[FIXED]Tektronix 2213A Vert mode problems. Ch selection and Add, Chop Alt modes. - Page 1
Forum section: electronics / repair

author: Coll
author_rank: Contributor
timestamp: July 24, 2016, 03:08:17 am
content: One of the last fixes I need on this thing is to fix the Channel selection. It does not work properly. Channel 1 selection and Dual channel selection work perfectly fine as you would expect. However, Channel 2 selection still shows both traces as if it was in dual mode. Section the Vertical selection modes do not seem to do anything. I tried getting them to work but they do not. Add, Chop and Alt does not affect the traces at all. I would like to get them fixed if anyone has any ideas I would be glad to hear them. Thank you.

author: Coll
author_rank: Contributor
timestamp: July 25, 2016, 11:43:01 am
content: I am starting on the Channel selection as I figure this might be the easiest place to start. After going through the manual I found that Switch S550 and a chip U540. U540 after checking ends up being a SN74LS74AN.I ended up taking some voltage measurements around that chip to see if it reveals anything useful.VCC = 4.3V I think this might be a little low.`PRE `PRE2 `CLR `CLR2 D D2 Q `Q Q2 `Q2Ch1 0V 0V 4.8V 138mV 295mV 4.8V 3.3V 295mV 0V 4.8VCh2 4.8V 0V 4.8V 138mV 1.82V 4.8V 1.8V 1.8V 0V 4.8VBoth 4.8V 0V 4.8V 138mV 1.82V 4.8V 1.8V 1.8V 0V 4.8VJust to reiterate Both and Ch2 selection show both channel traces and work perfectly fine like if I had two both settings.Now I am just a beginner in this field but based I what I know so far Q and `Q should be the opposite logic levels of each other unless in special circumstances. The datasheet for this chip says when `PRE and ` CLR goes low Q and `Q will toggle high. However in this case when `PRE goes high both Q and `Q don't even go high they just hit 1.8V. Is this due to the chip being busted? Or should I be locking elsewhere? Also if anyone has a schematic for this specific area or one from a similar model I would like to see it. It is tough not being able to see the circuit.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: July 25, 2016, 12:19:53 pm
content: Here you go, from the 2215a SM. Should be about the same.I've never been able to find a (free) SM with schematics for the 2213a but it turns out that the 2215a manual covers a lot of stuff that is different between 2213 and 2213a, such as the channel attenuator switches and etc.You might try downloading a SM for 2215a.

author: Coll
author_rank: Contributor
timestamp: July 25, 2016, 09:44:42 pm
content: Quote from: alsetalokin4017 on July 25, 2016, 12:19:53 pmThank you for this it actually works for what I need. From what I can see the chip is actually doing its job and the switch is working for the most part. From what I can tell it is something in the path keeping one of the lines high when it should be low. I believe the problem exists in the channel 1 line itself which I determined to be pin12 on my board.

author: Coll
author_rank: Contributor
timestamp: July 26, 2016, 08:28:15 am
content: After a another look over the line. I tested the switch and found out that was the cause of my problem. I took it out and opened it up seeing the main contact attached to the selector broken off. Used a bit of locktite epoxy and let it set for 6 hours and threw it back in. It worked. Fixed my Channel selection problems. Not only that but due to the wiring in this scope it fixed the ALT CHOP and ADD mode problems too. I am very proud of this. Thank you alsetalokin4017 for the schematic it really did wonders for this project.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: July 27, 2016, 04:31:37 am
content: You're welcome, glad I could help. I love my old 2213a and still fire it up occasionally.If you haven't done so already, you can download the SM with schematics for the 2215a and it will be useful for your scope in many cases. For example disassembling those pesky V/div switches and associated circuitry, which are _not_ the same as in the 2213 but _are_ the same as in 2215a. Guess how I found that out.....