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Old 30th Nov 2020, 6:59 pm   #81
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Default Re: HP 180A: chances of repair?

The fault with the calibrator shouldn't stop you from being able to use the scope, just makes it more difficult to set up the probe compensation without needing other equipment.

David
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Old 30th Nov 2020, 7:16 pm   #82
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Default Re: HP 180A: chances of repair?

I will definitely sort it out sooner or later, but another scope is out of the question this close to Christmas.
Cheers from Bill.
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Old 30th Nov 2020, 11:08 pm   #83
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Default Re: HP 180A: chances of repair?

The switch on channel A is very worn and has a twisted selector contact. Channel B is in much better shape, but very grubby. Is there any way to repair switch A, or would it need a total replacement of the mechanism?
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Old 1st Dec 2020, 6:57 am   #84
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Default Re: HP 180A: chances of repair?

If your just using your scope as a "is there a signal there of about the right size" then the calibrator doesn't matter much as you can use your sig gen to tweak the probe.

You might be able to fix the contact but they can be very fiddly,hard to access and easy to break. Either solder a jumper in for now on permanent AC coupling or whatever or show us a pic,one of us might have a spare.

Andy.
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Old 1st Dec 2020, 3:26 pm   #85
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Default Re: HP 180A: chances of repair?

Thanks Andy, I think I will get some pictures up later.

Just to check; the switch positions often give a brief flicker of signal as I turn the selector then blank out, or else I get two tiny dots on the left side of the screen. Only a few on each switch come on reliably.
I am right in diagnosing the switch as being at fault, aren't I?
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Old 1st Dec 2020, 7:18 pm   #86
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Default Re: HP 180A: chances of repair?

Had some more advice, and someone suggested was there a problem with the timebase? It seems a bit of a twiddle and we get much more response! I suppose these things were sent to try us, but I'm b******d if I know the reason. The sage advisor also suggested a grounding issue as the cause of the wonky square wave, which I will check out tomorrow. I have a schematic, so I will let you know how it goes.
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Old 1st Dec 2020, 10:05 pm   #87
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Default Re: HP 180A: chances of repair?

Homer Simpson moment folks: had the channel on AC, but triggering was on DC! D'OH!
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Old 1st Dec 2020, 10:22 pm   #88
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Default Re: HP 180A: chances of repair?

And in public, too! Now that's a powerful learning exercise.

Don't worry, you're getting there. The lucky ones of us did these whoopsies in private. The 8640B sig gen has a tiny toggle on the back panel to select ext/int reference for the counter. It's right where you knock it when wrestling with the instrument and it makes the counter appear to have failed.... A lot of people looked right prats when they'd carted the thing to the equipment maintenance department. One might have looked a bit like me.

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Old 2nd Dec 2020, 7:57 am   #89
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Default Re: HP 180A: chances of repair?

Quote:
Homer Simpson moment folks
Easily done, I have at least 10 a day, once your head stops hurting from the slap cherish this moment, it taught you an invaluable lesson you'll be unlikely to forget.

I spent weeks trying to find a fault on a scope timebase only to find one of the wires off on the CRT. As I said, scopes are sadists, it's something to do with the complexity, makes them feel all superior and special, a bit like economists.

Andy.
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Old 2nd Dec 2020, 4:44 pm   #90
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Default Re: HP 180A: chances of repair?

The ground issue is sorted! I have it all working (for now, at any rate). Looking at the internal boards, so glad that all the problems were reasonably simple, otherwise I fear it may have taken years to sort it!
Thanks to all who have chipped in with advice or encouragement.
A couple of final questions, if I may:
How do people store their plug ins to keep them clean?
Is it worth looking for a 1:1 probe?
Cheers from Bill.
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Old 2nd Dec 2020, 5:38 pm   #91
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Default Re: HP 180A: chances of repair?

You'll use 10:1 probes almost all the time, but a 1:1 does come in on rare occasions. The higher capacitance at the tip means occasions where you want more sensitivity but don't need the bandwidth.

The proper 1:1 probes use coax to the tip which has a much higher Zo than usual 50/75 Ohm types to help keep the tip C down so they do out-perform a lump of RG58

For wideband 1:1 work, it's usual to use 50 Ohm coax to the scope input and to put a 50 Ohm termination there... on a T-piece if necessary, or on the wider bandwidth 180 plug ins you'll find some of them had an internal 50 Ohm termination which could be switched in (also on the 1740 onwards, which is one advantage it has over the Tek 465)

On the very serious wideband scopes you get a termination and also a probe power socket, so you can use FET active probes to get high-Z 1:1 performance.

Just keep your eye open for a 1:1 probe and grab one if you see one. A switched 10:1/1:1 probe is compromised on 10:1, but not so bad on 1:1.

David
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Old 2nd Dec 2020, 5:45 pm   #92
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Default Re: HP 180A: chances of repair?

Cheers David, very useful info. Have a good evening my friend.
Bill.
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