[TenTec] TenTec Digest, Vol 192, Issue 25

MadScientist dukeshifi at comcast.net
Sat Dec 29 14:35:23 EST 2018

The use of dual diodes is likely an attempt to improve isolation at this point and also to allow use of that transistor to pull the signal point to ground, thereby improving attenuation here.

Are you talking the band pass tuning board or RF front end? The manual list no such board named RF front end.


> On Dec 29, 2018, at 1:03 PM, wes Bolin <k5apl41 at gmail.com> wrote:
> Halleluyah I found the problem!
> The circuitry is still a puzzle to me so hopefully someone can shed some
> light on it:
> The Diode D10 on the Front End Board is actually two small diodes in series
> in my radio.  The junction of the two individual diodes the Collector of a
> MPS6514 NPN transistor soldered to it. The
> transistor Emitter is soldered to the Jumper near C65, C66, and  Base is
> soldered into a hole on the circuit board.  The transistor is not in any
> documentation that I can find and the need to double up the diodes is not
> documented either.  The transistor was getting hot to my touch, so
> Unsoldered the Emitter and still hot, so unsoldered the Collector.  This
> allowed the signal path to not be attenuated any longer and the radio's
> sensitivity is back to normal.
> Questions:
> 1.  Why double dodes?
> 2.  Why the transistor?
> 3.  Do I need to replace the transistor or leave it out of the circuit?
> All receive signals go through D10, so it was where the Receive signal was
> being attenuated.
> Wes
> On Sat, Dec 29, 2018 at 11:00 AM <tentec-request at contesting.com> wrote:
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>> Today's Topics:
>>   1. OMNI V Failed (wes Bolin)
>> ----------------------------------------------------------------------
>> Message: 1
>> Date: Fri, 28 Dec 2018 15:41:39 -0600
>> From: wes Bolin <k5apl41 at gmail.com>
>> To: tentec at contesting.com
>> Subject: [TenTec] OMNI V Failed
>> Message-ID:
>>        <CALM7jM50KHwghA8gtYw5o36rrm6q+1iddJcJngNygL8GM5-=
>> rA at mail.gmail.com>
>> Content-Type: text/plain; charset="UTF-8"
>> Worked OK, turned it off.  Next day it turned on but no Receive.  It
>> belongs to my friend so I brought it home to troubleshoot.  What I know is:
>> 1.  It was intermittently working when it was turned on--sometimes the
>> display did not light up, other LEDs were On randomly....I found that the
>> N4PY chip was probably the problem after reading the book.  I put the
>> original chip back in and it turns On nicely. good display, etc.  (A
>> replacement N4PY chip is coming).
>> 2.  The radio transmits OK; power out and SSB all seem good
>> 3.  I tested the TRX-RX switch with Ohmmeter and it is switching OK
>> 4.  In RX Ant I get much stronger signal through the radio than in the TRX
>> Ant
>> connector on Receive.  On 14MHz the signal drops into the noise at about 20
>> microvolts in the RX input.  Even with S-meter well over S-9 (+30) with the
>> RX
>> input, I can hear it S1 or so through the TRX input.
>> So the receiver is pretty deaf with the RX input and unusable with the TRX
>> input.
>> 5.  The Attenuator works with the receive signals
>> 6.  I have tried 80M and 20M so its not band dependent
>> 7.  Measured voltages and they are correct
>> I suspect that my friend turned the radio Off and On by leaving the OMNI V
>> "On" and switching  the Power Supply  (Book says don't do this).  I'm
>> guessing a transient took out the microprocessor, and caused the RX
>> problem.
>> Any help or  ideas will be greatly appreciated.
>> 73
>> Wes
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>> End of TenTec Digest, Vol 192, Issue 25
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