Tektronix 2235 no trace - Page 1
Forum section: electronics / repair

author: BrookeAdams
author_rank: Newbie
timestamp: May 11, 2016, 03:19:16 pm
content: I apologize in advance if this has been posted, I tried to find related post but failed. I recently bought a Tek 2235 on eBay and when it arrived I found that I have no trace. The beam find function does allow me to see a dot and it can be positioned with the X Y controls. If I set it to line I can see a small horizontal trace about an inch or so but on int its only a dot. unless the beam find is depressed I see nothing. I do not yet have a service manual for this unit so any advice on a cost effective way to obtain one would be appreciated. I also have not yet opened the unit as I am still in the return negotiations stage with the seller on eBay. My guess it something related to the sweep oscillator or could be as simple as a loose connection. I also would like clarification on the model number. It simply has 2235 100MHZ on the front and no labels providing any other info on the back. Any help will be appreciated. If I get my 80 dollar partial refund refund as I am trying to do , I will have a total cost of 20 dollars for this unit. Forgive my lack of knowledge of this particular unit but I see small holes in the back that appear to be for a cooling fan but there is no sound and no air flow. They seem to be very small holes if in fact a non working fan is behind it.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: May 11, 2016, 05:22:36 pm
content: Hmmm.... the fact that you have a dot when pressing Beam Find is really good news. Did it have a trace in photos on the EBay listing, or was it sold "non working" ?Service Manual is here:http://w140.com/2235_sm.pdfAre you an experienced analog scope user? If so, please excuse the basic level of these instructions. Let's make sure there is in fact no trace before we go digging inside.Refer to the SM from the link above. Go to section 2-10,11 (page 28-29 of 229 in the .pdf) and set the scope's controls as listed there. Do you get a baseline trace?The 2235 doesn't have a fan.

author: BrookeAdams
author_rank: Newbie
timestamp: May 11, 2016, 09:02:38 pm
content: NO it did not have a trace and I had a bad feeling when I looked at the picture that showed a dot a bit more closely that you see a hand pressing the beam find.I had already made a bid so could not back out. Im kinda glad I got it anyway since even ones for parts are more than twice what I paid. The seller is not electronics oriented and made the mistake of listing it as used but fully functional as intended.Fortunately I received an $80.00 dollar refund so Im only out $22.00. I was glad to see the dot too guessing the CRT is ok. I am a bit rusty with one but I worked as a Motorola bench tech for quite awhile, around 25 years total in communications. I missed having a scope as it always seemed I needed one. I needed to see some automotive waveforms so I decided to try and get one. I am pretty sure it will not have a baseline trace as nothing is visible without the beam find. But to be sure I will do as you ask soon as I get a chance in a few hours. I have no doubt it can be repaired with a little TLC. Thank you so much for replying and I will repost with the results soon.

author: tautech
author_rank: Super Contributor
timestamp: May 11, 2016, 09:20:02 pm
content: OK Brooke so you're not a newbie to scopes but maybe rusty?Obvious next question: Trigger on Normal not Auto?Just checking.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: May 11, 2016, 09:20:12 pm
content: Could be something as simple as having the Trigger Mode set to "Normal" instead of "P-P Auto" with no signal input, or having the traces moved up, down, left or right offscreen with the V and H position controls. Many times I've seen scopes that were "not working, no trace" that were simply set wrong and actually had nothing wrong with them. Let's hope that is the case here as well.I just fired up my 2213A (which is fully functional, a great little scope) with no input, set it to "Normal" Trigger Mode (which blanks the screen unless the scope is triggered) , and duplicated this:QuoteExactly what mine does.So the very first thing to do would be to make sure that the "P-P Auto" Trigger Mode button is depressed and the Trigger Source is set to "Int" , Trigger Holdoff fully CCW ("normal") and vertical and horizontal position controls set to mid-range. (Set "Intensity" to 3/4 or fully CW just for this test, then back it off to a dull roar if the trace shows up). If no visible trace, then move the H and V controls through full range to see if the trace is just hanging out offscreen somewhere. All of this applies to the "A" trigger, see the manual pages I referenced above.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: May 11, 2016, 09:26:39 pm
content: Quote from: tautech on May 11, 2016, 09:20:02 pmIn the photo it's on Normal...

author: BrookeAdams
author_rank: Newbie
timestamp: May 11, 2016, 09:51:11 pm
content: When the photo was taken it was sitting all alone in the room I wasnt doing anything with it. I went ahead and followed the achieve baseline trace instructions.It still doesnt do anything more than I have been able to get it to do tinkering with it. If you hold beam find you see about an inch wide trace and it can be varies by the time adj to be a solid line or a slowly tracing dot. I included a few pics hopefully with the size limit you can see the detail. I have believe it or not used a fair number of scopes from analog to digital storage , and mostly the built in scope in a Motorola 1801 communications analyzer. Later I had a digital version of the comm analyzer but didnt care for the response time of the display. I turned up the time to show the trace that I can get , it leaves the center point and travels about an inch. Its just been about 14 years since I used one so yea a bit rusty but its still in me somewhere :p Horizontal amplifier ? Sweep board ? Im actually looking forward to fixing it , just hope I dont need a scope to do it :p

author: tautech
author_rank: Super Contributor
timestamp: May 11, 2016, 10:02:13 pm
content: You'll just have to work through the basics and check the functional blocks that a CRO is made from.Sweep is a good place to start.You might find this useful:http://www.sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdfThere should be plenty of waveforms in the service manual to reference to.Many also include DC voltages in the schematics but be aware the scope must be set a specific way for those DC value to be valid.RTFM.Do you have a working scope?

author: metrologist
author_rank: Super Contributor
timestamp: May 11, 2016, 10:52:19 pm
content: Looks like your trigger is set to channel 2.

author: BrookeAdams
author_rank: Newbie
timestamp: May 12, 2016, 12:06:48 am
content: It was prolly the slightly down angle of the camera Its on vert modeQuote from: metrologist on May 11, 2016, 10:52:19 pm

author: BrookeAdams
author_rank: Newbie
timestamp: May 12, 2016, 12:10:58 am
content: No I do not have a working scope. I will check a few things after dinner and a shower. Thanks for the link , a trouble shooting flow chart would be nice. I can do some basic thermal test see if anything changes and can def check voltages and the good old visual.Quote from: tautech on May 11, 2016, 10:02:13 pm

author: alsetalokin4017
author_rank: Super Contributor
timestamp: May 12, 2016, 01:45:08 am
content: In your photos it looks like the B trace Intensity (inner knob with pointer) is turned all the way down (CCW) , but I can't tell the A trace Intensity (outer knob) setting. If it's turned all the way down too you won't see a trace.Also, at 50 ms/div on the A trace timebase setting, it will take 500 ms (half a second) for the beam to move across the full screen from left to right. So you won't expect to see a line, just a moving dot. I suggest you set the A timebase to 1 ms/div while you are looking for a trace.Also the Single Sweep button looks funny. This is a non-locking button and should be all the way out. Maybe it's just the camera perspective, but you might try exercising this button just to make sure it's popping all the way out. When you press it in, it will pop the P-P Auto button out, so make sure that the Single Sweep button is out and the P-P Auto button is in when you do further testing.

author: BrookeAdams
author_rank: Newbie
timestamp: May 12, 2016, 04:04:10 pm
content: Ok by careful counter rotation of several T 10 lock down devices followed by skillfully using the left and right opposing thumb tools I achieved this.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: May 12, 2016, 04:17:00 pm
content: Looks like we fixed it. Where do I send the bill?(Were you getting ready to "shotgun" the thing just in case?)And did it come with the probe? You got a really really good deal, even if you don't get the 80 dollar refund.

author: BrookeAdams
author_rank: Newbie
timestamp: May 12, 2016, 09:17:27 pm
content: Yea the shotgun was to make it know I meant business, I hope thats not the only reason it works. Really I guess I need to know what places could be intermittent as in socketed devices or connections that mad need a cleaning before I put it back together. Everything I see is through hole components but I know better then to assume its ok just because its start working simply taking the cover off. I knew as soon as it powered up it was doing something because never had any trace or visible anything the CRT without the beam find. It seems to read fairly accurately. I have two probes but one is missing the tip end that has the ground and actual tip. The other one as u can see seems ok. Yea I think 22.50 was a good deal. I paid 102.50 got an 80.00 refund. It obviously is not in that bad of shape.

author: tautech
author_rank: Super Contributor
timestamp: May 12, 2016, 09:39:56 pm
content: Quote from: BrookeAdams on May 12, 2016, 09:17:27 pmCareful inspection of all mounting screws to ensure they're not connecting to anything they shouldn't when installed/tightened.The incorrect length screw installed in the wrong position can drive one crazy and only careful detective work will discover which one. As someone else has had her apart.....expect anything.PCB interconnects.But the most likely IMO is push button switches....now it's going to get some usage just the normal cycling of those switches might be enough otherwise some cleaning with IPA and switchexercisecould be needed.If these aren't fan cooled there's little reason why you couldn't run it naked for a bit to check if the cover installation wasn't the problem.Another keen shooter.

author: Cubdriver
author_rank: Unknown
timestamp: May 12, 2016, 10:51:20 pm
content: Glad to see it's working.I'd start by putting the cabinet back on and trying it again to see if it still works. If it does, you may well be good to go.If it craps out again, you might get a non conductive probe - perhaps a chopstick or something similar - and gently apply pressure here and there on the various circuit boards to see if anything makes it flake out or come back. That could help to isolate a bad connection. The screw length suggestion above is also a very good one - make sure the cabinet mounting screws aren't too long and grounding something.-Pat

author: alsetalokin4017
author_rank: Super Contributor
timestamp: May 12, 2016, 11:24:17 pm
content: To see just how good a deal you got.... take a look here:http://www.sphere.bc.ca/test/tek-parts/tek-knobs.html

author: BrookeAdams
author_rank: Newbie
timestamp: May 13, 2016, 01:19:58 am
content: I have been pricing them for awhile and most of the ones that are listed as broken or for parts only can go for around 200 ish. There are 4 screws, pretty sure the two on the power cord holders are ok, the other is a very short screw that goes into a metal standoff. On the side I think it goes into the power supply case and appears to come out into open space. I guess its not wasting peoples time too much until something else breaks. Im just happy that shows it is capable of working and not likely a serious failure.

author: H713
author_rank: Regular Contributor
timestamp: December 23, 2019, 08:35:30 pm
content: I know this is an ancient thread, but I have a Tek 2235 exhibiting exactly this same behavior. Any suggestions are greatly welcome.

author: teus
author_rank: Contributor
timestamp: December 23, 2019, 08:36:44 pm
content: Quote from: H713 on December 23, 2019, 08:35:30 pmI just created a thread for a similar issue!