Tektronix 2215 - Weird Waveform Issue - Page 1
Forum section: electronics / repair

author: Conjure
author_rank: Newbie
timestamp: November 11, 2016, 11:02:38 pm
content: Hi all,I just bought my first ever oscilloscope on eBay, a Tektronix 2215 (not 2215a). It was sold "as-is" and untested, but that it powered on and scanned.I got it today and when I first hooked it up, it worked great with my new function generator (see here:http://imgur.com/a/YLm6X). I then walked away from my bench while it was on, went and ate something, and came back to a weird issue. The position on both channels never gets even close to centered, and the waveforms seem to curl over now.See here:I'm suspecting a capacitor issue in the positive power rail, but I have no real way to diagnose that. I don't have a DVM or bench supply. I'm a bit disheartened and hoping I can get this fixed ASAP. I appreciate any help you can give. Thanks!EDIT: Serial number is B032656

author: tautech
author_rank: Super Contributor
timestamp: November 11, 2016, 11:18:05 pm
content: Welcome to the forum.You need a DMM at least to even start to diagnose any fault condition but there are high voltages within CRO's that exceed what a DMM can test. Don't worry about this for now, just check the simple stuff.Service manual:w140.com/tek_2215_service.pdfGood Tek troubleshooting guide:http://www.sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdfFirst, PSU supply voltages must be to spec, not nearly...to spec !You've got some reading and study to do now, so come back to us when you have a DMM and have done some basic checks.

author: Conjure
author_rank: Newbie
timestamp: November 11, 2016, 11:20:20 pm
content: Quote from: tautech on November 11, 2016, 11:18:05 pmApologies for the confusion, I should note that I do have a 40,000 count bench DMM.

author: tggzzz
author_rank: Super Contributor
timestamp: November 11, 2016, 11:33:04 pm
content: I'm not familiar with the 2215, but have delved into a 2445B and 2465.Most Tek scopes have fans, and if they aren't working properly then components can overheat and fail. That's certainly the case with 24x5s, where if you are running it with the case off you have to blow cold air across the board.It looks like the CRT HV (3kV) and EHT (17kV) voltages are roughly OK.Check all the internal PSU rails for their voltage and lack of ripple. (Fine tuning can wait until later). If anything is grossly amis, fix that first.Then start looking at the voltages on the CRT vertical plate connections. The two plates will have voltages around X+Y volts and X-Y volts relative to the chassis, where X is I guess ~45V and Y is up to~20V. When the beam is central Y=0. That means the differential across the two plates would be 2Y.My guess is that there is no voltage on the top plate, and you'll have to find out why. It might just be the connection has fallen off. But if it worked properly for a while and the fan isn't working, then the Y plate driver might have failed.The Yahoo! TekScopes group has a wealth of information and knowledge.

author: David Hess
author_rank: Super Contributor
timestamp: November 12, 2016, 10:18:31 am
content: It does not quite look like a power supply problem because it is not affecting the horizontal deflection but the low voltage outputs should be checked.These are not quite long shots but there are a pair of common problems which can produce the symptom you see and they are easy to check.1. Make sure that the vertical deflection leads are connected to the CRT. One may have fallen off. Be careful around the CRT pins because the pin to glass interface is delicate. These are on the left side of the CRT.2. The collector load resistors for the CRT vertical amplifier run hot and may fail open or partially open with age. There is a pair of 1/2 watt (going by memory) metal film 340 ohms resistors in series on each side of the differential vertical CRT amplifier located under the rear of the CRT neck. Visual inspection may show that the printed circuit board is discolored and that the coating on the resistors is flaking off and that the resistors are cracked.The 2215A which replaced the 2215 uses three resistors in series on each side to better distribute the heat.Quote from: tggzzz on November 11, 2016, 11:33:04 pmThere is no fan in the 2215.