HP 1980B Oscilloscope troubleshooting and repair

[Cubdriver]

I just received this beastie after purchasing it last week on the 'Bay, where it was listed as 'Doesn't power up...  ...missing fuse...'.  It arrived well packaged (actually double boxed), and while a bit rough isn't in terrible physical condition.  I 'borrowed' a fuse holder cap from another piece of equipment, popped in a new fuse and after plugging in BOTH ends of the power cord (for my initial try only the instrument end was connected - d'oh!!  ) it came at least partially to life, with the fan running, several indicators lighting up and a somewhat dim, not entirely focused display that's biased up from the center on the CRT and jittery in the vertical direction.  The only key that seems to affect it is the beam finder, which gets the four traces more or less to mid screen with reduced horizontal width.  It seems to completely ignore my poking and prodding at any of the other keys.

It displays a '25' on the numerical LED above the control knob; turning the knob causes no apparent change to anything.  I'm presently scrolling through the PDF scan on the Keysight website in an attempt to get some troubleshooting hints and try to determine if the 25 has any significance as a failure indicator, and have also ordered a copy of the paper manual from everyone's favorite auction site.

I expect it'll likely need filter caps at the very least, but I'm pretty encouraged by the fact that it displays text and traces.  If anyone who's worked on one of these wants to chime in with suggestions, all would be welcome.

-Pat

Powered up, overall view:


Controls:


Display:


Display with beam finder activated:

[Cubdriver]

More photos, showing the open chassis.  There are at least two electrolytics on the bottom that need to go...

Underside, overall:


Detail showing unhealthy electrolytics:


Topside, overall:

[Cubdriver]

A bit of disassembly revealed the source of a rattle that I thought I heard when unboxing the scope, but it stopped immediately, so I had hoped it was my imagination.  No such luck.  When I went to remove the second pair of vertical channels (a plug-in), it didn't want to come out, and the ejector handle seemed to be grinding.  A bit of digging revealed a small piece of white ceramic with a couple of pins on it wedged in among the mechanism.  Oh crap!!  Further examination after removing the side panel revealed the source of the chunk of ceramic - a crushed chip on the sweep control panel.  The panel was a bit of a bear to get out, and my guess is that at some point someone used a screwdriver to help 'coax' the panel out and broke the chip by prying on it.  My initial fear was that it was an EPROM of some sort, and would be unobtanium, but as it turns out it's simply a lamp driver IC (custom made by HP, of course) and replacements were found on the 'Bay and a pair have been ordered already.  And on that note, time to call it a night and hit the sack.

-Pat

Sweep panel:


Overall view of the rear, showing broken wall from 2x17 header and piece of IC package:


Detail of damaged IC package:

[mcfudge]

Your post and pics are much appreciated.  I received a 1980B last week and plugged it in a few days ago.  It worked for about 15 minutes then I heard the dreaded snap, crackle, and pop noises and smelled burned out components.  I still had an image on the crt and the front panel lights were on but I unplugged it promptly.  I suspect one or more caps popped.  I tried to remove the large top and bottom covers tonight without success.  The side covers came off by sliding them from front to back with some effort and after removing the handles.  I wonder if my top and bottom covers are sticky and will need some considerable prying.  Please advise.  Thanks in advance.

[AF6LJ]

Oh Dear You are lucky that chip is still available Wow.

[skennedy]

I too recently purchased a non working 1980B. Missing the second vertical channel strip entirely but otherwise looks complete. A pretty amazing scope considering how old it is. Upon power up I noticed the snap and pop, fearing the worst I investigated the source. It turned out the typical mains filter caps had totally spilled their guts. Removing them entirely and powering up the scope again gives a working front panel, horribly loud fan and an error code to do with calibration. The CRT fuse has blown so that would look to be the first place to start my investigation.

mcfudge, you should check the mains filter caps on your scope. To access just remove a few screws on the back panel around the mains input.

[wn1fju]

In addition to straightening out the caps in the power supply, be aware that these beasts use elastomeric connectors.  The four big rectangular white hybrid chips make contact to the boards via them as do many boards behind the front panel.  Over time, these connectors flatten out or tarnish, making the connections unreliable.  I was able to keep my 1980B running for a fairly long time by rotating or re-positioning the connectors, but eventually was forced to remove and mechanically clean them with very fine wet sandpaper (ouch!).  Probably not the best solution, but the scope has been fairly stable.   Also check the non-power supply electrolytics as I had one in the timing circuitry leak and go bad. 

[Cubdriver]

McFudge -

I haven't had a chance to do much more with the scope since starting this thread, but in the off chance that you haven't yet gotten them removed can tell you that the top and bottom covers are secured by a single screw each; the screw is located in the center of the back edge of the panel.  It should be a captive screw, with some sort of retainer on the inside of the panel to prevent its loss.  Once the screw holding the cover on has been loosened enough to come free of the threaded hole it's in (and, being captive it should draw the panel back with it as it is loosened), you should be able to pull the panel rearward another eighth inch or so and then lift it up and free.

I just grabbed one of them (I got a couple of more since for a song on the 'bay) and took a few quick iPhone pics of cover removal:

The retaining screw:


The cover position when the screw is tightened (note that the side cover is loose and slightly rearward of where it should be; it too should be even with the flat edge of the aluminum frame corner):


The cover position when the screw has been loosened to the point of disengagement with the frame:


The cover lifted away(note that once it moves back, it LIFTS up and away - it does not slide off straight rearward - you can see the edge that extends down slightly and fits in the groove along the side - if you try to slide it straight off this will catch and prevent the cover from continuing rearward):


I hope this helps.

-Pat

[mcfudge]

Cubdriver that was fantastic.  I now have the covers off.  Wow I cannot believe I overlooked the obvious frayed white hp stickers.

Thanks also to wn1fju and skennedy (good call!) for additional suggestions!  This will be a nice addition to my DSO if it works out.

[Cubdriver]

Glad to help, and yeah, I'd say that cap's best days are behind it...

Good luck with your repairs.  I need to get my butt in gear and start futzing with mine, too.  They're definitely cool old scopes.

-Pat

[woodchips]

I have a couple of these, and also a full set of manuals from Manuals Plus, and still can't work out what it is for.

It is a 100MHz analogue scope, but what is the point of all the digital stuff? Is it only to draw envelope diagrams on the screen for someone to check that the displayed waveform is inside the envelope? I have had a good search in the manuals and can find no details of whether it can digitise the actual waveform? What is the point of having deflection factors of 276mV/div or 101us/div? Strangely I have a flyer describing printing or plotting the screen, static as well as dynamic traces, so how were they captured? This printout also has strange calibration per division settings.

The good news is that by searching I found

emperoroftestequipment.weebly.com

which has a review of many pieces of test equipment, spent a good couple of hours reading it so far and not finished.

One 1980 was dead, one sort of works. Even with the manuals how do you get the sort of X and Y plug ins out? Had to near dismantle the whole scope and then the cables needed a steel fingered hand 2" wide for access. They are sort of plug ins because they have no release catch and then pull out as in every other scope. They are just front panels, but screwed to the main analogue board in the bottom of the scope. To get at the eleastomeric connections all this has to be dismantled. Seems a waste of time to me!

[Cubdriver]

The 1980s have been on the back burner for a while now, unfortunately, due to other projects and simply a general lack of time and motivation.  I hope to get back to them again as winter rolls around.  I e the meantime, I have plumbing and heating to get finished before the snow flies.

Thanks for the interesting link - that was a good read (still more to go, too), though his tastes seem to run to more 'modern' gear than mine generally do.  He needs to get a 3439A, 3440A, 3450A and 3460B for his voltmeter collection, and he's missing a bunch of counters as well.   

-Pat

[woodchips]

Yes, finished after three nights of reading.

I wonder how much time he spent on fixing it all, lots of hours it seems.

Seems to have missed that the 3581 wave analyser looks amazingly like the 3580 spectrum analyser. In fact if you use the 3581 self scan mode it is a not bad audio spectrum analyser. And cheap! No one knows what a wave analyser is now.

[fred-bloggs]

Dear Sir - Although some time as passed i was wondering if the HP1980B Oscilloscopes maybe available For Sale ? Regards Marc