[Icom] 746/756 SEND Relay
Dana Hoggatt
[email protected]
Tue, 26 Mar 2002 10:35:32 -0500
In regards to the 746/756 SEND relay discussions. The members
of the IC746 group at Yahoo have been working on this dilemma
for years. We've made a lot of progress. Maybe by explicitly
copying it here, I can help shed some light on the topic.
1. Icom Tech Support has given different answers to
different people at different times.
2. I did track down the specifications for the relay and
the information is in the IC-746 FAQ. They do not
match anything Icom has said above, possibly because
the part was mislabeled on the schematics.
3. Its clear that success/failure is determined by
more than a simple voltage/current specification.
There are people running successfully far outside the
relays specifications, and there are people who have
had failures well within the specifications.
I've included the relevant extract from the IC-746 FAQ
below for reference. Personally, I doubt we're ever going
to come to closure on this topic; there are just too many
variables. Back in January, I resigned myself to the fact
that I needed to make a seperate FAQ devoted soley to this
pesky relay. I simply haven't had the time yet.
I sincerely hope this information helps.
(BTW. This section of the FAQ has changed every month since
its inception. I don't expect that to change anytime soon.)
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Q:3.5.5 Why do I need an external amplifier switching relay?
Short Answer
Its far too easy to overload and damage the internal
switching relay, resulting in expensive and/or annoying
repairs. The external isolation relays are cheap
insurance for our rigs. Besides, even Icom technical
support reccomends them.
Long Answer
Given that the relay is prone to overload, the natural
question that arises is; just how much can it handle?
Things get both lengthy and muddy from this point
on, but since you're still reading, we'll press on.
Remember, you were warned.
This continues to be a process of discovery, so I'll
present what we know in that form.
# Instruction Manual
Page 79 of the instruction manual says that the SEND
jack is rated for 16 Vdc at 2A. Some rigs have failed
while well within those specs. Others seem to survive
conditions far in excess of that rating. Obviously,
the ratings in the manual don't tell the full story.
Homebrew explanations (and solutions for) the problems
abound. Some talk about bypass capacitors while others
talk about suppresion diodes. Folks debate inductive
vs resistive loads and ratings. Surge currents and
hot switching usually get brought up, as well as AC
vs DC loading. For years, the topic keeps coming up,
but with no consensus or dependable solution; except
that using an isolation relay/circuit seems to prevent
any failures.
# Tech Support
So, many of us turned to technical support, but received
different answers at different times. For example,
in the [email protected] archives for January 2000, we
see that tech support told AB2BK that there was a
misprint in the manual. The true rating was 12 Vdc at
20mA and Icom reccomended an external isolation relay.
While that would explain the failures, it makes some of
the successes almost unbelievable. On the other hand,
the archives for February 2002 show that tech support
told N1JM that "The real scoop is UP TO 16V -OR- UP TO
2 amps.", again, reccomending an isolation relay.
While the techs did not agree upon the ratings, they
did agree upon using the external relay. Unfortunately,
none of the answers from tech support have adequately
explained the odd successes and failures.
# Service Manual
All of this boils down to how much abuse relay RL1271 on
the Main board can take. The parts list on page 6-12
shows the relay as an OMR-109F. The obvious solution
is to look up the parts and see what they are rated for.
As of January, 2002, nobody had reveiled any spec sheets
for the relay.
# Internet Search
Searching for "OMR-109" on the Internet did turn up a
curious tidbit. Icom has used the OMR-109 before, as the
SEND relay (RL2) in the IC-761. It had problems too.
There is a Service Bulliten (#24287-001A) entitled
"Larger relay for keying non-ICOM amplifiers" which
reccomends:
Replace RL 2 (currently labeled OMR 109)
on the PA Connector Board with a SY-12 relay
(ICOM P/N 921-04696). This relay is larger but
can be squeezed into place. Glue this relay
to the board with RTV.
Check out:
http://www.qsl.net/kd4sai/mods/icom/ic-761.txt
http://www89405.temp.w1.com/Modifications/B2502
More searching did turn up information for the SY-12-K
relay, which lists a contact rating of 1 A @ 24 Vdc or
0.5 A @ 120 Vac (resistive). We can infer that the
OMR-109 specs are most likely less than these.
http://www.fceu.fujitsu.com/pdf/sy.pdf
Unfortunately, we still did not have many answers.
# Contact Parts Supplers
Finally, in February 2002, we found a listing for the
OMR-109F (thanks to the kind folks at Omron Electronics
for helping out). It doesn't say much, but does show
a contact current rating of 1 A.
http://catalog.tycoelectronics.com/TE/bin/TE.Connect?C=14894&P=87296,91080,86600,76287,76437&M=PROP&N=1&LG=1&I=81&G=G
However, the above link did show who the manufacturer is.
OMR relays are made by OEG. That finally led to some
actual data sheets.
http://www.oeg.com.cn/omr14.htm
http://www.qsl.net/kb9sss/IC-746/Parts/14_omr.pdf
Here are a few interesting pieces of info from the
datasheet:
Max. Switched Voltage: AC: 120V.
DC: 60V.
Max. Switched Current: 1A (OMR-F)
0.5A (OMR-H).
Max. Switched Power: OMR-F: 50VA, 50W.
OMR-H: 10VA, 10W.
Max. Switching Rate: 300 ops./min. (no load).
30 ops./min. (rated load).
Operate time: 1.0 msec
Release Time: 0.5 msec
Expected Mech Life: 100 million operations (no load).
Expected Elec Life: 1,000,000 operations (rated load).
First we see that the listed current/votage ratings do
not match anything we've seen or have been told before.
Curious that. Why has Icom technical support given out
at least TWO different sets of specs? One theory is that
the relay specs we have are still not detailed enough.
It turns out that there are two ways to report maximum
contact current. "Maximum Switched Current" is the
maximum current at switching time; when the contacts
are opening or closing. Once the relay is switched
on, the contact current may rise to as high as the
"Maximum Carrying Current", but must reduce again prior
to switching off. Thus, if the maximum carrying current
is 2A, then the answer from Feb-2002 could make sense.
# Switching Rates Explored
Closer examination of the maximum switching rates
reveils a possible problem. Suppose, for example,
I transmit at only 1 word per minute. We average 5
characters per word, 3 dit-dahs per character, and 2
switches per dit-dah. So, CW at 1 wpm will generate
30 relay operations per minute. That's the limit of
what the relay can handle at full load. 10 wpm will
generate 300 op/min, which is the no-load limit for
the relay. 30-40 wpm (what my local CW contesters do)
pushes us to about 1,000 op/min; which is well beyong
the relay's rating. The max internal keyer speed of
67 wpm (as per ARRL review) would yield a brutal
2,010 op/sec.
This could account for the varying results encountered in
the field. We'd all assumed till now that the problem
was simply one of current or voltage overload. Now we
can see that those operating QSK CW are overstressing
the part, no matter what the load. Pushing the part
that far beyond its operational limits would certainly
make it more failure prone, which could explain some
of the failures that have happened within the supposed
current limitations.
# Expected Lifetime?
Consider this: CW at 20 wpm would generate about 600
op/min, which would reach the expected mechanical
life of the part after less than 3,000 hours of
transmitting. But wait, if we apply that same rate
to the expected electrical life, we get less than 30
hours of transmitting time.
In contrast, AM/FM/SSB/RTTY operation would likely
require 200,000 to 2,000 hours (respectively) of
operating time to hit either expected lifetime.
# The Schematics
The schematic on page 11-4 of the Service Manual shows
the SEND relay as an AHY103, not the OMR-109F listed
in the Parts List on page 6-12.
(this is listed in the "Discrepancy" section of the FAQ)
Currently, we believe that the parts list is correct
and that the schematic is wrong. However, this might
help explain why Icom Tech Support has quoted different
specs at different times.
# Summary
We have now identified MANY possible failure conditions
for the SEND relay.
* Too much voltage
* Too much current (switching or carrying)
* V/C spiking from inductive loading
* Accidental AC operation
* Exceeding operational rate
* Exceeding expected lifetime
Those are the reasons for using an external SEND relay.
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