HP 1980B

[MarshallPlexi]

Anyone have a good deal of experience fixing an HP 1980B Oscilloscope?

I’ve just got one and it worked for 5 seconds after I got it then the screen and buttons faded out. I replaced all the defective caps in the unit and still no go on the screen.

I’m able to manually adjust the LED’s by inserting a voltage into the base of the front panel character transistor so I know they CAN work but at the moment not under their own strength.

The LED’s get bright when I remove the module from the front of the unit. I have no control over the RPG control. When it boots up almost all of the LED’s light up so it appears as if the front panel is not talking to the microcontroller.

I have a spare unit coming from eBay next week, but it’s a little frustrating when you see that item that you just purchase work very briefly. I know that it can work. More than likely, some little component died while it was turned on.

I should mention that all test points for voltages are spot on. Also I reseated and cleaned every DIP package IC with deoxit.

Also, because I was able to adjust the LED brightness by manually adjusting the control voltage, it makes me wonder if the CRT is working perfectly fine. It’s just that the control voltage that is just the car and Trace intensity be turned off?

[Poroit]

G'day,

The previous post may assist you.

https://www.eevblog.com/forum/repair/hp-1980b-oscilloscope-troubleshooting-and-repair/

[MarshallPlexi]

Thanks for the reply! I have read all the threads on this forum I could find about this unit and it appears that the zebra type connectors are what are giving people fits. I'll try pulling apart the front panel today and see if I can get the front panel to talk to the uC better....ie....at all.

[MarshallPlexi]

I'm at a stopping point with this one. I've tried using the poorly scanned service manual on it, and I can't find anything obviously wrong. I'm getting clock frequencies from my uC (10Mhz and 3.3333Mhz, respectively). I've tried detaching all cables in hopes of finding a short somewhere, all to no avail.

If the front panel buttons, front panel knob, and the CRT are not working at all, and I have perfect voltages in the low voltage supply, what could be wrong but something like the uC or one of the army of small DIP chips? I have no way of testing them to know if they are working.

I've cleaned every elastomeric connector pad, hoping there was a layer of corrosion keeping them from working. No joy.

I have yet another 1980B coming via eBay next week, so hopefully, I'll be able to make a hybrid unit from the two units I've purchased now. Still, it drives me crazy to have a unit that DID work for 5 whole seconds before it faded out. Know the feeling?

[MarshallPlexi]

I opened up the high-voltage section tonight, and it all appears to be working correctly. All the test points show the correct waveforms on the scope. Also, I was able to prove that the RPG is working correctly by scoping its output.

Another interesting thing tonight. After I had taken a lot of it apart and put it back together, when I fired it back up, I heard many relays clicking and the front panel LEDs were bright on their own without having to force them to full brightness manually. Interesting. I rebooted and the LEDs were dim again.

I'm starting to suspect that the uC is failing/failed since now I'm getting unpredictable results.

Also, the calibration test point on the front of the scope shows nothing but noise. Perhaps that reinforces the idea that the uC is dead.

[Wallace Gasiewicz]

I found that the Artek manual is much better than the others I have found on the net.I do have a 1980 and the Artek manual was much better.     

http://artekmanuals.com/manuals/hp-manuals/