tek 11801 Internal software error?

[cncjerry]

A guy I know called and offered me a Tek 11801 with an SD-26 sampling head for $100.  He said it powered on.   I told him I really didn't need another scope and he talked me into taking it for free.  If I saw value in it in the future, then I could give him the $100.

I didn't power on.  I swapped the power supply with one from an 11301, still no power and after a lot of screwing around, I found the power on switch to not be working.  I wired up the switch and then it hung on comm diagnostics.  I found a way to bypass them and also a note about taking U500 and U501 out of the battery backups.  It then got past the diagnostics and seems to be working.  I haven't got a trace yet for some reason, but all the controls work, etc.  I have a cable running from the calibration port, still no trace, but I'll figure this out.

Every now and then I get a "Internal software error, Power off and on" with some hex code below it. 

I suspect this is bad ROMs?  Any ideas?

Any other pointers will be appreciated as always.  I still have no money in it but it does seem interesting to play around with, assuming I get a signal.

Thanks,

Jerry

[KrudyZ]

It's a sampling scope and the only way to get a trace is with a trigger signal.
You cannot directly trigger on a signal going into the SD-26, so you would need to feed a separate signal to one of the two trigger inputs.
TDR heads (SD-24) can provide internal triggers from their pulse generator.

EDIT: I just noticed that you did run a signal from the cal port. That should give you a signal assuming you follow the instructions in the user manual on setting up the head and trigger.
If the instrument tells you that it is not triggered then most likely you do not have the trigger source set to "internal clock".

[cncjerry]

KrudyZ, Thanks. 

I figured out the internal clock triggering last night and scoped the internal clock signal from the front panel. That looked ok except I need an attenuator to reduce the overshoot.  I don't get anything out of the calibration port other than noise.  Would I need to bridge the internal clock output to the trigger input, setting the clock to external again, to see it?  Or does it have something to do with what I read where only certain heads have calibration?  I looked all through the utility menus to see if there was a calibration menu as on the 602a.  On the 602 you need to turn the calibration signal on.  You can also change it.

The scope presents a very fine line for what it captures on the monochrome green display.  I have a DSA602 so I knew how to operate it. Now I have to figure out this software error that halts it every so often.  But that seems like a lot of work.  It looks like there are ROM chips all over this thing.  So for $100 and a lot of work, what would I get?  The ability to see how square an edge is down to 2ps per devision is interesting at times, I agree. 

Thanks again.

[KrudyZ]

Nowadays, sampling scopes are pretty much only used for TDR or TDT measurements to check the impedance of a transmission line.
You would need an SD-24 head (good luck finding a used one that isn't blown up) to make good use of the instrument.
You could also use an external pulse generator (like Leo Bodnar's) and a splitter / combiner for TDR, but you would lose some bandwidth and introduce discontinuities.
If you don't have the need for impedance measurements, then there is little point in keeping a sampling scope and you should probably free up the bench space. Of course it would be easier to sell, if it was working...