless, please let me know if you see any other problems with the board. I'm also including a better pic of the D socket.

[Paul Birkeland]

OA and OB connect to the middle leg of each of the MJE5731As anyway, so that wouldn't be a huge concern.

[Dhouse7516]

Ah, of course they do. Thanks. Do you see any obvious issues with the board (top or bottom) or the D socket? I'm attaching another picture from the top of the board. Thanks much.

[Paul Birkeland]

You can get weird readings like what you got if the blue and white wires on the D socket get switched by accident when connecting to the C4S board above the D socket.

[Dhouse7516]

Not sure I am following. There are no blue wires connecting to the D socket, correct? Do you mean black wires? Sorry if I’m being dense.

[Paul Birkeland]

Sorry, the red wires leaving OA/OB and the white wires leaving KregA/B.  Having one pair of those wires swapped will result in odd regulator behavior.

[Dhouse7516]

Got it. All four of those were properly wired. I'm kind of at a loss. I think all the solder joints look fine.