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Bad SMD? Not likely due to age. However, for the long term every board should be pulled (only one or two at a time) and inspected anyway, see. See /g/TekScopes/photo/285143/3590895? Chemical hour meter will be leaking if still installed. Then the power supply needs attention, x2 y2 caps etc. on mains. I refer you to John Miles' notes which has detailed support info. Manuals are easily found by Google. Units are very maintainable too with parts available.

Bummer. It was worth trying.

On Wed, Jan 15, 2025, 11:02 AM Tim Wright via groups.io <al7ds=
[email protected]> wrote:

Just checked, and it does not. Different ACQ board altogether. I have a
540, and it is similar to that. Makes sense, same series.

Just checked, and it does not. Different ACQ board altogether. I have a 540, and it is similar to that. Makes sense, same series.

Same here, my caps were backwards. I also replaced a couple of the film caps there because they were DiFilm with high dielectric absorption which warped the low-scale reading. I found that polyester was too good, and ended up adding RC’s to simulate a selected amount of DA. That might be taking it too far but it was so satisfying to run the problem to ground at last.

Dave Wise

There are many ways to approach it. You should be able to do this with a 7904 + 7B92A in delayed trigger mode.

You'll need to display a complete frame with the main sweep and display the scan lines with the delayed trigger sweep. Just a few lines should do nicely.
You can input the RGBHV lines to the vertical channels as needed for viewing and selecting pulses of interest.

IIRC, you can put VSYNC directly into the main trigger EXT input and HSYNC into the delayed trigger EXT input and use both at the same time.
That might give you better triggering depending of the operational status of your 7B92A.

Play with it and see. I've used similar setups to watch live video on my 7904A.

The TDS520 component level service manual is available, not sure if it
applies to the 420.
Radu.

On Wed, Jan 15, 2025, 9:36 AM Tim Wright via groups.io <al7ds=
[email protected]> wrote:

All SMD caps replaced, board cleaned and inspected, via's reflowed if
showing corrosion signs. Still getting trigComparatorTest FAIL, ERROR ID
151 diagnostic test failure trigComparatorTest, TRIGA status after trigger:
exp = 1, act =0. ** alpha trigger (XTRIG), on the RS232 Debug port.
This tells me that there is still an open via somewhere. Since schematics
appear to be un-obtanium, I am wondering if anybody with experience on
these scopes can at least identify the part of the ACQ board I should look
at closer under the microscope. What chips handle the triggering? should
be close to the EXT trigger BNC connection on the PC, Yes? Only reason I
am fooling around with repairs on this "Antique" (Not so antique as my 511A
though) is for the challenge. It has become a big one. It would be great
if someone, ex-Tek repair tech, had the schematics on these things, but I
am not holding my breath.

All SMD caps replaced, board cleaned and inspected, via's reflowed if showing corrosion signs. Still getting trigComparatorTest FAIL, ERROR ID 151 diagnostic test failure trigComparatorTest, TRIGA status after trigger: exp = 1, act =0. ** alpha trigger (XTRIG), on the RS232 Debug port.
This tells me that there is still an open via somewhere. Since schematics appear to be un-obtanium, I am wondering if anybody with experience on these scopes can at least identify the part of the ACQ board I should look at closer under the microscope. What chips handle the triggering? should be close to the EXT trigger BNC connection on the PC, Yes? Only reason I am fooling around with repairs on this "Antique" (Not so antique as my 511A though) is for the challenge. It has become a big one. It would be great if someone, ex-Tek repair tech, had the schematics on these things, but I am not holding my breath.

When I first got this 7904 it has been stored unused for years. I turned it on and the scope, with some plug-ins, entered tick-mode. I spent months trying to figure out what was wrong to no avail. I could not see any over-voltage or over-current conditions. Over time the crackling sound went from unregular and rather modest to louder and louder combined with a hissing sound. Eventually the noise got unbearable.

I got a multiplier unit from a gentleman in the UK and replaced the bad unit. Now the scope was back in operation. I think the explanation is that when the internal HV multiplier arcing occurs the feedback signal to control circuit U1275, pin 10 and 11, phase detector is so distorted that the circuitry goes into tick-mode.

I know it is a nightmare going into this power supply. Some cables are thin and stiff. However, your situation is precarious, you have not much of alternatives. I would suggest that you try to replace the multiplier unit.

Good luck
G?ran

I read Alan Hampel's article on restoration of the above.

He asserts that "Surprisingly, electrolytics C99 (5?F) and C100 (25?F), factory originals, were installed backwards! Not surprisingly, they each had only about 10% of their rated capacitance and were very leaky". (These caps are in parallel to meter shunt resistors on 3p and 10p ranges).

The original Tek schematic does not label the meter +/- but it is clear that the RED wire (sorry you need the schematic to follow this) is the +ve. I have confirmed for sure that the meter operates correctly, with circuit disconnected, when the requisite ?A are applied to the this terminal of the meter

Having looked at my (original) 130, the electrolytics do indeed have their +ve going to what is declaratively the NEGATIVE of the meter as well. My S/N is 120xx

Has anyone been through this restoration? I'd be comforted for someone more experienced to confirm this apparently repeated build and documentary error by Tek. Thank you.

Hi, I read many of your posts on the 465m blowing HVPS fuse...I actually acquired a 465m looking almost brand new with the saga of the fuse blowing.. I just have one question, what is the voltage readind on your 465M at the 32v unreg post, on mine it is 56 vdc with almost no ripple..DO YOU HAVE THE SAME READING !!! By the way, I just found out about this group and I find it VERY useful when trying to fix Tek equipement, !!
Best reguard's
Richard

Thanks for the advice. Re. the nick in the HV lead, I have not used dielectric grease before, does it set or would I need some particular variant for the voltages involved? Also, would a better solution be a dab of grease to fill up the nick, then to contain the grease with a short length of 4:1 heatshrink such as this:



The product linked appears to have 36kV dielectric strength. I reckon one cm of this (16/4) would slip round the Alden connector (I know because I have some 14mm and that just gets round the leg of it , but it is 2:1 so sadly no use). The black HV cable is 5.5mm diameter in case anyone wants to know.

@G?ran; were the symptoms of the U1615 a quiet crackle, almost like a ticking at first but not regular? I can elicit the odd crackles from the HV ultor pink cable by poking it with a glass fibre rod but they have a different quality of sound and are not as quiet as the noise I'm concerned by. R1604 appears fine and looks original to me. Maybe if there is something wrong in U1615 it is not as advanced as yours was yet? Do you think I should swap over the 7 x cap multiplier for my spare just in case? I know its not clever to change without good reason, I can't even claim to be certain that the spare unit works (though it should do given provenance). My only reason would be to not have to dig into the PSU for a while after completing this particular task. Opinions/judgements on this anyone?

I am wondering

I have a recently acquired 465M with option 93. I can't seem to find and info on what that option is. Does anyone here know?

Evan

Just post them. Everyone and is dog expects to have to modify 3D printer files.

TIA

EJP

Hi Dave,

I know it seems that simple but I put some internal reinforcement
beams across the top of the bays where the plugins go. I also did one
over the row of controls over that and another L shaped one around the
CRT. I didn't want some impact hitting the cover to have an easy time
bowing the cover in. However, if all you're doing is protecting scope
from dust then you really don't need those. This is why I was so happy
to have a printer that would let me do this in 1 single piece. I kind
of don't want to do a dust cover because then I worry someone might
mistakenly use it to say ship something.

I use most of my scopes too much to worry about dust. The 11801C is a
spare for when the in use one breaks. The 7704A I could probably part
with but I had this problem. It (+ very specific plugin) could have
helped me with +14 years ago which it could have solved.

-Evan

On Tue, Jan 14, 2025 at 12:41?AM Dave Daniel via groups.io
<kc0wjn@...> wrote:

Evan,

Thanks. I have never seen a 7704 so I don't know if a 7704 cover would fit
on a 78xx or 79xx 'scope. I imagine that the only characteristics that
matter would be the outside dimensions of the 'scope bezel and the depth of
the front panel controls.

I'll wait to see what the dimensions of your cover are; at that point I
will be able to decide for myself.

I don't generally have a concern about damaging the front panel controls
but I do wish I had something other than random large plastic bags to keep
dust off of those controls. The same goes for my 547 and 76xx 'scopes.

And, no, I was not expecting you to print covers for me. I can probably
join a local maker shop and print them there.

Thanks.

DaveD
KC0WJN


On Mon, Jan 13, 2025 at 22:13 evan foss via groups.io <evanfoss=
[email protected]> wrote:

Hi Dave,

The 79xx scopes have different geometry on the front panel. The
display is lower down (smart), the power switch is in a slightly less
obvious place, I think the controls might be taller, among many
changes. The 7000 series had a common design style but the geometry of
the front panel and it's layout wasn't very uniform.

It would take a number of thin printouts of the outline to test fit to
make this work or you taking very careful and precise measurements of
some things. Or a 3D scan.

Keep in mind I am not trying to make a business out of this. I just
wanted to share the files and hopefully stop more innocent knobs from
being crunched by accident.

-Evan

On Sun, Jan 12, 2025 at 4:26?AM Dave Daniel via groups.io
<kc0wjn@...> wrote:

Will your 7704A cover fit on 79xx 'scopes? If so, I'd be interested in
having several (4 or 5) of them.

DaveD
KC0WJN


On Sun, Jan 12, 2025 at 00:40 evan foss via groups.io <evanfoss=
[email protected]> wrote:

Hi Folks,

I made a 3D printed cover for the front of my Tek 7704A. I was worried
about accidentally harming the switches while I move it off/on the
shelf. I could clean it up and share it but that would mean a large
reprint to test it and I wanted to gauge interest before wasting that
much plastic and electricity.

PS: I am planning to do one for the 11801 as well. Though I will
probably have to line that with copper tape or something.

Evan

Well, whaddya know. I found this while randomly searching for 2465B problems:



The description of the triggering problem was identical to the one I have... and sure enough, removing the J102 plug made the problem go away. The scope now triggers perfectly. The author of the above article never persued the fix any further, so I might just look into why the TV sync option is causing a problem on my 2465B.

- Keith

Jon,
Just to prevent a possible misunderstanding: I wasn’t talking about the ultor but the white two-part connector somewhere near the middle of the HV lead, where the (usually) red lead enters it.

Personally, I strongly dislike using tape to insulate a cable/wire. With the HV lead, I don’t think shrink tube exists that goes around either side of the lead and shrinks snugly around the lead, without disassembly, that is.

The silicone rubber becomes an integral part of the lead and looks nice because it tapers between lead and connector.

Raymond

Raymond the 21-24 KV CRT Ultor is polyethylene as is,the molded Alden connector.

Indeed any nicks or splitting of the cable will cause arcs or corona to the nearby grounds og the ch?ssis , doghouse cover, etc.

I would try to fix the fault on the cable with heavy duty shrink tube or high grade electric tape.

Jon

I guess something to realize is that an air gap from the HV lead core to the outside of the insulation isn't enough to prevent arcing or even flash over; The dielectric strength of air is far less than that of the lead's rubber insulation.
As an example, I once repaired an arcing cable by filling the area where the (red) lead enters the socket in the middle that runs past the chassis by making a gradual "glove" out of silicone rubber from the cable to the white socket. And yes, everything was clean but arcing slightly before that!

Raymond

Cross posting from Equipment For Sale group


Clean insde & out.
The selenium stack was open, I bridged it with 3A rated diodes. The variac had open windings, I replaced it with a corrrect one. Prior to me the front panel CB was replaced with a fuse holder. I replaced the handles. Otherwise stock.
I ran through the calibration and most adjustments were spot on.
The one picture shows the tracing of a 2N2369.
There is some warmup drift, and the intensity doesn't seem as bright as I would expect. Not sure if this is a HV transformer issue or ?
$250 includes manual (w/122C mod info) and cart.
Local pickup preferred, I'm located in Waukesha WI 53188.

Cross posting this from the Equipment For Sale group


Clean inside and out.
Serial #s 577: B108477, 177: B059426
Option 10 is a 10 x 10 cm display with an extra cm L & R edges.
Storage works, upper & lower. I did an "Etch-A-Sketch" in storage mode with the H & V position controls, see picture.
I have not run through a calibration.
Collector Supply knob is cracked.
Display is a tracing of a 2N2369.
Transistor fixture is not included.
$550, includes 577 & 177 manuals (with Option 10 info) and cart.
Local pickup preferred, I'm in Waukesha WI 53188. I can ship but will need a firm purchase commitment and time to construct a box. Shipping will be expensive!