I think I checked the T/R switch already, but I'll double-check. The
thing that's weird is that the DC voltages and resistance checks on the
finals are OK. I never got a Hi-Cur warning at any time before the
failure (or since). The rig draws about 600ma during xmit.
Thanks for the feedback.
Larry N8LP
Don Wilhelm wrote:
Larry,
With those RF voltage measurements, I would say that the final output
transistors have likely failed - that goes along with your earlier report
that the power out decreased rapidly to zip.
There is only one other possibility that I can think of, and that would be
the transmit signal being shorted somewhere - so before blaming the finals
themselves, check that Q2 is operating properly - the juction of D3 and D4
in the TR switch should be at a low voltage during receive and go up
somewhere close to 8 volts during transmit.
If the receiver is still functioning properly, a short in the Low Pass
Filter is quite unlikly because that kind of fault would drag the receiver
way down too.
73,
Don W3FPR
-----Original Message-----
From: Larry Phipps [mailto:[EMAIL PROTECTED]
Sent: Sunday, December 11, 2005 10:46 PM
To: [EMAIL PROTECTED]
Cc: [email protected]
Subject: Re: [Elecraft] K2 dead xmtr
Hi Don. The levels are high everywhere in the chain up through the bases
of Q7-8. Requested power is immaterial in this case, since the ALC sees
zero detected power, and therefore is pegged at 5v all the time.
I measured the levels with a scope, and divided the p-p values by 2.82
to compare with the voltage probe reference levels in the manual. BTW, I
removed the KAT2 and KSB2 to simplify access and minimize the number of
possible fault zones.
W6 - .28 Vrms
Q5 case- 1.4 Vrms
Q6 tab- 3.5 Vrms
Q7,8 base- 1.4 Vrms
RF out- .55 Vrms
Note: These waveforms are pretty dirty looking except on 10m, where I
made these measurements.
Larry N8LP
Don Wilhelm wrote:
Larry,
With the requested power set at 5 watts, send us the RF Voltage levels at
the W6 jumper, Q5 collector (case), Q6 collector (tab), Q7,Q8
base, and the
RF Output jack. With that info, we should be able to home in on
the problem
area.
73,
Don W3FPR
-----Original Message-----
OK. I'm hoping someone has seen this before I start tearing into things
(and tearing my hair out).
My K2 started to lose power yesterday. Within an hour, the output
dropped to close to zero (1mW on 160m, 40mW on 10m). There are no signs
of distress or burning odors.
I checked the ALC... pinned at 5v. Everything looks good in terms of
levels/frequencies thru the XMIT mixer and filters, except the rf levels
are higher than indicated in the manual. I suspect this is due to the
ALC being wide open.
The dc levels for Q5, Q6, and Q7-8 bases are normal, and the resistance
checks on Q7-8 are OK. 8T looks fine. But the rf levels are all
considerably high, and look pretty ratty except on 10m. The rig draws
about 600ma in xmit.
Anyone seen this before?
Larry N8LP
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