HP 1980B - Page 1
Forum section: electronics / testgear

author: MarshallPlexi
author_rank: Contributor
timestamp: November 15, 2024, 04:09:39 am
content: 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?

author: Poroit
author_rank: Frequent Contributor
timestamp: November 15, 2024, 04:38:22 am
content: G'day,The previous post may assist you.https://www.eevblog.com/forum/repair/hp-1980b-oscilloscope-troubleshooting-and-repair/

author: MarshallPlexi
author_rank: Contributor
timestamp: November 15, 2024, 07:39:54 pm
content: 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.

author: MarshallPlexi
author_rank: Contributor
timestamp: November 16, 2024, 04:21:11 am
content: 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?

author: MarshallPlexi
author_rank: Contributor
timestamp: November 16, 2024, 10:14:34 am
content: 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.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: November 16, 2024, 12:06:01 pm
content: 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/

author: MarshallPlexi
author_rank: Contributor
timestamp: November 17, 2024, 01:02:53 am
content: Artemis doesn’t have the 1980B. I looked on the site and wrote them.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: November 17, 2024, 01:19:33 am
content: Quote from: MarshallPlexi onTodayat 01:02:53 amI apologize, the manual I have is from Micromanuals: If you cannot find them I can get you a copy of mine.

author: MarshallPlexi
author_rank: Contributor
timestamp: November 17, 2024, 03:54:49 am
content: That site no longer exists. Could you email me at brad@jacksonaudio.net?

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: November 17, 2024, 12:46:03 pm
content: I put the files on Dropbox for Marshall. If he thinks they are any good, I can share them with anyone interested. If anyone else wants them email me

author: MarshallPlexi
author_rank: Contributor
timestamp: November 17, 2024, 10:55:40 pm
content: Thanks, Wallace! If I'm not mistaken, those are the same files you can get from the Agilent site. The scan quality looks identical.

author: MarshallPlexi
author_rank: Contributor
timestamp: November 17, 2024, 11:11:03 pm
content: Because I can't leave it alone and sleep seems to be optional here is what I've learned.I got a Klein thermal camera off Amazon and it seems to work nicely. I've been able to find the hot spots and have reported them here. I did find a tantalum cap that was over 200 degrees and was very optimistic that it would prove to be the fault in the a power supply I was looking for. I replaced it and no joy.Here are some other areas of the PCB's that concern me. There are quite a few hot spots but I'm not sure what temps are deal breakers.Starting with pic 6133, this is a thermal resistor in the low voltage power supply that is hotter than all hell. It's still passing plenty of current and voltage so I don't suspect it's an issue. I did replace it with a wire and even the wire is now getting hot. No changes when replaced.Pics 6135 and 6136 show two ceramic resistors that are very hot to the touch along with one of the transistors that has a heatsink mounted to it. Again I don't know what is a no go for heat on these. If I had one I'd replace it and see if the temps changed.Pics 6137 and 6137 show the wire that was used to replace the thermal resistor.

author: MarshallPlexi
author_rank: Contributor
timestamp: November 17, 2024, 11:12:34 pm
content: Here are more pics of transistors and ROM chips.

author: MarshallPlexi
author_rank: Contributor
timestamp: November 17, 2024, 11:14:15 pm
content: ROM chips

author: MarshallPlexi
author_rank: Contributor
timestamp: November 17, 2024, 11:14:49 pm
content: Digital side chips

author: MarshallPlexi
author_rank: Contributor
timestamp: November 17, 2024, 11:15:26 pm
content: Microcontroller chips.

author: MarshallPlexi
author_rank: Contributor
timestamp: November 17, 2024, 11:16:36 pm
content: Front panel pics. Notice how dim the LED's are under it's own power. When I manually drive the base of the transistors with 7.5V and set them to full brightness.

author: Wallace Gasiewicz
author_rank: Super Contributor
timestamp: November 17, 2024, 11:57:11 pm
content: As I recall, that thermal resistor is always quite hot. In my unit the board is even discolored from the heat. It is supposed to be that hot and there should be no effort made to cool it down..The controller chips and the ROMs do not get hot. I do not think that transistor should be hot but I do not remember.....There is something that is taking too much power from the source that also powers the front panel....possibly disconnect other boards that use this same volt source.....Too bad the manual was not better.....

author: MarshallPlexi
author_rank: Contributor
timestamp: November 18, 2024, 01:40:53 am
content: I’ll try swapping out transistors tomorrow. Maybe I’ll learn more.

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: December 21, 2024, 07:50:20 pm
content: To whom it may concern,I have one of these beasts, non-working, free to whomever wishes to pay shipping (USA only). It's heavy.PM me.ThanksRandallDavis CA 95616

author: MarshallPlexi
author_rank: Contributor
timestamp: December 23, 2024, 07:40:01 pm
content: Payment sent! Thanks Randall!

author: RandallMcRee
author_rank: Frequent Contributor
timestamp: January 09, 2025, 06:48:07 pm
content: Attaching operator manual for HP1980b