Electronics > Repair

CMU200 Rx level issue / failed loop test

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Sas:
This module 1718 is from CMU200 calibrated in 2018. Based on the dates on the power supply (January 2005), hard drive (October 2004), fan (week 33 2004), R&S Electrical Safety Inspected sticker (March 2006), I assume the unit was manufactured in 2005 and sold or safety tested in 2006 year. There are numbers 0301 on the power supply (production January 2005, i.e. 0301 is not a date). Other numbers on the modules are 0309 0608 4000 0208 1104 0400 0300 1500. If it were weeks and dates, the device would be rebuilt many times. In this device I am almost sure that if something was replaced it was only the txrx module, although it may be the original module.
I have another CMU200 calibrated in 2015 and it has a sticker 1607 on the rxtx module. The rxtx module is almost certainly not from this unit. I bought this unit incomplete, without the dsp module and repaired it. Then, in 2020, a buyer cheat opened it, replaced the parts (keyboard, ccfl lcd, rxtx, dsp) and returned the damaged one. Now he is trying to fix it again. Based on the dates on the power supply (September 2004), hard drive (July 2004), fan (week 12 of 2003), R&S Electrical Safety Inspected sticker (March 2006), I assume the unit was manufactured in 2004 and sold or safety tested in 2006 year. There are numbers 0301 on the power supply (production September 2004). Other numbers on the modules are 1300 0400 0200 3800 0203 0208.
Another CRTU calibrated in November 2006 by R&S has a sticker of 1026 on the rxtx module. I think it is the second calibration after a year from sale, traces of removing the first glue on the housing. R&S Electrical Safety Inspected sticker for testing performed in November 2006. Based on the dates on the power supply (August 2001, no additional sticker), fan (week 38 of 2000) and hard drive (August 2005, numbers 0100), calibration and stickers, I assume that the unit was produced at the end of 2005. Other numbers are 2700 (cpu) 0300 (main board) 0409 0500 0100 (hdd) and 1026 (rxtx). By suggesting that this date, it would be difficult to manufacture a device in January 2000 from parts from future years.
EDIT: The numbers 1026 on the module rxtx are: Part Number, Serial Number and Modification Index (e.g. the number 10.26 can be read after pressing the INFO key on the CRTU). It has nothing to do with the production date.

I have 1842 MHz filters. I ordered 836 MHz filters in the BHD version a month ago, when the topic of cmu / crtu repair came back.

Painting cavities with the Chemtronics CW2000 marker pen does not give positive results, it additionally damages the copper layer. Painting with a conductive fabric based on graphite does nothing. Painting with copper-based paint does not do anything, the layer is not electrically conductive. Painting with Armack Kupfer Spray advertised by the manufacturer as powdered copper in an aerosol (does not contain paint) gives little, the layer is not electrically conductive. I added various copper strips, it is better but it is not good, fails the 1-> 4 / 3-> 2 RF Loop Path 1 test. I have not tried to solder the surface, it will probably damage the filter irreversibly. Each piece of the filter is individually tuned on a ceramic core. The core has defects on the ceramic surface prior to the copper plating process. These surface defects are filled with a copper layer and affect the filter tuning. Perhaps later the filters are measured, grouped and marked. I will add photos from the microscope soon.

Edit: Here are two photos of a working filter. I am posting two more extremely corroded filters after being returned from a buyer cheat. He will post a few more photos soon.

Michael-VK2BEA:

--- Quote from: _Wim_ on January 05, 2022, 06:28:04 am ---
--- Quote from: Sas on January 05, 2022, 12:24:34 am ---
--- End quote ---
Would conductive paint be an option? Something like this: https://www.ebay.com/itm/194247218349

--- End quote ---
I tried silver paint but it only partially restored the loss. I assumed because of the higher resistivity (compared to the original electroplated copper).

Sas:
Photos of the 836 MHz filter before and after cleaning. The enlarged view shows the ceramic clearances without the copper layer. The ceramics are dark gray (inverted orange).

Sas:
Photos of the 1842 MHz filter before and after cleaning. The enlarged view shows the ceramic clearances without the copper layer. The ceramics are dark gray (inverted orange).

Sas:
Photos of the 1842 MHz filter from CMU in very bad condition, corroded, scratched by the buyer (from my previously edited post). The filter was soaked for one day in isopropanol and washed in an ultrasonic cleaner. As you can see, there is not much left of the copper layer. The core is tuned by cutting the sleeve from the inside.
Photo of another 1842 MHz filter, which shows well the damage to the ceramic core, which has been copper-plated. Each ceramic core has more or less damage before copper plating. The damage to the ceramic core is mainly at the edges. The tuning takes into account the copper-bonded faults of the ceramic core.
Re-alignment of the filter may be possible after supplementing the copper layer, taking into account the imperfections of the ceramic core.

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