HP 1980B oscilloscope Measurement System Analog/Digital 100MHz

[oz2cpu]

I just scored one, and fixed it.. i have a weakness for HP..
but I found a wierd bug, i think it is sw related,
cant really be hardware ? since i can reverse the problem from ch1 to ch2
depending on what ch i enable first,

If anyone here know this scope ? used one ? mine is the 2ch model,
there is also a 4ch model.

maybe you still own one that works ?
please see the bug i explain in this video,
and tell me : is this normal ?? are they all like this ?

HP 1980B oscilloscope Measurement System Analog/Digital 100MHz
https://youtu.be/Mux7XgN1E74?si=DahF5HBiSATP_nKJ

[Alex Eisenhut]

I don't know but I love the styling of this thing.

[Stray Electron]

   I liked the style of the HP 1980s as well. Maybe too well!  I found four of them surplus and I bought them and I mounted in a rack in my garage. They were one of those projects that I was going to get to but twenty years later and I literally haven't even turned one on so I have no idea if they work or not.

[oz2cpu]

please turn one one, and see if same issue in 2ch mode ?
but I recommend you perform deep going visual inspection before power up,
i found a few slimy things to fix before my first power on.

that big round oscillator unit ? is that standard ? or optional ?
I hear others complain about drift ?
mine dont drift, but I think my oscillator is a special better one.

[Raindog]

Interesting issue. I just acquired one of these scopes and have been having a blast with it. Mine does not have the issue you're describing in your youtube video. The one I have seems to be a base model with no other options, there are however 4 empty ROM sockets that are begging to be populated. The only issue mine has seems to have "fixed its self", the on-screen readouts would suddenly scrunch up to the left and then suddenly go back to normal, after several hours of running the issue has not reoccurred.

The issue you're having may be related to the CMRR (common mode rejection ratio) test discussed on page 4-20 of the service manual. Conducting this test may confirm whether the unit is working properly or not. One thing I like about this unit is the ability to store several different setups in the available registers, I wasn't expecting something like that. After messing around with this scope I can see why some like this instrument. According to the service manual there is a battery located in an enclosure located on the back of the instrument that backs up instrument calibration data. As far as I can tell my unit appears to have been serviced in the last 10 years, because I wouldn't expect the original battery to have lasted all these years.

[Wallace Gasiewicz]

I have had one of these for 20 years and have done all sorts of adjustments and repairs. Only recently I have moved on to an Agilent Infinium /   
I would suggest you get the HP 1980 User and Service manual from Artek Manuals, that is the only place you can get a decent copy..     

To switch trigger hit the INT button on the Right side Trigger Timing unit and then Push either channel 1 or 2.     
I think you figured this out.   
The blue button is an alternate button and when you push it the function that is labeled in BLUE is the one you activate.   
The unit appears to be in excellent physical shape.  I do not know why you have crosstalk between the channels, mine does not have this problem.   

The middle bay, the one with just a metal cover, is where another two channel unit would go or the freq counter/measurement system which I have. These can be switched out as they are plug in modules.

[Wallace Gasiewicz]

Another thought....     
The input FETS (6 lead dual FETs) on this unit are in sockets,     
As I recall they are accessible from the bottom of the unit near the Input BNCs under a metal plate..... Somewhere there...   
If you remove one of them you could isolate the fault to either before or after the FET.