C4S Upgrade Blown LED

[Paul Birkeland]

Please do swap out both transistors at once, just to be on the safe side.

[JosephDuffy]

Right, I've replaced the 5731A and 2N2907 transistors and I've still having issues getting any sort of readings. Once I removed the 5731A it seemed to be working as expected when I performed my resistance checks, which seemed a little odd. I've tested the resistors and as I said previously they seem to be ok. I also cannot find any other areas that seem to raise concern.

I'm hesitant to do much more soldering on it since I'm worried that I might start damaging the board after removing/replacing/reflowing so much.

I'm not sure what my next steps could be other, other than getting a replacement kit or simply removing the C4S and getting hold of some of the old resistors and putting them back in place. I'm still hoping that there's something silly that's gone wrong, but after replacing so many components it's just getting more and more confusing.

[Paul Birkeland]

Right, I've replaced the 5731A and 2N2907 transistors and I've still having issues getting any sort of readings. [...] I performed my resistance checks, which seemed a little odd.

You can post what you're seeing.  "any sort of readings" and "odd" aren't really enough for us to be helpful. 

It would probably help to put the 150K resistors back in to be sure the amp is still functional.

[JosephDuffy]

Right, I've replaced the 5731A and 2N2907 transistors and I've still having issues getting any sort of readings. [...] I performed my resistance checks, which seemed a little odd.

You can post what you're seeing.  "any sort of readings" and "odd" aren't really enough for us to be helpful. 

It would probably help to put the 150K resistors back in to be sure the amp is still functional.

Sorry, maybe the "odd" comment wasn't well formatted. I meant that it was odd that when I removed the 5731A the 5731A itself seemed to be working as expected (i.e. the resistance checks were showing the same as the new one I'd just received)

By "any sort of readings" I mean that I'm unable to get a reading (0 or more) from the OB to either of the side connectors of the 5731A, which is problem that I was having before I replaced the 5731A.

Edit: Sorry, forgot to add: I was going to try and replace the original resistors, but I was struggling to get them out originally so I cut them. I've only had a quick chance to look but I was unable to find replacements that looks suitable. I will take another look, but right now, I cannot replace them. All the resistance checks, other than B5 (the one on the left when it's unsdie-down, not sure if it's A or B), show as they should be from the original S.E.X. manual.

[JosephDuffy]

Right, so here's where I'm at now:
I've taken the 150K resistors from the C4S board and put them back in the main circuit, leaving out the C4S board completely. I've done my checks, turned it on, and am having no issues, so I'm going to installed the Output Transformer Switched kit since I've got some speakers arriving (hopefully) pretty soon.
I can't find any replacements for the 150K resistors so I'm planning on tackling the C4S kit again in a few days.
I took at look at just buying another C4S kit because it feels like starting over again might help, but the postage to the UK is $40. Is there any chance of getting that price down? The kit's fairly light and small and $40 seems a little high?

[Paul Birkeland]

I think we could do a USPS Priority flat rate box at the small size, which is still around $25.

The 150K resistor can actually vary quite a bit in value.  The maximum resistance that I would recommend would be 330K, and the minimum would be 120K.  At 330K, a 1W resistor is OK, at 120K, a 2W resistor will be necessary. 

[JosephDuffy]

I think we could do a USPS Priority flat rate box at the small size, which is still around $25.

The 150K resistor can actually vary quite a bit in value.  The maximum resistance that I would recommend would be 330K, and the minimum would be 120K.  At 330K, a 1W resistor is OK, at 120K, a 2W resistor will be necessary.

If I can get the shipping for $25 then I'll just get a new C4S kit and not bother getting any replacement resistors. How do I go about ordering a new C4S kit with the $25 shipping?

Quick question regarding the Output Transformer Kit: On page 14 it states, when discussing the wires leading from the binding posts to the boards: "Carefully confirm that each black wire is aligned to its respective transformer". How I do I know which transformer each wire should go in to? My kit came with 4 black covers (rather than 2 black and 2 red) so I can't say "the red/black side goes in to the left/right board". It seems to me that it would make sense if the black wire from the left binding post goes in to the left board, and the right in to the right, but I just wanted to confirm that.
Whilst I'm double-checking things, the picture on page 8 has the resistor in the reverse order that the bands are noted as. Do I do that for the resistor that I use? I've got it going "brown, gold, yellow, black, blue" when the board is the right up, from left to right.

Thanks, again, for all the help you guys have provided!

[Paul Birkeland]

My kit came with 4 black covers

Your binding posts have colors...  Each set of binding post goes to the transformer it is closest to.

Whilst I'm double-checking things, the picture on page 8 has the resistor in the reverse order that the bands are noted as.

Resistors are not directional parts, this doesn't matter.  (But still good that you're paying attention)

[JosephDuffy]

My kit came with 4 black covers

Your binding posts have colors...  Each set of binding post goes to the transformer it is closest to.

Whilst I'm double-checking things, the picture on page 8 has the resistor in the reverse order that the bands are noted as.

Resistors are not directional parts, this doesn't matter.  (But still good that you're paying attention)

Yeh, the actual binding posts do, but the little plastic covers on either side of the plate are all black, so I couldn't mention the colours that they have. Thanks for the clarification. I'll go over and finish the job now so I can do all the tests.

I'd noticed that resistors seemed to be put in any direction, but thanks for confirming that that applies for all of them!

[JosephDuffy]

I got the Transformer Kit installed and working, and after the "practice" on the C4S board, it was a lot easier to solder!

I'm a bit more convinced that I should be able to (successfully) complete the C4S kit, so how do I go about getting the reduced postage costs?

[Paul Birkeland]

I would e-mail the request to Eileen and she can send you a Paypal invoice.

-PB

[JosephDuffy]

I would e-mail the request to Eileen and she can send you a Paypal invoice.

-PB

Thanks for all the help! I think we're nearly there