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Author Topic: WELL KNOWN CERAMIC FILTER ISSUE... electromigration!  (Read 4828 times)
KD7RDZI2
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« on: March 22, 2018, 02:47:44 PM »

Just yesterday a couple of hams were discussing about the de-sensing of rather recent radios, not the vintage (... these old designs...). One of the guy said he had replaced the ceramic filters of two of his Yaesus and was going to replace it for a Kenwood as well. He was replacing them but he seemed to me not understand the reason of these recurrent failures. I had actually heard already about it regarding some mobile rigs, like the 857-897 but I thought it was due to a thermal issue. After reading one of the latest review about the same issue in a recent yaesu HT, I googled and found a possible reason .... http://sv8ym.blogspot.it/2010/07/mysterious-case-of-withering-filters.html .... electromigration! He says lots of interesting things among these: "The funny thing is, most of the manufacturers of amateur radio (and commercial) transceivers amazingly and inexplicably DON'T use the blocking capacitors, instead they boldly apply DC potentials directly at the filter's pins". I cannot believe it, please tell me this is not true... and he is wrong!!!
« Last Edit: March 22, 2018, 03:08:30 PM by KD7RDZI2 » Logged
K0BT
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« Reply #1 on: March 22, 2018, 03:25:27 PM »

It's true and the sky isn't falling!   Smiley

I have one of the affected radios, which I bought new.  I replaced the filters and sliced the old ones apart, finding green crud inside.  After reading that same blogspot article, I looked at the manufacturer's datasheets and the engineering data available on google scholar.

It was a batch of bad filters.  I did not modify the radio by adding blocking capacitors.  Like the TS-2000s before and after the affected date range, it now works as designed. 
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N1LO
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« Reply #2 on: March 22, 2018, 06:24:37 PM »

I'm getting ready to do this same repair and replace the three on board ceramic filters in a Yaesu ft 897.

Where did you buy your filters? I was looking for a source online.

Do I need to just call the Yaesu service center and ask for the parts department and ask for the three if filters for the 897/857?

I believe the original Toko part numbers are 455 e, 455 G, and 455 h

How much did they cost?
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K0BT
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« Reply #3 on: March 22, 2018, 09:04:02 PM »

I'm getting ready to do this same repair and replace the three on board ceramic filters in a Yaesu ft 897.

Where did you buy your filters? I was looking for a source online.

Do I need to just call the Yaesu service center and ask for the parts department and ask for the three if filters for the 897/857?

I believe the original Toko part numbers are 455 e, 455 G, and 455 h

How much did they cost?

I would check with Yaesu to see how much they want before hunting elsewhere. If the parts are available, their prices are usually not too far out of line.  I normally look at the schematic first for the part designations and (if possible) the original Yaesu part numbers to make sure we're both talking about the same parts.

The TS-2000 used one Mouser part number 81-CFWLB455KGFA-B0 and three of the 81-CFWLB455KEFA-B0.  They were just over $4 each back in 2012.

I just checked and the G filter is still available from Mouser in multiples of three for $3.12 each but the E suffix is not. Digi-Key doesn't stock them.





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N1LO
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« Reply #4 on: March 23, 2018, 05:10:25 AM »

Thanks Bob,

It seems that I just need to call Yaesu and get the parts from them
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K4JJL
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« Reply #5 on: March 23, 2018, 06:05:30 AM »

I had a Yaesu FT-2700 that went completely deaf.  Turned out the filters died in it.  I think replacements cost less than the shipping.
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AA4HA
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« Reply #6 on: March 23, 2018, 07:29:35 AM »

If you have the service manual for the 857/897 (it is on the internet) and you look at the schematic for the RF board (in the upper right quadrant of the schematic) you will see where the filters are in the circuit.

The design uses DAP222 (common dual anode switching diodes) to select the active filter. In the schematic they did not use capacitors in series to block the DC voltage from the filters.

The filters will work, for years, maybe forever in your radio, but it is not something that the filter designers originally thought would happen. The persistent DC across the filters does cause "electromigration" and can damage the filter.

A bad filter may have a sound like loud bursts of static (as if you were listening to a thunderstorm with a radio); If a filter fails it will need to be replaced.

There are mods that you can do to the circuit to add a series capacitor to each filter. It will require that you use a razor knife to cut traces and to solder very tiny capacitors across the gap in the traces. You can totally screw up a radio (unrepairable) if you do not know what you are doing or do not have a steady hand. There are a few guides on how to make these mods available in the internet.

You will need (2) .01 uFd SMD (surface mount) capacitors and a 4.7K ohm resistor (1/8 watt so its small). Only one filter needs the two caps added to isolate it from DC, the other filter already has the caps.

A good description of the problem as well as a guide on how to make the changes can be found here;

http://ara35.fr/wp-content/uploads/2016/05/FT-857-FT-897-CF1005-fix.pdf
« Last Edit: March 23, 2018, 07:37:30 AM by AA4HA » Logged

Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
K0BT
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« Reply #7 on: March 24, 2018, 04:53:25 AM »

I'm honestly curious about this.  I understand that different radio brands had similar problems with bad filters within certain date ranges, but radios manufactured prior to those dates still don't have the problem.  If this is due to "electromigration" rather than a bad batch, why haven't the earlier radios started to manifest the problems?

Looking at the FT-857 schematic, I'm even more puzzled because they use blocking caps on CF1004 but not on CF1002, CF1003, or CF1005.

The data sheet for the muRata CFWL series clearly states, "For safety purposes, connect the output of filters to the IF amplifier through a D.C. blocking capacitor.  Avoid applying a direct current to the output of ceramic filters."
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N1LO
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« Reply #8 on: March 24, 2018, 04:55:35 AM »

Hello all,

In order to close the loop on information for this repair I have typed up some things that may help others dealing with this problem.

I called the Yaesu service center yesterday and selected the parts department via the automated menu, and the technician who answered was extremely helpful and polite. I ordered the parts and they were very inexpensive. There is a limit of three for each filter per order.

I ordered three each of the three filter types and selected u.s. mail as the shipping method, and the total was less than $10, which I paid with a credit card.

I suspect that Yaesu has subsidized the cost of these perhaps because of past problems. They have changed the part numbers that are in the original service manual and manufacturers as well. They have switched from Toko to LTM as the manufacturer.

Replacement IF filters for the Yaesu ft-857d 897:

Parts can be purchased directly from the Yaesu service center in California at the following number:
714-827-7600. Be ready with the Yaesu part numbers.

The new replacement parts for the original toko IF filters that go bad and cause static crashes in receive are as follows:

Component# - NEW MFR # - NEW YAESU #
CF1002 - LTM455EW-A - H3900587
CF1003 - LTM455GW-A - H3900589
CF1005 - LTM455HW-A - H3900588

COST IN 2018 WAS APPROXIMATELY $0.70 APIECE PLUS SHIPPING

73,
Mark-N1LO
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KA5IPF
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« Reply #9 on: March 24, 2018, 02:52:46 PM »

The current data sheets for the Toko filters show a cap. If you can find an earlier one, 80's it doesn't show a cap. It called CYA
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N1LO
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« Reply #10 on: March 25, 2018, 06:00:45 AM »

After a little more research, it turns out that the manufacturer of the LTM series miniature Crystal filters is 'Token'.

 Murata also has equivalent products in the same form factor but when I did a search on them to purchase, at least one supplier had them marked as 'end of life' or 'obsolete'.
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K0BT
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« Reply #11 on: March 25, 2018, 01:32:33 PM »

Adding to the confusion, the new Token data sheets do not mention capacitors.
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AA4HA
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« Reply #12 on: March 25, 2018, 03:59:35 PM »

I would be picking the replacement filters based upon their shape factor, rolloff, pass attenuation and rejection numbers.

Since you are going to need to unsolder the old filter I would add the coupling caps to keep DC off of the filters
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Ms. Tisha Hayes, AA4HA
Lookout Mountain, Alabama
KM1H
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Posts: 5067




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« Reply #13 on: March 25, 2018, 05:11:20 PM »

The problem of silver migration goes back to the 50's when IF can manufacturers started saving money and used a deposited silver capacitor on a mica substrate instead of a real mica cap. About 30 years ago Silver Mica Disease (SMD) started to show up as static on the audio. The cure was to remove the coil from the can, clip out the substrate, and replace with a new silver mica cap. I said new as the older rectangular and square caps are showing up with SMD and even some of the modern (since the late 50's or so) dipped micas are acting up. Mouser stocks most values.

Carl
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N1LO
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« Reply #14 on: April 01, 2018, 08:01:17 AM »

Hello all once again. Just adding some feedback to this thread for any others who Are considering the repair.

I ordered the replacement filters from Yaesu on a Friday afternoon and they arrived in Virginia the following Monday!

This repair turned out to be a difficult job that took much longer than I expected. I'm definitely not an electronics technician professional, but I have been dabbling in electronics for years now. Desoldering and replacing components with standard tin lead solder has never given me a problem... Well...

I was completely unprepared for the difficulty of desoldering components assembled with rohs lead free type solder! My old Rat Shack desoldering iron with suction bulb barely even removed the top layer of solder from the solder pads. The board on this radio sucked tremendous amounts of heat away from the iron and I guess the new solder has a much higher melting point. My friend Mick, KU4KW, came over to assist.

I had to use the Hakko temp controlled soldering iron on its highest heat setting and supercharged my solder Wick using a new flux pen, as a more experienced friend recommended. I had to bear down rather hard to get the solder to suck out of the pads. It was a laborious, iterative process of sucking up a tiny amount of solder, trimming the solder wick, and repeating, as the original solder just did not want to melt freely and flow up the wick.

Finally we got the pads mostly clear.  We then proceeded to try to lift the old IF Filters off of the board. Instead, their covers popped off , revealing that all three were filled with the expected blue-green corrosion. I was going to take them apart anyway to confirm this.

 All the elements inside the filters are sandwiched together like slices of bread with loose Crystal elements interleaved between soldered metal plates that had contact pins on them extending down through the PCB board. I turned the board sideways over the trash can and used my tweezers to rake out the loose, corroded elements, leaving behind just the soldered plates. We had to clamp onto each plate after disassembling the filter, and tug on it with hemostats while touching the iron to the solder pad side. Finally, I had to rod out some of the holes with the shank of a pin to get them to open up completely. What an ordeal but we took our time and got it done.

Of course the replacement units plugged right in, and the PC board is marked with the appropriate letter matching the letters in the replacement part numbers for the appropriate pass bands, (E, G and H). Resoldering was a breeze, completed in about 2 minutes with classic 60/40 tin/lead solder!

I chose not to attempt cutting up the PC board traces to add blocking capacitors as some have suggested. Time will tell how well this repair holds up and I have two more sets of filters should the need arise again on this radio or another.

The radio seems to be working beautifully from 160m through UHF, especially on FM mode where the original problem was noticed. No more static crashes and the receiver was quiet in all my tests so far.

The original mh-31 hand mic had very poor output and very poor high frequency content. It turned out to be very easy to replace the old Dynamic element with a inexpensive Rat Shack condenser microphone element similar to mods that are available on the internet for this microphone. I used a 1 kilo Ohm resistor between the 5 volt power supply pin inside the mic and the element and a 10 microfarad tantalum coupling capacitor to take the audio back to the solder pad from the original Dynamic element.

Hope this information helps someone and if any of you more experienced folks can contribute some techniques to make this easier, please do so.

--...MARK_N1LO...--
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