IC-28A transmit section carnage

On May 11, 6:56 pm, "Phil Allison" <phi...@tpg.com.au> wrote:
**  FYI  -   tantalum bead caps look like this:

http://www.allproducts.com/manufacture97/suntanbe/product1.jpg

They are known to catch fire and emit smoke and bits of the tantalum oxide
"slug"  for no good reason.

If you found a "can" then the cap is an ordinary electro that overheated,
the electrolyte boiled and burst the seal.

...  Phil
Click to expand...
Didn't find a can, so almost certainly it's a tantalum. Good catch, i
probably would have replaced it with an electrolytic if you hadn't
said anything.

Hoping to get this thing put back together later this week. Been way
too busy to get to it 'till now. I'll let you know what happens.
 
"David Brodbeck"
"Phil Allison"
** FYI - tantalum bead caps look like this:

http://www.allproducts.com/manufacture97/suntanbe/product1.jpg

They are known to catch fire and emit smoke and bits of the tantalum oxide
"slug" for no good reason.

If you found a "can" then the cap is an ordinary electro that overheated,
the electrolyte boiled and burst the seal.
Click to expand...
Didn't find a can,


** Funny how you used that word earlier.

so almost certainly it's a tantalum. Good catch, i
probably would have replaced it with an electrolytic if you hadn't
said anything.

** Did you read the warning above about tants I just gave you ???

There is no reason to use them if space permits a normal electro.



..... Phil
 
On May 18, 3:36 am, "Phil Allison" <phi...@tpg.com.au> wrote:
**  Did you read the warning above about tants I just gave you  ???

There is no reason to use them if space permits a normal electro.
Click to expand...
OK, fair enough. I wasn't sure if they had different leakage
characteristics or something like that.
 
For those curious how this went:

I replaced Q17 and C54.

I now have correct voltages on all four pins of the PA module in
transmit mode, but still almost no power output -- I suspect a bad PA
module, at this point. Reinforcing this is the fact that I appear to
have more signal on the input of the PA module than I have on the
output.

I think I'm going to set this one aside and just use it as a receiver;
at this point it's not worth spending much more time on, unless I run
across another IC-28A with a different problem.
 
David Brodbeck wrote:

For those curious how this went:

I replaced Q17 and C54.

I now have correct voltages on all four pins of the PA module in
transmit mode, but still almost no power output -- I suspect a bad PA
module, at this point. Reinforcing this is the fact that I appear to
have more signal on the input of the PA module than I have on the
output.

I think I'm going to set this one aside and just use it as a receiver;
at this point it's not worth spending much more time on, unless I run
across another IC-28A with a different problem.
Your assumption is most likely correct... I can give you an idea how
Click to expand...
ever.. If you can remove the cover of the module, and inspect the board,
you may find a crack. You'll need a high temp soldering iron to put it
back together.. This is common with RF modules or various types.

I've done this 3 times already on different rigs and it worked. Most
of the time a crack develops, mostly from abuse. Other times, you have
a bad module..
 
On Mon, 31 May 2010 21:41:25 -0400, Jamie
<jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:

Your assumption is most likely correct... I can give you an idea how
ever.. If you can remove the cover of the module, and inspect the board,
you may find a crack. You'll need a high temp soldering iron to put it
back together.. This is common with RF modules or various types.

I've done this 3 times already on different rigs and it worked. Most
of the time a crack develops, mostly from abuse. Other times, you have
a bad module..
Click to expand...
It doesn't require abuse. See:
<http://www.11junk.com/jeffl/pics/drivel/slides/power-amp.html>
That's the guts of the VHF power module from my Kenwood TM-732A radio.
The circled areas are where I had to solder the trace back together.
The two failures were seperated by about 2 years and will probably
continue at the same interval. My guess(tm) is that it was caused by
either incomplete baking of the hybrid, or a bad solder paste mix when
the hybrid was silk screened.

The gaps were almost invisible and very difficult to see. They would
have been far more visible if I could have shined a light from the
back, but there's a big copper heat spreader in the way. Instead, I
found them with an ohmmeter. I started with the probes at the end of
the conductor trace, which showed no continuity. I slowly moved the
probes closer to each other and eventually closed in on the break.

Soldering was also rather difficult. The ceramic hybrid is a
wonderful heatsink and literally sucks all the heat out of the
soldering iron. I had to use a rather large 850C screwdriver solder
tip and still managed to do a lousy job of soldering.

Also note on the photograph the two big power xsistors. The goo
covering them is rather soft and flexible silicon rubber. Please
resist the temptation to push on it, or you'll break the wire bonds
underneath.

If desperate, you can get replacement PA modules from RF Parts.

--
Jeff Liebermann jeffl@cruzio.com
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060 http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558
 
On Mon, 31 May 2010 18:15:27 -0700, David Brodbeck ǝʇoɹʍ:

For those curious how this went:

I replaced Q17 and C54.

I now have correct voltages on all four pins of the PA module in
transmit mode, but still almost no power output -- I suspect a bad PA
module, at this point. Reinforcing this is the fact that I appear to
have more signal on the input of the PA module than I have on the
output.

I think I'm going to set this one aside and just use it as a receiver;
at this point it's not worth spending much more time on, unless I run
across another IC-28A with a different problem.
Click to expand...
No new PA available or is it too costly?
 
Jeff Liebermann wrote:

On Mon, 31 May 2010 21:41:25 -0400, Jamie
jamie_ka1lpa_not_valid_after_ka1lpa_@charter.net> wrote:


Your assumption is most likely correct... I can give you an idea how
ever.. If you can remove the cover of the module, and inspect the board,
you may find a crack. You'll need a high temp soldering iron to put it
back together.. This is common with RF modules or various types.

I've done this 3 times already on different rigs and it worked. Most
of the time a crack develops, mostly from abuse. Other times, you have
a bad module..


It doesn't require abuse. See:
http://www.11junk.com/jeffl/pics/drivel/slides/power-amp.html
That's the guts of the VHF power module from my Kenwood TM-732A radio.
The circled areas are where I had to solder the trace back together.
The two failures were seperated by about 2 years and will probably
continue at the same interval. My guess(tm) is that it was caused by
either incomplete baking of the hybrid, or a bad solder paste mix when
the hybrid was silk screened.

The gaps were almost invisible and very difficult to see. They would
have been far more visible if I could have shined a light from the
back, but there's a big copper heat spreader in the way. Instead, I
found them with an ohmmeter. I started with the probes at the end of
the conductor trace, which showed no continuity. I slowly moved the
probes closer to each other and eventually closed in on the break.

Soldering was also rather difficult. The ceramic hybrid is a
wonderful heatsink and literally sucks all the heat out of the
soldering iron. I had to use a rather large 850C screwdriver solder
tip and still managed to do a lousy job of soldering.

Also note on the photograph the two big power xsistors. The goo
covering them is rather soft and flexible silicon rubber. Please
resist the temptation to push on it, or you'll break the wire bonds
underneath.

If desperate, you can get replacement PA modules from RF Parts.

I use a mini gas torch that has nice tips for soldering, no flames get
Click to expand...
in there but the tip gets hot as hell. The heat sink has no chance of
holding back. :)
 
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