Re: Another War Story (from the front lines)
Those Tricky CTCSS Boards.
The Smoking Lamp is now Lit... Smoke'em if you've got'em.
For the fun of building repeater gear...
In what little spare time I have (as of late) I had
formed an informal assembly line to manufacture a number
of 224 MHz Repeaters as described in recent group posts.
These Repeaters are constructed using Hamtronics Exciter
and Receiver Modules mounted in an aluminum box (with a
center divider shield) with an old (now out of production)
Comm Spec TS-32 CTCSS (PL) Board.
http://groups.yahoo.com/group/Repeater-Builder/photos/album/1157128983/pic/list
I've just added a fair number of new pictures including
Repeater Number 2 and 3 already out the door. You'll see
very minor differences in each version. Regardless of what
some people might have said about the Hamtronics Boards,
these units do perform really well and are fairly priced.
I bought a number of used Comm Spec TS-32 CTCSS Encoder Decoder
modules to use, one for each repeater. Since these repeaters
take off and play pretty well right out of the starting gate
Yes I got a bit lazy in regards to pre-testing of the various
modules before final assembly. Well... I was almost bit by
a glitch from a used TS-32 CTCSS board.
I do pre-test the boards... figuring they're probably good if
a quick on the bench test sees a CTCSS tone coming out of the
encoder portion/section. One might "assume" all is well among
common parts within the same circuit?
Finish up the repeater, set the CTCSS tone (via the top mounted
dip switch) and start down the level alignment trail of happy
times after wiring the controller pig tail (connection lead).
The TS-32 is mounted with double sided tape and RTV Silicon
Glue as the tape eventually hardens and loses its grip on the
board. I route a wire from the TS-32 Encoder output pin, through
a chassis feed-through capacitor (as seen in the pictures) to
the exciter to provide Transmit CTCSS encoding. Transmit CTCSS
is a nice feature and very easy to include when using the
TS-32 Board.
I set the Tx level about 400 Hz Tx Deviation (because in the
real world it really doesn't need to be more than that) and moved
on to a function check... darn it no CTCSS Decode Logic indicated
on the external controller.
I was not looking forward to removing the already secured
and wired TS-32 from the chassis. Out with a Scope Probe to
try some initial testing before a board removal is required.
The TS-32 docs are very good and there are signal wave form
pictures at various stages of the circuit paths. Everything
looked OK with minor difference with the exception of what
appeared in the TS-32 decoder detector section. Quite the
head scratcher... a non matched decode situation.
Sometimes a change will do you good and in this case trouble
shooting a low frequency audio circuit at a higher frequency
might help ferret out a pesky problem. So I reset the TS-32
dip switches and the Service Monitor for the highest possible
CTCSS tone frequency.
Well looky here...
Now I've got a nice bright LED on the Repeater Controller
indicating a decoded CTCSS tone? Sure enough a few repeated
decode tests toggled with the Service Monitor and I've got
happy times.
Dip switches can become intermittent so I figured one of them
wasn't making good connection. I reset the desired 127.3 Hz
tone and the logic once again failed to toggle.
One can place a multimeter set on dc volts upon the main TS-32
IC Chip (proper pins of... ) to measure the tone selection
logic as you cycle the dip switches on and off. Through a
process of elimination I found the center dip switch logic
was not "rising high" with the corresponding proper switch
movement, but it was slightly changing value. The key point
here is the logic line was not rising enough, which would
lead some to believe the normally expected present logic
pull-up resistor is bad or not at home.
But there are no pull-up resistors shown on the circuit
diagram. That function is provided internal to the custom
TS-32 logic chip. Can the chip be partially failed on the
center number 3 logic address line?
Swapping is simple in the right situation...
So I swapped the IC over from my last known good TS-32 and
the entire range decode function started working. So yes it
appears the original TS-32 chip has a failed internal pull
up logic function on the number 3 address line.
One could use the chip for any CTCSS tone not in the range
of a/the third required address line. I marked the chip as
such and put it away.
I'm happy to report the latest 224 MHz Repeater Project works
very well and is already marked for installation. Once again
pictures of a few of these repeaters are available in the
Group Photos Section.
I will go back to testing the CTCSS modules before I
permanently install them into the chassis. As a sidebar note
I will mention I actually do solder down the original TS-32
snap on pins as they will often work themselves loose after
a time.
The no free lunch rule still applies unless you're a
trusting soul or a gambler.
cheers,
s.
ps: The Smoking Lamp is now Out.
