2215 Tektronix oscilloscope vertical adjust problem

Is this a dual-channel oscilloscope? Both channels affected? Affected about the same regardless of how you set the vertical sensitivity? (Small shifts up and down don't count.)

Check 2 things:

- Circuitry around the vertical position control;

- The vertical output stage, which is almost certainly push-pull and sounds as if it's losing one of its two transistors.

If the problem goes away as you turn down the vertical sensitivity, then check closer to the inputs.

I'm not familiar with the 2215. This is from vague memory of other scopes...

that

to

off

mnc_co snipped-for-privacy@yahoo.co.uk (Matt) wrote in news: snipped-for-privacy@posting.google.com:

1.Do you have a service manual? If not,you need one. 2.Does the problem occur on one or both input channels? 3.First check all the LV supplies to insure they are correct.

This is not a problem I've encounted before.(not a 'common' problem)

--
Jim Yanik
jyanik
at
kua.net

I second what Jim Yanik said -- one of your low-voltage supplies may have failed. If you have something like +12 and -12, see if the two are now mismatched.

"mnc_co snipped-for-privacy@yahoo.co.uk" wrote in news: snipped-for-privacy@c13g2000cwb.googlegroups.com:

I would look at the resistors in the vertical output stage.There have been resistors that changed in value(precision metal film),and that would affect gain and positioning.I'm thinking of the 1/2W resistors in the output stages,near where the CRT vertical leads join the main PCB. Accoring to my manual,they should be 340 ohm,1/2W MF,marked R378,379,388,389 on the PCB.

If you short the delay line at the front of the vert. ouput amp,the trace should approximately center if the output amp is OK.

--
Jim Yanik
jyanik
at
kua.net

One more thing while you're at it;a common failure;the focus string resistors increase in value until they open,and your focus goes bad. They were modded by TEK to use carbon composition 1 Meg 1/2w instead of the usual 1/2w carbon film,they are around the HV multiplier on the main board,5 of them;R878,879,880,881,882,884.

--
Jim Yanik
jyanik
at
kua.net

Thanks for all of your input so far. I'm having a service manual uploaded to me tonight. I'll checkout what you have suggested and come back with some news.

Matt

"mnc_co snipped-for-privacy@yahoo.co.uk" wrote in news: snipped-for-privacy@c13g2000cwb.googlegroups.com:

The circuit description is very good,I recommend reading it.

--
Jim Yanik
jyanik
at
kua.net

Back again, Had a look at the service manual and tested the resistors as you suggested there is one of them that is 100 Ohms out but I thought this cant be making such a drastic change to the output. I then started testing the 4 transistors of the output amplifier that connect to the + and - of the CRT vertical deflection plates(these being Q377,Q376 to the + plate and Q387,Q386 to the - plate). Turned out that Q376 was dead. Looking at the Service manual this is a BFR96 does this have to be an exact replacment transistor or is there an equiv out there? Just to double check that transistor was the offending part I replaced if with a 2n2222 . The trace now displyed fine and adjusted verticaly with no problems. The 2n2222 doesnt like it in there because it quickly rises in temp, done it's job for the test though. So now I know the exact problem I just need to locate a proper replacement.

Thanks for your help Matt

I read in sci.electronics.design that mnc_co snipped-for-privacy@yahoo.co.uk wrote (in ) about '2215 Tektronix oscilloscope vertical adjust problem', on Thu, 20 Jan 2005:

First hit on Googling for BFR96 gave:

Semiconductors from Dönberg Electronics Description:

BFR 96 SILICON NPN, UHF A/TR, 5GHZ

Packing unit: 1

Order Code: BFR 96

Net price per pack of 1: 0.76 ? (Euro)

It's a fast beast, and at that price I'd buy it.

--
Regards, John Woodgate, OOO - Own Opinions Only. 
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

Found a supplier in the UK

They had the BFR 96 in stock for £0.40. Ordered 10 for good measure

Thanks to everyone that helped

Matt

Mr Yanik:

What service manual for a tek scope would you recommend as the best circuit description for a good modern analog scope? By analog i mean without one-block-of-epoxy-does-all-this and another-block-does-that, by modern i mean: no valves. I've read the 545 service manual and was amazed at the detail they went. I would like to read something similar but more recent.

Best regards

--
Steve Sousa

"Steve Sousa" wrote in news: snipped-for-privacy@individual.net:

The last and best analog scope TEK ever made was the 2445/65 series,but those scopes used TEK-made hybrid ICs and were rather complicated,using a digital front panel control of analog circuits.Still a good study,though.

The next scope would be the simple 2213/15/35 series of scopes.

Then the biggest seller TEK ever had;the 465 scope.This may be the easiest manual to obtain.

All of these had excellent,detailed circuit descriptions.

--
Jim Yanik
jyanik
at
kua.net

Hello Steve,

here you will find a ton of interesting reading.

Two of the manuals that Jim mentioned are listed here

The 2213 and 465

I have no idea if they are complete or not so don't get too excited. :-)

Regards, John Crighton Sydney

After searching endlessly for a service manual for an Iwatsu DS6121 DSO (eventually found one, in english, imagine that!) here's my long list of manual sources:

Charts Site: ftp://anonymous: snipped-for-privacy@charts.ath.cx/

Manuals:

Ed Matsuda (send him an email no site yet) ematsuda.at.earthlink.dot.net or ematsuda.at.themall.dot.net

These are quite complete, so you can get happy with these. Note that the 465 is a 465B, and you need a (free downloadable) djvu viewer. Be assured, it is worth it.

Other source ist

for free download. hth, Andreas

In some mesages back several people sent urls for tek scope manual...

Hello:

Thank all of you guys who sent me those addresses, i got the manual for

465m, unfortunately it doesn't have the schematic, which hampers a lot of the understanding. Maybe i'll buy one for the 22xx series in one of the sites mentioned.

I'll keep looking.

Best Regards.

--
Steve Sousa