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Old 12-29-2017, 11:02 PM
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MadMan MadMan is offline
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B&K 1460 O-scope troubles

This is my go-to scope for all my actual work-related needs. It's a good runner but I'm afraid it's starting to have troubles. While monitoring a serial data stream on a Cadillac with communication issues, everything was fine, and the data 'on's or '1's were about 1 grid unit high. I left it on for about 10 or 15 minutes (the car and the scope) and when I came back, it was about 1/2 a grid unit high.

I'd never seen this on data before, but I have seen this several times on crank sensor signals - in fact, I've watched analog crank sensors lose their height (voltage) on the scope slowly until the car shuts off from lack of input. Nice way to confirm a bad crank sensor. So for a while I was fairly certain the scope was doing its job.

What I did this time was, I left the car on so the data kept on streaming, and turned the scope off for 15 minutes, then turned it on and sure enough, 1 grid unit high.

I'm eyeing the electrolytics. They're made by 'Elna' but none are visibly swollen or anything. There's also a very large square metal high voltage can capacitor near the power supply, made by Nichicon. I can't find a manufacture date but I'd venture it's in the 70s somewhere.

TLDR: My scope is partially losing it's vertical... amplification or deflection or something like that, when it warms up. What do?
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Old 12-30-2017, 03:09 AM
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Do you have a schematic?

http://bama.edebris.com/manuals/b&k/1460/

I would check supply voltages to see if anything drops as the scope fails. If the scope is connected to its internal calibrator, does that voltage appear to drop?

jr
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Old 12-30-2017, 12:37 PM
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Agree: check supply voltages.
Is it changing sweep width or brightness? I gather only vertical?

Also, can you determine if it drops suddenly or gradually? If suddenly, could be something intermittent in the vertical sensitivity adjustment. 2:1 change sounds suspicious.
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Old 12-30-2017, 01:20 PM
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Another vote for checking the power supplies. The unit is old enough to consider a "shotgun" replacement of electrolytics, especially if you rely on the unit for income generating work.
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Old 12-30-2017, 02:51 PM
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Quote:
Originally Posted by N2IXK View Post
................ especially if you rely on the unit for income generating work.
In light of N2IXK's statement above , if this is a needed part of your day to day employment I think I'd **(blasphemous suggestion warning)** get one of those apps that make your cellphone display the scope images and leave the antique stuff to be used working on the other antique stuff in your collection .
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Old 12-30-2017, 11:13 PM
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Quote:
Originally Posted by jr_tech View Post
Do you have a schematic?
http://bama.edebris.com/manuals/b&k/1460/
I would check supply voltages to see if anything drops as the scope fails. If the scope is connected to its internal calibrator, does that voltage appear to drop?
Well I do now, thanks. I have a pdf of the user manual - sans schematic. I'll have to do some testing to find out about the internal calibrator.

Quote:
Originally Posted by old_tv_nut View Post
Agree: check supply voltages.
Is it changing sweep width or brightness? I gather only vertical?

Also, can you determine if it drops suddenly or gradually? If suddenly, could be something intermittent in the vertical sensitivity adjustment. 2:1 change sounds suspicious.
Only vertical, no other noticeable changes. Definitely a gradual decrease, however, it occurs rather quickly, over perhaps 10 seconds. So it'll be fine for 15 minutes, lose vertical in span of 10 sec, but never lose it entirely.

Also, yes it is a 2:1 change, but not perfectly - when it's failing, you can observe the vertical slowly fluctuating bigger and smaller, just a little.

Quote:
Originally Posted by N2IXK View Post
Another vote for checking the power supplies. The unit is old enough to consider a "shotgun" replacement of electrolytics, especially if you rely on the unit for income generating work.
Yeah, I'm all for the shotgun method, I'm just trying to figure if this sounds like a capacitor related issue. Yet, part of my wonders if this is a transistor issue.

Quote:
Originally Posted by init4fun View Post
get one of those apps that make your cellphone display the scope images and leave the antique stuff to be used working on the other antique stuff in your collection.
lol 'antique.' You funny guy. My 1950s Simpson O-scope is my antique, this BK is my 'daily driver.' So to speak, I probably only use it once a month, but yes, for actual income generating work. Also - I've yet to see any professional smartphone o-scope thingies. They all seem to be project-type crap for fun and screwing around... when I use an O-scope, it's a tool. I'm not saying they won't work, I'm just saying I've yet to see one that's not just an exposed circuit board, or isn't way more than the $70 I spent on this scope. :/
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