Date
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Scratchy noise on RX
This morning, my IC7000 started producing a very loud "scratchy" noise when in RX. It is not RF since it will produce the noise with the antenna disconnected, band and mode don't affect the noise. The radio is normal at power-on, but the noise will start anywhere from a few seconds to a few minutes after power-on and comes from either the internal speaker or headphones. Reducing the AF to 0 silences the noise, and its level tracks the AF somewhat (the noise is VERY loud, so it is easy to hear even at the lowest AF setting above 0). I tried a different power supply and it took about 30 minutes after it had been off for several minutes. "Fiddling" with the power cable doesn't affect the issue either way.
Sounds like a thermal-runaway somewhere in the radio, but wanted to see if anyone else had seen this issue before I put the radio on the bench.
Cheers,
Joe
Sounds like a thermal-runaway somewhere in the radio, but wanted to see if anyone else had seen this issue before I put the radio on the bench.
Cheers,
Joe
After much hair-pulling, I have determined that the likely cause was a thru-hole via failure somewhere in the speaker amplifier circuit. This seems to be a common problem with ICOM radios (more common than I'd like, anyway).
Since the PCB has tented vias, I chose to run jumpers-wires to bypass most of the vias (this also saves me from having to remove several parts that cover one or both sides of the vias in question).
The bad news is that it is likely only a matter of time before another via fails in some other part of the PCB.
Thatisall.
Since the PCB has tented vias, I chose to run jumpers-wires to bypass most of the vias (this also saves me from having to remove several parts that cover one or both sides of the vias in question).
The bad news is that it is likely only a matter of time before another via fails in some other part of the PCB.
Thatisall.
So, this has been a painful journey. I have dim hope that it is nearing an end, but as is often the case, one can never be sure that an intermittent is fixed, but one can be sure when it has NOT been fixed. In this case, I got about a week of operation before the fault returned.
I looked at many possible culprits focused mostly on intermittent open conditions (in a via or component). The speaker amplifier turned out to be a dead-end, and there was nothing wrong with that circuit. After many disassembly-reassembly cycles, I finally found a cogent result: IC2551-B ended up being the stage where the "noise" was being introduced. This is a filter circuit used for all modulation modes OTHER than WBFM, AM, and the TV mode (a more careful examination of the behavior of the different modes might well have pointed to this part of the circuit much sooner -- lesson learned).
I replaced this IC with a close alternate (TL972IPWR). So far, the result is good. Until, it isn't.
I don't know if this will help anyone, but hopefully is does. If anything, it suggests that these "strange" faults can be repaired, but one should be very methodical and thorough. Learning the details of how the circuit works is also an important task to accomplish.
Cheers
I looked at many possible culprits focused mostly on intermittent open conditions (in a via or component). The speaker amplifier turned out to be a dead-end, and there was nothing wrong with that circuit. After many disassembly-reassembly cycles, I finally found a cogent result: IC2551-B ended up being the stage where the "noise" was being introduced. This is a filter circuit used for all modulation modes OTHER than WBFM, AM, and the TV mode (a more careful examination of the behavior of the different modes might well have pointed to this part of the circuit much sooner -- lesson learned).
I replaced this IC with a close alternate (TL972IPWR). So far, the result is good. Until, it isn't.
I don't know if this will help anyone, but hopefully is does. If anything, it suggests that these "strange" faults can be repaired, but one should be very methodical and thorough. Learning the details of how the circuit works is also an important task to accomplish.
Cheers
davebb123456
Hi Joe
It is always good to hear that all is well now, so many people do not update,
Thanks Dave
On Mon, 6 Feb 2023, 21:02 Joe KE0FF, <joeh@...> wrote:
[Edited Message Follows]
So, this has been a painful journey. I have dim hope that it is nearing an end, but as is often the case, one can never be sure that an intermittent is fixed, but one can be sure when it has NOT been fixed. In this case, I got about a week of operation before the fault returned.
I looked at many possible culprits focused mostly on intermittent open conditions (in a via or component). The speaker amplifier turned out to be a dead-end, and there was nothing wrong with that circuit. After many disassembly-reassembly cycles, I finally found a cogent result: IC2551-B ended up being the stage where the "noise" was being introduced. This is a filter circuit used for all modulation modes OTHER than WBFM, AM, and the TV mode (a more careful examination of the behavior of the different modes might well have pointed to this part of the circuit much sooner -- lesson learned).
I replaced this IC with a close alternate (TL972IPWR). So far, the result is good. Until, it isn't.
I don't know if this will help anyone, but hopefully is does. If anything, it suggests that these "strange" faults can be repaired, but one should be very methodical and thorough. Learning the details of how the circuit works is also an important task to accomplish.
Cheers
Input a signal source
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And trace the problem
On Feb 6, 2023, at 4:02 PM, Joe KE0FF <joeh@...> wrote:
[Edited Message Follows]
So, this has been a painful journey. I have dim hope that it is nearing an end, but as is often the case, one can never be sure that an intermittent is fixed, but one can be sure when it has NOT been fixed. In this case, I got about a week of operation before the fault returned.
I looked at many possible culprits focused mostly on intermittent open conditions (in a via or component). The speaker amplifier turned out to be a dead-end, and there was nothing wrong with that circuit. After many disassembly-reassembly cycles, I finally found a cogent result: IC2551-B ended up being the stage where the "noise" was being introduced. This is a filter circuit used for all modulation modes OTHER than WBFM, AM, and the TV mode (a more careful examination of the behavior of the different modes might well have pointed to this part of the circuit much sooner -- lesson learned).
I replaced this IC with a close alternate (TL972IPWR). So far, the result is good. Until, it isn't.
I don't know if this will help anyone, but hopefully is does. If anything, it suggests that these "strange" faults can be repaired, but one should be very methodical and thorough. Learning the details of how the circuit works is also an important task to accomplish.
Cheers