[450] IC-207H repair

[John Foege]

Hoorah on the fix! nice work ! and nice job finding/deciphering the german
info on the PA module !!

On Tue, Oct 27, 2015 at 7:21 PM, John Foege <john.foege at gmail.com> wrote:

> And because Google translate is garbage, I will translate this line,
> because it's the key line:
>
> Vermutlich durch unterschiedliche Ausdehnungskoeffizienten zwischen
> Keramik und Kühlkörper treten im Keramiksubstrat feine Risse auf, die mit
> dem Auge nur mühsam zu erkennen sind. Irgendwann führt das dann auch zu
> Unterbrechungen in den aufgedruckten Leiterbahnen, bei mir gleich an sechs
> verschiedenen Stellen.
>
> Presumably, fine cracks occur, which are only with great effort visible to
> the naked eye, due to the different thermal coefficient of expansion
> between ceramic and heatsink material. With time, this leads to cracking in
> the printed circuit board traces as well, which in my case, was present at
> six different places.
>
> On Tue, Oct 27, 2015 at 7:14 PM, John Foege <john.foege at gmail.com> wrote:
>
>> Vermutlich durch unterschiedliche Ausdehnungskoeffizienten zwischen
>> Keramik und Kühlkörper treten im Keramiksubstrat feine Risse auf, die mit
>> dem Auge nur mühsam zu erkennen sind. Irgendwann führt das dann auch zu
>> Unterbrechungen in den aufgedruckten Leiterbahnen, bei mir gleich an sechs
>> verschiedenen Stellen.
>>
>> This is, indeed, exactly what I had guessed the problem to be when
>> talking it over with Bill while you were off the air earlier. I told Bill,
>> that in my opinion, most likely it was the repeated thermal cycling of
>> heating and cooling that lead to cracks in traces on the power module.
>> Looks like I was right !! Really a very common mode of failure. If you were
>> a long-keyer, which you are not, I would have said de-soldered itself. But
>> knowing that you don't key long, I figured cracked traces from thermal
>> cycling.
>>
>> On Tue, Oct 27, 2015 at 6:57 PM, K1FSY <k1fsy at vhfwiki.com> wrote:
>>
>>> I was having intermittent power output problems with the IC-207H I
>>> received in trade from K1MAL. Noticed 35w power output on 2 meters which
>>> was reduced and then no output. After opening it up and desoldering the
>>> antenna connector to get the board out I did some troubleshooting in the
>>> APC circuit because the internet said it was a common fail point,
>>> however it shares the same APC circuit for both vhf and uhf and the 70cm
>>> side worked fine. Desoldered the PA module and popped off the plastic
>>> cover as per this page that john will appreciate, and sure enough the
>>> thing had microfractures in the ceramic board. Instead of going crazy
>>> with tiny wires I just added a little solder and reflowed the traces
>>> that the cracks were running under and buttoned it back up. Apparently
>>> Icom didn't bother putting heatsink compound on the bottom of the
>>> modules and just screwed them to the board, so eventually they heat up
>>> too much and snap crackle pop.
>>>
>>> http://www.dk7in.de/TM733.html
>>>
>>> _______________________________________________
>>> 450 mailing list
>>> 450 at lists.vhfwiki.com
>>> http://lists.vhfwiki.com/cgi-bin/mailman/listinfo/450
>>>
>>
>>
>
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