Tecktronics 2213 oscilloscope help needed

[Carl E]

Hi,
I'm looking for whatever help is available to repair my 2213 scope. This looks like a great place to start.
The symptoms are low intensity display, a little out of focus and I am unable to use the position control on either channel to move the display above the center line. The intensity control will change the display but it never gets bright enough to  see the vertical rise or fall part of the trace. The focus must be adjusted whenever the intensity is changed.  Using the 1Khz 50mv as a source, the top of the square wave is visible but  when I try to move the position of the trace up, it brings up the bottom of the trace and compresses the vertical display until it matches the top trace. The beam finder does not work. I've checked the voltages, -8.6, +8.6, 5, 30 and 100v and all are within spec, but I have not checked the 7KV as I don't have the proper equipment.  I've looked at the solder joints on the main board, especially under the power supply and I don't see and broken or cold joints.  I have the service and instruction manual. I am able to solder /desolder components without lifting PC traces.
I hope someone has some idea as to where to look and I really appreciate any help with this. Maybe I could help someone who has a problem with their Room8a or Pachislo machine.  It's a good instrument, I'd hate to send it to the bone pile.
Thank you
Carl E

[james_s]

A dim beam that goes blurry when the brightness is turned up is a classic symptom of a worn out CRT. In this case though I would not be so quick to condemn the tube as you have other symptoms that indicate faults clearly not in the tube. I'm not familiar with the 2213 but I did fix a 2215 once that had a fault with the focus, that turned out to be a bad resistor in the focus divider circuit. It had a chain of several identical resistors in series and one had gone open, another up in value. If the 2213 is similar that's where I'd start. It's possible that you have multiple unrelated faults.

[floobydust]

Not entirely likely the CRT is defective- weak or sagging HV (multiplier) also gives the same symptoms of a dim trace and focus blurring at higher intensity. I think you have two problems. The traces unable to move above center is another issue with the V deflection circuit. There's only +/-30V on those two CRT plates so you could check the voltages there.
The CRT socket is at -2kV though, so don't measure there unless you use a HV probe.

I would say you have to measure the anode HV to know the multiplier is working. Either make an HV probe (out of a resistor string) or borrow one.
https://www.eevblog.com/forum/projects/diy-high-voltage-probe-safety-concerns/msg2758872/#msg2758872

These scopes are getting old and the PSU needs new electrolytic capacitors, I replace them all.
Spreadsheet list of capacitors for the 2235 and 2235A PSU which are the same for 2213A/2215A. I spent around $15. The scopes are well worth the few dollars and time to fix them.

The common focus problem is the five carbon 510k resistors changing value and they can look cooked, discoloured. Can't recall if they load down the HV as a consequence.

[Carl E]

Thank you for your reply. I measured the 1M resistors and found they all were very close to 1.05M. The 5M pot for auto focus is in parallel with one of the 1M resistors. I lifted one leg of that 1M resistor and checked the 5M pot, it is OK.  I went back to the power supply and remeasured the voltages. The -8.6v measures -8.26 while the +8.6 measured +8.55. The power supply schematic of the 8.6 supply only shows a 840uf cap on either side of a 10uh coil. This is the only filtering I see after the bridge rectifier. If one or both caps are bad on the -8.6 supply, can they be replaced  with a 1000uf cap or are the values critical like a tuned circuit. I've looked at digikey, mouser and farnell for the exact cap and it appears the 840uf are no longer available. I do see that there are pix and blogs where some folks have used 1000uf caps as replacements in the power supplies.
Maybe this will fix the beam finder as well.
Thanks.

[bd139]

Possibly the multiplier is gone on it. That'll be difficult to replace. If you disconnect the red CRT HT cable shortly after it has been powered up and short it on the chassis it should produce a nice crack noise. If it doesn't then the multiplier is probably hosed. Do not touch the contacts!

2213 is same as the 2235. I've had two and they are absolute bastards to fix on the HT side of things. The multiplier cost as much as the scope did.

Edit: If the multiplier is bust then it should still display the normal trace but a lot smaller and dimmer however.

[CaptDon]

You definitely have a vertical deflection problem related to the upper side
or 'positive supply side' of the push-pull deflection circuit. There was a factory
mod to remove one turn of the filament winding on the HVT transformer. From
the factory the 6.3v filament was running nearly 8 volts. Later production units
were o.k. from new, but early units that were never modified killed the crt in
short order, mainly in labs where the scope ran 24/7.

[james_s]

Yikes, how did that slip through QC?

Running the CRT that far out of spec seems like something that should have triggered a recall and CRT warranty extension.

[CaptDon]

It actually did create a recall and free CRT replacement, but only for
a limited time, and only for those who cared enough to send in the
registration cards. Many slipped through the cracks and were never
modified. The company I worked for had a 2213 with early CRT death
and I bought a 2213 used that was never modded (I didn't know there
was a recall back then) which had early crt failure. The focus divider
chain used very poor quality resistors also. Most resistors go up in
value as they age, I saw some of the Tek resistors go down to about
10% of their original value.

[jdragoset]

Yikes, how did that slip through QC?

Running the CRT that far out of spec seems like something that should have triggered a recall and CRT warranty extension.

Agreed.
I have several 2215's a 2235 and a 2225
Are there similar recalls on these?
The DVM may not correctly read the HF but can be measured with an rf analog volt meter.
Watch out for the -2kv DC also present.
As a fix, one could always insert a series dropping resistor.

[Carl E]

Hello, I'm back and still need help . I replaced the x4 840uf caps with 1000uf in the 8.6 supply and both the + and - are in spec. I still can't get a baseline trace to swing above the center graticule. When turning the v position knob, the voltage on the + vertical  plate  swings from - 8v to -6v, the voltage on the - plate swings from -4v to +10v.

Will I do any damage to the scope if I swap the signal of the two Vertical plates to see if the trace will be at the top instead of the bottom?

I don't see a voltage change between  R378 and R379 when I press the beam find. I suspect that Q376 or Q377 is bad.
Anyone know where I can source these devices ?

Thanks
Carl

[CaptDon]

You can safely swap deflection plate leads. They should press onto
the little pins sticking out of the CRT neck. Don't force them.

[Carl E]

Thank you for your reply. I will swap the leads in the AM. If the trace problem follows the swap, the most likely cause is the two output transistors that are in the - plate circuit. The transistors are available so I should be able to get them.
Thanks again
PS: Once I get the vertical circuit fixed, I'll start on the focus and intensity problem.

[jdragoset]

Check the series string of collector resistors in the vertical amplifier output transistors, if one is open circuit the deflection will only be in one direction from center.

[CaptDon]

Indeed, he should find a schematic and begin measuring voltages!! The output of the
vertical and horizontal deflection plate amplifiers are push-pull and it seems like something
very simple is fubar and should be easy to figure out. Your idea about the open resistor
chain is a good one since those resistors run hot with current to get the fast bandwidth
on the final stage of the deflection amplifiers. I don't have the schematic in front of me,
but many of the Tek scopes had hybrid Tek part numbered I.C.'s driving the finals. Let's
hope it isn't one of those! I had to replace a hybrid in an SC504 80mhz modular scope.

[Carl E]

Hi, Here's an update': I swapped the vertical plate connectors and the trace changed as expected. I've ordered new 340 Ohm resistors for the voltage divider and the 2N2369 (151-0127-00). Schematics list this as S006075 but I can't find it on the web except the 2N2369 substitute number. The BFR 96 are hard to find except from China. I have reservations about using these but I ordered them anyway. There are x2 1.07K resistors that I can't find, if I find these are bad I'll have to make  them out of other resistors. When I ohm out the 340 Ohm resistors they are only slightly off the value. Wish me luck.  Thanks for the great help.

[james_s]

It's easy to test transistors, you should be able to determine with reasonable certainty whether they are ok or not.

[Carl E]

Update....
Vertical Position Fixed !!
I guess I can't see out of one eye and am blind in the other....I miss read the values of the 4 resistors that bias the vertical plates. One was open and read 5K in circuit. The other 3 read around .5K in circuit.
Thanks to all who commented back to me...
Now I'll wear my glasses and try to fix the intensity and focus problem,
And yes, the beam find also works.

 

[Carl E]

Hi,
Not sure if I should open a new thread for the next repair or should continue with my original post. The  2213 has no signal on Ch2. Ch1 works fine. Ch2 has a baseline trace, just no signal .

[Carl E]

Hi,
I think I've found the problem with channel 2 not working, but I'll run it by for comment (PLEASE). I'm comparing channel 1 and 2 to determine where I loose the channel 2 signal. I'm using another scope to see the signal. At the preamp level, channel 2 transistor Q257 has -7.3 volts on the collector and it should be -3.7. The other part of the push pull circuit, Q267 has close to the expected voltages and actually I can see the 1K probe adj signal although in order to see it the volts/div is at 2mv and AC. Is it possible to have only 1/2 of a push pull amp work?  Both of these transistors Q267 and Q257 feed an IC SL3127 ( 5 transistor package) that feeds the next stage. I've ohm'd the resistors in the circuit and all are close to the expected values ( this time I'm wearing my glasses). This said, I think I have a bad transistor or a bad IC.
Any comments are appreciated.
Thanks

[cdev]

I have a working 2211, (but no service manual) Same form factor, probably fairly similar.

[Carl E]

Update:
I just Ohm'd out the 10 transistors in the preamp circuit. E-B, C-B, C-E,  forward and reverse polarity, comparing Ch 1 to Ch 2 on each transistor at the same location in the circuit. The biggest difference in any reading was 200 Ohms (2.4K vs 2.6K in the Ch 2 inverse circuit.
I'm at my wits end. What am I missing ? 

[Carl E]

Anybody have a source for SL 3127 ( the 5 transistor array). Ebay has one for $ 25.00 (Whaaaat ?)

[james_s]

If it's an obsolete IC that's not necessarily unreasonable. Just be thankful you're not looking for one of the custom hybrid ICs used in the fancier Tek analog scopes.

For testing purposes you can probably get away with making one out of individual transistors. If they're well matched and in good thermal contact with each other it might even be good enough to leave.

[CaptDon]

I have had a lot of bad resistors and capacitors in Tek stuff.
Most of the resistors went open and it is strange because they
were in most cases only dissipating maybe 10% of their power rating.
They just seem to fail. Maybe poor supply chain quality?? Old
Tek stuff ran for 40 years until the electrolytics went bad. Their
old CRT's were good for 10's of thousands of hours. Somewhere
in the mid to late 70's things just slowly went downhill. I own tons
of Tek stuff but been thinking it's time to unload. I know of a company
that had over 100 of the lunch-box scopes TDS2XXX series and only had
two failures in ten years!!!! That is what convinced me to buy my
TDS2004B from Ebay for $500.00!!! Love it and it works great!!! Has USB!!
 

[jdragoset]

 I would use this as a good try:
https://www.ebay.com/itm/4X-HARRIS-CA3127E-5-CHANNEL-VHF-BAND-Si-NPN-RF-SMALL-SIGNAL-TRANSISTOR/113412986375