ZL3OZ
30-09-2016, 03:16 PM
Had a Yaesu FT857 come in for repair with very sick receive sensitivity on FM mode mainly VHF was reported.
I found it actually still worked but RX sens was about -62dBm and the squelch could not be opened from the squelch control.
Also on SSB HF seemed at a first listen to be still ok but both sidebands hearable at the same tune by. i.e. like a double sideband receiver. (Never checked TX)
Did a search on Google and found many hits. It seems this is caused by breakdown of one or more of the ceramic 455 filters.
Usual configuration is an AM, a wideband FM and a narrow FM. (i.e three filters)(main SSB filters and CW filters not affected) and the FM one is the most likely culprit because it is most often selected (i.e. for the longest periods) and the manufacturers did not isolate the filter with caps so that the diode switching selection voltage is applied to the filter input and output as a byproduct after passing through the switching diode. This causes electron migration and a crystal buildup occurs across the tiny ceramic slices inside, shorting them out. Theres a heap on Google about dismantling and cleaning then out. I tried it and it was about 90% successful but very fiddly and still lost about 3dB more than it should.
Do a google search on ft857 filter problem or ft897 filter problems, and the iceberg starts to take shape, and this only the tip.
Also affected that I know about is the FT897, Ft817, Kenwood TS2000 and there will be others, not sure about Icom but someone said one of their marine radios is affected.
The radios all built between late 90s and 2009. Now reaching the crucial age.
I contacted Coms Centre in ZL and requested replacements. Well that was a waste of time and an argument into the bargain, seems they may not have them, might not want to supply them to anyone anyway because they are so hard to get.
I saw on line someone had found them available on ebay so thought "wonder what Aliexpress has to offer". There they were at very reasonable prices.
So if you have that trouble either go to Ali or contact me as I bought lots of 20 of all three types. So far two types have arrived and running the sig gen over them they are indeed filters and not what i feared, tiny bits of cleverly painted
wood.
Thought I would post it here as there will be quite a few of these rigs among us.
Ken
ZL3OZ
I found it actually still worked but RX sens was about -62dBm and the squelch could not be opened from the squelch control.
Also on SSB HF seemed at a first listen to be still ok but both sidebands hearable at the same tune by. i.e. like a double sideband receiver. (Never checked TX)
Did a search on Google and found many hits. It seems this is caused by breakdown of one or more of the ceramic 455 filters.
Usual configuration is an AM, a wideband FM and a narrow FM. (i.e three filters)(main SSB filters and CW filters not affected) and the FM one is the most likely culprit because it is most often selected (i.e. for the longest periods) and the manufacturers did not isolate the filter with caps so that the diode switching selection voltage is applied to the filter input and output as a byproduct after passing through the switching diode. This causes electron migration and a crystal buildup occurs across the tiny ceramic slices inside, shorting them out. Theres a heap on Google about dismantling and cleaning then out. I tried it and it was about 90% successful but very fiddly and still lost about 3dB more than it should.
Do a google search on ft857 filter problem or ft897 filter problems, and the iceberg starts to take shape, and this only the tip.
Also affected that I know about is the FT897, Ft817, Kenwood TS2000 and there will be others, not sure about Icom but someone said one of their marine radios is affected.
The radios all built between late 90s and 2009. Now reaching the crucial age.
I contacted Coms Centre in ZL and requested replacements. Well that was a waste of time and an argument into the bargain, seems they may not have them, might not want to supply them to anyone anyway because they are so hard to get.
I saw on line someone had found them available on ebay so thought "wonder what Aliexpress has to offer". There they were at very reasonable prices.
So if you have that trouble either go to Ali or contact me as I bought lots of 20 of all three types. So far two types have arrived and running the sig gen over them they are indeed filters and not what i feared, tiny bits of cleverly painted
wood.
Thought I would post it here as there will be quite a few of these rigs among us.
Ken
ZL3OZ
