Tektronix 2215A Issue - Hot shorted to Ground on power input

[retro_gamer]

Hey everyone.  I recently picked up a 2215A locally in good condition and for a good price.  When I got it home I noticed the power cord had a ground-eliminator socket attached to it.  I didn't think it was necessary to use that so I removed it and as soon as I plugged it into the wall there was some sparks at the outlet.  The scope would not turn on and I could smell that the fuse blew.  I replaced the fuse and put the ground-eliminator back on the power cord and the scope fired up perfectly fine and worked great.

I've been playing around with the scope and getting familiar with it, but I want to get to the bottom of the short.  I opened it up and removed the shield over the power supply section and had a look.  The hot wire is shorted to ground.  I removed the ground wire from the chassis in hopes that the power socket was the culprit, but that wasn't the case here.  The hot wire is still shorted to the chassis. 

I'd like to get this sorted out and would appreciate any tips.

Thanks!

 

[med6753]

Unplug the scope and do NOT power it up again until you determine where the hot mains is shorted to the chassis. The scope in that condition is a shock hazard. Any exposed metal on the scope, including the BNC's, could have 120V on it. Who ever installed that ground defeat to bypass the short should be hung up by their gonads. 

So where is the short? Best candidate is the line filter. Check it. If that isn't it you are gonna have to dig deep until you find it. 

[bdunham7]

put the ground-eliminator back on the power cord and the scope fired up perfectly fine and worked great.

   Don't do that!

I'm a bit surprised that the scope didn't shock you.  Unless something weird is going on, the chassis and and BNC shells should have been live.  You can test everything with just a continuity tester, no need to plug it in.  I agree with the previous comment about starting with the line input filter. 

[retro_gamer]

I should've mentioned that after the fuse blew and I figured there was a fault I plugged it into my current limited isolation transformer when I played with it on my bench.  I just couldn't resist playing with it a bit before taking it apart.  All is well!
I will do some checking and hopefully find the short.

[bdunham7]

I should've mentioned that after the fuse blew and I figured there was a fault I plugged it into my current limited isolation transformer when I played with it on my bench.

 

Now, is the short between the hot and ground pins as measured at the plug, or between the hot and the chassis of the scope itself?  If the former, or both, then your fault does appear to be right in the line filter itself. 

[retro_gamer]

Now, is the short between the hot and ground pins as measured at the plug, or between the hot and the chassis of the scope itself?  If the former, or both, then your fault does appear to be right in the line filter itself. 

The short has been resolved, but it is pretty strange and not sure what was causing it in the first place now.  I removed the two screws holding the small power PCB at the rear of the scope and lifted it up (pictured) and the short went away.  I found a random screw laying under it that looked like it may have been wedged between the small PCB I removed and the main board.  Not sure if that screw was the culprit.  I was also thinking it was possible one of the wires you see there near that large capacitor has a small nick in it or something because when I lifted up on the board those wires sorta got re-oriented.  Everything happened so fast that I'm not sure what the problem was lol.  But the scope is no longer shorted!

[WattsThat]

A screw behind the filter board would definitely cause the short. The line voltage passes through that board which contains a common mode choke, MOV’s and a safety cap.

You’re lucky the screw was visible otherwise it couldn’t have remained a mystery with you never knowing what was wrong. You’re just lucky you didn’t touch the metal shell of the bnc connectors when it was first turned on with ground adapter. That would have been very unpleasant.

With a light cleaning, it will look as good as new. I have digital scopes but I still enjoy twisting the knobs on my 2245A.

[retro_gamer]

A screw behind the filter board would definitely cause the short. The line voltage passes through that board which contains a common mode choke, MOV’s and a safety cap.

You’re lucky the screw was visible otherwise it couldn’t have remained a mystery with you never knowing what was wrong. You’re just lucky you didn’t touch the metal shell of the bnc connectors when it was first turned on with ground adapter. That would have been very unpleasant.

With a light cleaning, it will look as good as new. I have digital scopes but I still enjoy twisting the knobs on my 2245A.

It wasn't behind it, but under it if that makes sense.  It was sitting on top of the main board on the bottom and under the edge of the filter board.  Maybe it was behind the filter board and then fell there when I removed the 2 screws holding it on... not really sure.  Right as I was about to start checking components on that filter board the short was gone!

Tomorrow I plan to give it a good dusting and maybe shoot some contact cleaner into some of the grimey looking pots. 

Also do you guys grease the chassis before sliding the blue metal cover back on?  That thing was a real PITA to slide off, almost like it was seized on there.

Thanks!

[retro_gamer]

Another interesting thing I noticed about this scope is that it was last calibrated in 2004, and then in 2006 it was rejected.  I wonder if it was rejected because of the short issue.  As far as I can tell the thing works perfectly fine lol.  Crazy to think it was shorted for 15 years and previous owner resorted to running it with a hot chassis instead of trying to fix it lol.   

[jdragoset]

I've had to use Deoxit fader lube to get a dented case off the chassis but then worked the dents out from the inside so the fit was easy.

[Allen49]

Thanks for the information on the short. I am working on a Tektroinx 2221 and now have a short to ground, chassis, which is kind of unusual since the main board is not grounded on the 5 volt line. I started out with a leg burnt off on Q9070 and a burnt resistor 909. I have not yet got the power supply working. I replaced Q9070 and fixed the burnt connector.

[p.larner]

wtf is a  ground-eliminator,ive never heard of such a device.

[BlownUpCapacitor]

wtf is a  ground-eliminator,ive never heard of such a device.

I'm pretty sure it's something like this: https://www.amazon.com/Cable-Matters-Polarized-Grounding-Adapter/dp/B01M0FXMFK?th=1

I know a couple friends in San Francisco California, USA, that use these because they don't have grounded apartments.