[SOLVED] Tektronix 2215 B timebase no sweep - Page 1
Forum section: electronics / repair

author: Basileus
author_rank: Regular Contributor
timestamp: January 12, 2017, 05:34:17 pm
content: Hi, i just got a nice Tek 2215 and started testing it to check if everything is working.Everything is perfect,apart from the delayed timebase: seems like i just cant manage to make it work.Now, i've never used a scope with a DTB, but after trying and trying again to play with the switches i cant get a magnified portion of a signal.I feed a signal in;I put the hor tb mode to ALT;Pull out and rotate clockwise the tb control;Nothing happens.If i select B hor mode i cant see anything at all. Am i missing something? Is the B sweep generator faulty (?)I also noticed thatthe B delayed tb position control doesnt go lower than 0.4. Is that intentional?Moreover, after being done with testing the scope, i decided to open it and do a visual check inside. I removed the back panel, unscrewed the screw on the right side on the scope,i cant slide off the cover. It got stuck after pulling it out for 5/7 cm, i tried to pull it out harder and made some progress, then i realized that cover was biting on the internal supports of the scope. "Screw that, i'm put it back again" and so i did. Now the situation got worse and i cant pull it out again easily for 5/7 cm like before. What is going on? Am i missing something? Should i spray some WD40 on the sides and try again?Thank you in advance.Update:I managed to get the scope out of the cover by spraying some dry contact cleaner in the corners. The frame is badly scratched and marked, i cleaned it a bit to make it slide more easily.Sorry, lighting is pretty bad.PS: the dent on the trace is caused by a dent in the filter, crt is perfectly fine.

author: tggzzz
author_rank: Super Contributor
timestamp: January 12, 2017, 06:19:33 pm
content: Quote from: Basileus on January 12, 2017, 05:34:17 pmDid you RTFM? If not, why not?QuoteProbably; I've seen slightly different values on different Tek scopesQuoteOnly if you are prepared to clean the oil ofallinternal surfaces. Hint: don't go there.

author: dan3460
author_rank: Frequent Contributor
timestamp: January 12, 2017, 06:34:40 pm
content: I had one of this scopes long time ago, but I do remember that when you use the B delay the trace was very faint, you needed to get full brightness to see a faint trace.As per the case, WD40 will not cause any mayor problem as it is not conductive, I use it when cleaning pots. But cleaning will be a good idea as it is not fun to work on a messy scope.I have a few scopes that the case was very hard to get out, because they have been damaged previously. It helps, at least for me, to put on the floor to make sure that is pulling straight. I use a small mirror to see if there is anything held in between the frame and the case. And I just keep pulling, pull left 1/8th of an inch, then go right and pull 1/8th of an inch and repeat. My record is about one hour fiddling with the thing, because you got to be careful as from where you can push or pull.

author: Basileus
author_rank: Regular Contributor
timestamp: January 12, 2017, 06:42:15 pm
content: Yes, i read the section of the operating manual about the delayed timebase. Couldnt do it. I select alt hor mode and the only thing that happens is two dots appear at the beginning of the A sweep and they are only visible with beam find. There is no sweep i guess. Those two dots can be moved vertically. Tried both B and ALT hor mode at max trace intensity: no trace, same two dots on beam find.Thanks for the advice on disassemblying: i ll try to take my time and slide it off. I hope this problem are one time thing because its driving me mad.

author: Basileus
author_rank: Regular Contributor
timestamp: January 12, 2017, 07:03:09 pm
content: Im not doing much progress though. Im checking both sides with a torch, i think there is some kind of debris stuck on the sides. The scope on the exterior looked good, but stuck behind the rear cover there was quite a lot of dust, the sticky kind. The bag was stained by this sticky black dust too, i guess its the same thing on the inside. I pull the cover out scratching everything, then ill clean and polish the frame again.

author: Tom45
author_rank: Frequent Contributor
timestamp: January 12, 2017, 07:30:33 pm
content: I don't have a 2215, but based on Tek scopes that I do have:With just the A time base set up to get a stable clear trace with normal A trigger.Then pull out the time base knob. You should see the same trace as before but with a small intensified region some place on the trace.If OK so far, turn the time base knob (still pulled out) clockwise. The intensified region should get smaller.Edit: the B trigger control should be Run after delay (fully clockwise)

author: Basileus
author_rank: Regular Contributor
timestamp: January 12, 2017, 09:08:20 pm
content: Uploaded a video. Sorry for the lighting, its pretty bad.

author: Tom45
author_rank: Frequent Contributor
timestamp: January 12, 2017, 11:27:21 pm
content: It looks like your B time base isn't being triggered. You need to turn the B trigger knob fully clockwise and leave it there. Then it should trigger a fixed delay time after the A sweep is triggered. The delay time is controlled by the 10 turn pot.

author: Basileus
author_rank: Regular Contributor
timestamp: January 12, 2017, 11:51:01 pm
content: Quote from: Tom45 on January 12, 2017, 11:27:21 pmTried again with B trigger level fully clockwise, nothing happens.

author: Tom45
author_rank: Frequent Contributor
timestamp: January 13, 2017, 04:08:22 pm
content: If you put the horizontal mode to B only can you get a trace at any setting of the B slope and trigger level?

author: Basileus
author_rank: Regular Contributor
timestamp: January 13, 2017, 04:40:59 pm
content: Quote from: Tom45 on January 13, 2017, 04:08:22 pmNegative. With cal signal fed it, you can only see two dots (only visible with beam find on) and can be moved with the channel pos control.

author: Tom45
author_rank: Frequent Contributor
timestamp: January 13, 2017, 05:27:08 pm
content: Quote from: Basileus on January 13, 2017, 04:40:59 pmSure looks like the B sweep is dead. Nothing with either internal trigger, or trigger after delay.Do you have the service manual fromwww.w140.com?For the best help I'd suggest joining the Yahoo TekScopes group.

author: Basileus
author_rank: Regular Contributor
timestamp: January 13, 2017, 06:10:15 pm
content: Quote from: Tom45 on January 13, 2017, 05:27:08 pmI bought the oscilloscope with service and operator manual, pouch, front panel cover and two coline m12sw 250 MHz probes (no hook terminals)I guess that when i have a bit of time i'll open the scope and check the test points on the A13 b sweep generator board

author: Basileus
author_rank: Regular Contributor
timestamp: January 13, 2017, 08:22:12 pm
content: I did some test and..B sweep signal is missingB trigger signal is notTest points on A13 board, fig 9-11 of the manual:35 - ok36 - ok37 - ok38 - untested, couldnt reach it39 - wrong, reads 23,6 v DC40 - wrong, reads 84,3 mV DC41 - wrong, reads 4,41 V DC42 - wrong, reads 3,6 V DC43 - wrong44 - (?) Pulses are present but are not isolated like in the immages45 - wrong46 - ok47 - ok48 - wrong49 - ok

author: Basileus
author_rank: Regular Contributor
timestamp: January 14, 2017, 01:08:03 pm
content: After making those tests and mining in the service manual, i ve found out that:Transistor Q662 on the alternate sweep board (A13) measures 1100 ohms on his Base-Emitter junction (reverse polarity) instead of open.Also, there is a slight deviation of voltage on one of R662 ends, being -8,2 V instead of the reference -8.6V.You can see in the image, the wrong test points marked and the dodgy transistor. I would desolder it to test it but the solder joints are flush against one side of the PSU and its no quick job.I would like to hear your opinion about it. Meanwhile, i'm looking for a substitute. It seems to be a quite cheap component. Cant find original Tek parts, but seems like a 2N3904 should do the trick.

author: tautech
author_rank: Super Contributor
timestamp: January 14, 2017, 01:14:35 pm
content: This should help:http://www.sphere.bc.ca/test/tekequiv.html

author: Basileus
author_rank: Regular Contributor
timestamp: January 14, 2017, 01:17:09 pm
content: Quote from: tautech on January 14, 2017, 01:14:35 pmThanks!Already checked it.TO-92 151-0190-00 2N3904, TO-92 Used $1Still, i'm not going to get the parts from Canada, shipping to Italy would take too much time and money.

author: Basileus
author_rank: Regular Contributor
timestamp: January 14, 2017, 01:33:01 pm
content: In the manual there is written that if you have to desolder components from the alternate sweep board, you have to desolder the 27 pins that connect it to the main board. I want to hear somebody else opinion before trying it

author: Basileus
author_rank: Regular Contributor
timestamp: January 15, 2017, 10:44:11 am
content: The manual "troubleshooting you oscilloscope" from Tek suggest a fault at the SWEEP START GATE. This should indicate a fault in the circuits controlling the timing for the start of the sweep. There arent troubleshooting guides on the DTB specifically, but from what i understand, such role is played by the delay time position comparator section, which drives the sweep logic that produce the B GATE signal that drives the sweep generator.Important update!I made an error: TP 38 is NOT good. It measures 22 V DC with fast, exponential spikes with a Vpp ranging from a max of 1.2V to 0 V depending by the position of the B delay time position knob. I would also add that the trace is quite noisy, but i dont know if its the scope or the DUT. I'll check the components in the area but it will be difficult because they are in a tight spot and its not easy to probe around with a DMM.Now i assume Q662 is good and the problem lies higher in the circuit.Thank you in advance.PS: Hi! im Basileus from the future, when i fixed this scope. This ^ up here is going in the right direction

author: Tom45
author_rank: Frequent Contributor
timestamp: January 15, 2017, 11:56:23 am
content: Examine components in that area for bad solder joints, bulging capacitors, or any signs of overheated components. Of course capacitors are the usual suspects.Even if Q662 does turn out to be bad, it is likely that something else could be wrong that contributed to its failure.

author: Basileus
author_rank: Regular Contributor
timestamp: January 15, 2017, 01:21:56 pm
content: Quote from: Tom45 on January 15, 2017, 11:56:23 amLooks like the base collector junction of U648B measures OC in both directions. I'm not 100% sure about it because the pins are quite difficult to reach. I'll make some L shaped probes and test it more.Talking about the replacement, looks like is a CA3096AE-17.I cant find it on the net, but i can find a CA3096AE. What does that 17 mean?The ic on the board has the tek code and "RCA223", which assume is the name of the producer and.... dont know what 223 stands for.Anyway, this CA3096AE:http://www.ebay.it/itm/CA3096-INTEGRATO-CA-3096-/282114519889?hash=item41af55f351:g:rPQAAOSwENxXmHowHas RCA 936 written on it. Does that number refer to production date or something? Is it a suitable replacement?

author: Basileus
author_rank: Regular Contributor
timestamp: January 20, 2017, 07:17:20 pm
content: Good news!All solved. After finding the fault, i got some extra help from the tekscopes yahoo group. The guys in there are amazing.Hopefully, U648(B) was the only fault in the scope: i replaced it and it works perfectly fine. The service manual, another scope and the guide "troubleshooting your oscilloscope" proved to be crucial for me to figure out how to repair the 2215.here are some photos and videos:TP35(A sweep) was really dodgy because of the feedback caused by the faulty transistor (U648B): because of this, the b delay time pos control influenced the signal on tp35.

author: cheeseit
author_rank: Regular Contributor
timestamp: January 21, 2017, 11:17:36 pm
content: Nice work, persistence pays off.Enjoy your scope!