left channel dies after 5 minutes

D

denti alligator

New member
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.
 
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...
 
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.
 
Deluk said:
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.
Click to expand...

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

 

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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.
 
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.
 
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.
 
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?
 
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 

 
Hey Sam, I had a similar problem in my Eros (lost a channel after 4-6 minutes, and this was also after having decent operation for months before the problem exhibited itself.)

You may have already re-soldered these, but for me, it was a 2N2907A--one of the solder joints on the legs wasn't solid. I don't use a lot of solder on those little joints, and I guess it wasn't enough.

I ran across this when I was trying to figure out if it could have been the 2N2907A:

https://www.head-fi.org/t/476650/crack-bottlehead-otl/8115#post_13288157

Possibly worth a shot if you haven't already tried it. Good luck.

Mary
 
It probably wouldn't hurt to try a different 6080 as well, but your voltage measurements have me suspicious that replacing the 2N2222 and TIP50 on the offending side might be in order.

DO NOT reheat the solder joints on the LED's.  The HLMP-6000 is hygroscopic and after such a long time out in the open, reheating the LED's with a soldering iron may cause them to crack.

-PB
 
denti alligator said:
I have swopped out the 6080 and it makes no difference. Are there any joints you suggest I re-try before we try replacing parts?
Click to expand...
Both of the transistors on the big C4S board that feed that offending side.  Also check for loose or broken wires.

-PB
 
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