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Icom IC-M411 With the dreaded reception problem

Discussion in 'Radio Circuits, Repair & Performance' started by SV9OFO, May 4, 2012.

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  1. SV9OFO

    SV9OFO Ham Member QRZ Page

    Well, a fellow ham (SV9ABL) has a boat in which there was an Icom IC-M411 installed.

    Suddently the rig stopped hearing anything but very strong input signals, and only if squelch is off (fully counterclockwise).

    He passed it to me and I did some research on the net about the issue. It seems that it is a common problem with that model. But unfortunately boat operators usually give it back to were they bought it from for repairs. That specific radio was bought on ebay and the cost of sending it back exceeds the purchase price.

    Well, I put it on the bench and made some testing. All Mixing, LO and IF are purely fine, demodulation is deaf and noisy and Squelch suffers.

    I thought there could be the quadrature demodulator chip, a TA31136F. Luckily, there is a ch70 DSC receiver next to the AF receiver which uses the same chip. I did the swap, thinking that if it was it, I could order a chip while having the transceiver enabled. But the chips are fine, since the problem remains the same.

    I am out of thoughts. The tranceiver is made of SMD's and while voltage testing shows every voltage within specs, the receiver refuses to work.

    Is there anyone that has encountered the same problem with the IC-M411 and found out what usually breaks inside?
  2. SV9OFO

    SV9OFO Ham Member QRZ Page

    Ok, got it. What was it? Let there be here to be, that the 2nd IF filter which works after the AGC is lossy and needs replacement. part number is LTM450EW, a black box ceramic filter with three ground pins aligned, one input and one output. Z input - output is 1,5 KHz.
  3. W9GB

    W9GB Ham Member QRZ Page

    Last edited: May 5, 2012
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