Hey guys,

I'm new here. found the forum while searching for info on my problem. So far, i've come up with nothing. I'm hoping someone here can help.

Here's the issue:

I have a very early Tek 2215 scope. The baseline trace is VERY noisy, with nothing connected. (see photo) Flipping the coupling switch to ground reduces the amplitude about 10x, but it's still not a flat trace. Ch A and B do the exact same thing. See photo for what the trace looks like. This is with NOTHING connected. 2mv/div & 10 microseconds/div

I assume it's probably a noisy power supply, right? unfortunately, I do not have access to another scope to check the power supply. Do i just start changing power supply capacitors? Anyone know which of the voltage supplies would cause this kind of noise? any circuits in this scope run at 27khz? (looks like about 27khz if i did the math right)

There is a service manual for the tek 2215 floating around online, but apparently mine is too old (S/N B021808). Virtually none of the component numbers on the PCB match the schematics in the manual. So i'm flying blind, unless someone has a copy of a very early manual.

Can anyone help me? or even point me to a different forum where somebody might be able to help?

 

Hello,

It looks like the ripple of the powersupply is effecting the trace.
Check if the elco's in the powersupply are working correctly.

Are you sure it is the 2215 and not the 2213 ?
The 2213 can be found at BAMA.
http://bama.sbc.edu/tektroni.htm

Greetings,
Bertus

 

it says 2215A right on it.

Elcos? i'm not familiar with the abbreviation. How do i check them?

 

Hello,

Elco's are the electrolitic capacitors.
These are used for buffering in the powersupply.

Here is an example of an elco.

Here is some more info in the elco's.
http://www.uoguelph.ca/~antoon/gadgets/caps/caps.html

Greetings,
Bertus

 

Thanks! i know what they are, i've just never heard the term "elco" before. i usually see "caps" for capacitors.

How do i check them? with a DMM "cap check"? don't i have to pull them out of the circuit to do that? is there a way to check them in the circuit?

 

Hello,

Sometimes when an elco (cappacitor) is defective you can see some brown looking stuff on or beside it.
Sometimes they are not flat anymore but cracked on the top.
Sometimes they get hot when it is used for some minutes.
All these symptoms will tell you it is a bad capacitor.
It is hard to measure them.
You could try to measure if there is AC on the capacitor when the powersupply is on. (BE VERY CAREFULL).
Normaly you would measre a low AC, when the capacitor is bad a high AC.

Greetings,
Bertus

 

they all look fine.

I took a high-value cap i had lying around, and through some test leads, paralleled it with some of the power supply caps. there was one on the +8.6v supply that made a big difference. i'll probably change them all, since the scope is kind of old, and knowing where it came from, it probably saw a LOT of hours of on-time.

Thanks!

 

See if you can get Dean Huster's attention at Electro-Tech. He used to work for Tektronix, and is very knowledgeable.

 

There are a total of 8 caps you need to replace. The first 4 on the +8 and -8 supplys (2 each on each supply) orignally were 840 uf 12v you can use 1000uf @ 15 to 25v this will help with reliability. The next 2 on the 5 volt supply (depending on version of scope) also will be 840uf replace them as the orignal were very leaky. On the 100 v supply you will see 33uf @ 160 volt seen ths bad as well it will let the ripple on that supply run over 300mv it should be less then 200 mv. On the 30 volt supply you have 270uf i have changed this to a 330 @ 50v and worked perfect. that pretty much covers this supply for secondary voltages and filters.
The ripple should be <200mv on 100v ,<50mv on the 50v, 10mv on the 5v,8v,-8v supplys

 

Jtvdude, Thanks for the ripple information. My 2215A has about 1mv ripple on both channels with open inputs (1/10 of mike944's photo) but still seems noisy. Do you know what is typical of a good 2215A? My power supply ripples are all well under your specs.

 

Your going to have a fun job on your hands. If those caps are anything like the ones in my Tek they are really buried. I have been crossing my fingers hoping my caps are ok and some replaced them before I got the scope.


You might also want to get some tips from the Tekscopes group on Yahoo. Those guys are great. If you have trouble finding it let me know I will look it up.