Re: Trying to fix up my 2213A


Fabio Trevisan
 

Hello Lukus,
See some answers next to your questions...

On Sun, Apr 8, 2018 at 05:57 pm, Lukus wrote:
On April 3rd, I picked up a 2213A. While testing it, I noticed that the trace
does not fill the whole display regardless of position settings. I tried
messing around with the controls to see if I could fix it without opening the
scope, but I had no luck doing that.
Also, I found that sometimes a signal was
displayed even when the trace was set to ground.
Indeed it's a weird waveform. Did you try to change the sweep speeds (Time/Div), and or the input attenuator (Volts/Div) settings? Does that change the way that "wave" shows on the screen, this may tell you/us something about where this "signal" is sneaking into the circuits.

The other day, I opened up
the scope (the cover won't come off all the way, but it comes off enough for
me to access the boards) so I could calibrate it. I bought a copy of the 2213A
service manual, and proceeded to adjust the horizontal amplifier gain.
Usually the Tek manuals are very comprehensive and you should get instructions on how to open it properly.

However, even with the gain turned to the max, the trace does not fill the
display. Both the trace after adjusting and the mysterious waveform are shown
here: https://i.imgur.com/46gAXwu.jpg
I wouldn't have jumped directly into changing the scope's calibration, without first checking the basics, and I`m afraid that even doing that, you didn't really ruled out anything.
There are two things that you will see on this forum, which are general and mandatory advice before diving into anything more involving (like fiddling with the calibration adjustments):
1. Check the "so called" low voltage power supplies...(LVPS is everything that is not the C.R.T. High voltages) not necessarily a "low" voltage. Among the low voltages there are usually voltages in the 50~60 volts ballpark, and in the 100~140V ballpark.
1a.for correct voltages (you will need a VoltMeter, at least, and preferably one that you can trust the measurement).
1b. For ripple, and since this is the first oscilloscope you have, I suppose you can't check the ripple and/or power supplies waveforms, so it must suffice you measure the AC voltage of the DC power supplies. Those ripple voltages are usually in the millivolts arena, at most, in the 100ths of volt, so you will need a relatively sensitive AC voltmeter (again that you can trust).

2. Looking for signs of false-contacts or conditions that are usually associated to false-contacts, like signs of corrosion, excess of dust or dirty innards, signs of humidity... and preemptively, trying to clean the easily accessible switches with I.P.A. or contact cleaner. If the latter, make sure you use a contact cleaner that's safe to plastics... The manual is your friend here. Don't apply any cleaner without first checking in the manual if that switch in particular has special recommendations for cleaning. In doubt... don't.
Exercising the switches and potentiometers usually help to clean them, and also reveal if they are showing signs of dirtiness / false contacts. It's common that some lubricants dry out and leave an insulating film that sometimes render the switch or potentiometer totally dead or opened, and often this is not an irreversible condition.
One example to this topic is the "Beam Finder" switch, false contact on it is known to cause this kind of problem (of compressed gain, on either X, or Y axis).

The wave disappears if I ground the shroud surrounding the CRT. I will try to
get the cover off so I can check connections and voltages.
The strange waveform may be nothing, it may just be noise pickup that's happening because the cover is partially opened (so that it's natural connection to ground is broken, as it remains grounded while closed) but at the same time, it's in close range to sensitive electronics that will pickup noise from the nearby big piece of metal... or the cover, while ungrounded, may be picking up strong EMI interference from the Power supply, and transmitting it (by capacitive coupling) to the sensitive parts that it may be nearby.

Can someone help me work through calibrating this scope and getting it to work
properly? For your information, this is my first ever oscilloscope.
You came to the right place. I don't know the 2213 in particular, but surely other folks will jump in and help.

If you want more information and/or details, please let me know; I would be
happy to provide them.
Let us know about the Low Voltage power supply voltages... and if the manual helped you with opening the scope (completely).

By the way, how do I properly reply to a reply on a topic? I tried posting a
reply 3 times the last time I posted, but none of them showed up.
Do you use an e-mail client? or you read / reply directly from Tekscopes Groups.io web interface?
Rgrds,
Fabio

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