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Author Topic: 756 PROII Won't Turn On  (Read 1884 times)
AD6KA
Member

Posts: 2232




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« on: March 04, 2013, 11:44:59 AM »

Hello To All:

I was operating in the ARRL DX SSB Contest this weekend.
Antenna is a roof mounted HF6V with good SWR's.
After about 100 successful contacts (barefoot) my PROII
began suddenly and quickly turning itself off during transmissions.
I thought perhaps RF was getting into the radio, but I have
operated this radio and antenna with an AL80A before and
never had this problem. After rig turning off, I turned off the power
supply (Astron SS-30M), turned it back on, and the radio would
boot back up again. (The PROI->III series takes about 10 seconds).
This happened about three more times. So I decided there
was a problem or intermittent in the power cord or PS. It checked out
OK on the DVM. Nevertheless, I didn't want to mess with it during
the contest, so I used another, almost new power cord and switched
to my backup PS, a Samlex SEC-1223. This worked fine for
a while then the problem happened yet again. This time however
the radio will not turn back on at all.


I have gone through the new power cord with the DVM and all
connections are solid and not corroded, fuses intact and in place.
I have tried the new power cord with the Astron too and the output
reads the proper voltage but the radio still won't turn on at all.

It may be my imagination, but when this problem first started
happening, when I turned on the PS power with the radio plugged
in, I THOUGHT I heard a slight relay type "click" from the PROII.
I admit I could be wrong about this.
Is there some sort of relay in the power switch rail?

So now the rig won't turn on at all no matter what I try.
Has this happened to you or anyone you knew?
And do you know what the problem turned out to be?

I am hoping and praying that it is something simple
and cheap like a resettable fuse that blew or maybe a
switch or diode.

I don't have the skills to hop on and troubleshoot this
rig, but something like a resetable fuse or diode I could check
and replace. I am very handy with a soldering iron, including
SMT.

Or perhaps it's best just to bite the bullet and send it
to Icom Service in Bellevue and have them go all the way
through it.
$84 per hour service plus shipping and
insurance both ways.

Any and all thoughts and experiences appreciated.
TNX ES 73, Ken  AD6KA
PS: Finished the contest with my TS-940S/AT. Sweet
rig but boy did I miss the digital IF filters of the PROII. Grin
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KE3WD
Member

Posts: 5694




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« Reply #1 on: March 04, 2013, 02:56:36 PM »

Before sending it in, I'd at least open it up, do a visual examination for anything out of the ordinary, then I'd remove and replace every internal board connector one at a time, to wipe contacts clean, then I'd hand tighten every circuit board hold down screw I could find in there, as many times, one or more of the screws is how the board is grounded to chassis and these are rather notorious for becoming poor contacts over time.

Good Luck es 73
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N4NYY
Member

Posts: 4742




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« Reply #2 on: March 04, 2013, 03:36:49 PM »

Ken,

Send it to Malcom Technical Support. He is first class with Icoms, and he will not charge you Icom prices.

He also lists this on his website:

http://www.angelfire.com/biz2/mts/756series.html

"ICOM 756 Series

In General the 756 series has few issues from a "normal" use aspect. Nearby lightning strikes and voltage surges do the most damage.
Occasionally I get in a 756 that won't power up. This is usually the Main unit 5v regulator or the main Dc/Dc converter on the sub-logic unit. This is rare though."
« Last Edit: March 04, 2013, 03:56:14 PM by N4NYY » Logged
AD6KA
Member

Posts: 2232




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« Reply #3 on: March 04, 2013, 04:13:14 PM »

Many thanks for the advice, Clark and Vinnie.

Yeah, at least opening it up and looking for something
obvious, cleaning & tightening connectors and boards sounds like
a great idea. Nothing to lose there. I was just getting ready
to box this puppy up, glad I read these posts.
Will let you know if I find anything obvious amiss.

I will look at the schematic and see if I can find that
5v regulator.

TNX AGN ES 73, Ken  AD6KA
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N4NYY
Member

Posts: 4742




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« Reply #4 on: March 04, 2013, 04:52:17 PM »

Many thanks for the advice, Clark and Vinnie.

Yeah, at least opening it up and looking for something
obvious, cleaning & tightening connectors and boards sounds like
a great idea. Nothing to lose there. I was just getting ready
to box this puppy up, glad I read these posts.
Will let you know if I find anything obvious amiss.

I will look at the schematic and see if I can find that
5v regulator.

TNX AGN ES 73, Ken  AD6KA

Finding it on the schematic won't be a problem. I have not worked on any 756 series. But I did work on a couple 746 series with the notorious IC-151. The biggest problem is that the interior is packed in like sardines. I am hoping it is not the case with you. In any case, if you are lucky to have easy access, I would try the regulator anyway. Then if it still don't work, send it to MTS.
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AD6KA
Member

Posts: 2232




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« Reply #5 on: March 05, 2013, 12:36:48 PM »

Quote
I am hoping it is not the case with you. In any case, if you are lucky to have easy access, I would try the regulator anyway. Then if it still don't work, send it to MTS.


After an email with Malcolm, I think that I am going to
send it in and not try to fix it myself. According to Malcom:

"Troubleshooting is the hardest part.  The boards are 4 layers of traces,
only top and bottom are documented.
"

and:

"The sublogic is behind the front panel, the dc/dc converters
are on that board as part of it's circuitry, unidentified as such
.
  They all convert a positive voltage to a negative
voltage.  Usually the Dc/Dc converter run ALC and s-meter circuits."

Looking for a fault in an unidentified circuit in a four layer
trace board is WAY beyond my capability. I can replace
a driver or PA transistor and tweak the proper bias and current
using the Service Manual, but the above I cannot do.
Discretion is the better part of valor.
I am going to let a pro do it.
Many thanks for the advice by all..
73, Ken  AD6KA
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N4NYY
Member

Posts: 4742




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« Reply #6 on: March 05, 2013, 01:15:40 PM »

Good deal. He is really first class.
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