[Elecraft] KSB2 Problem Continued

[Don Wilhelm]

Gareth,

Yes, 100mV audio should be adequate to drive the KSB2.
Do you have the K2 wired to use an Elecraft or Icom microphone?  If so, 
try lifting the bias resistor to see if the DC bias is interfering with 
the output level of your audio generator - instead of lifting the bias 
resistor, you could put a capacitor (1 to 10uF) between the signal 
generator and the K2 mic input.

I need to know which KSB2 board you have installed (there are 3 
different ones and you can only tell me what I need to know by physical 
inspection of KSB2 U3.
First, is this a new KSB2 board (purchased within the last year) or is 
it the older type with an SM2165 at U3?  Is U3 an SMD component or is it 
a thru-hole device?

Your first check should be to measure the DC voltages to KSB2 U3 - they 
should agree with the voltages listed in the KSB2 manual.
If the voltages are not within reasonable agreement with the chart, then 
U3 is your problem.

Did your KSB2 board work properly in the past?  If so, something has 
failed and the challenge is to find it.
OTOH, if this is a newly built board that has never worked before, check 
all the components for proper values and placement and check all diodes 
for proper orientation.

If all else fails, do you have access to an oscilloscope with a 10x 
probe?  If so, I can give you some typical AC voltage values at given 
points along the signal path to isolate the problem to a particular stage.

73,
Don W3FPR

On 1/15/2015 2:07 PM, Gareth - M5KVK wrote:
> K2 S/N 03885
>
> Symptoms: low power and no ALC action when on SSB.
>
> CW
> With E= 13.0V on the K2 display, if I transmit CW into a dummy load PWR=10
> gets me 10W according to my un-calibrated power meter and draws 2.3A (40m).
>
> SSB
> If I inject 1kHz sinewave into the Mic socket, for 100mV pp i/p I see about
> 6W out. Current varies between 1.9 and 2.2A and E comes down to 12.5 under
> load.
>
> Interestingly, there's zero action on the bargraph in ALC mode.
>
> Needing 100mV to get 60% of set power seems high. I thought I should get
> 100% with 50mV. Even with 1.6V pp i/p, I only see 8W o/p
>
>