[fishski13]

Quote:

The heatsinks on the Sigma 22 are cool with nothing connected.

I didn't notice any smoke for the first Beta 22 board, but I did notice a smell. Perhaps something was burning? I went ahead and tried hooking up another channel and I had the same problem: really hot heat sinks, low positive and negative rail voltages, and a strange smell. This time though, I also noticed a small amount of smoke. Unfortunately, though, I couldn't tell what part it was coming from.
 
How sensitive are Q1-Q4 to heat? When I was soldering the boards, I noticed I had put those parts in wrong at first, as per the Beta 22 instructions, and had to desolder them. I wonder if I gave them too much heat when I was trying to remove them.

you need to double check the component values and ohm out the B22 boards.  you're drawing way too much current and have a short and/or dead components.  i would post questions to over at http://www.amb.org/forum/.  Ti is at BAF in S.F. today and may not be able the reply right away. 
 

 

[jackmccabe]

Oh yeah whoops I forgot to mention I am planning on purchasing a pair of akg k1000 and I have recently purchased a pair of k340's that's why I was looking at such high gain.
Also I have not decided on an attenuator yet but I am willing to spend a fair amount.
Thanks for your reply

 

[deathg0d]

Quote:

The heatsinks on the Sigma 22 are cool with nothing connected.

I didn't notice any smoke for the first Beta 22 board, but I did notice a smell. Perhaps something was burning? I went ahead and tried hooking up another channel and I had the same problem: really hot heat sinks, low positive and negative rail voltages, and a strange smell. This time though, I also noticed a small amount of smoke. Unfortunately, though, I couldn't tell what part it was coming from.
 
How sensitive are Q1-Q4 to heat? When I was soldering the boards, I noticed I had put those parts in wrong at first, as per the Beta 22 instructions, and had to desolder them. I wonder if I gave them too much heat when I was trying to remove them.

components usually can take the heat of the soldering iron rod unless you delibrately hold them too long for it to burn, thus from normal soldering and desoldering, it cant cause damages.
if you are unable to find out or determine which part is wrong. this will be a pretty silly sugguestion but i used it myself on my bad board. just let a single board runs on slightly longer till you can notice which component is giving out smoke but you really gotta be quick and have sharp eyes.

 

 

[qusp]

hahahaha...thats awesome!!

 

[wink]

 
Quote:

 if you are unable to find out or determine which part is wrong. this will be a pretty silly sugguestion but i used it myself on my bad board. just let a single board runs on slightly longer till you can notice which component is giving out smoke but you really gotta be quick and have sharp eyes.

 

 
That's what's called the old smoke test.......
 
SMOKIN"

 

[chronomitch]

components usually can take the heat of the soldering iron rod unless you delibrately hold them too long for it to burn, thus from normal soldering and desoldering, it cant cause damages.
if you are unable to find out or determine which part is wrong. this will be a pretty silly sugguestion but i used it myself on my bad board. just let a single board runs on slightly longer till you can notice which component is giving out smoke but you really gotta be quick and have sharp eyes.

 

 
Unfortunately, the smoke that I did see at first was very small, and now I don't see any more after turning on the power. I am really afraid I am going to do some major damage to other parts if I leave the power on too long due to the ridiculous amount of heat coming from the heatsinks.
 
OK. This may be a stupid question, but I will ask anyway. Are the pads for mounting the on-board heat sinks isolated? I assumed they were, so I mounted the mosfets to the heat sinks without any isolation pads. I am using Glass Jar Audio kits, which provide small metal cylinders already mounted in the heat sink mounting holes (presumably for easy mounting to the Beta 22 boards). As such, I simply soldered these metal shafts to the aforementioned heat sink mounting pads. I figured it would be the simplest way to mount them. Everything I read on the AMB website seems to indicate this is OK.

 

[deathg0d]

Quote:

 
Unfortunately, the smoke that I did see at first was very small, and now I don't see any more after turning on the power. I am really afraid I am going to do some major damage to other parts if I leave the power on too long due to the ridiculous amount of heat coming from the heatsinks.
 
OK. This may be a stupid question, but I will ask anyway. Are the pads for mounting the on-board heat sinks isolated? I assumed they were, so I mounted the mosfets to the heat sinks without any isolation pads. I am using Glass Jar Audio kits, which provide small metal cylinders already mounted in the heat sink mounting holes (presumably for easy mounting to the Beta 22 boards). As such, I simply soldered these metal shafts to the aforementioned heat sink mounting pads. I figured it would be the simplest way to mount them. Everything I read on the AMB website seems to indicate this is OK.

I sorry but i am not very clear on what you are trying to describe on the mosfets mounting. all i can say is that, the mosfets are screwed onto the heatsink together with the 'coolant' pad (sorry i forgot the name) inbetween them to help heat transfer. also, heatsink are usually very hot, for my case, all my heatsinks are so hot that i usually cant touch them more than a minute with my finger after they have been running for 30 mins.
 
so i guess somehwere on your solderings could have went wrong which is why you cant get the readings. maybe you should start looking from the psu that all readings are correct then to start looking on each boards.
 

 

[ShinyFalcon]

It's safer to have isolation pads installed. The pads to mount the heatsinks to the β22 board should be isolated.

 

[sachu]

That's just irresponsible. Rather than saying, its fine..go ahead..use the heatsink insulators and you may save your skin when you go poking around in there. Always be safe and err on the side of caution. Will only take you another 5 mins to mount the insulators and 5$.

 

[jdkJake]

The pads also provide for thermal conduction (assuming you did not use any form of thermal paste). You get far better heat transfer along with electrical isolation.

 

[Anonanimal]

Quote:

Are the pads for mounting the on-board heat sinks isolated? I assumed they were, so I mounted the mosfets to the heat sinks without any isolation pads. I am using Glass Jar Audio kits, which provide small metal cylinders already mounted in the heat sink mounting holes (presumably for easy mounting to the Beta 22 boards). As such, I simply soldered these metal shafts to the aforementioned heat sink mounting pads. I figured it would be the simplest way to mount them. Everything I read on the AMB website seems to indicate this is OK.

The pads are isolated.  When in doubt, break out the multi-meter!  What you need to worry about, and amb describes this very clearly on the site (for the others saying this is taboo), is if the heat sinks are in very close proximity to the enclosure when installed.  If so, then there is potential for them to short to the chassis (and therefore each other), which would then be a problem.  I wouldn't say it's irresponsible by any means to leave those out if you know what you're doing, but I do agree that it's always good to err on the side of caution if you're not sure.

 
Edit: Directly from the Instructions page on the site.
Quote:

Since each MOSFET's mounting tab is internally connected to the drain pin, it will carry live voltages and should not be shorted to the chassis, ground or other parts of the circuit. If your onboard heatsinks will be in close proximity to the top metal cover when the board is installed in your chassis case, then you should mount the MOSFETs to the heatsinks using TO-220 mounting kits. If you use offboard heatsinks, then TO-220 mounting kits are also required. Otherwise, you may mount the MOSFETs directly to the heatsinks using #4-40 or M3 machine screws and hex nuts, after applying some heatsink thermal paste to the mating surfaces.

 

[chronomitch]

The pads are isolated.  When in doubt, break out the multi-meter!  What you need to worry about, and amb describes this very clearly on the site (for the others saying this is taboo), is if the heat sinks are in very close proximity to the enclosure when installed.  If so, then there is potential for them to short to the chassis (and therefore each other), which would then be a problem.  I wouldn't say it's irresponsible by any means to leave those out if you know what you're doing, but I do agree that it's always good to err on the side of caution if you're not sure.

 
Edit: Directly from the Instructions page on the site.

 

[size=medium]

Thanks for the info guys, but what I was really referring to were the screw holes which connect the heatsinks to the PCB, not the mosfets to the heatsinks. As per the instructions on the AMB website, I did not use isolation pads between the heatsinks and the mosfets because the heatsinks were not going to touch anything else. What I was worried about instead, was that soldering the heatsinks to the PCB using the screw holes would connect all of the heatsinks together, and, in turn, the drain pins of all of the mosfets.
 
I will start measuring some voltages across resistors tonight to see if I can find anything abnormal and report back.
​

[/size]

 

[Anonanimal]

Quote:

 

Thanks for the info guys, but what I was really referring to were the screw holes which connect the heatsinks to the PCB, not the mosfets to the heatsinks.
​

 
That's what I was referring to as well in my very first sentence.  Sorry for any confusion, but I was in fact answering your original question.  I was simply expanding on my answer with the other info because some of the previous posts suggested you had done something horribly wrong by leaving out the thermal pads.
 
Of course if you want to be sure, the quickest way to check is still w/ a multimeter.  Just set your multimeter to ohms mode and check between the MOSFET mounting holes and the heat sink mounting hole pads.

 

[chronomitch]

 
That's what I was referring to as well in my very first sentence.  Sorry for any confusion, but I was in fact answering your original question.  I was simply expanding on my answer with the other info because some of the previous posts suggested you had done something horribly wrong by leaving out the thermal pads.
 
Of course if you want to be sure, the quickest way to check is still w/ a multimeter.  Just set your multimeter to ohms mode and check between the MOSFET mounting holes and the heat sink mounting hole pads.

I took your advice about using a multimeter and confirmed that there were no issues regarding the heat sink and mosfet mountings. I haven't had a chance yet to investigate the main problem yet, but hopefully I will have sometime in the next few days.
 
I did have time to take a hard look at the soldering work on the underside of the board. I previously cleaned the boards really well using some 99% isopropyl alcohol. Unfortunately, I did not see any obvious problems. There were no solder bridges between contacts, and all the joints looked like they were fine.

 

[Anonanimal]

Good to hear that there are no issues there.  Check out the Troubleshooting section of the Initial Setup page on amb's site for a good start on what to check.
 
Other than that, one of the first things I'd check is the orientation of your trimpots.  I've seen a number of blown boards on the forums here that occurred from trimpots installed upside down.