Video: Repair of a Kenwood TM-D710 transceiver with a faulty IF ceramic filter

[w2aew]

This video shows the repair of a Kenwood TM-D710 dual-band FM transceiver that has a faulty ceramic filter in the 2nd IF.  A modification is also performed to correct a design flaw (DC bias applied to the ceramic filters).

[dr.diesel]

Thanks Alan,

I any idea if this issue is present in the  TM-D710GA?

[jancumps]

Some nice bodge soldering. Well done  .

[w2aew]

Thanks Alan,

I any idea if this issue is present in the  TM-D710GA?

Not sure. I know it's there on the 710A and 710E.  You'd have to check the schematic on the GA to be sure.

[nixfu]

Alan these repair videos are such fun to watch.  Thanks for making them. 

73

[w2aew]

Alan these repair videos are such fun to watch.  Thanks for making them. 

73

I don't do too many repairs, but I try to make vids of the interesting ones. I just fixed the power plug on my niece's laptop, but that was just a mechanical repair. No vid on that one.

[HighVoltage]

Thanks for another great video.

It looks like you have a nice vacuum sucking de-soldering gun.
May I ask, what brand it is and if you are happy with it?

[David Hess]

I was intrigued by the issue of DC bias on ceramic filters making them unreliable and correctly guessed electromigration but before asking here, I watched your video in detail and you answered it.

Is electromigration in this case a significant problem if contamination is not present?

A lot of crystal oscillator circuits have a DC bias across the crystal and I do not remember a reliability problem in connection with them but the crystals are also usually (always?) hermetically sealed.  I think all of the failures I have encountered with them were do to shock causing the crystal to dislodge from its mounts.

I have a lightning damaged IC-706 that is now deaf on 2 meters which is hardly unexpected but the exact cause has stumped me so far because tests reveal no problem in the front end other than being deaf.

[w2aew]

Thanks for another great video.

It looks like you have a nice vacuum sucking de-soldering gun.
May I ask, what brand it is and if you are happy with it?

It's a Hakko 808, and I'm very happy with it.  A little bulky, but it is fully self-contained, thus doesn't take up any bench space, and works very well.

[w2aew]

I was intrigued by the issue of DC bias on ceramic filters making them unreliable and correctly guessed electromigration but before asking here, I watched your video in detail and you answered it.

Is electromigration in this case a significant problem if contamination is not present?

A lot of crystal oscillator circuits have a DC bias across the crystal and I do not remember a reliability problem in connection with them but the crystals are also usually (always?) hermetically sealed.  I think all of the failures I have encountered with them were do to shock causing the crystal to dislodge from its mounts.

I have a lightning damaged IC-706 that is now deaf on 2 meters which is hardly unexpected but the exact cause has stumped me so far because tests reveal no problem in the front end other than being deaf.

I'm not an expert on electro-migration, but I think it requires a DC bias as well as some moisture/contamination.  If the filters were hermetic, I don't think this would have been an issue at all.  I've also read that these same filters suffer no problems with long-term DC bias if they were properly cleaned and dried during manufacturing.  It really has nothing to do with the ceramic or crystal elements, just the trapped moisture/contaminants on the metal parts coupled with the DC bias leading to dendritic growth and ultimately shorting across one of the narrow ceramic elements.

[David Hess]

Is electromigration in this case a significant problem if contamination is not present?

I'm not an expert on electro-migration, but I think it requires a DC bias as well as some moisture/contamination.  If the filters were hermetic, I don't think this would have been an issue at all.  I've also read that these same filters suffer no problems with long-term DC bias if they were properly cleaned and dried during manufacturing.  It really has nothing to do with the ceramic or crystal elements, just the trapped moisture/contaminants on the metal parts coupled with the DC bias leading to dendritic growth and ultimately shorting across one of the narrow ceramic elements.

That agrees with what I was thinking.

The fired ceramic terminal strips with silvered notches Tektronix used in their old oscilloscopes suffered from electromigration or something similar which in some cases led to the silver migrating between notches causing failures.  They were of course exposed to contamination but I think they had strict cleaning requirements if repairs were made to prevent this problem.

[ironcurtain]

I will likely message you privately, but I just finished this mod. The VFO A turned out deaf, it gets the signal from my SG, which in B gets full bars (about -86dbm should yield that?).
Not sure what went wrong... I want to confirm what VFO corresponds to what side of filters. If the VFO A is the side with the IC486, or the other one.
A bit disappointed if I botched the job. VFO B is perfect.