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Old 15th Nov 2011, 9:50 pm   #2
Darren-UK
Dekatron
 
Join Date: Apr 2003
Location: Blackpool, Lancashire, UK.
Posts: 4,061
Default Re: AF11x transistors, 'tin whisker' problems and solutions.

This post with its links, intended as a follow-up to that above, may duplicate some of the information given in post #1. However, rather than sticking to digesting only one person's waffle, it's often interesting to read about the opinions, experiences, solutions and outcomes posted by other members. The links given below therefore lead to just a few existing threads on the subject. As this guide was originally produced back in 2007, many more threads have appeared since the list below was compiled.

To read more about the 'tin whisker' problem see here. Please note that this link more or less centres upon the NASA research as already linked to in post #1.

To read more on the 'repair' of faulty AF11x transistors see here or here.

To read more on the substitution, including with Silicon, of AFxxx transistors see here, here, here or here. The latter link discusses the Silicon BF450/RA.

This thread may also be of interest, especially the posts concerning short circuits not involving the screening ie between e, b and c or any two of those.

As stated in post #1, if any members have a question or problem not covered via any of the information given in this thread, please create a new thread in the relevant forum section.

There are two more points perhaps worth mentioning.

Firstly, with a typical, for the time, AM radio the AF11x transistors, or any other type for that matter, will be visible on the chassis/PCB. However, other radios - in particular but not exclusively - those with VHF/FM - will very likely make use of screened modules. These modules may also contain AF11x transistors. To save yourself a lot of work, and grief, you are advised to check via the service data before commencing your repairs.

Secondly, if you fancy experimenting with different transistors for the replacement of AF11x's yourself, obtain some old wreck of a Bush TR82 series radio (but not, of course, that silly TR82/97 imitation thing). Obviously, make sure it's a version which uses AF11x's though as some used OCxx type transistors and, if you're a transistor newbie, it might be wise to avoid the VTR103 - the VHF/FM version of the original TR82. These TR82's have several advantages for this work; quick and easy access without (hopefully) the need to remove the chassis, metal chassis so no risk of PCB damage from soldering iron heat and, best of all, the transistors are easily installed and uninstalled due to being mounted on little metal posts.

To conclude, this guide is not intended, deliberately or inadvertently, to be the very last word on the subject. That said, myself and the other moderators hope the guide will be of interest and also will, hopefully, prove useful.

Good luck and happy repairing and dewhiskering .
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