Bottlehead Forum
Bottlehead Kits => S.E.X. Kit => Topic started by: Mordicai on March 13, 2017, 08:57:49 AM
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Had my Sex 2.1, plus C4S board & Output Transformer Switches for over a year and just love it. A few weeks ago the Left(black) channel started clicking off and then back on. Yesterday it clicked off and stayed off. I traced into the C4S board where the (B) D-1 LED was barely lit, and the two 150k resistors had blacked areas on their leads and around their leads on the board. They still measured 150.7K. I resoldered the D-1 LED leads and both the 150K resistors leads. Fired it up and it worked fine. After a 30 sec it clicked off, back on, off and then back on. Its been playing for about a half hour with no problems. I assume the blacked leads on the transistors are from a poor connection, but I really don't know enough about all this to assume anything. I live in the country and my AC is 125. Any feedback would be appreciated......Max
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Played for about an hour and and then went back to right channel only. Play with it again tomorrow.
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Have you swaped tubes to see if the problem moves with a tube?
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Yes Doc, Thats the first thing I did. Switched tubes and rca inputs. Even though the slightly fried 150k resistors still test ok, I wonder if they could change when they warm up. Perhaps I need to try replacing them.
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Is it normal for the 150k transistors on the C4S board, to have heat blackened leads ? If so I'll stop worrying about it.
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No, it is not normal. It would be a sign they have been overstressed with too much current.
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It would help to know what voltages accompany the problem. The main voltage you want to measure as at the output of the board on each side (OA and OB), as well as the voltage across the 1000uF capacitor on each tube socket.
-PB
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Paul, when measuring voltage across he 1000uf just clip on each side? No attachment to ground ? Or clip to ground and one side of the condenser?
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The striped side of the cap is grounded, so you can just measure from ground to the end connected to each tube socket.
-PB
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Paul the voltage numbers are: OA 66.2 ; OB 56.1
Voltage across 1000 cap is L 19.4; R 18.9
Cleaned the tube sockets for a third time and like before, the headphones played great for a few minute and then the Left track quit. Changing tubes again did not help.
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Are those the voltages after the left channel faded out?
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The amp was only firing on the right channel. I moved it to the bench, flipped it over, plugged it in,turned it on and took those measurements. There was no source plugged in and no headphone attached, so I can only assume it was still only working on one channel. If it would help I can test it tomorrow as its playing while hooked up to the system
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Yes, you'll want to confirm that the offending channel has dropped out when you take measurements. A cheap (small) test speaker and some music playing through the SEX from your phone can make this process a lot easier.
-PB
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Paul, Sorry about that. Wasn't thinking. When the left channel clicks off the voltage at OB is 0 volts. OA is still 66.2. I reflowed the connections at OB with no success. It played for 1/2 hour and sounded great, and then started clicking on and off and finally just off. Again the only obvious problems with that B side of the board is the black burned ends where the 150K attach to the board. Both still measure 150. The 499 ohm resistor on the B side has slightly burned ends. The 499 on the A side is still bright and shiny. Both measure 499.
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Does the voltage across the 1000uF cap on that channel also drop to 0V when this happens?
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Paul, I tried three times to get that reading. Seems when I turn the sex upside down it want to play on both channels. And when I turn it right side it wants to play on the right channel only. I just barely got that 0 volt reading in on the OB before it strted playing both channel again. I played it for about fifteen minutes and couldn't get it to drop a channel, and started getting concerned about the heat from the tubes. Do you think playing it upside down for a long time hurt anything from the heat. I will try again tomorrow.
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Hmmmmm. If it works upside down but not right side up then gravity is completing a broken connection with the amp upside down. And since your amp has worked for over a year I would suspect a wire that was not soldered or more likely a wire that is broken under the insulation which usually happen when you nick a wire while stripping the insulation. If I were you I'd do the chopstick test with the amp playing using cheap speakers or headphones. Concentrate on moving wires looking for one that makes the channel drop.
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Ken is spot on!
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When this upside down magic started a few days ago, I of course felt the same way and started poking everything. My feeling was its a broken wire as Ive been over the amp many times without finding a bad connection. I was hoping to narrow down the search area a bit. What broken wires would cause the C4S resistors to burn like that? Back at it!! Thank god for the Stereomour. At least I can poke about to the Stones.
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When this upside down magic started a few days ago, I of course felt the same way and started poking everything. My feeling was its a broken wire as Ive been over the amp many times without finding a bad connection. I was hoping to narrow down the search area a bit. What broken wires would cause the C4S resistors to burn like that?
You're going to have to post a photo of what you're seeing.
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http://www.pbase.com/mordicai/image/165195657
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As you can see Paul both 150 are blackened. Only the 499 on the B side is blackened. The A side is shiny.
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Just for a point of reference, for how long do you generally leave your SEX amp on, and what's the approximate ambient temperature in the room? (Celsius is OK)
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Well, since we have the same problem, my room is air conditioned @ around 26°.
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Paul, My amp goes on about 5 AM,and off about 9 PM. Temperature in the winter about 50-68 F. I live in the high desert so summer temps can be about 65- 90. If it gets hotter then that I turn on the air. Could the poor connection to the MJE5731A, cause the heat?? That has now been fixed and seems like everything is ok
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summer temps can be about 65- 90.
If your room is 90F then there is a potential for problems. Your cell phone and computer will also not last nearly as long as they should while operating at these temperatures.