Electronics > Repair

HP 1980B Oscilloscope troubleshooting and repair

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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.

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