Fading sound [solved]

[Fielitz]

Hello everybody, I´m writing from Spain.

Last April I bought a Bottlehead Crack. Since I fix it in June, I've always used the crack while the air conditioning in the room was on (in Seville, Spain it is almost a must since June). One day I turned it on with the air conditioning off. The temperature in the room was 25ºC-27ºC, what is not high for the functioning of any appliance. So I was working on the computer while listening to music with my Bottlehead Crack and a HD600.

What happened was that about 45 minutes later, the sound faded and gradually disappeared, though the valves were still on. I must remark that with the air conditioning on, the Crack has usually worked for several hours perfectly well without any problem. To test the influence of the air conditioning, I have made the amplifier work repeatedly with and without air conditioning, and the problem is always the same. In the cool room there is no problem and when I turn off the ac, the sound fades after half an hour or even 15 minutes.

It also happens that when the sound fades, if I touch the power cord to match the plug on the power entry module and force it to move to one side or I press it, the sound comes back. However, the moment I lose contact the sound disappears again. If I move the plug forcing the plug connection, the sound appears again and so on.

So, apart from a ventilation problem, at first I thought there might also be a contact or welding problem in the body of the mechanism power entry module, so I resoldered the whole area again, but the problem persists. I've also changed the fuse with a new 0.5A which is the mark instructions, but the problem persists. Maybe it's a bad contact of the fuse or the power entry module is defective. I do not know.


When I checked the voltages all of them were right, compared to the values ​​given in the instructions. I've been looking through the forum but I cannot find any similar problem, so I’m presenting it. I attached some pictures.

Best regards.
José Luis

pd.
These are the resistance and voltage values:
Terminal      Resistance
3         0 ohms
6         2.48 k
7         2.93 k
8         0
9         2.94 k
10         2.48 k
12         0
14         0
20         0

B3         2.93 k
B6         2.94 k
RCA jack
Groun lug      0
Center pin      97/97.8



Terminal      Voltage
1         86.4
2         163.6
3         0
4         164.1
5         89.6
6         0
7         105.5
8         0
9         107.6
10         0
11         0
12         0
13         163.4
14         0
15         184.1
20         0
21         206

A1         89
A2         0
A4         0
A5         0
A6         85
A7         0
A9         0

B1         89
B2         162
B3         105
B4         88
B5         163
B6         107
B7         0
B8         0

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi1371.photobucket.com%2Falbums%2Fag288%2Fjoseluisbezos%2FDSC_0192copia_zpsbb530e5c.jpg&hash=214fc117bcb170674d4aedd8b7bb1734022fc236)

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi1371.photobucket.com%2Falbums%2Fag288%2Fjoseluisbezos%2FDSC_0187copia_zps9ea07836.jpg&hash=6bd96a734899ccbbd4af0a190317473b81fb9bf2)

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi1371.photobucket.com%2Falbums%2Fag288%2Fjoseluisbezos%2FDSC_0184copia_zps9323e981.jpg&hash=e8686f7f6155aa068bda9f74ec92e24de8673d88)

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi1371.photobucket.com%2Falbums%2Fag288%2Fjoseluisbezos%2FR11_zpsc66357ef.jpg&hash=b48bc329635857546cf773dcee9ea8587f0dada7)

[Doc B.]

It sounds like the IEC power entry module may have a loose pin. This can happen if the pins are overheated when soldering the wires to them. If this is what happened, attempting to resolder the connections might actually make it worse. This condition could also be aggravated by the room being more warm.

I would suggest replacing the IEC socket as a start.

[Paul Birkeland]

In addition to Dan's suggestions, jiggling the power cord may just be reconnecting a loose wire.

When the sound drops, do the tubes stop glowing? (It may take a few seconds for the tube heaters to cool enough to stop glowing strongly)

If the sound fades and the tubes  continue to glow indefinitely, you have a loose connection in the amplifier that is unrelated to the IEC socket and its associated wiring.

-PB

[Fielitz]

In fact, when the sound fades, the tubes remain lit. But I've revised several times the conections arround the power entry module and it seems fine. I think I'll buy a new power entry module and also recheck the conections arround it. Thanks

[Paul Birkeland]

The power entry module is not your issue.  This is an issue of a loose wire in the amplifier. 

The one that I most often see is the long black wire that goes from the power supply above the power transformer up to the headphone jack.

-PB

(You can still replace the IEC jack, but rest assured that it is not your issue)

[Doc B.]

Yeah, what PB said. If the tubes are staying lit the problem can't be at the power entry. You need to go back and very carefully inspect all the connections on the terminal strips on ether side of the power transformer.

[Fielitz]

It works!!!


As you adviced me, I carefully inspect all the welds and connections and it seemed to me that everything was fine, except the points B3 and B6 and then, again soldered.

Also, like the problem seemed to be related to the connections around the power entry module, I remove all the tin of the marked points in the image i attached and soldered again these points.

Finally I soldered again the points 12 and 14 because I remember that once I found it difficult to weld (if they were wrong).
I decide to stop here for sectorizar arrangement. I check again resistances and voltages and all good.

Now, I´ve had more than 3 hours on the amplifier! (and continue as I write this), I was able to enjoy a perfect sound without any problem and without fade, and without air conditioning (today we have 37 degree weather in Seville! )

Indeed, for some reason, some of the welds around the power entry module was not quite right and when moving the module and the heat, the problem would occur.

Thank you very much for the help,

José Luis

(https://forum.bottlehead.com/proxy.php?request=http%3A%2F%2Fi1371.photobucket.com%2Falbums%2Fag288%2Fjoseluisbezos%2FDSC_0190_sentildealadocopia_zps733ee201.jpg&hash=d00fc6e9f17db202336dd3237257300a97f1682c)