| Electronics > Repair |
| CMU200 Rx level issue / failed loop test |
| << < (3/15) > >> |
| _Wim_:
--- Quote from: Michael-VK2BEA on January 04, 2022, 03:27:57 pm ---From what I can tell, the corrosion is just on the top surface (and top edge). If push comes to shove, it may be possible to electroplate copper back on to that surface. --- End quote --- I did a "quick & dirty" test with some copper tape as a proof of concept. I think the results speak for themselves. This is still with the shield/heatsink of the board removed. Some more careful tape-cutting and maybe soldering it in place (to prevent the glue from coming loose in the hot environment with the shield installed) is definitely a worthwhile improvement! And I would add a layer of capton tape on top to prevent future corrosion for the RF absorber foam. |
| _Wim_:
For those who are wondering about the pattern in the tape, my role of copper tape is similar to this: https://www.newark.com/3m/1245-tape-1-2/tape-copper-foil-54ft-x-0-5/dp/66F1197?st=3m%201245 (part number mentioned on mine is 3M 1739-7) |
| Sas:
Not all CMU200 units have this problem. Some units, probably newer ones from the end of production, have rx / tx modules which do not have this problem. The originally fitted RF absorber is much thinner and does not touch the filters. The modules can be recognized without opening, because they have the serial number printed on the pcb, not glued on the sticker. I don't know if this is the rule. For about 20 CMU200s, only 3 had such a newer module with a similar serial number without the problem of corrosion of the filters. They passed the test 1-> 4 / 3-> 2 RF Loop Path 1. I attach a significant fragment of the module photo without this problem. The copper foil should be smooth, thin, without glue, adhere as well as possible to the ceramics and not cover the larger BPF holes. For me, using the foil, it was not possible to get the correct test 1-> 4 / 3-> 2 RF Loop Path 1, i.e. +/- 2 dBm in the entire range. Later I will attach photos of modules and filters with problems and I will try to explain more. The original 836.5 MHz murata filter is probably impossible to get, I have been looking for it for 2 years. It can be desoldered from a damaged FSH3 board. I am looking for a method of home copper coating of ceramics without the use of electricity and an initial layer of carbon or palladium. Service companies dealing with catalytic copper plating, after learning about the size of the object and the problem of covering the holes, just laughed at me :-) |
| Michael-VK2BEA:
Interesting.. The number to the right of the S/N is probably the date code. Yours shows 17/18, mine shows 14/09 (maybe 2014 week 9). Its likely that they began seeing the problem after several years and fixed the design. The 1842 MHz filters are available from one source I found in Italy. The 836 MHz filters are unobtanium in the original pinout but can be found in a slightly different package (BHD). |
| _Wim_:
--- Quote from: Sas on January 05, 2022, 12:24:34 am ---The copper foil should be smooth, thin, without glue, adhere as well as possible to the ceramics and not cover the larger BPF holes. For me, using the foil, it was not possible to get the correct test 1-> 4 / 3-> 2 RF Loop Path 1, i.e. +/- 2 dBm in the entire range. --- End quote --- Would conductive paint be an option? Something like this: https://www.ebay.com/itm/194247218349 I only have copper tape with structure currently available. Another option might be to this the surface with a layer of solder (for less badly corroded parts at least, so the solder has something to adhere to) |
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