[Elecraft] K2: I killed my KPA100

[Don Wilhelm]

Jim,

OK since you have good voltage at the inside of J3, all should be well 
(did I misunderstand you for the side of J3 that you measured?).

The resistance measured at J3 would normally start out at a lower 
resistance and increase as the voltage from the DMM charges C51. If you 
have a strong light shining on the PA transistors, they will produce 
some small voltage.  Shade the PA transistors and try that measurement 
again.

Since you say that D9 is blocking DC to the base K2, then it must be 
installed backwards.  D9 should conduct from the anode to the cathode, 
but not the other way around.  It is there to protect the base K2 (but 
not the KPA100) from reverse polarity.

Check the contacts on J4 - the spring fingers seen through the 
rectangular holes should have snapped into place locking the contacts to 
the housing.  If you do not see the spring fingers through the 
rectangular hole, the contacts have not been properly inserted.

You should also check the Anderson Power Poles.  Look in the end - the 
contact blade should be latched over the spring finger.  If you can see 
both the spring finger and the contact blade, give the contact blade an 
extra push to seat it.

73,
Don W3FPR

On 2/7/2019 10:41 AM, Jim KO5V wrote:
> Don,
>
> I finished the amp a few weeks ago. Both the amp and the KAT100 in the EC2 have been working as they should, and I've made many QSOs, many with transmit times long enough to cause the fan to switch to the high-speed.
>
> When I started looking for this problem, I found the transistor mounting screws loose (Forgot to check them!). After I tightened them up, the amp passed the resistance checks in the manual.
>
> J3 is correct, I checked the K2's supply voltage at the cathode-end of D9, and measured +12V. It is then blocked by D9.
>
> When I measured the KPA's power supply's no-load voltage it was at the Power Pole end of the cable, so the fuse and cable should be good. When the power supply is connected to the KPA, I measure 1.5V across J3.
>
> Measuring between ground and J3+, I see a momentary continuity indication. On a higher resistance scale, the resistance started at at >10k ohms, then reduced, eventually going through zero, and then back up to a very high resistance. It looks like the meter might be charging a capacitor (C83?).
>
> I'll check all of the soldering, and the 12PA points.
>