Electronics > Repair
CMU200 Rx level issue / failed loop test
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Ringmodulator:
Hi,

my unit seems to have the same poblems.

Can someone point me to a source for these filters, which delivers to Germany?

Chris
_Wim_:

--- Quote from: Ringmodulator on February 12, 2023, 03:07:46 pm ---Hi,

my unit seems to have the same poblems.

Can someone point me to a source for these filters, which delivers to Germany?

Chris

--- End quote ---

For the 836MHz part, Arrow electronics as listed above: https://www.arrow.de/products/search?q=B39841B4147U410++&r=true
DavidAzulay5000:
progress report
The filter 1842.5MHZ
Works perfectly
B39182-B4139-U410 1842.5MHz SAW Filter 50 Ohm SMD

In addition there was a problem with the 9DB attenuation filter
So I made a filter from three size 0402 resistors
t filter
2 24 ohms
1 47ohm
In addition the RF SPDT SWITCH
UPG2179TB
was broken
So I looked for a replacement in other devices
I found the component on the WIFI board
of XBOX 360 E
I removed it and replaced it
The problem remained in the 836.5MHZ filter from the Data Sheet

I think the problem is that the attenuation is too high
at frequencies from 1200 MHz to 2000 MHz
The TYP attenuation
It is over 50DB
And that's why there is a failed internal loop test
Frequency 1200 to 2200
All other frequencies with an accuracy of 0.3 dB
the 1842.5mhz filter of epcos is perfect
B39182-B4139-U410 1842.5MHz SAW Filter 50 Ohm SMD

I do not recommend purchasing the EPCOS 836.5MHZ filter
model B39841-B4122-U410 836MHz SAW Filter SMD
I tried to replace about 4 units with the input and output polarity changed
Exactly the same results in all the tested filters regardless of the polarity of the filter
I thought the minimum attenuation . Maybe you will fall on one of the filters being tested
But they were all measured the same.
_Wim_:

--- Quote from: DavidAzulay5000 on February 16, 2023, 07:17:24 am ---The problem remained in the 836.5MHZ filter from the Data Sheet

I think the problem is that the attenuation is too high
at frequencies from 1200 MHz to 2000 MHz
The TYP attenuation
It is over 50DB
And that's why there is a failed internal loop test
Frequency 1200 to 2200

--- End quote ---


Not sure if I misunderstood you, but the goal of this filter is to ONLY allow 836.5MHz to get through (the fixed frequency filter in the attached block diagram), all other frequencies must be attenuated as much as possible. So attenuation can only be too high at 836.5MHz, at other frequencies, it must be as high as possible.

(block diagram copied from here: https://electricalworkbook.com/spectrum-analyzer/)
_Wim_:

--- Quote from: DavidAzulay5000 on February 16, 2023, 07:17:24 am ---progress report

--- End quote ---

Do you have an SDR dongle (or other spectrum analyzer) to check if something arrives at the filter (like I have done here: https://www.eevblog.com/forum/repair/cmu200-rx-level-issue-failed-loop-test/msg3917207/#msg3917207)?

My best guess is some RF-amplifier or RF-switch if broken upstream, certainly as you already had to replace another switch in the unit.
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