[TenTec] continuing: Omni 6+ no receive and very low power on 12/15 m

[Steve Bookout]

Hello Bob,

I do appreciate your input.  Thank you.

I sorta had my head up a 'dark place'.   I think I had originally stated 
it was 15/17.  Something in the back of my mind had told me that they 
used the same low pass filter, but it is indeed 12/15 that do NOT share 
the same filter.  Based upon that bad memory, and having heard that the 
relays can be an issue, I bought a few relays.

With relays in hand, I just replaced the two relays on 15m. Then, out of 
the circuit, I checked them and they were both fine. It was only on the 
15 m section that I did check all the components.  And, I did find the 
inductors that you mentioned, which were fine.  I did check the 
resistors, caps and inductors feeding each relay set.  With the 
connectors supplying the DC to/from the board (#'s 8 and 14) I applied 
my own DC from a bench supply and could easily hear each pair of relays, 
on all filters, switching in/out.  I had previously confirmed that I did 
have voltage at conn #14, on the appropriate pins, when each band was 
selected.  This is the connector and cable ass'y that comes from the 
front end board.  So, have voltage and relays are switching. Used a head 
mounted jewelers loupe to check out the traces and the solder joints for 
issues.

This, of course, doesn't reveal why 12 m isn't working either, but first 
things first.  Not going to worry about 12m, when I can't get 15m 
working either.

I did as you suggested and looked around the front end board. After 
disconnecting all the RF and control cables, the diodes looked fine, as 
least the same.  About 800~ ohm forward and inf reverse.  Checked anode 
to anode to see that the two inductors feeding the diodes were not open, 
the bypass caps weren't shorted and the 100 ohm R was fine.  I did not 
check any of the discreet filter components, as I left the board in the 
chassis and could not access the solder pads.

Of course, if/when I figure this out, it will all make sense, as it 
always does.  I'm a retired R&D machinist, so this is not in my DNA, but 
like doctors, my first rule is 'to do no harm' and, so far, I have not 
made things worse.

73 de Steve, NR4M

On 4/29/2018 11:12 PM, Bob McGraw K4TAX wrote:
> The best thing is to pull the Low Pass Filter board and check all of 
> the relays.  This can be done with the relays on the board. The coils 
> are wired parallel.  Typical resistance for the pair of good relay 
> coils as I recall will be about 450 ohms, if a relay coil is open then 
> you'll see about 900 ohms.    The relay pairs for the 10/12M band and 
> the 17/15M band will measure a bit higher as there are inductors in 
> series with the coils.
>
> The 10M and 12M bands are handled by K2 and K3 where as the 15M and 
> 17M band is handled by K4 and K5.   Also check the inductors which are 
> in series with the relay coils.   Those are L12, L13, L14 & L15   I 
> have found instances where one or more may open.
>
> Your description of no output on 12M controlled by K2 & k3 and 15M 
> controlled by K4 & k5 indicates both filters sections are not 
> switching correctly.    I doubt than any of the specific filter 
> inductors or capacitors have failed.     Relays are prone to have open 
> coils.
>
> As to no receive, this is more likely on the Front End Band Pass 
> Filter board.  There are 2 diodes per filter sections.  You can check 
> them on the board with a normal diode test using an ohm meter.   
> Replace any which are suspect.
>
> 73
> Bob, K4TAX
>
>
> On 4/29/2018 8:40 PM, Steve Bookout wrote:
>> Hello all,
>>
>> Several days ago, I reported my Omni 6+ had no power or receive on 12 
>> meters and 15 meters.  From what I remembered and what I saw here, I 
>> thought it would be in the output filters.  I bought and received 
>> some replacement relays and installed them.  When I checked the ones 
>> I removed, they were fine.  Put it back together and fired it up, 
>> with the same results.
>>
>> Tore into it again.  Made sure I had 12 volts on the connector 
>> terminal when the switch was on 15 meters.   I applied my external 12 
>> volts to the dc input connector (#14?) and relays would click just 
>> fine.   Inspected the 15 meter trace under a magnifier and checked 
>> the 100 ohm R's on one end of the 12 volt buss and the inductors on 
>> the other end.  In the selected filter, all L and C components looked 
>> to have nice shiny and clean solder joints.    I removed all caps 
>> specific to the 15 meter filter and checked them.  I removed 
>> everything but the inductors specific to 15 meters
>>
>> My actual power is about 1 watt out, not totally zero.
>>
>> What else might cause this issue?  I'm confident I've done all I can 
>> on the LP filter board.  Or, does someone have a suggestion?
>>
>> 73 de Steve, NR4M
>>
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