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I re-read the manual description of the circuit after posting, and I think I was seeing one of the tunnel diodes switch to its higher-voltage state. I was testing it with no signal input.

CRT scopes typically are easy to arrive damages to CRT even if we'll packed.

A 50 ..100 mm drop of the box can move the electron gun electrodes enough for geometry distortion.

As the screen and CRT dimensions increase the chance for damages is worse.

In general buying off eBay and risking the seller to pack and freight carriers to gently handle a large heavy delicate electronics is risky.

We pickup scopes at ham flea's, street sales, estate sales and hand carried.

Just my experience

Jon

Hi teamlarryohio,
"Adjust Y-Axes Alignment", chapter 7, Calibration service, Service Manual page 2/8 is of course done. No effect. The remaining idea is a permanent magentic field emanating from the CRT shielding (or tilted plates inside the CRT = fatal fault). I have the possibilty to return the 7613 to the seller!
Regards
Loetroelli

Obviously Mr Wilson's probe is the killer of all probes. Superb work "chapeau bas" as we say here.
Renaud

Are you making measurements with a volt meter? Try with a scope instead and compare the waveforms while having the settings set up correctly according to the manual.

Benjamin

My 475 is now triggering with a new U520 chip, but not perfectly. As recommended on here, I found the 475 SN B250000 and up service manual that includes voltages at various points in the trigger circuit and tested them.

Everything looked good until I got to one of the tunnel diodes, CR556, where the schematic states the anode should be at 0 Volts.

At turn-on, the voltage on the anode of CR556, the arming tunnel diode in the A Trigger circuit, rises to 0.02 Volts and climbs as high as 0.04 Volts over 30-40 seconds. Then, it starts jumping around rapidly and ends on ~0.410 Volts where it remains. This is repeatable with each turn-on cycle.

Is this the typical behavior of a failing tunnel diode? There are several components connected to this circuit point. I swapped transistors Q556 and Q566, and that made no difference. I don't know much about the normal behavior of the thermal resistor RT559. I work a lot more with vacuum tubes, but this looks like the behavior of a semiconductor that works when cold and then fails as it warms up.

How risky is it to swap the tunnel diodes themselves between A and B Trigger circuits? I see they are socketed and not soldered.

Thanks for helping a newbie at scope repair. I'm working on the learning curve.

I added it to the TekWiki:

Someone else can add it to BAMA... for Tek stuff I usually go directly to the Wiki

Soumds like the y-axis alignment (R1190, on the z-axis board beside the geometry pot) needs to be tweaked.
-ls-

Hi Benjamin,
Be sure that I checked all kinds of everthing. The plug-ins were inserted and drawn. No, it seems to be a CRT fault. Meanwhile I had the possibiltiy to return the 7813 to the seller! The 7613 is already in a parcel.
Regards
Loetroelli

Hi Brian,
good luck with your 7834. My "new" 7834 has a working mainframe including a good storage CRT. I saw already pictures that shows me that cleaning has to start with the aid of a fire brigade hose. Therefore the price.
The 7613 is already in a parcel.
Regards
Loetroelli

Upon examining the images with more scrutiny, the answer actually seems to be much more simple.

The leveling head uses pins 1 and 4 for temperature compensation, and pins 2 and 3 for leveling.

In your image, the PCB header is utilizing only pins 2 and 3 on the header, with nothing connected to pins 1 and 4. Looks like maybe the original 4 pin LEMO connector was damaged and was replaced with a 2 pin LEMO to conserve the vital function of leveling, but not temperature drift.

There is a number of different possibilities, but the main thing is that your SG504 is just using a 2 pin connector which is operating for only the vital functions.

It would be like having a fancy interface connector with 8 pins, but only using 2 pins for serial data transmission.

Benjamin

From what I can tell from the service manual, the 4 pins have two functions. Two pins are meant for temperature compensation in the leveling head, and the other two are for the actual pk-pk detection of the output signal in the leveling head.

Juding by the pull tab type, I'm going to guess yours is a later serial number and Tek figured out a way to conpensate for temperature drift without the need for another two pins. Perhaps it is 3 pins, two for leveling, and one pin is shared with temperature compensation which is referenced to to ground.

Benjamin

I got an SG504 where the LEMO connector for leveling head has only two pins (instead of regular 4 pins).
Pictures uploaded in (afraid you'll have to go backwards, from last to first, to have some logic - not sure why they arranged themselves in that order):
/g/TekScopes/album?id=296499
Sure I'd like to hear if someone else is aware of this variant (maybe unique?) and what details could share - for my benefit, but maybe for others too. Specially the leveling head, what schematic or solution was used to rely on only two pins.
Thanks for attention
Titi

How about BAMA too. I usually look for instruction books there first.

--
Richard Knoppow
Los Angeles
WB6KBL
SKCC 19998

On Fri, Jul 19, 2024 at 10:01 PM, Luca wrote:

Anything against uploading it to archive.org or the TekWiki?

Off course not. I'd prefer TekWiki.
/H?kan

Thank you for the super fast service! If we manage to find the fault I'll update the thread.

Anything against uploading it to archive.org or the TekWiki?

Can we confirm the problem is not in one if the plug-ins?

Hi , I would be thinking of returning the 7613 as that seems possible . I would be very happy to get a 7834 with plug-ins of any kind for as little as that - as long as the HV is ok and the CRT shows a waveform . I have one at the moment with an HV problem that I am trying to get working - the screen went blank and the scope wont power on now when I was using it a while back .fortunately so far the HV transformer and multiplier seem to be ok as the fault seems to be in the cathode supply side of things - I suspect some of the diodes in the voltage multipliers maybe failing .

regards
Brian(UK)

On Fri, Jul 19, 2024 at 12:20 PM, Luca wrote:

That would be very nice..

OK, done
It is here for some time:
/H?kan

Hi Brian,
Thank you for your assistence! That is the point. If the CRT is damaged then the 7613 as a complete device will be lost. I try to contact the seller, a former Tektronix employee directly, who is living in CH. It is not so easy, because I got the device with help/support of a ?man in the middle¡°. But meanwhile I got the information that I can return the 7613! I am wondering, what he will do with the scope.
Hobby moves on. In a couple of weeks I will get a 7834 including 7A24, 7A22, 7B92A and 7B71. Mainframe ok, half of the plug-ins defective. 50€ for all, so you can not complain.
Regards
Loetroelli