left channel dies after 5 minutes

[denti alligator]

My Crack has started to act funny. With Speedball.

After about 5 minutes of playing the left channel goes out. The LEDs on the Speedball go dead, too. If I let it sit an hour or so and flip it back on I get another 5 minutes before it goes out.

I'll resolder around the Speedball and see if that helps, but thought I'd probe the forum for any obvious fixes.

[denti alligator]

So I reflowed a bunch of joints, including everything on the main speedball board. Still, after 5 minutes the left channel goes out. The LEDs on the big board go out.

What would be causing this? How could I be getting great sound out of both channels, but only for 5 minutes. Each time! It must have something to do with the heat that's being generated...

[denti alligator]

Tested voltages, which are all on.
Tried it again. 4:52 minutes and the left channel goes out with a pop.
I'm giving up for now.

[Deluk]

I had this "pop" on my non Speedball crack and it tuned out to be a poor connection on one of the leds on the small valve. Dab of new solder fixed it. As mentioned if they are fitted too tight they can break a lead if the valve is moved or replaced. Worth a look. Might need to gently lever on the connections.

[denti alligator]

I had this "pop" on my non Speedball crack and it tuned out to be a poor connection on one of the leds on the small valve. Dab of new solder fixed it. As mentioned if they are fitted too tight they can break a lead if the valve is moved or replaced. Worth a look. Might need to gently lever on the connections.

Thanks, I just tried this. There seemed to be no issues, but I reflowed the joints anyway. Unfortunately, I'm having the same issue. 5 minutes of stereo audio, then a pop, then only the right channel.

[adeep42]

Have you tried a different 12AU7(the small tube)? It has two sides.

[denti alligator]

Have you tried a different 12AU7(the small tube)? It has two sides.

Yes, I have. I'll try yet another one.

[Doc B.]

As always it is helpful to see voltages and photos of the installation in order to offer some suggestions.

[denti alligator]

The voltages were on, but I'll re-test and post them with photos after this next try (just re-soldered one of the wires going to the large pc board that might have been loose).

[denti alligator]

something seems to be wrong with terminal 9. It's measuring 1.472
Maybe the cap has been damaged?  (I only have a matching replacement pair of 100v 250uF caps, which won't work here, or?)

[Paul Birkeland]

If the cap was drawing down the voltage, it would explode and blow its guts out all over your amp.  Since it hasn't done that, it's not the problem.

Are your 270 Ohm power supply resistors starting to discolor a lot?  Improper installation of the TIP50 transistors onto the heatsinks can cause a low voltage like that, but you'll have low voltages everywhere else in the Crack.

How are the solder joints on the TIP50 feeding terminal 9?  You might want to reheat those joints.

[denti alligator]

No discoloration.

Just a note: I had this amp up a running for a long time (over a year) without problems or significant changes. But I moved, so something might have been bumped loose? I'll reheat the joints at 9 and leading to it.

[denti alligator]

I reheated the joints leading to 9, including the TIP50 connections.
Again, it's fine for almost exactly 5 minutes. The voltage at 9 reads right. Then, suddenly, the LEDs behind the TIP50 go out and the voltage drops (and the sound goes out in the left channel).
Any idea what could be causing this? I find it especially odd that I get 5 minutes worth of power every time.

[denti alligator]

Tried reheating some other joints. 5 minutes later, the LEDs are out again. Here are the post-5 minute voltages:

1   76.2
2   199.4
3   0
4   199.6
5   76.5

6   0
7   90.1
9   1.465
10  0

12  0
13  199.6
14  0
15  212

19  92.9
20  0
21  225

A1  76.6
A2  0
A3  1.564
A4  0
A5  0
A6  76.5
A7  0
A8  1.565
A9  0

B1  76
B2  199
B3  90.1
B4  76.8
B5  199.1
B6  1.457
B7  0
B8  0 

Reheated A3, A8 and B6. Same problem. What's with the 5 minute delay?

[JamieMcC]

Have you tried reflowing the LED joints on the pcb board ofside thats not working? I had something along the same lines happen with my Eros and it took a while to track down, after a fair bit of prodding with a wooden chopstick while the amp was running the problem turned out to be the solder joint on one of the LED leads. After about 10mins I am guessing the joint would heat up enough and expand enough to break the contact. The amp had run fine for many months prior and the issue only came after moving the amp to a new location.

Its a easy enough thing to check