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Can a Cab Break a Head?

#41
Sign next to my company’s service desk:

To avoid a host of bloody messes
Bring it in for repair
Skip the brilliant guesses
​
If I had a nickel for the number of borked motherboards and RAID cards we had to replace because some optimist decided to ditz around inside his business’s server or his expensive laptop to “try and fix it” my spare change jar would be pretty heavy right now.
 
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#42
newfuture said:
I don't doubt that for a second. I would be shocked if it were environmental, especially as the rest of the interior was pretty clean.
I wonder what was used. WD-40? Engine degreaser? Deep woods off?
Click to expand...

Oven cleaner???
 
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#43
Fair criticisms. I had some electronics classes in college but am by no means an expert. Enough to identify most of the components on the PCB and steer clear of the caps, though. I don't think the head is worth paying to repair. I may just toss it or sell it for parts.

My biggest concern is whether this brand new cab caused the head to fail or not. I don't want to replace the head with something new just to have the new one die on me, too. What's the consensus on probable cause here? Coincidence, or head was murdered by cab?
 
#44
NeckPickup said:
Of course I don’t know the qualifications of the posters on here except for the ones who are obviously pro designers and repair people, but I’ve read enough times how there can be juice present in totally unplugged gear that I won’t go near it. Maybe that’s just me.
Click to expand...

And I think this is a wise choice. It's possible to know enough to work on them safely without being a design engineer though. And qualified repair techs are getting increasingly hard to find in many places.
 
#45
Without testing and troubleshooting/diagnostics, everything is just a guess.

Identifying components is different than understanding the circuits, how they are supposed to work and how they can fail.

I see the results of failed repair attempts gone wrong almost every week.
 
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#46
NeckPickup said:
I read this entire thread so far, and my only reaction is that when I do a cost/benefit analysis on trying to find a problem myself by popping open an amp vs. the risk of getting electrocuted, it’s simply not worth it, regardless of how much getting it serviced will cost. Of course I don’t know the qualifications of the posters on here except for the ones who are obviously pro designers and repair people, but I’ve read enough times how there can be juice present in totally unplugged gear that I won’t go near it. Maybe that’s just me.
Click to expand...

You're a very smart person.
 
#47
Jimboradley said:
My biggest concern is whether this brand new cab caused the head to fail or not. I don't want to replace the head with something new just to have the new one die on me, too. What's the consensus on probable cause here? Coincidence, or head was murdered by cab?
Click to expand...

It's impossible to know but if the head was working fine while you were using it and still fine with no changes when you turned it off, but then was dead when you plugged it in at a new location I would bet the most likely cause of the problem was the moving the thing around rather than the cab.
 
#49
Jimboradley said:
Fair criticisms. I had some electronics classes in college but am by no means an expert. Enough to identify most of the components on the PCB and steer clear of the caps, though. I don't think the head is worth paying to repair. I may just toss it or sell it for parts.

My biggest concern is whether this brand new cab caused the head to fail or not. I don't want to replace the head with something new just to have the new one die on me, too. What's the consensus on probable cause here? Coincidence, or head was murdered by cab?
Click to expand...

The BL600 is class H, no overload protection. For the cab to "kill" that head it would have to be shorted and the fuse in the head would quickly blow. You would not have been able to use the DI out. I would vote pretty solid on coincidence. Assuming your old cab no longer works with the head and you did hear a low thump when the 9volt battery test was done on the cab something odd happened in the amp head maybe simple but no way to know without seeing the head in person.
 
#50
B-string said:
The BL600 is class H, no overload protection. For the cab to "kill" that head it would have to be shorted and the fuse in the head would quickly blow. You would not have been able to use the DI out. I would vote pretty solid on coincidence. Assuming your old cab no longer works with the head and you did hear a low thump when the 9volt battery test was done on the cab something odd happened in the amp head maybe simple but no way to know without seeing the head in person.
Click to expand...

The Backline 600 is class AB, not class H and there is overcurrent protection which latches the amp into a protective mute condition.
 
#51
Oh interesting. I found the user manual online and it's got this snippet:

If the Backline unit senses any unsafe operating
conditions, the output signal is immediately muted and the power light changes from Green to Red.

However the power light didn't turn Red, so maybe that's not the mode it's in.
 
#52
Jimboradley said:
Oh interesting. I found the user manual online and it's got this snippet:

If the Backline unit senses any unsafe operating
conditions, the output signal is immediately muted and the power light changes from Green to Red.

However the power light didn't turn Red, so maybe that's not the mode it's in.
Click to expand...

That's what happens when it senses one of several faults, it resets at power-up.
 
#53
agedhorse said:
That's what happens when it senses one of several faults, it resets at power-up.
Click to expand...
Whoops sorry. I wasn't very clear there. Under normal operation, the light starts red, then turns green after a few seconds and the amp starts making noise. On my amp with no output, it still starts red and goes green. It doesn't stay red or go back to red. So I don't think it's detecting any faults. Unless of course the circuit that flips it back to red itself is faulty
 
#58
Jimboradley said:
Whoops sorry. I wasn't very clear there. Under normal operation, the light starts red, then turns green after a few seconds and the amp starts making noise. On my amp with no output, it still starts red and goes green. It doesn't stay red or go back to red. So I don't think it's detecting any faults. Unless of course the circuit that flips it back to red itself is faulty
Click to expand...

Not 100% sure on this series, but do you hear a "click" of the mute relay engaging when the LED goes green? (The -RB2 series has this, and the startup/protect seems similar). If not, the amp proper may be fine, but the mute relay has failed . . .
 
#59
There’s a lot of stuff going on with the (power amp) mute circuit, some amp faults will not cause the relay to close. It’s likely not the relay itself.
 
#60
tadawson said:
Not 100% sure on this series, but do you hear a "click" of the mute relay engaging when the LED goes green? (The -RB2 series has this, and the startup/protect seems similar). If not, the amp proper may be fine, but the mute relay has failed . . .
Click to expand...
No audible sound when light goes on. I can't remember if I ever noticed a click before, but that's definitely a great lead to follow. Thanks!
 

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