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Electronics Repair (sci.electronics.repair) Discussion of repairing electronic equipment. Topics include requests for assistance, where to obtain servicing information and parts, techniques for diagnosis and repair, and annecdotes about success, failures and problems. |
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#1
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Velodyne F1800R Subwoofer - Hum, and occasional LOUD popping
This sub hums a lot when first turned on, and once in a while starts popping
very loudly shortly thereafter, at which point I have to turn it off. It seems "unstable" at turn on, making funny noises before the popping. The rest of the time, the hum fades down to barely noticable, and everything is OK other than the low hum. I talked to the manufacturer, who said this old design had this problem, and the only solution was to send the amp to them for repair/replacement for $285. They describe this amp as a "beer-can" amp or something like that, IIRC. The power amp part is in an aluminum can of some sort. If anyone has dealt with this unit and this problem, I would love to receive hints for repair. My first thought is just to replace the large filter caps and see if this helps. |
#2
Posted to sci.electronics.repair
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Velodyne F1800R Subwoofer - Hum, and occasional LOUD popping
This sub hums a lot when first turned on, and once in a while starts popping
very loudly shortly thereafter, at which point I have to turn it off. It seems "unstable" at turn on, making funny noises before the popping. The rest of the time, the hum fades down to barely noticable, and everything is OK other than the low hum. My first thought is just to replace the large filter caps and see if this helps. Certainly a good place to start. I'd also suggest the "tap on the PC board and components with a piece of dowel or other insulated stick, and see if you can make it pop" trick. I suspect that there may be a broken and thus intermittent solder connection somewhere in the amp. Transistor leads soldered to the PC board traces are probably the first place to check. These leads can carry a lot of mechanical stress... as the amp heats up and cools down, the expansion of the leads can fatigue and eventually break the solder junction. Re-do the junction with fresh solder (a drop of RMA flux doesn't hurt) and you may well fix the problem. I had an amp go flaky in this way last year, with symptoms that sound like yours... popping, snaps, and a sort of sizzling hiss in one channel. One of the driver transistors on the main PCB had cracked loose in this way. -- Dave Platt AE6EO Friends of Jade Warrior home page: http://www.radagast.org/jade-warrior I do _not_ wish to receive unsolicited commercial email, and I will boycott any company which has the gall to send me such ads! |
#3
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Velodyne F1800R Subwoofer - Hum, and occasional LOUD popping
Dave Platt wrote:
This sub hums a lot when first turned on, and once in a while starts popping very loudly shortly thereafter, at which point I have to turn it off. It seems "unstable" at turn on, making funny noises before the popping. The rest of the time, the hum fades down to barely noticable, and everything is OK other than the low hum. My first thought is just to replace the large filter caps and see if this helps. Certainly a good place to start. I'd also suggest the "tap on the PC board and components with a piece of dowel or other insulated stick, and see if you can make it pop" trick. I suspect that there may be a broken and thus intermittent solder connection somewhere in the amp. Transistor leads soldered to the PC board traces are probably the first place to check. These leads can carry a lot of mechanical stress... as the amp heats up and cools down, the expansion of the leads can fatigue and eventually break the solder junction. Re-do the junction with fresh solder (a drop of RMA flux doesn't hurt) and you may well fix the problem. I had an amp go flaky in this way last year, with symptoms that sound like yours... popping, snaps, and a sort of sizzling hiss in one channel. One of the driver transistors on the main PCB had cracked loose in this way. Remembering something else the Velodyne guy said on the phone. The power amp in the "can" is supposed to be a "3-dimensional" circuit inside the can. I don't know exactly what this means, but he implied that it was not repairable. Thus, the hope it is just the caps, perhaps. |
#4
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Velodyne F1800R Subwoofer - Hum, and occasional LOUD popping
"Bob F" wrote in message
... This sub hums a lot when first turned on, and once in a while starts popping very loudly shortly thereafter, at which point I have to turn it off. It seems "unstable" at turn on, making funny noises before the popping. The rest of the time, the hum fades down to barely noticable, and everything is OK other than the low hum. I talked to the manufacturer, who said this old design had this problem, and the only solution was to send the amp to them for repair/replacement for $285. They describe this amp as a "beer-can" amp or something like that, IIRC. The power amp part is in an aluminum can of some sort. If anyone has dealt with this unit and this problem, I would love to receive hints for repair. My first thought is just to replace the large filter caps and see if this helps. Look for the obvious, like a separated surround. IIRC this may have been one of the units with the accelerometer in the woofer and a servo circuit. Separated surrounds would cause this kind of symptom on them. Leonard |
#5
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Velodyne F1800R Subwoofer - Hum, and occasional LOUD popping
Leonard Caillouet wrote:
"Bob F" wrote in message ... This sub hums a lot when first turned on, and once in a while starts popping very loudly shortly thereafter, at which point I have to turn it off. It seems "unstable" at turn on, making funny noises before the popping. The rest of the time, the hum fades down to barely noticable, and everything is OK other than the low hum. I talked to the manufacturer, who said this old design had this problem, and the only solution was to send the amp to them for repair/replacement for $285. They describe this amp as a "beer-can" amp or something like that, IIRC. The power amp part is in an aluminum can of some sort. If anyone has dealt with this unit and this problem, I would love to receive hints for repair. My first thought is just to replace the large filter caps and see if this helps. Look for the obvious, like a separated surround. IIRC this may have been one of the units with the accelerometer in the woofer and a servo circuit. Separated surrounds would cause this kind of symptom on them. The surround look perfect. Pushing in on the cone, I notice it seems to have a very stiff suspension. |
#6
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Velodyne F1800R Subwoofer - Hum, and occasional LOUD popping
"Bob F" wrote in message
... Leonard Caillouet wrote: "Bob F" wrote in message ... This sub hums a lot when first turned on, and once in a while starts popping very loudly shortly thereafter, at which point I have to turn it off. It seems "unstable" at turn on, making funny noises before the popping. The rest of the time, the hum fades down to barely noticable, and everything is OK other than the low hum. I talked to the manufacturer, who said this old design had this problem, and the only solution was to send the amp to them for repair/replacement for $285. They describe this amp as a "beer-can" amp or something like that, IIRC. The power amp part is in an aluminum can of some sort. If anyone has dealt with this unit and this problem, I would love to receive hints for repair. My first thought is just to replace the large filter caps and see if this helps. Look for the obvious, like a separated surround. IIRC this may have been one of the units with the accelerometer in the woofer and a servo circuit. Separated surrounds would cause this kind of symptom on them. The surround look perfect. Pushing in on the cone, I notice it seems to have a very stiff suspension. Lots of their amps are made with a heat sink wrapped around most of the amp circuit. They are a PITA to service. With that kind of symptom, I'd be looking for a cap or a leaky FET, possibly an op amp going bad. Leonard |
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