tektronix 2247a horizontal problem? - Page 1
Forum section: electronics / testgear

author: pa2ees
author_rank: Contributor
timestamp: June 11, 2014, 04:06:20 am
content: I'm looking for a decent analog oscope, and have found someone selling a tektronix 2247a, but in the pictures, it seems like the horizontal alignment is out a little. Is this fixable? is it not worth getting? Is it simply the horizontal position knob needs adjusting?Here is a picture:It's selling for a fairly good price, should I go for it?

author: tautech
author_rank: Super Contributor
timestamp: June 11, 2014, 04:34:15 am
content: If pic displays the calibrator signal, you need to know that this signal is NOT a precision source.They wander with age, just as scope calibration does.It could be the scope calibration or the probe calibration signal.Either can be tweaked.

author: pa2ees
author_rank: Contributor
timestamp: June 11, 2014, 04:39:36 am
content: Thanks for the response. I'm not too worried about the signal source, but mainly the actual display. Here is another picture, and I'm concerned about the words on the right side are partially off the screen.

author: tautech
author_rank: Super Contributor
timestamp: June 11, 2014, 04:50:03 am
content: Start of sweep is a little too far right and displaying words too far right.Can be tweaked.Download a manual and see if you are competent to make the adjustments.

author: rf-loop
author_rank: Super Contributor
timestamp: June 11, 2014, 07:00:48 am
content: It looks easy problem. But pictures do not tell whole truth.If there is vertical level problems with separate V/div ranges after cal and or selfcal problems are typically in front end relays. This repair is possible but it is not entry level work. But it is other story. You tell only horizontal problem.Download manual example herehttp://elektrotanya.com/tektronix_2247a.pdf/download.htmlAfter then, read this manual BEFORE start any kind of "blind" adjustments.Follow exactly pargraph "Adjustments" procedures and also working order is important.Carefully look "Internal adjusments and adjustment interactions"Do not try be "clever" and jump directly to some adjustment point without knowledge you can do it.It can of course go directly to one or two adjustment and adjust so that in simply look your eye is satisfied for horizontal positions but after then whole scope is more or less out order.(It looks like just horizontal position is wrong but...and many but... these pictures do not tell at all enough what is wrong. (there need check geometry, horizontal position of text and horizontal position of trace and not only position but also gains and so on. So only what can tell, start with service manual and follow adjustment procedure just as described in manual including what is order for adjustments. I have done several times whole service adj/cal and example front end "renew" for these scopes, including in some cases also all or partial frontend relays change.Tektronix engineers who write service manuals really know what they write.And always start service so that check every power supply voltages are inside specifications including also ripple (and it need know how to measure it). If this check fails in any point. Stop and repair these first.If adjust +7.5V rail level, then need do nearly whole service adjustment/calibration procedure. Check (before touch any adjustment) that you have needed equipments.It is quite easy if you follow this whole procedure or partial procedures as it read in serv manual.Adjustment locations are in end of this section 5.If you are buying it and you know only these images.IF only problem is this horizontal, in most of cases it is very easy and need just do adjustments.BUT if there vertical problems, these pictures do not tell it. And these scopes vertical range selection relays are one typical source of problems related to scope age and how it is used.It is nearly so that if there is vertical level steady or specially random problem and what is also so that different level bands work different and if people need ask how it is repairable my answer is that jump over this case. It can do but perhaps people can use his time for some other things.If there is burned some special resistor networks... it is better to find next unit what is in better condition.If I can (in live) check that vertical is "hardware ok" (adjustment is no problem) and there is only this horizontal problem what can clearly see in images and if I need this kind of scope I will buy it (with its risks). When this scope works all ok, it is very nice equipment with nice features.

author: pa2ees
author_rank: Contributor
timestamp: June 11, 2014, 02:50:02 pm
content: Thank you for your responses. I am fairly competent with repairs, so I'm thinking I'll get it. From what you all have said, it's a matter of following the repair manual (thanks rf-loop for the link). Besides, it will be a good learning experience if it is a more comprehensive repair (a task which I wouldn't mind doing).

author: grumpydoc
author_rank: Super Contributor
timestamp: June 11, 2014, 02:58:48 pm
content: These do contain the infamous "U800" custom chip although the symptom of that failing is usually that the display gets pulled completely over to theleft.If possible let the 'scope warm up and check that the horizontal displacement stays the same - if it does then it should be adjustable. If it wanders around as things warm up itcouldbe a questionable U800 horizontal drive IC.Edit, no that's the 2445/2465/2467 - sorry obviously visually saw the 2, 4 and 7 and missed the lack of a 6 somehow.U800 is a problem sometimes in those 'scopes though and does often manifest itself as everything deviated to the left (frequently only atfer a few minutes warm-up).

author: rf-loop
author_rank: Super Contributor
timestamp: June 11, 2014, 05:12:16 pm
content: Quote from: grumpydoc on June 11, 2014, 02:58:48 pmWrong.These do NOT contain this "famous" U800 what is IC what have some truths and myths.What ever... right information is that 2247A Horizontal output amplifier is quite realiable and it is made by discrete components. Preamp is IC.

author: grumpydoc
author_rank: Super Contributor
timestamp: June 11, 2014, 06:30:12 pm
content: QuoteWhoops, sorry - mis-read the model number completely.You're absolutely correct these have nothing to do with the well known U800 problems.Sorry for the mis-post.

author: Electro Fan
author_rank: Super Contributor
timestamp: June 12, 2014, 02:57:06 am
content: If you think you can fix it great; if not there might be an easier answer - just pick a different unit. The one you are looking at might have a problem or it might not - but there are others to choose from. In any event, the 2247A is a great model with an excellent set of features.

author: SAUL BRITTO
author_rank: Frequent Contributor
timestamp: June 12, 2014, 05:34:34 am
content: Hi.Look all resistors on the signal line from the pré amp to the H-OUT,any days ago i fixed a problem in a HP much like this,was two resistors that works very hot 2W.Before make adjustments,dont forget: Look resistors! Even if you notice small changes, do not hesitate, replace! And of course, the caps too.