Troubleshooting help: Wrong Voltage reading with C4S intalled [solved]

jeffsax · 2218

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Offline jeffsax

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on: January 27, 2014, 08:47:14 PM
I have built my new S.E.X. last week.
After enjoying it for a week I decided to add it with the C4S upgrade

I checked the Voltage after intalling the C4S board, The IB to terminal 13 reading is negative 140 (which it should be approxiamately positive 75). The reading on the IA to terminal 13 is correct.

So there is no sound coming from the left channel in the moment... :'(
« Last Edit: January 28, 2014, 07:35:49 AM by Caucasian Blackplate »


Offline Zimmer64

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Reply #1 on: January 28, 2014, 02:57:09 AM
Did you double check the C4S board? Are all parts in the right place and the right orientation, such as the LED's?

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Offline ffivaz

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Reply #2 on: January 28, 2014, 03:03:33 AM
First, I don't have a S.E.X. but all the BH C4S boards have some things in common. I would say that the negative voltage is linked to a ground wire not (or not correctly) connected. Check the black wires across the C4S, and all the black wires that are connected back from the board. Also check the middle legs of the transistors, there aren't easy to solder correctly.
« Last Edit: January 28, 2014, 03:06:54 AM by ffivaz »

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Offline Paul Birkeland

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Reply #3 on: January 28, 2014, 03:33:28 AM
Quote from: jeffsax on January 27, 2014, 08:47:14 PM

I checked the Voltage after intalling the C4S board, The IB to terminal 13 reading is negative 140 (which it should be approxiamately positive 75). The reading on the IA to terminal 13 is correct.



OB should be 75, IB should be quite a bit higher.  Neither should be negative. 

The ground connection is common on the PCB, do you have the bA/bB jumper installed?

What is your IB reading? 

Paul "PB" Birkeland

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Offline jeffsax

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Reply #4 on: January 28, 2014, 05:54:28 AM
Thank you all for your reply!

Yes my bad... I mean reading on OB is negative

Everything else except OB reading looks fine. I re-soldered bA, bB, and the black wire connect to the chasis. The reading on OB is still negative

IB and IA readings are both 3XX

I guess I needa re-do my entire C4S soldering...


Offline Paul Birkeland

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Reply #5 on: January 28, 2014, 06:15:55 AM
Hit the center leg on the MJE5731A on that side with your soldering iron, and I'll bet that things snap into line.

Paul "PB" Birkeland

Bottlehead Grunt & The Repro Man

Offline jeffsax

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Reply #6 on: January 28, 2014, 06:39:07 AM
YESSSSSS!!!!!

Problem solved! Excatly what you guys think! THANKS BROS!

*The C4S upgrade is really awesome! The improvement to the S.E.X is way beyond what I would expect


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