Trouble with KDSP2, need help

[Marcus Busch [DL1EKC]]

Hi All,

just finished assembly of my latest K2/100 (the fourth K2 I built) and for
thefirst time I'm having trouble getting things running.

During testing I noticed a strange behaviour: Some of the option modules
are getting lost sometimes and being displayed as "not inst". Tracing
things down I found the AUXBUS being pulled down to 1.9 V whenever the
KDSP2 option is plugged in. K2 is working so far even with this low AUXBUS
voltage, but I think it's no sufficient voltage for reliable operation.
With KDSP2 being unplugged the AUXBUS voltage is at 5 V.

KDSP2 itself is working (I have audio, LED lightening for 0.5 s on power-
up). Switching the audio filters via the AFIL button is also possible, but
the K2 displays "stnot in", that is the "not inst" message shifted in a
strange way. The KDSP2 menu (DISPLAY key) does show up only occasionally
after powering-up the K2 and pressing DISPLAY. If it gets lost, it's lost
until switching the K2 off and back on.

Tracing the AUXBUS circuit on KDSP2 I found, that:

AUX2 is 0 V
AUX3 is 1-2 V

I think AUX2 = 0V enables  the AUXBUS driver Q2 for data transmission and
this might be causing the trouble.

But I'm not sure wheter I understand the circuit correctly.

Is it true, that

AUX1 = AUXBUS read
AUX2 = AUXBUS drive enable inverted
AUX3 = transmission data

What should I do next? I fear the AUX2 output of the KDSP2 MCU (U1) is
defective making it impossible for the module to send data to the AUXBUS
and pulling it down continuously. Any other suggestion?

Your help is very appreciated.

VY 73 de Marcus, DL1EKC

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft   
Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com

[Marcus Busch [DL1EKC]]

Hi All,

the problem was solved:

A defective 2N3904 (Q3 on KDSP2 board) was showing a huge leakage current
and this way was loading down the AUXBUS. Just didn't believe this plain
old bipolar could be the reason.

Witch a new 2N3904 AUXBUS stays at 5.6 V.

Thanks for help.

VY 73 de Marcus, DL1EKC

_______________________________________________
Elecraft mailing list
Post to: [hidden email]
You must be a subscriber to post to the list.
Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft   
Help: http://mailman.qth.net/subscribers.htm
Elecraft web page: http://www.elecraft.com