Re: [Kenwood_TS50] Red LED
- Here is an easy way to check the finals:
Unsolder the tabs farthest from the large balun. These
are the base leads of the PA transistors.
Using a DVM on Diode range, check for about 0.7 volts
forward, measuring from base to either emitter lead of
each transistor, or to ground (the emitters are
grounded). Check for infinite or no conductivity going
the other way.
Do likewise from base to collector. The collector
leads are connected to the large balun, but they do
NOT have to be desoldered to test the transistors;
only the base lead does.
Likewise you can check the drivers, only unsolder the
base lead. This is usually the left-hand lead on the
TO-220 transistors. Check from base to emitter, and
base to collector.
If you check from collector to emitter and see 0.7
volts, do not fear; some transistors have protective
internal diodes that are reverse biased in normal
operation; this protects the finals from any
negative-going transients on the 12v line (nah, we
don't have any of THOSE in our mobiles, do we?).
As for setting bias, if you can be certain this has
not been changed since the radio came from the
factory, you can leave it alone; I have found that if
this is the case, the bias is always within ten
percent of the factory recommendation even without
--- goddardcat <NZ0T@...> wrote:
> I took the rig apart to see how hard it is to get toWhen in doubt, MODIFY...
> the finals and
> it's much easier then I thought it would be so I
> think I'll give it a
> try, It looks to me like only the finals were
> replaced by the shop as
> the drivers look like they have been there a while -
> the grease on the
> driver with the diode looks old compared to the
> grease on the new
> finals. I'm wondering if I should just try
> replacing the drivers
> first? Maybe they went and the finals are OK?
> Anyway, I noticed after I put the rig back together
> that there is a
> red LED glowing on the little vertical board that
> the SWR protection
> pot is on. I don't remember seeing it before - is
> that an indication
> of something wrong or did I just miss it before?
> Again thanks all for any help!