I really can’t figure out why no one thinks that the crystal oscillator board
might be at fault, as I had suggested 2 weeks ago.
This is the ONLY part of the radio that can cause a simultaneous failure on
both 12 and 15 meters. A bad solder joint (a Ten Tec specialty in that era) on
the filter array that feeds the LO amplifier after the mixer on that board will
kill both receive and transmit on 12 and 15 meters.
A bad solder on any part between D43 and D38 will kill the LO on both 12 and 15
meters and produce exactly the symptom described. Both oscillators will work
but their output (which, by this point, is mixed with the 5.0 to 5.5 “VFO")
will not reach Q6, the first stage of the amplifier of the LO signal.
Gary
> On Apr 30, 2018, at 10:16 AM, Steve Bookout <steve@nr4m.com> wrote:
>
> 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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>>> TenTec@contesting.com
>>> http://lists.contesting.com/mailman/listinfo/tentec
>>
>>
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