Help, another Tektronix 2225 faulty scope

[ParsonsUnknown]

Hello, I'm a total newbie with scopes, I've had this Tektronix 2225 for about 8 years and didn't fancy tackling it

Now I'm feeling a bit more confident and up for the challenge to get this beauty up and running, so I can put her into service in my shack

Problem seems to be with the horizontal, any traces from a signal in or the test point seem to show on the right side of the CRT

I've taken a few videos to explain further, because I'm not always that great at explaining things

If anyone can give me a few pointers in the right direction, I would greatly appreciate it

Trevor



[url=http://cloud.tapatalk.com/s/59bbd18be5aaf/MOV_0303_002.mp4]http://cloud.tapatalk.com/s/59bbd18be5aaf/MOV_0303_002.mp4[/URL]http://cloud.tapatalk.com/s/59bbd198eadd3/MOV_0305_001.mp4

Sent from my F3311 using Tapatalk

[bd139]

I can't look at the video unfortunately here but this is usually one of the deflection wires has come off the CRT or one of the load resistors has burned on the relevant amplifier.

First step is crack it open and take a look. The CRT will have holes with two wires in each for the horizontal and vertical. Check them. Then look for burned resistors where they are connected to the board.

[David Hess]

For simplicity, leave the horizontal mode at x1 for now.

What does the horizontal position control do?

Possibilities:

1. Beam finder stuck on?
2. A lead may have fallen off of the horizontal deflection plate pins on the neck of the CRT.  These are located along the bottom of the CRT.
3. The horizontal CRT amplifier may be damaged.  At a slow sweep speed, measure the output volt for each lead.

[ParsonsUnknown]

I've taken the cover off, can't see any visible signs that something has burned out. However I've taken all the interconnections out and reseated them, and I took the plastic cover off the back of the CRT and a couple of the connections look like they could do with the soldering iron over them

Sadly, I've no lights in the shed, so tomorrow I'll run some power up to the shed and see if anything occurs, before I start digging deeper

Thanks for the replies so far 👍

[David Hess]

2. A lead may have fallen off of the horizontal deflection plate pins on the neck of the CRT.  These are located along the bottom of the CRT.

It looks like I was wrong about this.  Most Tektronix CRTs have the deflection leads at the neck of the CRT instead of the rear connector but the 2225 is slower so its deflection connections appear to be at the socket in the back.  This should still be checked however.

[ParsonsUnknown]

I've resoldered the CRT connectors, servisoled the pots. Nothing seems to have changed, although I've measured all the rails and they seem to be within spec:

5.088
-8.60
8.72
38.29
98.5

I'm shooting in the dark a bit with this to be honest. Maybe it's a front panel issue? I've downloaded the service manual, which I'll have a look through over the weekend

[ParsonsUnknown]

Just had an idea, I read a post a while ago about the trimpots, some are cajoled to fit in places and cause excessive oxidisation and therefore affect the conductivity over time

I can't find my plastic trimmer tool, so I'm going to nip and pick one up and try to see if the problem lies in the vertical and horizontal gain trim pots, it's certainly worth a punt, at this stage I have nothing to lose I reckon

[ParsonsUnknown]

Update:

I've taken the attenuator/timebase card out, still no visible signs of dry joints or any burn outs, so I'm going to reseat the front panel connections, I'm a bit buggered because the only torx size I haven't got is a T9

Anyway, I powered up and I've got a nice dot on the CRT, which is a damn sight better than what I normally get, HI

Figured out why probe adjust never seem to work, link wire was brittle and came off at the motherboard, gave all the CRT connections on the motherboard a bit of fresh solder too, just in case, got to say I'm bloody enjoying this

I'll keep plodding on

[ParsonsUnknown]

I've given this scope a fair bit of time, I've even taken the CRT out and checked all the connections, front panel pcb taken off, cleaned and replaced

Still no change at all, think it's a problem in the vertical section as everything is squashed down, oddly now I've reconnected the probe adjust wire, I get nothing from it when I connect any probes, channel 2 is currently not usable due to the 47 ohm resistor crumbling to bits

Any ideas guys, cos I'm punching way above my weight here?

[ParsonsUnknown]

 Well probe adjust is now working of sorts, this is as far as I'm willing to go, I've taken a pic, any ideas before I take a sledge hammer to it?

[bd139]

Got to be horizontal amp dead then.

I'd probably at this point try and lose it and get a working one. Don't kill it though; someone will be able to repair this but it's going to require extensive work by the sounds.

[tautech]

Can the voltages to the H plates be checked in XY mode in these scopes ? That way you don't have the changing voltages from the sweep gen. This info should be in the SM.

This can be useful too:
http://www.sphere.bc.ca/test/tek-parts/troubleshooting-scopes.pdf

[David Hess]

Can the voltages to the H plates be checked in XY mode in these scopes ? That way you don't have the changing voltages from the sweep gen. This info should be in the SM.

Yes, horizontal deflection, vertical deflection, and differential balance may be checked in XY mode.  I suggested how to test the horizontal amplifier earlier but ParsonsUnknown did not bother.  It is not real clear at this point how many problems exist do to lack of information.

[tautech]

Can the voltages to the H plates be checked in XY mode in these scopes ? That way you don't have the changing voltages from the sweep gen. This info should be in the SM.

Yes, horizontal deflection, vertical deflection, and differential balance may be checked in XY mode.  I suggested how to test the horizontal amplifier earlier but ParsonsUnknown did not bother.  It is not real clear at this point how many problems exist do to lack of information.

He did say he was a newbie but we'll get him over the line. 

[ParsonsUnknown]

Fair point, I'll check your final suggestion in your original post, thanks again 👍

[ParsonsUnknown]

Thank you for your patience lads, and I appreciate your input. I apologise for my lack of smarts in this field and my lack of useful feedback, I assure you I am trying

Would I be in the right neck of the woods, checking the voltages around these transistors? 

[bd139]

Yes. Make sure you set the scope up as per the service manual's instructions though or the voltages may be wrong.

[tautech]

Thank you for your patience lads, and I appreciate your input. I apologise for my lack of smarts in this field and my lack of useful feedback, I assure you I am trying

Would I be in the right neck of the woods, checking the voltages around these transistors?

Voltage checks to be valid are normally done to a specific setup, RTFM. 
The manual will give specific instruction on how to and then I'd be going to the H plates while in XY mode to ensure the values on each H plate where the same, or very close to it. A balanced voltage is what keeps the dot in mid display...ie zero deflection.
This can indicate the output stage is crook or you might have to look harder into the preamp stage.
XY mode is really the only way to trace a fault in the H plates.
It could be as simple as something wrong in the H Position circuit.

A few clues and a little understanding will point you in the right direction.
You should be pretty familiar with her guts now so all you need is to put all the bits together in your mind and you should have it sorted before too long.

[ParsonsUnknown]

Cheers mate, I'm in the process of tracking the trannie down, then I'm setting everything as per the destructions 😉

[David Hess]

Instead of measuring or messing with anything else, clear up what is not working correctly.

1. What are the volts/div and time/div controls set to?
2. What is the input signal producing that square wave?  We need to know the amplitude and frequency being applied to the vertical input.
3. Maybe take a photograph of the control panel so we can see the other control settings.
4. What is the horizontal and vertical position range?
5. How does changing the horizontal and vertical position affect the display and especially the display linearity?

The reason these things are important is that there is a big difference between problems which only affect horizontal deflection and problems which affect both horizontal and vertical deflection.  It is not clear at this point what if anything is wrong.

[ParsonsUnknown]

David Hess, bd139 & tautech. I would like to thank you all for reminding me to read a bloody schematic correctly. I was looking in obvious places and getting it all wrong. I nipped up to the shed and got looking around in better detail and depth. Got the lamp on the board and noticed that link W791 (+40v link) didn't look too clever, while I had the soldering iron on, I gave all the CRT connections on the boad under the neck a heat up and a push, also gave all the transistors in that area a heat up too.

Powered up and I've got perfect lines, so I put a probe on channel 1, as 2 is temporarily down until the resistors arrive in the post, and I've got good vertical and horizontal. Chaps I'm humbled and very thankful for you giving me pushes in the right direction. I reckon when I've replaced the BNC input resistors for new one's and the 33R's going into the attentuator board, I think she might be in the ball park and ready for calibrating.

Once again, I am absolutely feeling foolish for missing an obvious fault, however in my defence it was under the metalwork at the back. I've learned so much this morning and I would gladly buy you chaps a pint.

[tautech]

David Hess, bd139 & tautech. I would like to thank you all for reminding me to read a bloody schematic correctly. I was looking in obvious places and getting it all wrong. I nipped up to the shed and got looking around in better detail and depth. Got the lamp on the board and noticed that link W791 (+40v link) didn't look too clever, while I had the soldering iron on, I gave all the CRT connections on the boad under the neck a heat up and a push, also gave all the transistors in that area a heat up too.

Powered up and I've got perfect lines, so I put a probe on channel 1, as 2 is temporarily down until the resistors arrive in the post, and I've got good vertical and horizontal. Chaps I'm humbled and very thankful for you giving me pushes in the right direction. I reckon when I've replaced the BNC input resistors for new one's and the 33R's going into the attentuator board, I think she might be in the ball park and ready for calibrating.

Once again, I am absolutely feeling foolish for missing an obvious fault, however in my defence it was under the metalwork at the back. I've learned so much this morning and I would gladly buy you chaps a pint.

That's now we learn. 
Regarding Cal, unless you have the gear and know how, just verify it's close to spec and use it for now.
Probe cal output shouldn't be relied on as deadly accurate so don't attempt to adjust anything to it, rather use it as a sanity check in times of confusion during normal usage.

Enjoy.

[ParsonsUnknown]

Thank you, sir