[R-390] Mechanical Filter Failure?
Bob Camp
ham at cq.nu
Wed Dec 19 19:53:10 EST 2007
Hi
The filter is basically a "ladder" of very small hockey pucks
connected by stiff wires welded to the edges. From your description I
would guess you broke a wire at a weld.
The filter can just unsolders. Since the filter is dead at this point,
pulling it apart won't hurt anything. It might be something you can fix.
Bob
On Dec 19, 2007, at 7:37 PM, Jon Schlegel wrote:
> Hi all,
>
> Looks like it's case closed for the 2 kHz filter. Connected a 10k
> in to out like Bob suggested and got signal. Removed the filter
> from the chassis and ohmed the in/out coils and again got around 50
> ohms DC for both. Checked for shorts to case and found none. For
> that matter, was able to resonate in and out coils to 455 kHz with
> 130 pF or so of shunt C so it looks like the coils or ok. It's fate
> was sealed though when I swept the filter and found virtually zippo
> transmission. Thanks Bob C and John K, for the termination info on
> the filter.
>
> Is the filter possibly fixable or should I be looking for a
> replacement?
>
> Regards,
> Jon
>
>
>
> At 10:14 AM 12/18/2007 -0500, you wrote:
>> Hi
>>
>> Before you go to crazy - sling a 10K ohm resistor between input and
>> output directly on the filter. That should give you a quick
>> verification that the signal path does not have any "gremlins" in it.
>>
>> Bob
>>
>>
>> On Dec 17, 2007, at 11:09 PM, Jon Schlegel wrote:
>>
>>> Hi guys and gals,
>>>
>>> I'm working on bringing up an R-390A and have no response through
>>> the 2 kHz mechanical filter. It's my understanding that the usual
>>> failure mode for these is an open coil on the input or output yet I
>>> measure 40 - 50 ohms DC on both input and output of the 2 kHz
>>> filter. Checked the rest of the signal path around the filter
>>> especially the rotary switch and all checks ok. Is there anything
>>> else I should look at before thinking about finding a replacement?
>>>
>>> Regards,
>>> Jon, WA3MVM
>>>
>>>
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>
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