As far as I know the manual with circuit diagrams that you can download
from Tentec is all the "service" manual there is. Looking at it I have
found that there is an S-meter sensitivity adjustment R45 on the IF/AF
board along with an S-meter offset R43. It looks like R43 sets the zero
and R45 sets sensitivity from low to very high. I don't know the value,
but there is no fixed resistor to limit hypersensitivity. Providing the
AGC is enabled, you should be able to adjust R45 to any sensitivity you
like, providing the pot hasn't gone bad with age. If the pot has an open
resistive element it may only work set up way too high. The pot may have
an identification resistance on it to allow finding a generic
replacement or to allow a will guess for value, at about 1/2 the pot's
total resistance to be put in as a fixed resistor.
The other thing that can cause an S-meter to be hypersensitive is leaky
bypasses on the AGC line so that AGC control is poor, e.g. that it takes
a large AGC voltage to reduce the RF and IF gain. Maybe the RF gain
controlled stage is on another board and the cable between them is open.
It might be two common Tentec service procedures are in order. One is to
tighten all the board mounting screws to make sure the grounds are good.
The other is to apply a quarter drop of DeoxIT to each cable connector
pin and slide the connector off and on a few times to get a solid
connection again.
If all that's needed is setting R45, you will have to judge by ear what
signals are strong and weak, like we did before we could run AGC on a
receiver on CW or SSB, and adjust the meter for a satisfying reading
that matches your perception by ear.
If R45 proves to be open, Cramolin who makes DeoxIT makes a pot restorer
product that might work.
73, Jerry, K0CQ
On 9/17/2010 7:54 PM, Frank Kirschner wrote:
I just bought an Omni V with the N4PY mod. It works great, except for the S
meter. I was told when I bought it that it was hypersensitive, and that is
true.
Is there a "most frequent" cause for this? I sold or gave away all my test
equipment years back, so can't do much exploration at this point. I'd
appreciate ideas. I have the regular operation manual, but no service
manual.
Also, the knobs are a little greasy. Is there a mild solvent people have
used to clean the knobs without removing the paint?
Thanks.
73,
Frank
KK4PR
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