Tektronix 2213 trace starts in middle of screen - Page 1
Forum section: electronics / repair

author: moose
author_rank: Contributor
timestamp: April 21, 2025, 03:36:17 am
content: Hii have a Tek2213 that is used ocassionally as a 2nd scope.The current time that i wanted to use it i noticed the following...the trace started near the middle of the screen. If i tried to reposition (with horiz position control) the trace to the left, it would simply bunch up at the point the trace started.Moving the trace line right functioned as per normal.i swopped left & right crt deflector leads & that merely reproduced the issue, but now on the right.As per service manual, i set it to trigger-auto, chan 1-gnd.Looking at the waveforms (24/25) on the main scope both waveforms mirror images of each other except the left values were 10V higher.i then looked at the waveforms of the sweep generator...those also looked fine.is it possible the horiz position control pot itself could be faulty? what should the resistances at both extremes be?any suggestions as to where to focus next? i did check all PSU voltages & they are all fine.thanks in advance

author: neillnz
author_rank: Contributor
timestamp: April 21, 2025, 09:45:57 am
content: The manual says the horizontal postion pot is 5 k Ohm. It shows it as a Voltage divider for the +8.6 V and -8.6 V rails, see the fold out 7 which is page 187/224 of the PDF from Tek:https://w140.com/tektronix_2213_service.pdfWhat is test point 23 doing? Does it swing +1 V to -1.3 V?I Used to fix these things for the NZ distributor in the early nineties. Cannot recall seeing this particular fault, it was almost always power supply issues. One day an engineer from Beverton was visting and he asked what was a typical fault, I told him that's easy it's almost always PSU and he said that's odd because they rarely had PSU issues, I always wondered if it was an issue with using a primarily 110 V design at 230 V.

author: moose
author_rank: Contributor
timestamp: April 21, 2025, 02:01:02 pm
content: Hi NeilThanks for that info (& history - saved for future ref!).as for TP23: it shows the right shaped waveform.With the Horiz controller positionedmax left +2.2 to +0.28centre +0.8 to -1.46max right -0.18 to -2.56I'm uncertain whether this is good, bad, or indifferent..TP22 also had right waveform swinging from +11.4 to +0.2 (regardless of horiz controller position).cheers

author: bdunham7
author_rank: Super Contributor
timestamp: April 21, 2025, 04:43:28 pm
content: You can put the scope into XY mode with no inputs (and both set to GND) and then you'll have static voltages on all of the horizontal amplifier sections. Try to center the dot and move it around to see how each half of those amplifier sections responds to the horizontal position control.

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: April 21, 2025, 07:15:23 pm
content: If I were to make a wild guess, one of the supply rails for the horizontal amp is bad. Check supply voltages near the horz amp.Also do some signal tracing to figure out whether the horz amp is really the problem. Perhaps it's only the sweep not going to the negative (or positive maybe it's inverted) when that happens, but considering the horizontal position is experiencing the same effect, I would bet supply voltages in the horz amp.

author: moose
author_rank: Contributor
timestamp: April 22, 2025, 03:38:07 am
content: thanks for the suggestions...XY mode - whilst the dot was centered i could only move it vertically. And when i connected a diode & a cap to view the waveform it was basically a kinky line. So i must assume that XY-mode is non functional (something else to investigate ).i had a look at all the voltages as per the circuit diag 5 (sweep generator & logic) and circuit diag 7 (xy amp/horiz output) ....everything appears to be close to what its supposed to be & the pwr rails inputs are spot on. Admiteddly i ignored the XY section.Checking the horiz position knob output voltages, they varied correctly so i can exclude that.

author: bdunham7
author_rank: Super Contributor
timestamp: April 22, 2025, 01:38:20 pm
content: Can you pull out the 10x horizontal magnification knob on the timebase knob? Do that with a normal trace showing in auto trigger mode, see if the trace expands to cover the screen. If so, I think your problem may be Q730 or very near it. You can just measure the voltages (referenced to ground) at all 3 pins of Q730 and Q731 and report back. Do that with the horizontal knob centered and in XY mode with both inputs set to GND, then with the horizontal knob turned a bit to the left and then a bit to the right.

author: moose
author_rank: Contributor
timestamp: April 22, 2025, 03:02:06 pm
content: the 10x mag merely magnified the signal over the same portion of the right side of the screen......a few days ago when i 1st started with this it did go right across the screen.Q730 -0.32 +0.4 -7.68Q731 -0.32 +0.4 -7.64(pain to find them & then get to them!)however, something happened in the last few hours...the right side of the trace is now chopped before the extreme right of the screen...and...the waveform (at R788 & R778) going to the L & R horiz deflection plates is not as clean as it was.is it possible that transistors Q789/785 and Q779/775 are faulty??Also, i noticed today that pin 5 & 12 of Q603 (diag 5 F4) remains at 3V...i'm sure that yesterday there was a square wave on it...so does that mean Q603 is faulty

author: bdunham7
author_rank: Super Contributor
timestamp: April 22, 2025, 03:26:58 pm
content: It looks like the issue is further down the line. You can try probing the voltages on all of those transistors in the same way without worrying too much about exactly what they are doing--just look for about 0.7V from base to emitter. Include Q736 just to be complete, but anywhere between point 23 and 24/25 is game. Don't overlook the beam find circuit and Q747 as a malfunction there would certainly cause the symptoms you are seeing. Maybe even check Q747 first.

author: moose
author_rank: Contributor
timestamp: April 23, 2025, 01:28:46 pm
content: i am really at a loss now...i checked voltages at the following:Q736, Q763, Q753, Q765, Q770 and Q747 - none of the voltages were much out of what was written on the schematics (and all base/emitter were around 0.6-0.8 V.

author: bdunham7
author_rank: Super Contributor
timestamp: April 23, 2025, 01:34:04 pm
content: Quote from: moose on April 23, 2025, 01:28:46 pmWhat about Q775/779/785/789 and Q780?Where is the dot on the screen when you are doing this? If it is approximately where it is supposed to be then perhaps the voltages won't be off. Try moving the horizontal position all the way towards the side that the dot won't go to and try again. And check points 24 and 25 each time as well.

author: moose
author_rank: Contributor
timestamp: April 23, 2025, 01:41:25 pm
content: ahh, my bad...all the above were with chan 1 GND, sweep 0.1mSi will redo with chan1 & 2 at GND, and sweep at XY and horiz pot at full left.

author: moose
author_rank: Contributor
timestamp: April 24, 2025, 04:52:13 am
content: ok, done..values are 1st horiz full left & 2nd horiz full right, a single value indicates no change left/rightB E CQ747 -5.1 -5.7 -2.8/-4.2Q763 -1.6/+1.2 +0.8/-2.1 +4.6/+4.8 base/emitter high.....faulty??Q753 0 -0.8 +5Q765 +6.8 +6.2 +8.5Q770 +5 +6.2 -0.5 base/emitter high.....faulty??Q779 +96 +97 +50/+63 base/emitter high.....faulty??Q775 0 0 +50/+63Q789 +96 +96 +44/+33 surely this & Q779 should match??Q785 0 0 +45/+33 surely this & Q775 should match??Q736 -7.7 -8.3 +2/-1Q730 -0.3 +0.3 -7.7Q731 -0.3 +0.3 -7.7Q720 -0.4 0 -1.5also, i noticed that when the horiz control was full right, the dot would wonder left to right over the width of the sweep which is about 1".

author: bdunham7
author_rank: Super Contributor
timestamp: April 24, 2025, 05:19:52 am
content: You missed Q780?I'll sleep on this, perhaps something will come to me. The output portion of the horizontal amp is not really balanced or symmetrical in design but the output should shake out to be pretty balanced--and yours obviously isn't. It also lacks range. Can you also check the voltage across VR781 and also confirm that your -8.6V supply is good? Measure that at R771 and R881, one leg of each should be at -8.6V.

author: moose
author_rank: Contributor
timestamp: April 24, 2025, 05:58:43 am
content: yes..the voltages at R771 & R781 both spot on -8.6, voltage across VR781 14.95 (and at each end -13.95 & -0.6)

author: bdunham7
author_rank: Super Contributor
timestamp: April 24, 2025, 03:54:49 pm
content: I'll agree that Q763 looks problematic if you look at it in isolation. If I'm thinking clearly (no guarantees) it looks like it is reversed biased in one case and should be completely off but it still allowing current through and in the other you have +3.3VBEand it appears to not be fully on. I'd still like to see what Q780 is doing. As for the other two transistors that you marked as possible problems, I'd leave Q779 alone for now (but keep it in mind) and IDK what to say about Q770. That can be replaced with a 2N3906 if you have one and want to do a quick substitution. Q763 is designated as a "select" MPS918 which may be a bit of an issue as the p/n is obsolete so you may not have an easy time getting one let alone an assortment from which to select one--if we even knew the selection criteria. Central Semiconductor has the PN918 which appears to be a drop-in replacement for the MPS918, but the "select" part IDK about.Looking at the circuit as a whole, it also appears that your signal (difference when you change the knob position) appears at the base of Q763 as expected and really never appears beyond that. If you have the time and inclination--as in you prefer precision diagnosis to shopping for a few parts--you might try another set of measurements, one with the horizontal position knob set so that you get exactly 0.00 volts at the base of Q763 (get Q780 readings this time) and another with the same settings but using a scope with a 1kHz 1Vp-psignal on CH1 (X) with that channel set to 0.5V/div. With the scope probe (10X at least, 100X 100M if you have it) find the signal at the base of Q763 and then start tracking it through the circuit.

author: moose
author_rank: Contributor
timestamp: April 24, 2025, 11:59:30 pm
content: thanks for all that....it may take a few days to get all done.

author: moose
author_rank: Contributor
timestamp: April 25, 2025, 12:52:54 am
content: oops...i somehow skipped over Q780 from my results sheet with the rest of the values from yesterday.B E CQ780 +5.2 +4.4 +14.0Q763 -1.6/+1.2 +0.8/-2.1 +4.6/+4.8Q780 is spot on the expected values.i'll get on to your suggestions...

author: moose
author_rank: Contributor
timestamp: April 25, 2025, 06:31:41 am
content: i thought i would relook at U603 (sweep generator & logic waveforms, sheet 7)Putting the scope as per their settings, the waveform of TP3 is as theirs, however, the waveform of TP5 & TP6 is NOT!With TP5, the hi time is fine, but the low time is 1/2 a cycle of the TP3 wave.Similarly with TP6, its low for the correct time, but its high time is also 1/2 a TP3 cycle.And with TP14, the high lasts also 1/2 a TP3 cycle.Looking at the input signals (S,R,C) for the output (Q) at pin9, pin10 (S) is constant H..is THAT supposed to vary H/L?And pin 13 (R) is low for 5 cycles (of TP3), but comes hi for only 1/2 a TP3 cycle...is that supposed to be like that?So perhaps the issue is somewhere in the sweep circuit?

author: BlownUpCapacitor
author_rank: Frequent Contributor
timestamp: April 25, 2025, 04:04:06 pm
content: If X-Y is not working, that means that the sweep circuit is likely fine and that the fault it else where.. I suggest putting it to X-Y mode again, but this time feed a sine wave into CH1 and use another oscilloscope to follow the signal from WFM22, check your way through the the A12 board circuit making sure to follow the signal, and then go to WFM23. Then check the base of Q780.If possible, please post photos of the waveforms. There should be no huge voltage offsets.The fault is likely not in the trigger circuit nor before it because if it was, the sweep should work fine. Having both X-Y and normal sweep be faulty indicates a problem in schematic 7, the XY AMPLIFIER/HORZ OUTPUT circuit.This is assuming there is only one fault though, not two. But two faults reproducing the same error seems unlikely.

author: bdunham7
author_rank: Super Contributor
timestamp: April 25, 2025, 04:14:16 pm
content: Quote from: moose on April 25, 2025, 06:31:41 amThe manual I'm looking at has the sweep generator and logic on sheet 5. Do you have a link for yours or can you post it?QuoteI think that pulling out the 10X horizontal mag and not seeing the trace expand acorss the screen pretty much rules out the issue being at any point prior to that area. Also, you're seeing a significant shift at the base of Q763 as you change the horizontal position in XY mode. At this point I'd recommend obtaining a replacement transistor for Q763 and also getting a few 2N3906, if you don't have them on hand, to replace Q770.

author: moose
author_rank: Contributor
timestamp: April 25, 2025, 11:56:20 pm
content: appologies....yes, sheet 5 not 7 (it would appear dont know my 5s from my 7s)i'll order some of them 2N3906 chips...on that note, trying to establish equivalent parts for obsolete parts i find rather problematic.what would be valid replacements for the following (or are my choices valid?):Q789 SPS6700 -> MPSA92 (?)Q780 S032077 -> ?Q763 SPS8002 -> MPS918 -> BC237/2N5209Q731 SPS8223 -> MPSH69 -> 2N4557Q736 SPS8224 -> MPSH11 ->BC847being so far away, shipping costs are more of an issue than component costs so i tend to order from aliexpress (2 weeks shipping).

author: bdunham7
author_rank: Super Contributor
timestamp: April 26, 2025, 12:31:05 am
content: Is that SP8002 number for Q763 from the manual or is that what is on the transistor body? I've no datasheet for that, but the MPS918 that the manual lists has a relatively low gain (min=20) and a 600MHz ft. So I don't think your listed subsitutes will work properly. But I suppose you could just put a 2N3904 in there for testing, you should then be able to determine if that was the problem or not. You should stock 2N3904/2N3906 if you're going to have electronics as your hobby!It's probably going to be hard enough to readjust and calibrate the scope after replacing Q763 (there's a reason they are "select" and I'm guessing it is gain related) so once you verify that's the issue as best you can, I'd recommend getting as close a match as possible even if you pay some shipping. The Central Semi PN918 would probably be your best bet.AliExpress and eBay aren't totally terrible places to do some semi shopping, but the risks are pretty high and I'd be reluctant to buy anything that I don't have the capability to verify the specs on myself.Edit: Element 14 Australia has MMBT918LT1G in a SOT-23 package with a minimum order of 5. If you have good fine soldering ability you could make that work temporarily, although I think the power dissipation is less than the TO-92 version.

author: moose
author_rank: Contributor
timestamp: April 26, 2025, 08:03:10 am
content: sheesh....typo...SP8002 should have read as SPS8802-1i'll stock up on the 2Nxx & get a few PN918 as you suggested.element14/mouser/rs-comp/digikey all have a shipping fee of NZ$19 or thereabouts...but if i get all the components at once it at least brings down the per item cost.

author: moose
author_rank: Contributor
timestamp: May 05, 2025, 01:16:19 pm
content: the components arrived today...so i can give an update.I removed & checked the following:Q763 hFE=6 so replaced it with SS9018 hFE=154Q780 hFE=154 so kept itQ785 hFE=104 so replaced with 2N551 hFE=157Q789 hFE=84 so replaced it with MPSA92 hFE=162Q779 hFE=162 so kept itQ775 hFE=101 so replaced it with 2N551 hFE=161net result was a marginal improvement so the problem is not with that circuit.i didnt check Q770 or Q765 as i dont see them being the cause.Could the caps in the left part of the horiz circuit cause this issue at all??On the other hand could it be that the trace is simply starting too late?and if so wouldn't that indicate a blanking timing issue or a sweep issue?

author: bdunham7
author_rank: Super Contributor
timestamp: May 05, 2025, 01:48:48 pm
content: Well that's frustrating.I'd recommend you trace an AC signal through the system as I suggested at the end of reply #15. Also, since things didn't work out, I'd revisit Q765 and Q770. The symptoms do remind me of beam find operation but only in the X-axis so even though we didn't see any problem with the measurements it would be worth a look.As far as using a transistor tester, I'm not suggesting that this is the case here but measuring hFE at low levels can be misleading and to be sure you need a curve tracer that can test over the actual in-circuit operating conditions.

author: moose
author_rank: Contributor
timestamp: May 05, 2025, 02:18:51 pm
content: thanks for suggestions, will do.the transistor tester i have is a peak atlas DCA55.i've was looking at the waveforms for waves 5 & 12 superimposed on wave 3 a short while ago before i shut everything up for the night.the waves are just completely wrong.wave 5 has an hi time of 2 periods of wave 3 and a lo time of 6 or 7 periods of wave 3and wave 12 was similar.could it be that ic u640 is problematic??

author: bdunham7
author_rank: Super Contributor
timestamp: May 05, 2025, 03:30:53 pm
content: Quote from: moose on May 05, 2025, 02:18:51 pmI don't see offhand how that could affect the XY mode. If you can't position an XY dot all over the screen--and off the edges--then I think you have to fix that first.

author: moose
author_rank: Contributor
timestamp: May 05, 2025, 11:34:39 pm
content: very true..but given that both XY-mode AND normal probing both are affected perhaps it points to something that is common to both operations (aside from the horizontal amp)?

author: bdunham7
author_rank: Super Contributor
timestamp: May 06, 2025, 04:38:49 am
content: Quote from: moose on May 05, 2025, 11:34:39 pmYou had a varying signal at the base of Q763 and the rest of the circuit appeared to not respond properly to that. So logically I wouldn't expect the problem to be anywhere before that point. Still, I'm puzzled as to what is actually going on and I'd be curious to know if any of those readings changed. But since it isn't fixed yet I suppose we should keep an open mind. Why do you suspect U640?

author: moose
author_rank: Contributor
timestamp: May 06, 2025, 06:56:48 am
content: the reason i mentioned the peak atlas was as an indication of establishing whether the transistor was still ok or not.the reason for wondering about u640 is due to the signal i see (or lack of) at TP 12.as an aside, when checking TP14 should TP3 still have that square wave of 1KHz? (given that CH1 is set to GND for TP12)will check Q765 & Q770 shortlyalso, my other scope can capture waveforms to file if it would be of any assistance.

author: moose
author_rank: Contributor
timestamp: May 06, 2025, 11:31:32 am
content: i've attached a file showing various captured waveforms..maybe something will stand out..

author: moose
author_rank: Contributor
timestamp: May 09, 2025, 04:10:23 am
content: something else i've just noticed....i was checking around Q720 (G5 sheet 7), whilst the voltages are in the ballpark of those indicated on the schematics, the resistances are really odd.eg Q720 - collector to gnd = 2.4K base to gnd = 1.6K (R723 measured 1.6K not 6.1K as specified so that explains the base reading)So perhaps Q720 is faulty...to check &/or replace it (&R723) means removing board A12; is there an easy way to do this??[edit/update] i removed the A12 board & checked 'every' resistor, cap & transistor thats indicated on the A12 in schematic 7...all were ok!