Extenede upgrad C4S issues

[baddog1946]

Hi Doc:
I'm having some probs finding out why of one of the C4s board will not light up the LED's on the "A" side only. I have swapped tubes checked every wire at least 3-4 times and everything looks good except no LED's.
It worked fine when I finished the foreplay III part then I did the upgrade and now I am stumped. Resistances and voltages are all good. Could use a little advice here.
Thanks

[Grainger49]

Just to check, did you just upgrade/extend your FP III?  Have you checked the LED orientation?  That is the most often thing that can go wrong.  The next most often thing that can give problems is the transistors.  They can get swapped around, backward.  And I will admit on my first C4S project I had a solder joint that I hadn't soldered.

We all miss these things once in a while.

[baddog1946]

I rechecked the LED orientation and it was fine. Good point about the transistors It is possible that one could have been damaged during installation by heat but I will have to replace it to find out.
The problem is that I will have to go to an equivalent transistor type if it is because I cannot find the same ones here (Costa Rica).

I will try a NTE39 for the MJE350 or a NTE157 for the MJE340.

If you think they are not acceptable I guess I will have to order the originals from Doc. and see how long it takes to get them down here. Thanks for the tip I'm on it.

[Grainger49]

The Queen can send you one if that is the problem.  I know Bottlehead stocks them.  I would guess it takes a week to get to you.

But first there are some checks that can be made, voltages before and after the transistors. I am unfamiliar with them so here I can be no help.

Sorry!

[Paul Birkeland]

I'm having some probs finding out why of one of the C4s board will not light up the LED's on the "A" side only. I have swapped tubes checked every wire at least 3-4 times and everything looks good except no LED's.

Are these the LED's on one of the outside boards, or the center board?  Don't go pulling transistors just yet.

[baddog1946]

The LED's  that will not light up are on the "B" side of the left hand C4S board when the amp is upside down. Some of the other LED's also do not light up evenly. The two on the "A' side of the board in question can barely be seen to be lit up. On the other side the two "A" side are brighter and the rest appear to be evenly lit including the LED's on the tube bases. I pulled the board in question to see if there was anything obvious on the underside and re-soldered a couple of spots that looked a little dull but when I re-installed it was as the same as before. Th voltages and resistances are all within acceptable margins +-10%. Still looking. Suggestions would be appreciated

[Paul Birkeland]

OK,

[baddog1946]

very elusive problem so far. I might have to order all the parts for that board and start over if no one has a better idea.

[Paul Birkeland]

Argh, what happened to my long post!

Half the LED's lighting on that outside board is indicative of an LED that is improperly oriented on the dim side, or improperly paired transistors. Be sure the MJE340 is with the 2N2222 and the mje350 is with the 2N2907. I suspect an LED is backwards in the dim pair more than anything.

[baddog1946]

OK.
I did find a mismatched transistor pair on the board that was most brightly lit and swapped it with the correct partner. That board now lights up evenly with the tube bases and the LED's on the center board. I pulled the half dead board out and removed the LED's to check them and they were correctly oriented.

The board still behaves as follows:
When the amp is turned on 1/2 of the board lights up as does the tube base LED but in a second or two it dies down to a barely detectable glow and its the same with the LED on the tube base. As a point of interest when I disconnect the red wire on the tube base #7 that goes to the RED lead on the "Auricap capacitor then the half of this board that light up for a second or two then dies down stays lit at a normal level.

The "B side of this board is dead and does not light up at any time. I reconnected the lead to the capacitor and it behaves the same as it did before. It lights up for a second or two then dies down to barely detectable.

Could this dying down be the transistor prob you mentioned. Is that the kind of behaviour one sees in that case? I have checked everything else like the wires and the socket connections going to that board.

Everything there looks good at this point. I can't figure it out if you senior members have any more suggestions I would like to hear them. I am waiting on swapping out the transistors on that board as you suggested until I exhaust all other options. there is always a logical explanation but in this case it has escaped me.
Help?

[Doc B.]

At the risk of sounding like a broken record, in most cases the problem is a mis-wire. Check all of the solder joints on the board for solder bridges between pads where there shouldn't be any. Then check and verify the jumper wiring. Then check and verify the connections of the PC board wires to the rest of the preamp circuit. We just tracked down a problem on a prototype crossover here yesterday, that was found to be a mis-wire issue on one of those little green C4S/shunt regulator PC boards.

[baddog1946]

 OK I'm back with my C4s board problem (damn it).
I pulled that sucker out and went over it very carefully with a 20x magnifying glass and examined all the points and welds.
Everything was correctly oriented, jumpers in the right place and there are no arcs that could be detected by me and my magnifying glass.
I then had what I thought was a good idea.I swapped the boards side to side and the same board acted as it did on the other side.
It lights up the LEDS on the "A" side of the board and the tube base LED for a second or two then they all die down to almost nothing, so we can safely assume it is the board and not part of the rest of the circuit.
 
I did notice this time when I disconnected it that the LED on the tube base lit up brighter for a few seconds after it was unplugged before winking out but the two "A' side LEDS just stayed out during these few seconds.

Since this is not part of the board and it does the same thing when the board is on the other side it may be a clue for some of you more knowledgeable members.
I can absolutely confirm after several hours of working on it that the LED's are in there correctly and it is connected correctly to the circuit.
 I have triple  no make that quadruple checked all the wiring going to the tube bases and the boards.

Does that leave the transistors or other components to look to for an answer? Am I still missing something?
 
I have built some of other kits (Dynaco ST-70 and two mkIII mono blocks). I also built a Gamma II DAC. so I am not a complete newbie to all this so if there is an answer it must lie somewhere else than in a bad solder joint or arcing on the board at least IMHO.

Can anyone explain the dying out behavior which I think must be the clue to what is happening? I am almost ready to pull the board and send it to Doc to check it out. That would be a last resort as I live in Costa Rica.
Hope someone can give me a pointer here. I'm stumped!

[Grainger49]

BadDog,

You have mentioned the tube socket LED several times, and that is a good thing.  This indicates that when the C4S board hasn't come up to voltage, "turned on," that the tube end of things is just fine.  Of course, the problem is in the board.

You are also in luck, you have one good board and one bad board.  You can compare both of them with that big magnifying glass you have.  Compare the values of the resistors in each position.  Your swapping the boards and the problem swapping sides says that the problem is on the board, not the connections.  I suggest not beating your head against the wall with that anymore.

Since you have checked the LED orientation several, ok, 10 times let's leave that alone too.  You had a couple of transistors swapped.  You need to find out from the Bottlehead crew if that might have caused a problem with either of the transistors. 

[baddog1946]

Thanks Grainger:
I will be checking those resistances and voltages side to side to see if anything turns up.
cheers

[baddog1946]

Still having the same problems.

Well I have been at this for two more days and there is still a problem with my C4S "B" socket board. The problem is the same. The "B" socket C4S board lights up for a few seconds then fades to almost nothing on the "A" side and the "B" side is dead. The center pin "B" socket LED lights up briefly but also fades although not completely out.

I have been over the entire build again from the beginning and there are two items that do not add up.

What happens to the red wire that goes from 21 to 32? In the final demolition section on page 16 it says to cut this red wire at the 21L end leaving the other end attached at 32L. Yet in several subsequent pictures including the final two photos of the completed demolition it still shows this wire in its place uncut.
 
In fact several pages later it still seems to be present namely on page 29 in third from the top photo and possibly in the top photo as well. Although that one goes out of the photo's margins.

page 30 also appears to show this wire in the top photo. In the following photos on the same page it appears to be missing.Two photos on page 32 show it missing as well.

Later in the build on page 38 it says to attach and solder a red wire from 32U to the second pad "O" on the "B" end of the shunt regulator board.Therefore is this is  another new wire from 32U??  There is still no mention of what happened to the red wire left at 32L. Where does it go??

The manual then moves on to the "A" socket from there.

Finally on page 40 two steps appear to say to connect two wires to the same place. The third item on this page of  the "B" socket instructions says to connect the red wire from B1 to pad "I" on the "A" end of the C4S board  and the next step says to connect a red wire from 32U to pad "I" on the "A" end of the "B socket C4S board.

That is two connections to the same hole.
Is it supposed to mean connect this red wire from B1 to the "O" pad as it seems to show in the photo?? Or have I lost it??

Is this a typo?? Does B1 go to pad"O" or "I" and does the red wire from "32U?" go to "I" or"O"?? The photos show it as so. that is also how it works in the "A" side C4Sas well.What am I to believe the photos or the written instructions.

As I mentioned the wire from 32L was shown in place after it was supposed to be removed and appeared in the final demolition photo intact.
 I'm confused about what should be followed. Photos or instructions?? No mention is ever made of where to connect 32L again. Should it remain connected as it was originally or is there a typo here that confuses this wire with 32U?? and it should be connected somewhere??

there are a lot of wires going to 32U. 21 and 32 are corresponding points on "A" and "B" contact strips what is the correct number of connections to 32 "L" or "U" or both??

My final observation is that if the wire from 32L that was supposed to be cut remains connected between 21 and 32 I get the LEDS on the "B" socket C4S board to light up on the "A" side and stay lit but "B" side remains dead. If it is disconnected then "A" side lights up then fades to almost nothing.The "B" side is always dead.

My question remains what happens to the red wire that was left at 32L?? How can I fire up the "B" side of this board?

Sorry to be such a pain but I am really stumped by this and I still wonder if any damage was done to the transistors by any of this. If that is possible what should I check for first? All the resistances and voltages appear to be within the 10% margin of error.

Looking for clarity here.