[Yaesu] Kenwood TS-940 CAUTION!

[Martin Sole]

An interesting point but I think that this has been worked around with some
12 volt devices and a regulator.

My TS-940 uses MRF485 driver transistors, are these the ones to which you
refer? My TS930 uses the same devices, but also my schematic for the FT1000D
shows that also uses the MRF485 drivers, infact the 200 watt FT1000D PA
schematic is essentially identical to the TS940 schematic with the exception
of a few resistor wattage ratings. Maybe the 990 is different, there was a
DC model so maybe it's just a 100 watt 12 volt PA but I'm wondering about
the value in buying a secondhand 1000D if they are likely to suffer the same
problem.

73's
Martin, HS0ZED


-----Original Message-----
From: yaesu-bounces at mailman.qth.net [mailto:yaesu-bounces at mailman.qth.net]
On Behalf Of KC3VO at aol.com
Sent: 12 June 2004 07:47
To: yaesu at mailman.qth.net
Cc: kenwood at mailman.qth.net
Subject: [Yaesu] Kenwood TS-940 CAUTION!

 
They are both nice radios, but the KENWOOD is likely to become an expensive
paperweight if you have a failure of the DRIVER TRANSISTORS in the R.F.
power amplifier!  The plastic cased, "flat-pack" MOTOROLA  24 volt devices
used in this radio have not been manufactured for many years, and FINDING a
suitable, "Low-beta, Matched pair" is about like finding a winning lottery
ticket! To my knowledge, there are NO substitutes that will PHYSICALLY and
electrically fit the position.  Often, due to cooling fan failure, power
surges, or other causes, the POWER SUPPLY pass transistors in the 940 will
SHORT, placing approx 40 volts onto the 24-28volt circuitry, resulting in
the  DESTRUCTION of these parts, which can render the radio useless, as far
as  TRANSMITTING is concerned. I WOULD NOT pay much for one,( UNLESS it came
with  SPARE driver transistors!)--NOW you have the info, the DECISION is, of
course,  up to you, but 
this type difficulty is ONE of the HAZARDS of buying OLDER  RADIOS.   Even
the 
radios such as the ICOM IC-706,  YAESU FT-920,  and FT-100  have been
affected by this Non-availability of MOTOROLA  transistors. (The ICOM and
YAESU used the #MRF-255 transistor, which is no  longer being made, although
there ARE a few still available, but at higher than  normal prices.--73, and
GOOD
LUCK!-----------------------------------------------------------------------
------------
--------------------------------KC3VO,  Bob

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