popping and static noise in an Altec 1592A - diyAudio
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Old 5th March 2009, 11:13 AM   #1
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Default popping and static noise in an Altec 1592A

Hello- My Altec 1592A is exhibiting random 'pop' noises followed with small bursts of 'static' type noise. They begin about 5 to 10 min after the unit is powered up. They are not attenuated by the master volume or any of the input channel volumes. I can turn all volumes to zero and still hear the noise. Should this be telling me where to look for the problem? There is no 60Hz hum present in the output. I've considered recapping the main output card as well as changing all the transistors but what I'd really like to know is how to troubleshoot the faulty component(s) more accurately. My knowledge of circuits is at the novice level so please bear with me. Any suggestions or tips?
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Old 9th March 2009, 05:47 AM   #2
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noisy transistor.

buy a can of "freeze spray" (assuming they still sell it) and one at a time, with at least 30 secs or more inbetween sprays, spray each transistor starting from the front end (input) of the PCB and go to the output. This will take some time. When you hit the bad transistor, it should quiet the noise when listening to the output until it reheats up again - which is why you work slowly, since there can be overspray that effects the nearby transistors. Spray close and don't blast it.

Replace the bad transistor.

Assume you can solder and follow a schematic... you can ask here about what to use for the replacement, and please post the schematic of the driver board and if there is a regular number on the transistor (and not a "house" number) that would help too.

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Old 9th March 2009, 08:29 AM   #3
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Thanks Bear -

There's 8 "house" 2712s which were listed on Altec's replacement guide as equivalents to 2N3394s, 2s, or 3s. One of these had previously been replaced with a 2N5308. There's also a pair of 2N 3053s which someone replaced the stock units with. I'm still working on digging up a schematic. Looks like I'm gonna have to just buy a service manual. The only thing close online was for the 1592B on the Altec Heritage page and that was virtually unreadable. I'll try the freeze it spray this evening.
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Old 13th March 2009, 01:47 AM   #4
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Default small bursts of 'static' type noise

I have that problem too on one channel only of my brand new DIY power amp. But it happens only occasionnally. Sometimes it takes several hours to happen. I tried the freeze trick but can not hear any difference since it does not make the noise usually.... I was able to pin point the problematic PCB by doing swap of boards between left and right channel.

I have already replaced randomly a few transistors but I do not want to replace them all since doing so may damage the PCB sometimes and I will not abe able to make it for Saturday where we have a DIY demonstration show...

Can you please suggest something?
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Old 13th March 2009, 05:26 PM   #5
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heat.

apply heat selectively to the suspected device, if it is intermittant that often causes it to act up.

check ur solder joints, they can be sneaky too. look good, but be bad. I'd touch up all the solder joints on the bad board, and/or inspect carefully with an eyeloupe... make sure all leads are visible and pass through the solder - sometimes a lead is floating in point contact with a bubble of solder over the top on the PCB.

A bit depends on the nature of the noise - a LF POP or a higher freq tick may indicate different things being a problem.

A burst of actual noise is likely a bad transistor - try the heat to make it go nutz.

Check the current through each device too... one may have funky current or else funky Vbe number...

Anything is possible, and if it does it only once every few hours and stops, you've got a problem.

May be a static build up or other charge build up and discharge.
Can't tell from here.

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Old 13th March 2009, 05:48 PM   #6
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Quote:
Originally posted by bear
heat.

apply heat selectively to the suspected device, if it is intermittant that often causes it to act up.

check ur solder joints, they can be sneaky too. look good, but be bad. I'd touch up all the solder joints on the bad board, and/or inspect carefully with an eyeloupe... make sure all leads are visible and pass through the solder - sometimes a lead is floating in point contact with a bubble of solder over the top on the PCB.

A bit depends on the nature of the noise - a LF POP or a higher freq tick may indicate different things being a problem.

A burst of actual noise is likely a bad transistor - try the heat to make it go nutz.

Check the current through each device too... one may have funky current or else funky Vbe number...

Anything is possible, and if it does it only once every few hours and stops, you've got a problem.

May be a static build up or other charge build up and discharge.
Can't tell from here.

_-_-bear

The noise on my my mixer is a very distinct low frequency 'pop' with a clearly audible 60Hz hum component that briefly follows the pop then disappears. There's also the pillowy static type noise that tends to last a bit longer than the pop/hum component. I haven't been able to utilize the freeze spray method very well because the problem seems to not want to act up when I've got the chassis open. Fairly predictably the noise starts just after power up and once it subsides after 10 - 15 minutes (sometimes much less) it doesn't act up anymore. How do I apply HEAT to the component?
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Old 13th March 2009, 11:45 PM   #7
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if it has a 60hz component it may be a cap.
still could be a transistor.
or the solder connection opening and closing.

how do you want to go about applying heat?
think about it.

_-_-bear
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Old 14th March 2009, 03:25 AM   #8
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hmmm . . . Continuous hot signal? I was still thinking about that in terms 'freeze it' spray. I did try putting a plastic baggie over the board and that actually worked but I still haven't got the freeze it to show one of the transistors definitively. The board still stabilizes once the 'heat's' off. Caps will be changed out soon though. It still has the original Callins.
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