Re: RS-485 Question (Troubleshooting)

On Jul 30, 10:59�pm, "Michael A. Terrell" <mike.terr...@xxxxxxxxxxxxx>
wrote:
mpm wrote:

On Jul 30, 9:01 pm, "Michael A. Terrell" <mike.terr...@xxxxxxxxxxxxx>
wrote:

I think that DMX-512 protocol was brand new while I worked at Ch. 55,
and never had to work on it.

WCNC-TV (6) Charlotte had an ugly, old Kligel system.
(The kind you had to plug in by hand - patch cables everywhere...)

Was still in use when they moved to their new studios. �Back around
1990.
It looked like a nightmare, starring Lily Tomlin. � :)

I don't think the Strand uses DMX, but it might.?
I am just going to assume that if it's spitting out any data at all,
then is OK.
If it's not, it won't matter because it's all surface mount, and I
don't have that much time to donate to the Church. � It's a really
nice controller, though. �Strand wants a fortune for a service call.
(Out of Atlanta, daily minimums, etc...)

I did manage to get their fire alarm, burglar alarm, and PBX back up
today.
Mostly just blown fuses and an occasional reset here and there.
(Don't tell anyone.)

The Strand has about a 200-foot antenna, er, I mean RS-485 link.
It's also in outside conduit - a clear sign of an afterthought if ever
there was one...
The Strand looks to have taken the brunt of the "non-easily-fixed"
damage.

I'm kinda hoping the new 485 transceivers do the trick.
If it's a burned cable, that's gonna be a bitch to pull...

-mpm

� �That sounds like the damage to the original Ch 55 studio & offices in
Leesburg. I lost the 11 GHz CARS used as the original STL, (long story)
all the computer terminals, the KTU cards & power supply in the 1A2
phone system, some U-Matics, four LNAs, electrical outlets & switches,
and other odds & ends. It took all day to get the phones & computer
system limping by with one terminal, and arrangements to hand carry
tapes to the transmitter site. I managed to borrow a bucket truck from
the local CATV office to change the LNAs. �It was six months before
everything was repaired, and back in full service. It was day two when I
learned to troubleshoot bad SMPS 'non field repairable' power supplies.
:( I didn't have much choice. �We couldn't find any available
replacement terminals, and the ALTOS 986 computer was running the entire
accounting & membership database under North Star Basic.

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Well, here's the update (after several hours working today..)

It's a Strand model 300, which they don't make anymore. (8 years old)
It does use DMX512. I scoped the bus and nothing coming out the XLR's
on the back.
Programming looks good.

On the dimmer packs, I shotgunned all the LTC485 transceivers, but (of
course!) that did not help.
So, I un-did all the screws and plug-in jacks to peek at the bottom of
the board for lifted traces, etc..
No problems there.

Did a continuity check on the cabeling - everything looked good there
too.
I was able to control the lights manually (panic mode), and also dim
them with the analog controls.
So, it looks like the dimmer pak might actually be repaired now - even
though I can't test it.
(I wish I had another DMX transmitter of any sort..!!) Do they have
test gear for this??

So, back to the 300 controller. Opened it up, took out the XLR card,
and starting looking back "earlier" in the circuit.
Low and behold, just in front of this output card, I can see the data
every time I move a slider...!!

So, it looks like the daughter board has a problem. It's a simple
circuit, but too much time to trace out by hand. Also, the parts are
surface mount, etc.. You know the drill.

There are surface mount components labeled D1, D2, etc, and some
marked Z1. I'm guessing these are diodes.
The seem to meter out OK in-circuit, but that might not mean too
much. My guess is the protection is blown on this board, and that
what's killing the comm-link to the dimmer pak.

Either that, or I am about to send back the wrong component to the
repair depot. ;?

-mpm
.

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