HW-101: failure found :-)!

[JOSE V. GAVILA (EB5AGV/EC5AAU)]

Hi gang,

Yesterday was a memorable day at my shack / radio hospital. After fixing a
Yaesu FT-707 I got for real cheap (US$70, shipping included, and all the
trouble was just a bad soldering job), I went again for the HW-101. This
time, I used an 'scientific approach', going from the antenna into the rig
circuits. I got my trusty HP-8640B generator and put it on 14.200, -73dBm
output. When applied to the antenna input, it produced only a faint signal,
with no S-meter deflection, as expected. So I put same signal directly in
RF amplifier frid (V10). Same result. I added 20dBm (so -53dBm) and put it
in the grid of first mixer (V11). No great difference. So I selected the
corresponding IF signal (about 8.9MHz, I think) and put it at the input of
T-202 bandpass filter and still got low signal output. So I put it at the
output of T-202 and... got a S6 in the S-meter!!!. So the filter was
attenuating a lot the signal. With the aid of my recycled (got for free
from work and repaired by myself) vacuum pump solder station, I got the
filter out of the circuit and opened the aluminum can. It is made of three
toroidal transformers along three fixed mica capacitors and three ceramic
trimmers. Visually all seemed fine, but checking with the DVM, one of the
toroids was open!. Checking it in detail, I found an small greenish looking
spot. It was not easily viewed due to the gummy potting compound used to
keep the filter at place. So I took the offending toroid out of the filter
and located the trouble: the wire was broken due to oxide buildup. So I
dismantled the toroid, carefully counting the turns (it has also an
antermmediate connection) and wrote down a drawing of the exact
configuration. It was late, so I could not rewind and check it, but what is
clear is that it was the culprit of the large signal attenuation. I will
let you know what I find once I rewind the toroid and check the filter.

I am a really happy camper today. This is a good way of ending this week/
month/ year/ century/ millenium :-)!

Best regards and HAPPY 2001!!!

JOSE
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  73 EB5AGV / EC5AAU - JOSE V. GAVILA
     La Canyada - Valencia (SPAIN)

  EB5AGV Vintage Radio Site: http://www.geocities.com/eb5agv

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