I've said from the beginning I'm no technician ...
Spent about 8 hours yesterday and today assembling the 38 special,
with the 5 watt mod.
Put everything together, took my time. Everything looked good. Had
to locate some caps -- no problem. Electronic supply house in town
is moving. No TO-220 installation kits available, or 4-40 nylon
screws either. OK, get them when it's ready for the case. Look at
the board one more time. Hmmm. Are these electrolytics oriented
right? No. Take them out, and reverse them. The banded end is
*negative*. OK, the folks said simple, not idiot-proof.
Power on -- nothing. Oh s**t. The leads on the power cord are
backwards! OK, no tragedy. Also forgot to turn on the power
supply, so no power actually applied. Switched the power leads,
turn on supply, and voila! Power. No smoke.
Next step, align receiver. Uh Oh. No antenna available. OK, we
just need a signal, right? Break out the trusty-rusty outbacker.
Plug it up for 30m, attach to mount on vice grips, attached to the
chain link outside. No transmitting, so no problem. Problem. No
signals. Anywhere.
Hmmmm. Perhaps this SWR thingy from MFJ can come in handy. Set it
for 10.110. Lots of noise, but a signal, even through the dummy
load connected to the 38S. Peak TC1 for max signal. Only one peak.
Why? Unknown. Must continue. Getting late. Peak for max signal
and leave it.
Plug in key -- hit the key. No smoke. Ugh. Good. Connect
wattmeter in line. No movement at all on meter. Is meter or rig
broken? Dunno.
Take it over to the computer, plug up the Probe Scope. Read
instructions from three different sources -- no keying waveform. No
voltage on output. Nice sidetone, though. Break out the DX-440.
Signal is OK -- still not showing any power on the wattmeter, but
I'm hearing it in the DX-440, from 10.103 to 10.126 or so. Not bad.
Time to check voltages. Where was that paper? Oh yes, here it is.
Thorough job by Paul to check all this. U1 looks fine. U2 -- pin
11 keeps dropping on transmit, slowly. Starts at 6.6, drops to 3V
or so over about a four second transmit period. Pin 12 and 13 show
7.7 V rather than 5.6. Possible problem. Keep checking voltages.
Hmmm. What about the transistor? Emitter looks good -- right on
target. Collector looks good also on receive and Base is fine.
What about transmit? Emitter ok. What about base? Boy this probe
tip sure is sharp. Hit the right spot, Marty. Hit the ...
KKAAA--ZZZZZAAAAAAAPPPPP! PoP! Crackle!
Houston, we have a problem.
Marty immediately drops *EVERYTHING*, and possibly has a myocardial
infarction ... That wasn't fun at all. No damage. Just scared the
crap out of me, thankfully not literally.
No smoke. No "zap" points on the board, no apparent damage to any
components. Nice heat smell, though. What's that noise? Tone,
weak and whiney, coming from my headphones now dangling off the
table near the floor. Unplug power. Need to ... regroup ... think
.... must ... work ... this ...
OK, have a smoke and relax. Maybe a wiskey. No, hands are
trembling enough already.
Recheck voltages on U1. 10V on pin 4. Pins 1, 2, and 3 on U2 also
have 10V. Diodes are showing 10V. Regulator shows 10V.
Checked the wattmeter -- it works. I didn't have RF out, or at
least not enough RF to register.
Seems like we (I) have another debugging contest on our hands. I'm
pretty sure I shorted the transistor out somewhere along the way.
May have had more problems than that. Have I fried the transistor?
Are the ICs now just so much raw material for the glass factory?
This is pretty frustrating, obviously. Any help would be
appreciated. Seems prior to the zap, I had little if any recieve,
and (apparently) no RF but a nice sidetone. Can't give any o-scope
information. I think I may have zapped the Probe Scope in the
process. Don't know. Like the radio, I didn't know what it was
supposed to act like normally, so I cannot tell if it's broken or
not.
What can I do differently next time? (If there is indeed a next
time -- not sure if kits are still out there, and even more not sure
the wife will let me pop for another $25 bucks for the kit until I
get a job ...)
I do have a Radio Shack DSP I'll swap for a completed and tested
38S, with or without case. Prefer 5 watt mod only. Actually, I can
handle mods -- it's starting with no basis of something working that
throws me.
72 es 73 de
Marty, KM7W
__________________________________________________________________
Jackson, Tennessee e-mail: mdwatt@usit.net
http://www.public.usit.net/mdwatt
"The Curmudgeon's Corner"
NorCal #???? - ARCI #7514 - QRP-L #953 - AK/QRP #098 - Grid EM55oq
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