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Hi again: I have for a short period of time a JBL PRX718XLF sub and a JBL PRX712 top box in for repair. They both have the same problem: Both make a slightly percussive noise as soon as they turn on with a pink noise like in the background as well, until they go into standby after about 4-5 minutes without a signal.
When a signal is applied to the input it does come through, but at a very low level and is not affected by the input trim pot. I was able to get the sub to work properly for about a day by wetting my finger and placing it on the solder side of the pre-amp board in different places until it caused the problem to disappear.
Was able to turn the unit on and off several times over a period of about 20 hours and functioned fine for an hour or more with no symptoms of the problem. Then at some point the issue returned. I didn't replace any parts or even unsolder anything so I didn't expect it was fixed. I was not able to get the same results from the PRX712. I'm thinking that the root cause might be a failed small can type electrolytic cap, of which there are quite a few used in this design. But touching them does not seem to affect the problem directly. I understand from the posts on youtube that this is not an isolated incident but regular occurance with the PRX series, however have not found a remedy anywhere. Any suggestions?
When a signal is applied to the input it does come through, but at a very low level and is not affected by the input trim pot. I was able to get the sub to work properly for about a day by wetting my finger and placing it on the solder side of the pre-amp board in different places until it caused the problem to disappear.
Was able to turn the unit on and off several times over a period of about 20 hours and functioned fine for an hour or more with no symptoms of the problem. Then at some point the issue returned. I didn't replace any parts or even unsolder anything so I didn't expect it was fixed. I was not able to get the same results from the PRX712. I'm thinking that the root cause might be a failed small can type electrolytic cap, of which there are quite a few used in this design. But touching them does not seem to affect the problem directly. I understand from the posts on youtube that this is not an isolated incident but regular occurance with the PRX series, however have not found a remedy anywhere. Any suggestions?