Powering up a Tektronics 2440 scope after 8 years

I have had a scope sitting idle for about 8 years and am about to power it up.

Should I use a variac and build up the voltage slowly. or just power it up?

Any suggestions will be welcome.

 

The dim bulb tester is a better option. You just put a 1000 watt incandescent in series with the power line. It limits current so if something is shorted it will not cause further damage. In fact on a scope you might want to use a 60 instead. The 100 watt is more suited for like audio amps in the 200 WPC range, the scope does not pull nearly as much.

Tektronix scopes are not known for having deadly shorts. Their power supply design is like "interdependent" sometimes only using one Zener for one source, like the -50 volts that has a very light load and using that as a reference for all the other sources. Also, since in a scope the current drain on each source can be calculated quite accurately, it is designed only to put out the current necessary, making smoke alot less likely.

Problem with variacs is they do not limit current. At what voltage do you expect to see a trace ? Nobody knows really. With the DBT it should reach full voltage fairly quickly.

Though unlikely with a Tek, it may be possible with a variac to cause a condition where the CRT bias is not right and cause a screen burn. If there are no shorts, the DBT should allow it to get full voltage and you won't have that problem.

All it takes is a standard light fixture, incandescent lamp, standard outlet and an AC power cord. Or, you could just pull the main fuse and clip lead the DBT there. On many units you can just leave the power switch off and jump it with that but don't, don't because there are so many weird designs out there and Teks are full of them. They had some REAL engineers. So just use the plug and cord method.

Only eight years ? I give it a 90 % chance of just firing up and working fine. Might need some filters but they probably won't be shorted, and that is really the only issue. Other things don't just short out from sitting unused. But there could be some that need to be replaced. We had to replace like ten of them in one to get the hash out of the trace, but none of them were shorted. What was that ? I think a 2225. A good scope but not one of my favorites. I prefer a 465.

I am downloading the manual now from bama.

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OK, I see it is a digital scope. In that case I would say not to use a variac on it. It might damage the data/program. I got that problem in an HP spectrum analyzer and you just can't get a flash for it, and your scope being from 1988 if you ask Tek for anything about it the will tell you to pound salt.

If the bulb does not dim in a few seconds, turn it off, take the cover off and then locate the power supply, plug it in directly and look for signs of heat. I mean take your finger and see what is getting hot. Don't let the thing dangle at half voltage or whatever. The most valuable thing in there is the data, as they cannot be replaced. Maybe in 1989, but not today.

Good luck.

 

Oops, of course I mean 100 watts.

The debounce on this laptop is terrible. And I can't see worth a shit, and it was scrolled off by the time I hit the button.

 

[frank]

c4urs11 <c4urs11@domain.hidden> wrote:

On Tue, 05 Jul 2016 02:03:33 -0700, jurb6006 wrote:


My 475A was frying its mains transformer from leaking supply caps.
The (old) mains fuse thought all was OK, so I tossed it on the go.

well, I have another experience with it:
I was troubleshooting around an old computer when the 475 suddendly flashed
and shut down (only the indicator lights remained on, all else, including fan
was off).
I didn't shut the power down very quickly, I rocked some knobs then I finally
powered it down.
I had a look at the schematic and I saw that the fan was on the +15V line.
I opened the case, and sure enough there was a dead short on +15V line,
tracked quickly down to a drop orange tantalum capacitor, 0.14 ohms across
it.
I thought this kind of fault would fry all the power regulation, when
it happened on a HP-5328A, I had to change also the +15V pass transistor
for example (and the fuse that should have protected it).
After replacing the tantalum capacitor, the scope revived as nothing
ever happened. So the power regulation circuit looks really well protected.
It coped with a dead and prolonged short without damaging itself.
Just for the record.

Frank IZ8DWF

 

[c4urs11]

On Tue, 05 Jul 2016 02:03:33 -0700, jurb6006 wrote:

> Tektronix scopes are not known for having deadly shorts.

When in doubt, recap.

My 475A was frying its mains transformer from leaking supply caps.
The (old) mains fuse thought all was OK, so I tossed it on the go.

Cheers!