TEK 2440 cal

[cncjerry]

Hey there, not like I don't have enough scopes.  A guy I met gave me a 2440 a few months ago for $25.  I followed instructions widely posted and replaced the NVRAMS.  It generally boots and runs the diags successfully with errors pointing to calibration.  I do the Atten Gain and then next to is is "CHAN DLY" .  I think the signal input signal for this calibration is supposed to be 120mv P2P at 100Khz.  I cant find specific instructions and nothing is on the screen but I've tried a number of different input signals to both channels, including just leaving them off.  When the "CHAN DLY" is pressed it runs "REPET Calibration #1" or something like that and then fails.  I've tried running "REPET" cal from the main ext cal screen and that fails as well.  I've checked all the voltages, etc, cleaned the hybrids, etc.  Can't seem to get past this step.  Interesting thing is that "REPET" turns on/off and looks fine under normal operation. 

I can calibrate the triggers and run the "CTE" cal using my input signal of 100Khz with a 10ns rise time.   Just the REPET that is failing now.  I'm digging in the manuals more now and wanted to get this up on the board incase someone has a pointer.

Any ideas?

Jerry 

[David Hess]

The signal requirements for the channel delay calibration are not difficult to meet.  I just used the fast rise trigger output from my function generator which was like 10 nanoseconds.  But you need delay matched cables between the splitter and each vertical input.

The service manual has full details.

[cncjerry]

David,  Thanks, yes, I have matched cables, etc.  I have a couple of sources with less than 10ns rise time at 100Khz.  I didn't see any other frequency listed than that.

The primary failure is on the REPET calibration which it does first on the CHAN DLY cal.  If it fails, the manual then suggests probing TP291 with REPET on.  I can't get a solid trace there but when I turn on REPET when looking at relatively fast signals, it works fine.  This test must have something to do with the phase of what is on TP291 and whatever clock is used for the REPET sampling.

The gains, Trigger, CTE all pass. I'll keep screwing with it.

Thanks.

Jerry

[cncjerry]

I went back to the manual and started the jitter debug as they suggest.  You probe TP291 on the main board in REPET while looking at other signals.  The interesting thing is that channel 1 wouldn't look with REPET turned on.  Channel 2 did.    I only see this on that signal though.  Other signals I probe lock in REPET or not.

So I'm going to keep going down this path and see where it leads me.   The fact that channel channel seems to be ok gives me something to compare against.

More to come.

Jerry