Tektronix 2230 Oscilloscope Repair Part 4: Vertical Attenuators Fixed!

In this video I receive some parts I needed to make additional repairs - mainly the 10x and 100x Attenuators for the A2 attenuator board (for an interesting teardown of these Tektronix Attenuators, see IMSAI Guy's vid here • #1714 Tektronix RC Com... ). looks like the vertical attenuation for both channels is now repaired!
Still need the switches for the A10 storage board (I accidentally ordered the wrong kind). But I did order the correct replacements this time! Once I get those in, I can move forward with finalizing the last of the repairs to this unit (at least the electrical ones. The unit still has some mechanical problems like broken knobs that will take longer to address). Then I can move on to performance testing and potentially some calibration depending on what I can accomplish with the tools I have in-house.
Part 5 here • Tektronix 2230 Scope R...
0:00 - Quick recap
2:50 - Parts received & plan for repair
7:23 - crack in #2 memory switch revealed
8:07 - attenuators installed!
8:40 - Analog circuitry isolated & initial test of probe adj signal
10:38 - Issues with CH1 vertical attenuation greater than .5V/div (or 50mV/div at 1x)
13:30 - Checking probe adj signal with CH2 (success!)
17:20 - Checking CH2 with external function generator
19:20 - Trigger issues at higher frequencies on CH2
21:39 - Checking CH1 with external function generator
23:44 - Verifying amplitude of FG with DMM
25:50 - More testing of CH1 with FG
28:05 - Checking probe adj signal again with CH1 (success!)
30:10 - Triggering on 11MHz sine wave CH1 & CH2 (success!)
31:45 - Wrap up

[@fmashockie]

Update: So that issue with CH1 came back after I finished the video - incorrect attenuation of the signal on vertical settings > 50mV/div (.5mV/div). It turns out it was just poor connection with the new attenuators I put in. They are socketed so I just had to reseat them and the problem went away!

[@thanhhuynh272]

LOOK’N GOOD, No faults in the analog path of both channels….that’s a whole lot of extra work you Don’t have to do! Triggering seemed a bit “sluggish” St first, but seemed to improve as time went on. I tend to find this a lot in older gear, probably electrolytics reforming after decades of idleness.
The reasin the attenuators stopped working in your initial cal square wave measurement was probably some tiny piece if loose crud under the gold plated leaf contacts of the attenuator cam switch and simply working the switch caused it to fall out or be squeezed through…so possibly a bit of solder flux on the contact surface.
At 12 minutes in, where you get those integrated pulses, (i.e. the jumps in the square wave only)….the same effect can be simulsted by placing a small 10-ish pF capacitor in series with the input, it lets the edges through but not the “continuous higs or lows. I had this exact issue with the 2445 I have here. Worked “hunky-dorey” on Ch-1; but INTERMITTANTLY did this on Ch-2. Thos 2445 was fitted with option 05, the Analog TV composite video signal advanced triggering option which also featured a black-level clamp, but this was only available on the Ch-2 input. I deduced that it probably had belonged to a TV station or TV repair guy and the Ch-2 inout saw a heck of a lot of use because of the black level clamp. At some point, some Ham-Fisted Yargon had either reefed in the BNC in Ch-2 or bumped the connector…bay at any rate he’d broken the pin at the back of the Ch-2 input BNC off the attenuator board…which was ceramic substrate, thick film…like yor sttenustors there but bigger and more complex. They do this st the inputs to minimize parasitic reactances, i.e. long component leads adding stray inductance and stray capacitance.
So I got dtuck into it snd thought I’d just take it bum off, take off the screenibg can for the Ch-2 input….a blob of solder and “Bob’s your Uncle” it would be fixed…..Noooooo….had to literally pull the whole damn thing to bits, yhe whole analog board out, the whole Ch-2 attenuator can off that board once it WAS out…Tek ste brilliant st electronic design, but their mechanical layout leaves a LOT to be desired! Once it was out, I looked with the magnifing lens st the rear pin of the BNC, and yep, a hairline crack in the solder!
The whole process was Deja-Vu…I felt Inhad done it all before, or someine I knew had done it and bemoaned the whole story to me…possibly one of the Techs st Uni, 30 years sgo…I think the Ph-D’s .in EE got to use Tek 4K series back in the day, Undergrads only got to use Aarons or Hang Chengs! At any rate I got it sll back together and fixed.
I also have a 2213 here, it looks just like this 2230, but without all the digital stuff at the top if the front pannel…so basically almost exactly the same as your 2230 with the digital part disconected. When I got this 2213, I had to do the ubiquitous Rifa change in the power supply, but looking st the manual…it reccommenced another check of the EHT transformer where there in an overwind for the tube heater…it was three turns, but they reccommended removing half a turn, i.e. instead of both ends of the winding leaving the same side of the core, pull it back through on one end so one end left each side of the core…as the reckoned the tube heaters were being worked too hard and reducing the life of the tube. This 2230 looks like it has exactly the same EHT transformer, so this might be worth checking . The psrt number for the Transformer is 120-1348-00 but this should be changed to 120-1348-01 with the half-turn pulled off but isn’t always, so trust the turns you can see (they sre right on top) rather than the psrt number of the transformer. You sre dupposed to pull the half turn off then stick s sticker with “01” on it over the “00” suffix of the number on the core, but such a sticker could fall off and get lost!
I say this because your tube seems over bright…my cameras here actually “see” scope traces BETTER thsn my eyes do, so in only neied very low intensity settings when filming. If you have worked on enough thermionic valve (electron tube) gear, you will be aware of the importance of heater voltages.
Really looking forward to seeing a reolacement (or repaired) switch rack beibg fitted. Oh, if the contact leaves fell out of the broken back of the switch, they might be rattling about loose or stuck somewhere inside it, might be worth checking for them as they cauld cause you grief later if thsy sre still dtuck inside somewhere!
Oh:
“Broke” = run out of money, empty bank account
“Broken”= deliberately dammaged…i.e. smacked with a hammer or pushed down a flight of stairs
“Faulty”= Ceased to function correctly
From your hot water cylinder video: 3/4 = “three QUARTERS” not “three fourths”! For some reason our language seem ems to be “going to pot”…ot sure why! The broken = faulty is the most annoying.

[@fmashockie]

I think you hit the nail on the head as usual Globe Collector! Very interesting that you've seen that issue with the vertical attenuators before. I guess that's something you only get with additional experience! But yep seems to have gone away with some additional exercising of the switches. I agree with you regarding layout of Tek equipment - I think HP does a much better job with serviceability. Was not a big fan of the mechanical layout of this scope either. Real pain to remove some of the pcbs. Like the front panel board for example - had to desolder ~40 pins from the main board to get a better look at it! Nothing like my HP 54600 series - so much easier to work on. The 576 curve tracer also was a real pain to access some of the boards in there as well! And yes I think I just had intensity turned up a bit too high on the CRT - it didn't look too bright in person. Gotta be careful there - I don't wanna burn out the tube before I get the whole thing fixed! 😂 I'll also make sure to replace that RIFA hiding underneath the line filter board before I'm done with this guy, too! I'll be sure to check for anything loose like those contact leafs before I finish up - would hate to have one short something out after all this work! And yea I'll be careful with those grammer mistakes - I can't afford to piss you off with all the experience and wisdom you bring to each video! 😂 Thanks as always for watching and your comments! 🙏🙏

[@fmashockie]

so that issue on CH1 came back - incorrect attenuation on settings > 50mV/div. It was just a poor connection to the attenuators I just put in. They are socketed after all. But after pressing on them a bit more firmly to seat them, the issue went away!

[@thanhhuynh272]

Nother of your countrymen just had an issue with this very type of switch in a 2465, take a look…IqwmQgTszEo…just a single DPDT switch, not the whole rack p, like in yours.

[@fmashockie]

Just watched it... Those style button switches will get you every time! @@thanhhuynh272

[@andymouse]

Quick question If I may. When you were looking at probe compensation I didn't see you switching the probe to 10X and adjusting the cap on the probe lead itself as I'm sure you know that the comp will only effect 10X, did I miss it ? congrats on the Attenuators working....cheers

[@fmashockie]

Sorry maybe I didn't make this clear when I started the video - I was only using the probe adjust circuitry just to check the operation of the attenuators (I had verified in part 1 that the probe adj circuitry was working properly with an external scope). The probe I was using can be switched btw 10x and 1x. I started at 10x. Initially, it looked like all the vertical attenuator settings were fine except for anything above 1V/div (or .1V/div) was not working properly. So then I switched the probe to 1x to also verify this and it still seemed like attenuation was off for those settings. After messing around with the scope a bit more, it seemed like this might have been due to poor triggerring or something else because both channels appeared fine towards the end of the video. I wasn't using the probe adj signal to actually compensate the probe as you nromally would. Actually, based on the square wave, the probe seemed to be compensated just fine already! Hope that answers your question!