Marc PA1O concluded that Yaesu applied strong glue, Yep.
In fact they
used very strong one, and this can make capacitor removal bit tricky, as it can’t be just
warmed and desoldered. The best idea is to suck the tin on each side (i.e using smart
thing like “solderWick” tape by Chemtronics) and use small tweezers to catch the
capacitor and turn him gently applying some heat together. Warming the capacitor
with more heat or bigger soldering iron will not help, as this is silver mica one
spreading the heat around on PCB, and will not move as standard SMD device.
More heat can only burn the track, and/or PCB itself.
After removing You will probably see that bottom side of cap is still on PCB, but
that’s is easy to solve. You can remove this with sharp knife. Just apply small drop of
IPA alcohol at the place where cap was fitted, letting IPA penetrate under the
capacitor foil. Then use solder at the one solder point and try to lift the foil in the
middle. It will easy move up then, leaving only small Japanese mega strong glue.
(Tested on two different 847).
After cleaning the place You should get something like that:
50% Job is done now. But.
At this place, I will propose, that if we already made efforts to remove this PCB,
we should do general inspection to avoid suprises when using our TRX in the future.
Depending on your TRX age, and intensity of use in the past without the TX mod you
will see melted or even partially evaporated solder on SMD capacitors and legs of
toroidal colis in filter stage! There’s the place where famous L5022 is.
More less, I did found these „heat signs” and even partially evaporated tin in two of
four modded 847, and these clean ones were not QRV on 4m at all. Answer should be
obvious for those who read Marc’s articles.
I will not discuss why it was happen, and is this possible or not, or am I right
about 45MHz second harmonics is guilty for that.
I just did some test 2 days a go when preparing to mod this TRX.
Transmitting 15W for 10minutes on dummy load causes temperature rise of about
10°C at the L5022. Would it be more when longer period of transmission?
Possibly. Or better to say: YES. I’m pretty sure.
Whatever the cause really is, there’s no significant temperature rise after TX filter
mod. You can make conclusion yourself.
